2022 Presentation Information

Table of Contents:

  1. Keynote
  2. Plenary
  3. Atmospheric Chemistry in Public Health and Regulatory Applications
  4. Chemical Regimes
  5. Fundamental Studies of Atmospheric Chemical Mechanisms
  6. Mechanism Development and Reduction
  7. Modeling at multiple scales of chemical complexity and spatial resolution
  8. New and Emerging Air Pollutants (HAPs, VCPs, PFAS)
  9. Sulfur Oxidation Advancements – Improving mechanisms and modelling

Keynote


Considering Multiple Dimensions of Complexity in Atmospheric Chemistry Models

By: Kelley Barsanti, University of California Riverside; National Center for Atmospheric Research

Presentation: Chemical mechanisms describe the reactivity of compounds in the gas phase. Due to computational constraints, most widely used chemical mechanisms have been simplified (i.e., reduced), such that a limited number of reaction pathways, intermediates, and products are considered when applied in air quality models. The reduction approaches largely were developed when extreme ozone formation events under high nitrogen oxides (NOx) levels were the primary regulatory concern. Advances in emissions control technologies and successful regulatory and mitigation efforts have succeeded in shifting our atmosphere to a regime in which chemistry under lower NOx levels has become increasingly important, multipollutant predictions at lower concentrations are required, and new sources of pollutants are emerging. Wildland fires are one such emerging source, and will be used here to illustrate multiple dimensions of complexity in the application, development, and reduction of chemical mechanisms for air quality modeling. The representation of hundreds of organic compounds by a limited number of model surrogates, the linkages between gas-phase chemistry and secondary organic aerosol formation, and the sensitivity of predicted air quality endpoints to complexity in model representation will be presented. This presentation reflects over a decade of collaborative research seeking to improve model representation of secondary pollutants, including from emerging sources and under evolving conditions.

Additional Authors: Samiha Binte Shahid, UC Riverside, Jia Jiang, UC Davis, Qi Li, UC Riverside, David Cocker, UC Riverside, Julia Lee Taylor, NCAR, Louisa Emmons, NCAR, John Orlando, NCAR, Christine Wiedinmyer, CIRES/NOAA, Robert Yokelson, University of Montana, William Carter, UC Riverside


Plenary Presentation


Deeper insight into atmospheric reaction systems from the laboratory: RO2 isomerization and ROOOH formation

By: Torsten Berndt, TROPOS Leipzig

Presentation: Biogenic and anthropogenic emissions are released into the Earth´s atmosphere with a total annual strength in the order of 10(9) metric tons of carbon. The detailed understanding of their oxidation pathways is still a challenging task. For example, in the last years it has been discovered that isomerization steps of peroxy (RO2) radicals, which represent the key intermediates in the course of atmospheric oxidation, can outrun the “traditional” bimolecular RO2 radical reactions with NO or HO2 radicals, resulting in a distinctly changed product distribution. In our laboratory measurements, we use flow systems that allow for the investigation of the early stages of an oxidation reaction for close to atmospheric conditions. Direct monitoring of RO2 radicals and resulting closed-shell products is carried out by chemical ionization mass spectrometry applying a set of different reagent ions. Detection limits for oxidized compounds can be as low as 10(3) - 10(4) molecules cm(-3), i.e., below ppq level. The reaction conditions are chosen in such a way that solely the formation of initially formed RO2 radicals and their unimolecular pathways can be studied. Addition of a second reactant allows to follow the product formation from a selected bimolecular RO2 radical step. Possibilities and limits of this experimental approach are discussed. Recent results on RO2 radical isomerization and hydrotrioxide (ROOOH) formation in the OH + isoprene reaction are presented.

Additional Authors: Andreas Tilgner, TROPOS Leipzig, Erik H. Hoffmann, TROPOS Leipzig, Frank Stratmann, TROPOS Leipzig, Hartmut Herrmann, TROPOS Leipzig,


Atmospheric Chemistry in Public Health and Regulatory Applications


Long-term Trends of Impacts of Global Gasoline and Diesel Emissions on Air Quality and Human Health for 2000-2015

By: Ying Xiong, Wayne State University

Presentation: Global economic development and urbanization during the past two decades have likely caused changes in vehicle tailpipe emissions associated with aerosols and trace gases. However, long-term trends of impacts of global gasoline and diesel emissions on air quality and human health are not clear. Here we employ the CESM CAM6-Chem in conjunction with the Community Emissions Data System (CEDS) to quantify the long-term trends of impacts of global gasoline and diesel emissions on air quality and human health for the period of 2000-2015. Global gasoline and diesel emissions contributed to regional increases in annual mean surface PM2.5 concentrations by up to 17.5 and 13.7 µg/m3, and surface O3 concentrations by up to 7.1 and 7.2 ppbv, respectively, for 2000-2015. However, we found substantial declines of surface PM2.5 and O3 concentrations over Europe, the US, Canada, and China for the same period, which suggested the co-benefits of air quality and human health from improving gasoline and diesel fuel quality and tightening vehicle emissions standards. Globally, we estimate the mean annual total PM2.5- and O3-induced premature deaths are 139,700-170,700 for gasoline and 205,200-309,300 for diesel, with the corresponding years of life lost of 2.74-3.47 and 4.56-6.52 million years, respectively. Diesel and gasoline emissions create health-effect disparities between the developed and developing countries, which are likely to aggravate afterwards.

Additional Authors: Yaoxian Huang, Wayne State University


Optimization of air pollutant control policy based on the nonlinearity of atmospheric chemistry

By: Jia Xing, Tsinghua University

Invited Presentation: Serious ambient PM2.5 and O3 pollution is one of the most important current environmental challenges of China, necessitating an urgent cost-effective co-control strategy. Herein, we introduced a novel integrated assessment system to optimize the multiple air pollutant control strategy for the synergistic reduction of ambient pollution and associated impacts on human health and ecosystem. Focusing on the Beijing–Tianjin–Hebei cities and their surrounding regions, which experience the most serious PM2.5 and O3 pollution in China, we determined that NOx emissions reduction (64%–81%) is absolutely essential to meet the air quality standard no matter how much VOCs emission is reduced. However, the synergistic VOCs control is strongly recommended when considering substantially human health and crop production benefits. Notably, such benefits will be greatly reduced if the synergistic VOC reduction is delayed. NH3 abatement still remain controversial in China for its effectiveness in reducing PM2.5 pollution and nitrogen deposition but with potential risk in enhancing acid rain. We further extended the response surface model to deposition and found that one third of Yangtze River Delta cities exhibit considerable large (15%-71%) NH3 control potentials which become even greater when more strengthened controls are applied on SO2 and NOx. Greater NH3 control potential towards to more strengthened air quality standards, leading to additional avoided premature deaths with limited cost.

Additional Authors: Dian Ding, Tsinghua University, Zhaoxin Dong, Tsinghua University, Shuxiao Wang, Tsinghua University


Accounting for the chemistry of reactive toxic VOCs for community level modeling

By: Zhen Liu, California Air Resources Board

Invited Presentation: Community level exposure modeling and health risks analysis may need to consider the chemistry of reactive toxic VOCs. While conducting full chemical transport modeling at a community level remains challenging, we utilize a hybrid approach that involves dispersion modeling and post-modeling adjustment derived by a 0-D or 1-D chemistry model using an explicit (MCM) or condensed (e.g., SAPRC07) chemical mechanism. Chemistry adjustment factors are estimated to reflect the effects from both photochemical loss and secondary production. Sensitivity modeling analysis shows that the extent of chemistry effect is a function of the residence time of individual toxic VOCs and their precursors within the community of interest. The upper bound of secondary production of carbonyls (e.g., formaldehyde and acetaldehyde) is estimated through mass balance calculations based on emission inventories and chemistry product yields. We will present results from two case studies in California and discuss the implications for future modeling of toxic VOCs at a community level.

Additional Authors: Pingkuan Di, CARB, Jeremy Avise, CARB


Characterizing the impact of volatile chemical products (VCPs) and cooking on air quality in major US cities

By: Matthew Coggon, National Oceanic and Atmospheric Administration

Invited Presentation: Declining emissions from motor vehicles in US cities has resulted in an urban atmosphere where understudied sources of pollution - such as consumer products, solvent use, and cooking emissions – are becoming the dominant source of urban VOCs. Recent work has shown that volatile chemical products (VCPs) are as important to urban VOCs as fossil fuel emissions. Chemical transport models used to simulate urban air quality often misrepresent the magnitude and chemistry of VCP emissions, which leads to uncertainty in simulations of ozone. For example, oxygenated VOCs such as glycols and glycol ethers are major ingredients in consumer VCPs, but their chemistry in is often represented by lesser-reactive hydrocarbons in reduced chemical mechanisms. In this presentation, we will demonstrate the impact of VCP emissions and chemistry on air quality simulations of ozone and other secondary air pollutants in New York City. We will show that VCP emissions significantly contribute to maximum daily 8-hr ozone, and that the representation of VCP emissions using oxygenated VOC chemistry significantly impacts simulations of peroxy acyl nitrates (PANs), a reservoir for NOx. We will also present recent evidence that points to the important role that cooking VOCs have on urban reactivity. Cooking VOCs constitute another source of urban air pollution that requires further investigation.

Additional Authors: Geogios Gkatzelis, Forschungszentrum Jülich, Brian McDonald, NOAA, Jessica Gilman, NOAA, Chelsea Stockwell, CIRES / NOAA, Lu Xu, CIRES / NOAA, Aaron Lamplugh, CU Boulder, Qindan Zhu, CIRES / UC Berkeley, Rebecca Schwantes, NOAA, Karl Seltzer, EPA, Steven Brown, NOAA, Carsten Warneke, NOAA


Chemical Regimes


THE DEVELOPMENT OF AN ISOPRENE MECHANISM FOR ANOXIC ATMOSPHERES AND THE IMPLICATIONS FOR TRANSMISSION SPECTRA FOR N2-RICH EXOPLANETS

By: Alexander Archibald, University of Cambridge & NCAS-Climate

Presentation: With continuing advances in exoplanetary detection and transmission spectra resolution, the accurate modelling of potential biological signatures (biosignatures) in exoplanet atmospheres has become an important area of scientific research. In this study, the first extended exoplanet mechanism for isoprene, a specialised biosignature with no known geochemical source, has been developed and implemented into ARGO, a one-dimensional numerical model. From simulations of four N2-rich exoplanet atmospheres, isoprene was found to be the most promising isoprenoid biosignature. The concept of isoprene as a photon sink is proposed, acting to slow CO2 photolysis, and a possible transition from CO2-initiated to isoprene-initiated CH2O formation with increasing isoprene emissions is identified. The implications of these regimes for carbonyl transmission spectra at 5.7 μm are discussed, with the potential for alterations in transmission possible below Earth emissions of isoprene in simulations with the early Sun. Additionally, the contributions of isoprene decomposition products and CH2O to the overall carbonyl optical depth are found to be comparable in some cases. The newly developed anoxic chemistry is found to dominate (>1014 times) over previously known isoprene (O2-rich) kinetics; therefore, we encourage its integration into pre-existing numerical models, originally designed to model the atmosphere of modern Earth, in future studies of isoprene in exoplanet atmospheres.

Additional Authors: Thomas Elgar, University of Cambridge, Paul Rimmer, University of Cambridge


Ozone photochemistry and free radical budgets in the Los Angeles basin: A comparison of ground-based observations in 2021 and 2010

By: Michael Robinson, NOAA CSL

Presentation: Radical precursors and termination products are important factors to understanding sensitivities of ozone (O3) production to nitrogen oxides (NO + NO2 = NOx) and volatile organic compounds (VOCs). During the summer of 2021, an extensive set of photochemical measurements were conducted at a ground site on the Caltech campus in Pasadena, CA to evaluate emissions and photochemistry in the Los Angeles (LA) basin. Here we present measurements of important radical precursors and compare them to observations from the CalNex 2010 field intensive. Major radical sources include formaldehyde (HCHO) and other aldehydes, nitrous acid (HONO), nitryl chloride (ClNO2), ozonolysis of alkenes, and O(1D) + H2O. In addition to radical precursors, radical termination products were measured, including peroxy acetyl nitrates (PAN), nitric acid (HNO3), organic nitrates and organic peroxides. The comparison of radical precursors and termination products illustrates shifts in photochemical regime resulting from NOx and VOC emissions changes over the past ten years in the LA basin, as well as other influences such as temperature, seasonality and day of week.

Additional Authors: J. Andrew Neuman, NOAA/CIRES, Patrick R. Veres, NOAA, James M. Roberts, NOAA, Matthew M. Coggon, NOAA, Lu Xu, NOAA/CIRES, Carsten Warneke, NOAA, Chelsea Stockwell, NOAA/CIRES, Jessica B. Gilman, NOAA, Aaron Lamplugh, CU-Boulder, Andrew W. Rollins, NOAA, Kristen L. Zuraski, NOAA/CIRES, Jeff Peischl, NOAA/CIRES, Shang Liu, CARB, Toshihiro Kuwayama, CARB, Jason Surratt, UNC, Steven S. Brown, NOAA


An exploration of changing ozone production under new chemical regimes in three cities

By: Beth Nelson, University of York

Invited Presentation: Understanding how changing chemical regimes impacts the formation of harmful secondary pollutants, such as ozone, is crucial in megacities and urban centres where most of the global population live. Chemical box models are important tools used to understand the detailed chemical processes occurring in any atmospheric environment. Where chemically detailed observational data is available, tailored box models can be used to investigate the key drivers for in situ ozone production. Observational data from three recent field campaigns in Beijing, Delhi and Manchester has been used to constrain chemical box models and investigate in situ ozone formation. These models incorporate the near explicit Master Chemical Mechanism (MCM), which allows for the modelling of detailed oxidation chemistry. The concentrations of both volatile organic compounds (VOCs) and NOx are varied, revealing insights into how ozone production may change under future chemical regimes, where different air quality and climate policies are implemented. This work investigates the current chemical regimes in the three cities and explores changes in ozone production under future emission scenarios. The sensitivity of ozone production to chemical species, both individually and grouped by class, is also examined. A detailed understanding of the chemical processes leading to ozone production will play a crucial role in informing on how future pollution and climate policies will impact urban air quality.

Additional Authors: James Lee, University of York, Andrew Rickard, University of York, Jim Hopkins, University of York, Jacqui Hamilton, University of York


Chemistry of Reactive Organic Gases in Mega-cities of China: Insights from Vertical Gradient and Eddy Covariance Flux Measurements

By: Bin Yuan, Jinan University

Invited Presentation: The oxidation of reactive organic gases contributes to the formation of ozone and fine particles. A large number of organic gases with different formula, structure, and reactivity are emitted in urban regions from various sources (e.g., vehicles, solvent and fuel evaporation, plants). However, the chemistry of reactive organic gases and the subsequent effects to secondary pollution remain with large uncertainties. In recent few years, my group conducted vertical gradient measurements and eddy covariance flux measurements in mega-cities of China, including Beijing, Shenzhen and Guangzhou. These measurements along with ground-based observations of reactive organic gases provide additional constraints on the chemistry of these species and their contributions to ozone and particle formation.

Additional Authors: Xiaobing LI, Jinan Univ., Yibo Huangfu, Jinan Univ., Xianjun He, Jinan Univ., Xin Song, Jinan Univ., Sihang Wang, Jinan Univ., Yubin Chen, Jinan Univ., Suxia Yang, Jinan Univ., Min Shao, Jinan Univ.


Fundamental Studies of Atmospheric Chemical Mechanisms


Identification and Quantitation of Products Formed from the Reaction of Alkenoic Acids with OH Radicals in a Low NOx Environment

By: Anna Ziola, University of Colorado Boulder

Presentation: According to results from the CalNex 2010 and LAAQS 2020 field campaigns, the concentration of mid-day NO, a prominent component in many VOC (volatile organic compound) oxidation mechanisms, decreased in Los Angeles by about 75% during the decade between campaigns. Although there have been many studies of VOC oxidation in high NOx environments, less is known about this chemistry in the absence of NOx. Here we present results of environmental chamber studies in which a series of alkenoic acids (linear 1-alkenes with a terminal carboxyl group) were reacted with OH radicals formed by H2O2 photolysis while using an iodide chemical ionization mass spectrometer (I-CIMS) to identify products. Because the I-CIMS is very sensitive to carboxylic acids, the presence of this functional group tag provided an easy way to detect both the parent VOC and the products. When possible, authentic standards of identified products were synthesized and used to calibrate the I-CIMS for product quantitation, allowing us to determine mechanistic branching ratios for some reaction pathways. The studies explore the effects of carbon chain length and oxidation regime (RO2 + RO2 and RO2 + HO2) on products, mechanisms, and secondary organic aerosol formation from the oxidation of alkenes, a major class of VOC emissions, in a low NOx environment.

Additional Authors: Paul Ziemann, University of Colorado Boulder


Particle-Phase Accretion Forms Dimer Esters in Pinene Secondary Organic Aerosol

By: Christopher Kenseth, University of Washington

Presentation: For more than a decade, multifunctional dimer esters have been identified using advanced MS techniques as significant components of SOA formed from oxidation of α/β-pinene, and have been implicated as key players in new particle formation and growth, particle viscosity, and cloud condensation nuclei activity. Particle-phase reactions of closed-shell monomers (e.g., esterification and peroxyhemiacetal/diacyl peroxide decomposition) and gas-phase reactions involving early-stage oxidation products and/or reactive intermediates (e.g., SCIs, carboxylic acids, and RO2) have been advanced as possible dimer ester formation pathways. Due to a lack of authentic standards, however, structures of the dimer esters are inferred from accurate mass/fragmentation data and, therefore, mechanistic understanding of their formation remains unconstrained. Here, informed by detailed structural analyses (MS and MS/MS, 13C and 18O isotopic labeling, and H/D exchange), we synthesize the first authentic standards of several major dimer esters identified in SOA from ozonolysis of α/β-pinene. Based on a series of targeted environmental chamber experiments using LC/ESI-MS for analysis of SOA molecular composition, we conclusively demonstrate that these dimer esters are formed through particle-phase chemistry and propose a unifying accretion mechanism that accounts for the observed regioselectivity, dynamics, and environmental dependencies (e.g., oxidant type and RO2 fate) of ester formation.

Additional Authors: Nicholas Hafeman, Caltech, Samir Rezgui, Caltech, Yuanlong Huang, Caltech, Nathan Dalleska, Caltech, Brian Stoltz, Caltech, Paul Wennberg, Caltech, John Seinfeld, Caltech


Organic Aerosol Multiphase Aging: Rethinking the Chemical Mechanism under Atmospherically Relevant Conditions

By: Haofei Zhang, University of California, Riverside

Presentation: Multiphase oxidative aging is a ubiquitous process for atmospheric organic aerosols (OA). But for decades, the process was considered too slow to impact air quality and climate on atmospherically relevant timescales based on results from laboratory studies. Here we show that OA heterogeneous oxidation may be 2 – 3 orders of magnitude faster when the gas-phase oxidant, hydroxyl radicals are at atmospheric levels. Direct laboratory measurements coupled with kinetic simulations suggest that an autoxidation mechanism mediated by particle-phase peroxy radicals greatly accelerates OA heterogeneous oxidation, with enhanced formation of organic hydroperoxides, alcohols, and fragmentation products. With autoxidation, we estimate that the OA oxidation timescale in the atmosphere may be only a few hours to several days. Thus, heterogeneous oxidation of OA can have more significant atmospheric and climate impacts than previously expected. Furthermore, our findings reveal the nature of heterogeneous aerosol oxidation chemistry in the atmosphere and may reconcile the discrepancies between atmospheric observations and laboratory studies on OA aging.

Additional Authors: Wen Zhang, UC Riverside, ZIxu Zhao, UC Riverside, Chuanyang Shen, UC Riverside


Ring-opening yield and auto-oxidation rate of the first-generation hydroxy peroxy radical (C10H17O3) from OH-oxidation of ⍺-pinene and β-pinene

By: Joel Thornton, University of Washington

Presentation: Monoterpene oxidation contributes significantly to particle number and mass concentrations due, in part, to the ability of their peroxy radicals to undergo autoxidation leading to highly oxygenated molecules. We report on the yield of the isomer of the hydroxy peroxy radical formed from the OH radical addition to the C=C double bond, thought to be responsible for the majority of OH-initiated monoterpene-derived HOM. The OH addition leads to the opening of the C-4 ring and formation of a new C=C double bond with the shift of the alkyl radical center. We constrain the yield and autoxidation rate of this isomer by using isotopically-labeled precursors such as D3-⍺-pinene and by directly measuring peroxy radicals and their fate in competition with the reaction with nitric oxide at a fixed reaction time (~0.7 s). Based on observation of sequentially oxygenated peroxy radicals, organic nitrates, and alkoxy radical fragmentation products, and quantum chemical calculations of alkoxy radical fates, we find that the yields of the ring-opened first-generation peroxy radical isomers are 0.05 to 0.2 and 0.06 to 0.25 for ⍺-pinene and β-pinene, respectively. The autoxidation rates of the corresponding peroxy radical are 2.7 and 0.4 per sec, respectively. These rates and yields are lower than recent determinations but in general agreement with HOM yields determined from independent methods and in a range where OH driven monoterpene HOM formation will be atmospherically important.

Additional Authors: Ben H. Lee, University of Washington, Siddharth Iyer, Tampere University, Henrik G. Kjærgaard, University of Copenhagen, Kristian H. Møller, University of Copenhagen, Theo Kurten, University of Helsinki, Regan J. Thomson, Northwestern University


Formation yields of organic nitrates in reactions of organic peroxy radicals with NO

By: John Orlando, Atmospheric Chemistry Observations and Modeling (ACOM) Laboratory, NCAR

Presentation: Ozone formation in the troposphere occurs via the oxidation of volatile organic compounds (VOC) in the presence of nitrogen oxides (NOx). Central to this process is the reaction of organic peroxy radicals (RO2) with NO, a reaction that can occur through two pathways: RO2 + NO → RO + NO2 (1-α) RO2 + NO + M → RONO2 (+ M) α As the formation of organic nitrates occurs in parallel to NO2 (and hence ozone) production, larger values of α coincide with reduced ozone production efficiency. Further, formation of organic nitrates (particularly as overall NOx emissions decrease) is known to be a major NOx sink, thus controlling NOx levels and distributions. Despite many studies over the years regarding organic nitrate yields from numerous RO2 (particularly those derived from alkanes), uncertainties remain. In this study, we have conducted systematic lab studies of the yields (α) of organic nitrates formed in the oxidation of the alkanes. The work includes linear and branched species containing 5-8 carbon atoms. We demonstrate that, while nitrate yields increase with molecular size, the structure of the radical (1ry, 2ry, 3ry) has no effect. As an extension of that work, studies of ketones and ethers are being conducted, and preliminary results on these species will also be presented. The work will provide input for more accurate modeling of air quality, and provide more confidence in mitigation strategies designed to limit the formation of ozone and other secondary pollutants.

Additional Authors: Geoffrey S. Tyndall, NCAR ACOM, Frank M. Flocke, NCAR ACOM, Qing Ye, NCAR ACOM, Paul Ziemann, University of Colorado, Anna Ziola, University of Colorado


Oxidation of naphthalene in atmosphere: A computational perspective

By: Prasenjit Seal, Tampere University

Presentation: Anthropogenic volatile organic compounds often dominate the urban atmosphere. Amongst them, naphthalenes are one of the most abundant aromatic hydrocarbons those are reactive in ambient atmospheres. Although benzene and toluene usually considered to be the primary anthropogenic precursors in secondary organic aerosol (SOA) formation, studies also reveal the importance of these polycyclic species. One of the chemical sink of naphthalenes in the atmosphere are their reactions with atmospheric oxidants like OH, HO2, NO, etc. radicals and so studies of its oxidation are of paramount importance in understanding the role in aerosol formation. In this work, we focus our attention to the possible pathways leading to naphthalene oxidation in atmosphere and thereby aiming to predict formations of highly oxygenated organic molecules (HOM). Density functional theory was used as the prime investigating tool to obtain the optimized geometries of the species involved. Further refinement of the energies were made for certain systems of interest at coupled cluster level of theory and their rate constants were also estimated using master equation simulations. Our recent NO3- inlet mass spectrometric observations also justify the possibility of HOM formation from naphthalene oxidation and hence strengthen our proposed mechanistic pathways.

Additional Authors: Olga Garmash, Tampere University, Siddharth Iyer, Tampere University, Avinash Kumar, Tampere University, Matti Rissanen, Tampere University, University of Helsinki


Formation of Accretion Products in the Self-Reaction of Ethene-Derived Hydroxy Peroxy Radicals

By: Sara Murphy, California Institute of Technology

Presentation: Quantifying the relative importance of various peroxy radical pathways is crucial to understanding of the effect of anthropogenic and biogenic emissions on air quality. In the troposphere, possible bimolecular reactions of peroxy radicals include reactions with NOx, HOx, and other peroxy radicals. Previously, it was believed that the self-reaction of peroxy radicals in the gas-phase proceeded primarily via two pathways, forming alkoxy radicals or an alcohol and carbonyl. However, recent studies have suggested that a third pathway, forming peroxides, may proceed at rates far greater than previously expected. In this study, we measure the rate of formation of the accretion product from ethene-derived peroxy radical self-reactions using CF3O- GC-CIMS. We demonstrate that the accretion product is formed in the gas-phase and confirm its identity by comparison to synthetic standards of the ROOR. Our results are consistent with recent suggestions that the formation of these accretion products is more important in the chemistry of the troposphere than previously recognized.

Additional Authors: John Crounse, Caltech, Nicholas Hafeman, Caltech, James Park, Caltech, Samir Rezgui, Caltech, Brian Stoltz, Caltech, Paul Wennberg, Caltech


Investigating the Atmospheric Oxidation of Methylamine with Multiplexed Photoionization Mass Spectrometry: Insight into the Reactivity of C-centered and N-centered Radicals with O2

By: Sommer Johansen, Sandia National Laboratories

Presentation: CO2 capture and storage relies heavily on amine-based adsorbents. This has resulted in an increase in emissions of these amines and their degradation products into the atmosphere, necessitating an in-depth understanding of their atmospheric oxidation pathways. Methylamine (CH3NH2) is a common degradation product of CO2 capture agents and is also emitted through other natural and anthropogenic processes. Here, we present experimental results of the oxidation of CH3NH2 using multiplexed time-resolved photoionization mass spectrometry coupled to tunable synchrotron VUV radiation from the Chemical Dynamics Beamline at the LBNL Advanced Light Source. This sensitive probe method enables simultaneous measurements of multiple products and transient intermediates. CH2NH2 and CH3NH were produced within a slow-flow quartz reactor tube through the reaction of CH3NH2 with either OH or Cl, generated by pulsed-laser photolysis of H2O2 and Cl2, respectively, before reacting with O2. Using selectively deuterated methylamine (CD3NH2), we were able to discriminate between the CH2NH2 and CH3NH reaction channels. Potential energy surfaces were calculated with the program KinBot at the CCSD(T)- F12a/cc-pVDZ-F12//ωB97X-D/6-311++G(d,p) level of theory to assist with intermediate and product identification. We will discuss our efforts to quantify the reaction kinetics of this system, and what our results demonstrate about the differences in reactivity between the C-centered and N-centered radicals.

Additional Authors: Arkke Eskola, University of Helsinki, Leonid Sheps, Sandia National Laboratories, Judit Zador, Sandia National Laboratories, Kendrew Au, Sandia National Laboratories


Recent Computational Results on RO2 + R'O2 Reactions

By: Theo Kurtén, University of Helsinki

Presentation: The detailed mechanism of peroxy radical self- and cross reactions (RO2 + R’O2) remains elusive despite the importance of the process e.g. for aerosol-related atmospheric chemistry. Using multireference methods, we have confirmed that RO2 + R’O2 reactions inevitably proceed via RO4R’ tetroxides, which in turn rapidly decompose to yield triplet O2 and a triplet complex of two alkoxy radicals. This complex can further decompose to free alkoxy radicals, react to form carbonyl and alcohol products, or undergo an intersystem crossing (ISC) leading to ROOR’ formation. In sufficiently complex systems, additional reaction channels, e.g. formation of ROR’ products through RO scission reactions, may also be competitive. The results of our recent computational work can be condensed into three conclusions: 1)The overall rate of RO2 + R’O2 is determined by the formation rate of the RO4R’. 2)If the barrier to RO4R’ is low, this rate can be roughly estimated using simple MD techniques. When the barrier is high, transition state calculations can be applied – however high-level methods are needed to assess the barrier. 3)The branching ratio for ROOR' formation is determined primarily by the ISC rate of alkoxy complex intermediates. This rate, which requires expensive multireference calculations to evaluate, varies by up to 10 orders of magnitude depending on the RO2 and on the complex conformer. This is much larger than the variation of the competing dissociation and H-shift rates.

Additional Authors: Christopher Daub, U. Helsinki, Mikael Ehn, U. Helsinki, Lauri Franzon, U. Helsinki, R. Benny Gerber, Hebrew University Jerusalem, Thomas Golin Almeida, U. Helsinki, Galib Hasan, U. Helsinki, Otso Perakyla, U. Helsinki, Matti Rissanen, U. Helsinki, Vili-Taneli Salo, U. Helsinki, Rashid Valiev, U. Helsinki, Itai Zakai, Hebrew University Jerusalem


Reconciling Disparate Mechanisms for Oxidation of Hg(0) to Hg(II) in the Gas Phase

By: Theodore Dibble, State University of New York - Environmental Science and Forestry

Presentation: Quantum calculations and experiment support a two-step oxidation of Hg(0) by Br via a BrHg• intermediate. BrHg• is sufficiently stable to react with NO2, HOO, and other atmospheric radicals to form stable Hg(II) compounds. The analogous HOHg• intermediate in the OH-initiated oxidation of Hg(0) is much less stable, and had been thought to decompose rather than forming Hg(II), except in the uppermost troposphere. We recently found that HOHg• can react with ozone to form a radical form of Hg(II), namely, HOHgO•. Assuming the same rate constant as that recently measured for the analogous BrHg + ozone reaction, the fraction of HOHg• forming Hg(II) easily reaches 50% in the continental U.S. boundary layer and 100% above 6-8 km. Many chemical transport models have assumed irreversible oxidation of Hg(0) to Hg(II) by OH and ozone, separately. These assumptions ignore the fact that no known thermodynamically and kinetically plausible mechanism can rationalize these oxidations under atmospheric conditions. Models of mercury over continental areas tend to require these implausible reactions (as opposed to Br-initiated oxidation) to explain field observations. We expect that modelers will no longer need to invoke those unlikely mechanisms once they incorporate our new results: that OH and ozone, together in a two-step mechanism, can efficiently oxidize Hg(0) to Hg(II). Preprint on ChemRxiv, DOI: 10.26434/chemrxiv-2022-5v0tt

Additional Authors: Pedro J. Castro (SUNY-ESF)


Speciated Monitoring of Organic Peroxy Radicals with Proton-Transfer Mass Spectrometry: First applications in the laboratory

By: Barbara Noziere, KTH, Royal Institute od Technology

Invited Presentation: In spite of important progress over the last decade, the chemistry of organic peroxy radicals (“RO2”) in Earth’s atmosphere is still not fully understood. This presentation reports the development of mass spectrometric approaches based on proton transfer ionization with the objective of monitoring individual RO2 in the atmosphere. First applications of these techniques to the investigation of RO2 reactions and mechanisms in laboratory are also presented, in particular, the first study of RO2 + alkene reactions under atmospheric conditions (298 K). A kinetic study, performed in a flow reactor and monitoring the consumption of individual RO2 by alkenes, reported significantly larger rate coefficients (x10 to x100) than expected from high-temperature literature data. A product study then showed that the slow epoxide formation channel proposed in the literature was not the main reaction pathway under atmospheric conditions, but was bypassed by a faster peroxy radical formation channel. Thus, under atmospheric conditions these reactions are not kinetically limited by the epoxide formation but by the first (and faster) addition step, in agreement with our recent kinetic study. In the atmosphere, the RO2 sinks due to their reactions with unsaturated compounds such as isoprene or terpenes would be more significant than expected until now from the literature data, and possibly non-negligible for some RO2. Monitoring individual RO2 is thus important even in laboratory investigations.

Additional Authors: O. Durif, E. Dubus, Department of Chemistry, KTH, Royal Institute of Technology, Stockholm, Sweden; F. Fache, Université Lyon 1, CNRS, UMR 5246, ICBMS, Villeurbanne, France


Ozonolysis of α-pinene and Δ3-carene – influence of molecular structure on aerosol formation and chemistry

By: Marianne Glasius, Aarhus University, Denmark

Invited Presentation: In both experimental and model studies, α-pinene is often used as a standard monoterpene, but how well does it represent the chemistry of other monoterpenes? In a series of chamber studies combined with off-line analysis and quantum chemical calculations, we investigated the similarity in formation and composition of secondary organic aerosols (SOA) from ozonolysis of the structurally similar monoterpenes α-pinene and Δ3-carene. We observe that ozonolysis of α-pinene produces a higher particle number concentration than ozonolysis of Δ3-carene, while the SOA mass depends on experimental conditions such as the monoterpene-to-ozone ratio. More SOA mass was formed from both monoterpenes in experiments at 10C and 0C compared to 20C in line with previous work. Analysis by liquid chromatography coupled to quadrupole time-of-flight mass spectrometry shows that ozonolysis of Δ3-carene yields a simpler product distribution with fewer products in the particle phase compared to α-pinene, with the major product being the dicarboxylic acid cis-3-caric acid. Only few dimer esters were observed from Δ3-carene and at lower levels than for α-pinene. According to the quantum chemical calculations cis-3-caric acid is expected to be more efficient in condensing on already existing particles compared to the analogue cis-pinic acid from α-pinene, in good agreement with the experimental results. Recent results from studies of ozonolysis of mixtures of α-pinene and Δ3-carene will also be presented.

Additional Authors: Ditte Thomsen, Aarhus University, Lotte Dyrholm Thomsen, Aarhus University, Emil Mark Iversen, Aarhus University, Þuriður Nótt Björgvinsdottir, Aarhus University, Sofie Falk Vinther, Aarhus University, Jane Tygesen Skønager, Aarhus University, Thorsten Hoffmann, Johannes Gutenberg University, Mainz, Bernadette Rosati, Aarhus University, Jonas Elm, Aarhus University, Merete Bilde, Aarhus University.


Tunneling, Roaming, and Oligomerization Kinetics of Criegee Intermediates Elucidated through Theory and Experiment

By: Stephen Klippenstein, Argonne National Laboratory

Invited Presentation: The kinetics of Criegee intermediates (CI) are challenging to study experimentally due to their highly transient nature. Furthermore, the resonance between zwitterionic and singlet diradical forms, presents challenges for theoretical studies. In recent years, the experimental challenges have been met with in situ syntheses coupled with photoionization mass spectrometry to obtain direct measurements of the thermal rate constants. Furthermore, supersonic expansion based cooling of the nascent CI together with IR excitation and UV laser induced fluorescence based detection of OH has yielded energy resolved determination of the rate constants. Meanwhile, the implementation of high level theoretical methods, based on the coupling state-of-the-art electronic structure evaluations (including multireference methods as necessary) with sophisticated transition state theory and master equation treatments, has yielded high quality predictions for the kinetics. In this talk, we will review some of our recent joint theory and experiment studies (with experiments performed by the Lester, Caravan, and Taatjes groups) of the kinetics for a variety of CIs. These studies highlight the (i) role of a multistage sequence of roaming reactions, (ii) possibility for oligomerization through successive addition of CIs, and (iii) physical aspects (tunneling, multidimensional rotors, conformational dependence, and structural effects) of the initial H transfer step in the unimolecular dissociation.

Additional Authors: None


SOA and volatile product formation from the nighttime oxidation of various terpenes, and the ICARUS database

By: Tran Nguyen, UC Davis

Invited Presentation: A diversity of terpenes (C10H16) is emitted by plants during both daytime and nighttime. Their reactions with the nitrate radical (NO3) can represent important formation pathways for both secondary organic aerosol (SOA) and organonitrates, which in turn provide critical reservoirs or sinks for NOx. However, the volatile product and aerosol formation of these reactions are poorly understood mechanistically, and are often heavily simplified in atmospheric models through the lumping of terpene reactants and the omission of product species. Here, we use atmospheric chamber studies to investigate the nighttime oxidation of nine abundantly emitted terpenes and pinonaldehyde, under conditions designed to mimic the biogenic-anthropogenic chemistry regime of the Southeast US, including high humidity (>60%), mixed NO3/O3 oxidation, and RO2 reactivity dominated by HO2 and RO2. Control ozonolysis experiments enable the isolation of SOA and product yields from the NO3 pathway. We propose mechanisms consistent with the products observed. We discuss the implications for terpene lumping methods in atmospheric models and provide model constraints for organonitrate and SOA production mixed biogenic/anthropogenic regions. We also discuss the open-access discovery and sharing of atmospheric chamber data in the ICARUS database (https://icarus.ucdavis.edu) for model mechanism development, with a demonstration of database capabilities and typical data management workflows.

Additional Authors: Kelvin H. Bates, UC Davis and Harvard


Mechanism Development and Reduction


Detailed multiphase chemistry modelling of methylamines with CAPRAM

By: Erik Hoffmann, Leibniz Institute for Tropospheric Research (TROPOS)

Presentation: Methylamines (MAs) are important atmospheric organic nitrogen compounds. Laboratory and field studies demonstrated their importance for new particle formation, increase of secondary organic aerosol mass and the aerosol acidity. However, high uncertainties exist regarding these effects because the complex multiphase interactions of MAs are not yet studied by near-explicit atmospheric chemistry models. Therefore, a detailed multiphase MA chemistry mechanism, the CAPRAM Amine module, has been developed to describe the oxidation of ammonia (NH3), monomethylamine (MMA), dimethylamine (DMA) and trimethylamine (TMA). Overall, the mechanism contains 537 reactions, thereof 233 gas-phase reactions 52 phase transfer processes, and 252 aqueous-phase reactions. Box model simulations of marine and remote environments were performed investigating the chemical multiphase processing of MAs and their products under both cloud and non-cloud conditions. Simulations indicate that uptake is a main loss term for DMA whereas it is gas-phase oxidation for TMA. The chemical rates analyses revealed that during cloud conditions TMA, DMA and MMA are degraded into DMA, MMA and NH3, respectively. Furthermore, autoxidation processes dominate the gas-phase oxidative fate of DMA and TMA. Because of the importance of DMA and TMA for new particle formation, the uncovered processes have to be included into higher-scale atmospheric chemistry models.

Additional Authors: Andreas Tilgner, TROPOS, Hartmut Herrmann, TROPOS


Designing chemical mechanisms for ozone and secondary organic aerosol endpoints

By: Havala Pye, US Environmental Protection Agency

Presentation: Chemical mechanisms are traditionally designed to predict ozone and related gas-phase endpoints, and mass is often duplicated for purposes of predicting secondary organic aerosol (SOA). In this work, we use the recently developed Community Regional Atmospheric Chemistry Multiphase Mechanism (CRACMM) to show that coupling gas-phase radical chemistry and SOA formation can have benefits for representing the full range of atmospheric reactive organic carbon (ROC). We find that considering SOA and retaining intermediate and lower volatility emissions expands the coverage of primary ROC mass by 40%. In addition, considering SOA products in gas-phase mechanisms sequesters HOX, decreasing ozone formation compared to default assumptions. In cases where traditional gas-phase products were previously represented as smaller carbon-number products, consideration of SOA also improves conservation of carbon mass throughout the system. Furthermore, linking SOA formation to gas-phase products allows CRACMM to represent SOA precursors not included in earlier generation mechanisms. Newly included precursors, such as phenolic, furanone, and aldehyde species that are produced in later generations from species such as benzene and terpenes, further increase the amount of SOA that can be captured in models.

Additional Authors: Bryan Place, ORISE Fellow at US Environmental Protection Agency; Ben Murphy, US Environmental Protection Agency; Karl Seltzer, US Environmental Protection Agency; Emma D’Ambro, US Environmental Protection Agency; Chris Allen, General Dynamics Information Technology; Ivan Piletic, US Environmental Protection Agency; Sara Farrell, ORISE Fellow at US Environmental Protection Agency; Rebecca Schwantes, NOAA Chemical Science Laboratory; Matthew Coggon, NOAA Chemical Science Laboratory; Emily Saunders, US Environmental Protection Agency; Lu Xu, NOAA/CIRES at University of Colorado, Boulder; Golam Sarwar, US Environmental Protection Agency; Bill Hutzell, US Environmental Protection Agency; Kristen Foley, US Environmental Protection Agency; George Pouliot, US Environmental Protection Agency; Jesse Bash, US Environmental Protection Agency; William R. Stockwell, University of Texas El Paso


A Broad View of Structure-Activity Relationship Performance for Alkanes and Haloalkanes

By: Max McGillen, CNRS

Presentation: As a subset of the gas kinetic database, the alkanes and haloalkanes possess some remarkable properties. Considering that they each share a common reaction mechanism with atmospheric oxidants, this group displays a wide range of reactivity. Furthermore, because of long-standing concerns over their effects upon climate, the ozone layer and climate, they have attracted a large amount of interest since the 1970s. As a result, there is a wealth of information that is known about them in terms of their kinetics, spectroscopy, thermodynamics and many other properties besides. The performances of the structure-activity relationships (SARs) and linear free-energy relationships (LFERs) that are available to the alkanes and haloalkanes are investigated. Well-known approaches such as the group-additivity approaches of Atkinson and co-workers and DeMore are found to perform well. However, there are many other methods including the LFERs between oxidants; with ionization potential; bond-dissociation energy; and other thermochemical approaches. These estimation methods also demonstrate good predictive power. Combining these developments with a new electrotopological approach that is unique to this study, a new level of coverage of the prediction-space of this family of compounds is achieved, and the possibility of an ensemble SAR prediction of rate coefficients is explored.

Additional Authors: John Orlando, NCAR Boulder


Multi-phase chemistry surrogate modeling with a recurrent neural network

By: Xiaokai Yang, University of Illinois Urbana-Champaign

Presentation: Modeling atmospheric chemistry and physics is computationally expensive, and the computation cost arises mainly from solving high-dimensional systems of stiff differential equations. Previous work has demonstrated the promise of machine learning (ML) to accelerate air quality model simulations but has suffered from numerical instability during simulations of seven days or longer. Here we use a recurrent neural network-based multi-phase chemistry surrogate model to predict the concentrations of air pollutants. First, we couple the near-explicit gas-phase Master Chemical Mechanism (MCM) with the state-of-art Particle-resolved Monte Carlo Model for Simulation Aerosol Interactions and Chemistry (PartMC-MOSAIC). The combined multi-phase chemical mechanism has more than 6,000 species and 16,000 chemical reactions. Second, we use an autoencoder to learn a compressed representation of the state of the chemical system to reduce memory usage and computational expense. Third, we structure our surrogate modeling framework as a series of first-order reactions for each chemical species, where each reaction rate and equilibrium concentration are predicted by a neural network. Preliminary training results on a small dataset of five cases and one day’s simulation are promising; we are currently working to scale up our training workflow to realize the full potential of this approach.

Additional Authors: Christopher Tessum, UIUC, Nicole Riemer, UIUC, Zhonghua Zheng, UIUC, Lin Guo, UIUC

An adaptive auto-reduction solver for speeding up integration of chemical kinetics in atmospheric chemistry models: implementation and evaluation within the Kinetic Pre-Processor (KPP) version 3.0.0

By: Haipeng Lin, Harvard University

Invited Presentation: Integration of chemical kinetics is a major computational bottleneck in the modeling of atmospheric chemistry. Chemical mechanisms for models typically include hundreds of coupled species, but a large fraction of the simulation domain typically does not require the complexity of the full mechanism. We develop an adaptive auto-reduction chemical solver which reduces any mechanism on the fly based on local conditions, partitioning species as “fast” or “slow” based on their production and loss rates. We use a dynamically defined partitioning threshold based on the production and loss rates of species central to the mechanism. We implement this solver as an option in a new version 3.0.0 of the Kinetic Pre-Processor (KPP) chemical solver software package, allowing it to be immediately applicable to any atmospheric chemistry mechanism using KPP, maintaining the same diagnostic and output capabilities as the full mechanism, and without requiring changes when the chemical mechanism is updated. We apply this adaptive solver to the GEOS-Chem global 3-D model and demonstrate a 32% reduction in solver time while maintaining a mean error lower than 1% for key species in the troposphere.

Additional Authors: Michael S. Long, Harvard University, Robert M. Yantosca, Harvard University, Rolf Sander, Max Planck Institute of Chemistry, Lu Shen, Peking University, Daniel J. Jacob, Harvard University


Comparing GECKO-A and MechGen as a basis for evaluation of simplified mechanisms

By: Julia Lee-Taylor, NCAR

Invited Presentation: Regional atmospheric chemical-transport models require chemical mechanisms that are greatly simplified in order to reduce operational computational demands. These reduced mechanisms must satisfactorily represent not only the influence of the precursor mixture on the tropospheric gaseous oxidative environment, but also its ability to form secondary organic aerosol. We have developed a framework for comparing two explicit benchmark models, GECKO-A, the “Generator of Explicit Chemistry and Kinetics of Organics in the Atmosphere” and MechGen, the “SAPRC Mechanism Generation System” in terms of bulk properties of their product mixtures. We present comparisons between the two model systems of parameters including OH and NO3 reactivity, and volatility and Henry’s law coefficient distributions. We compare bulk functional group analyses to diagnose differences between the model systems. We intend to use this framework to evaluate the output of simplified mechanisms against that of the explicit benchmark models.

Additional Authors: John Orlando, NCAR; Kelley Barsanti, UC Riverside; William Carter, UC Riverside; Samiha Shahid, UC Riverside; Bernard Aumont


Recent advances in SARs for the unimolecular chemistry of peroxy radicals

By: Luc Vereecken, Forschungszentrum Jülich GmbH

Invited Presentation: It is increasingly recognized that the chemistry of peroxy radicals, RO2, is more complex than previously thought. The current research focus has shifted towards atmospherically relevant environments with lower NOx concentrations, where the RO2 lifetime can easily exceed tens of seconds, and unimolecular chemistry of the RO2 radicals becomes important. This chemistry leads to formation of products that differs significantly from that in high-NOx environments; the observed formation of highly oxidized molecules, HOMs, through autoxidation processes, and their subsequent impact on SOA formation and growth, is a clear indication of this rich RO2 chemistry. Incorporating these RO2 processes in atmospheric kinetic models is demanding due to the complexity of the chemistry, and speciated experimental observation of the RO2 radicals remains difficult given the plethora of RO2 radical species and isomers being formed. To guide the construction of kinetic models, several structure-activity relationships (SARs) were recently formulated based on an extensive set of theoretical kinetic calculations. The SARs span a wide range of RO2 substitutions, and focus on the H-migrations and ring closure reactions that allow autoxidation of VOCs. It is found that unsaturated groups and oxygenated functionalities can lead to fast reactions with rates exceeding 1 s-1, while fast "scrambling" interconversion reactions between RO2 isomers by H-migration further increase the autoxidation chain length.

Additional Authors: Barbara Nozière, KTH Royal Institute of Technology, Stockholm, Sweden ; H. M. T. Nguyen, Hanoi National University of Education, Hanoi, Vietnam ; Giang Vu, Hanoi National University of Education, Hanoi, Vietnam ; Andreas Wahner, Forschungszentrum Jülich GmbH, Jülich, Germany ; Astrid Kiendler-Scharr, Forschungszentrum Jülich GmbH, Jülich, Germany


An Online-Learned Neural Network Chemical Solver for Stable Long-Term Global Simulations of Atmospheric Chemistry

By: Makoto Kelp, Harvard University

Invited Presentation: A major computational barrier in global modeling of atmospheric chemistry is the numerical integration of the coupled kinetic equations describing the chemical mechanism. Machine-learned (ML) solvers can offer order of magnitude speedup relative to conventional implicit solvers but past implementations have suffered from fast error growth and only run for short simulation times (<1 month). A successful ML solver for global models must avoid error growth over yearlong simulations and allow for reinitialization of the chemical trajectory by transport at every time step. Here, we explore the capability of a neural network solver equipped with an autoencoder to achieve stable full-year simulations of tropospheric oxidant chemistry in the global 3-D GEOS-Chem model. We find that online training of the ML solver within GEOS-Chem is important for accuracy, whereas offline training from archived GEOS-Chem inputs/outputs produces large errors. After online training, we achieve stable 1-year simulations with 5x speedup compared to the standard Rosenbrock solver with global tropospheric normalized mean biases of −0.3% for ozone, 1% for hydrogen oxide radicals, and −5% for nitrogen oxides. There are however large regional biases for ozone and NOx under remote conditions where chemical aging leads to error accumulation. These regional biases remain a major limitation for practical application, and ML emulation would be more difficult in a more complex mechanism.

Additional Authors: Daniel J. Jacob, Harvard Haipeng Lin, Harvard Melissa P. Sulprizio, Harvard


Modeling at multiple scales of chemical complexity and spatial resolution


Modeling the multiphase chemistry of isoprene-related organic hydroxy hydroperoxides and epoxides with MCM/CAPRAM

By: Andreas Tilgner, Leibniz Institute for Tropospheric Research (TROPOS)

Presentation: Oxidation of isoprene under low NOx conditions leads to formation of oxygenated organic hydroperoxides, ISOPOOHs and ISOP(OOH)2, and epoxides (IEPOX) that chemically interact with deliquesced particles and clouds. A CAPRAM mechanism module is developed focusing on the multiphase chemistry of these compounds. For ISOPOOHs/ISOP(OOH)2 the module contains phase transfer, aqueous photolysis, thermal decomposition, S(IV) oxidation and OH oxidation. In the base mechanism, no Fenton-like reactions for ISOPOOH/ISOP(OOH)2 are considered due to potentially uncertain reaction rate coefficients. But for sensitivity studies recently published constants were tested. For IEPOX, uptake, aqueous OH oxidation of IEPOX and its reaction products were included. In total, the module contains 12 gas-phase and 142 aqueous-phase reactions as well as 20 phase transfer processes. The CAPRAM module was coupled to the multiphase mechanism MCMv3.3.1/CAPRAM4.0. Subsequently, detailed box model studies were performed for remote non-permanent cloud scenarios. The simulations show that ISOPOOH and IEPOX chemistry contribute substantially to aqSOA formation. Sensitivity studies demonstrate that Fenton-like chemistry of ISOPOOH has high impact on aqueous-phase HOx. Thus, aqSOA yield under remote conditions depends on multiphase chemistry of isoprene oxidation products and Fenton-like chemistry. The studies exhibit the need for more kinetic and mechanistic process knowledge to build more sophisticated mechanisms.

Additional Authors: Erik H. Hoffmann, TROPOS, Marvel B. E. Aiyuk, TROPOS, Hartmut Herrmann,TROPOS


Climate forcing from vegetation emissions strongly influenced by the chemical mechanism employed.

By: James Weber, University of Sheffield

Presentation: Emissions of biogenic volatile organic compounds (BVOCs) affect climate via formation of organic aerosols and their influence on cloud properties, and via atmospheric oxidation changes influencing the greenhouse gases ozone and methane. Despite recent scientific advances, there remains considerable uncertainty between model simulations in the net impact BVOCs have on climate. One contributor to this uncertainty is the description of BVOC chemistry (i.e. the chemical mechanism), hitherto minimally assessed in a climate context. Using the Earth system model UKESM1 we quantify the influence of chemistry by comparing the climate response to a doubling of BVOC emissions in a pre-industrial (PI) atmosphere with standard and state-of-science chemistry mechanisms. The net feedback from BVOCs is positive in UKESM1, regardless of the mechanism used. The negative feedback from enhanced aerosol scattering is outweighed by positive feedbacks from increases in ozone and methane, and changes to aerosol-cloud interactions (ACI). Contrary to prior studies, we show the ACI response is driven by reductions in cloud droplet number concentration (CDNC) via oxidant-driven suppression of gas phase SO2 oxidation. However, with the state-of-science mechanism the feedback is 43% smaller due to lower oxidant depletion yielding smaller methane increases and smaller CDNC decreases. This illustrates the significant influence of the chemical mechanism on the climatic impact of BVOC emission changes.

Additional Authors: Scott Archer-Nicholls, University of Manchester, N. Luke Abraham, University of Cambridge, Youngsub Matthew Shin, University of Cambridge, Paul Griffiths, University of Cambridge, Daniel P. Grovesnor, University of Leeds, Catherine E. Scott, University of Leeds, Alex T. Archibald, University of Cambridge

Urban and Remote cheMistry modELLing with the new chemical mechnaism URMELL

By: Marie Luttkus, Leibniz Institute for Tropospheric Research (TROPOS)

Presentation: For a better representation of NMVOC chemical degradation a new chemical mechanism has been developed suitable for Urban and Remote cheMistry modELLing (URMELL). URMELL is based on the chemical mechanism ECHAM6.3-HAM2.3-MOZ1.0 JAM version 002b (Schultz et al. 2017). The mechanism was first updated using the latest recommendations of kinetic reaction rate constants as well as oxidation products mainly using IUPAC and MCMv3.3.1 as well as recent publications (e.g. Cox et al., 2020; Jenkins et al., 2018 & 2019; Mellouki et al., 2021; Sheps et al., 2017; Vereecken et al., 2021; Wennberg et al., 2018). The central focus of the mechanism development has been the integration of a comprehensive anthropogenic (mainly aromatics) and biogenic (mainly isoprene) VOC degradation scheme focusing on the formation of SOA compounds enabling a direct SOA determination. About 90 possible substances have been identified, whereby the volatility of the substance decrease with increasing level of functionalisation with hydroperoxides showing the most significant SOA forming potential. Here, an explicit SOA module has been established and applied in a CTM to investigate the BVOC/O3/NOx/SOA interrelations.

Additional Authors: Ralf Woke, TROPOS, Andreas Tilgner, TROPOS, Erik Hans Hoffmann, TROPOS


Plans For Enhanced Research Capabilities for Atmospheric Chemistry within NOAA’s Unified Forecasting System

By: Rebecca Schwantes, NOAA Chemical Sciences Laboratory

Invited Presentation: NOAA’s Unified Forecasting System (UFS) is a community-based Earth modeling system that plans to provide a framework to efficiently incorporate research advances into NOAA’s operational forecasts. Currently, the simplified aerosol scheme, GOCART, is incorporated into the UFS with minimal gas-phase chemistry. We will discuss our plans for adding innovative research capabilities for improving chemistry and aerosol processes and thereby predictions of air quality and atmospheric composition into the UFS. These enhanced research capabilities will include: 1) Options to use gas and aerosol chemical mechanisms of varying complexity. 2) Ability to easily couple different mechanisms to different physics options. 3) Development of a more flexible emissions processing system. 4) Further investment of model evaluation tools like MELODIES-MONET (https://melodies-monet.readthedocs.io) that efficiently compare model results against a variety of observations. These capabilities will be added into a flexible, easy to modify, and well-documented infrastructure. In this work, we will use the Model Independent Chemistry Module, which is a component of the MUlti-Scale Infrastructure for Chemistry and Aerosols, led by NCAR. By discussing our plans, we hope to get input early in the process on whether these enhancements will meet the needs of the research community, so as to ensure the UFS accomplishes one of its main goals to efficiently update NOAA’s operational forecasts with research advances.

Additional Authors: Georg Grell, NOAA Global Systems Laboratory, Barry Baker, NOAA Air Resources Laboratory, Mary Barth, NCAR, Lori Bruhwiler, NOAA Global Modeling Laboratory, Larry Horowitz, NOAA Geophysical Fluid Dynamics Laboratory, Shobha Kondragunta, NOAA National Environmental Satellite Data & Information Service, Jian He, CIRES & NOAA Chemical Sciences Laboratory, Siyuan Wang, CIRES & NOAA Chemical Sciences Laboratory, Meng Li, CIRES & NOAA Chemical Sciences Laboratory, Brian McDonald, NOAA Chemical Sciences Laboratory, Greg Frost, NOAA Chemical Sciences Laboratory, Li Zhang, CIRES & NOAA Global Systems Laboratory, Shan Sun, NOAA Global Systems Laboratory, Jordan Schnell, CIRES & NOAA Global Systems Laboratory, Ravan Ahmadov, CIRES & NOAA Global Systems Laboratory, Patrick Campbell, George Mason University & NOAA Air Resources Laboratory, Youhua Tang, George Mason University & NOAA Air Resources Laboratory, Louisa Emmons, NCAR, Gabriele Pfister, NCAR, Matthew Dawson, NCAR, Alma Hodzic, NCAR, Fabien Paulot, NOAA Geophysical Fluid Dynamics Laboratory


Developing a new ocean-atmosphere exchange model to calculate iodine emissions and better constrain their role in tropospheric chemistry

By: Ryan Pound, University of York

Invited Presentation: Marine emissions of iodine play an important role in regulating tropospheric photochemistry. In the troposphere iodine chemistry removes approximately as much O3 as is created by isoprene. The largest source of atmospheric iodine is from inorganic ocean emissions of HOI and I2. HOI and I2 production in the ocean surface microlayer (SML) is initiated by O3 deposition to the ocean and is dependent on physical,chemical, and biological processes. Despite iodine’s importance in atmospheric chemistry and a growing body of research on this, many uncertainties in iodine emissions still remain. We will present a new, multi-level model of the SML which couples O3 dry deposition to SML chemical and physical processes to calculate the atmospheric flux of HOI and I2. We parameterize this model to allow implementation of an improved representation of iodine fluxes into the atmosphere in a 3D chemistry transport model (GEOS-Chem). This more advanced representation of iodine emissions is used to further constrain and understand the role of iodine in global tropospheric photochemistry.

Additional Authors: Mat Evans, University of York, Lucy Carpenter, University of York


New and Emerging Air Pollutants (HAPs, VCPs, PFAS)


Personal care product VOC emissions: Indoor air quality impacts and estimated inhaled dosage from use

By: Amber Yeoman, The University of York

Presentation: Historically, air quality concerns have focussed on outdoor air pollution. Interest in indoor air pollution has only more recently been piqued, particularly since the Coronavirus pandemic. As we spend on average 90% of our time indoors the quality of the air we breathe is important to our wellbeing. A major contributor to indoor air pollution is the VOCs stemming from the use of personal care products (PCPs). Whilst exposure to these pollutants can cause negative health effects in all, the risk is significantly greater for those applying products to themselves due to the close proximity of application area to the inhalation exposure pathway (nose and mouth), particularly for facial products. Solvents and fragrance compounds dominate emissions, but more surprising contaminant species such as benzene and toluene are also present. Utilizing Quadrupole-Time of Flight Gas Chromatography/Mass Spectrometry (Q-TOF GC/MS), Selected-Ion Flow-Tube Mass Spectrometry (SIFT-MS), and an innovative in-house built applicant respiration replica we identify and quantify VOC emissions from facial PCPs and replicate real-life use to determine the resulting inhalation risks. This talk outlines the investigative process, experimental setup, key VOCs identified and their emission factors, and negative outcomes from a health perspective to both product applicants and those breathing ambient indoor air.

Additional Authors: Alastair Lewis, NCAS, UoY, Marvin Shaw, NCAS, UoY, Stephen Andrews, NCAS, UOY


Chemical characteristics of indoor aerosol particles and surface films

By: Rachel O'Brien, University of Michigan

Presentation: Indoor surfaces and the films on them play important roles in indoor air quality due to the high surface area to volume ratios in our homes. These films are formed from the deposition of aerosol particles and the sorption of semi-volatile organic compounds and are thus often complex mixtures of organic chemicals. The composition of these films will play a role in their behavior indoors, so an improved understanding of the important chemical classes found in these films will help model predictions for partitioning of organic chemicals in indoor air. Important sources for chemicals in these films are cooking, cleaning, and aerosol particles from outdoors including wildfire smoke. Cooking can be a large source for semi-volatile and lower volatility organic compounds. Cleaning processes can generate aerosol particles and leave behind lower volatility material on indoor surfaces. Depending on the distance of the building from the fire, biomass burning organic aerosol particles (BBOA) can reach indoor spaces at different levels of aging. Here, we investigate the chemical composition of surface films formed on impermeable surfaces during different activities. We also investigate the correlations between this composition, and the composition of size resolved aerosol particles collected at the NIST (National Institute of Standards and Technology) Net-Zero Energy Residential Test Facility during the CASA (Chemical Assessment of Surface and Air) field campaign.

Additional Authors: Amy Hrdina, MIT; Emily Legaard, William & Mary; Churchill Wilkinson, William & Mary; Kathryn Mayer, Colorado State; Sumit Sankhyan, CU Boulder; Dustin Poppendieck, NIST; Delphine Farmer, Colorado State; Marina Vance CU Boulder


Drivers of Perfluorocarboxylic Acid (PFCA) Gas-Particle Partitioning: Modeled Properties and Observational Constraints

By: Trevor VandenBoer, York University

Presentation: The atmospheric fate of perfluorocarboxylic acids (PFCAs) is attracting increasing attention due to the role of the atmosphere in global transport of these hazardous chemicals. There is a gap in our understanding of their gas-particle partitioning, limited by available measurements, and accurate partitioning properties. We model phase partitioning of C2-C14 PFCAs in the atmosphere including deprotonation and phase partitioning equilibria among air, aerosol liquid water, and particulate water-insoluble organic matter using a range of model-derived PFCA properties. Water and organic matter content are systematically varied across a full range of atmospheric conditions. Except during severe organic matter pollution episodes, shorter-chain PFCAs are predicted to mainly partition between air and aqueous phases, while for C12 and longer PFCAs, organic matter becomes the dominant particle phase sink. The partitioning framework underestimates the particle fraction of C2-C8 PFCAs compared with several ambient observations, with discrepancies increasing for longer-chain PFCAs. One to three orders of magnitudes higher particle/gas equilibrium ratios are required to fulfill the agreement. The discrepancy could result from externally mixed dust components, non-ideality of aerosol liquid water, and missed interactions between organic matter and charged PFCA molecules. High time resolution measurements of ambient PFCAs are needed to improve environmental fate modeling of ambient PFCAs.

Additional Authors: Ye Tao, York University, RenXi Ye, York University, Cora Young, York University


Volatile Organic Compounds inside Homes Impacted by Smoke from the Marshall Fire

By: Joost de Gouw, University of Colorado Boulder

Invited Presentation: The Marshall Fire in Colorado started as a grass fire on 30 December 2021, grew uncontrollably in hurricane-force winds, and burned more than 1,000 homes and commercial buildings in different parts of Boulder County within hours. Smoke from the fires infiltrated into undamaged homes surrounding the burnt areas, left ash and soot behind, and impacted indoor air quality very noticeably to the evacuees returning to their homes. Our group started making measurements of volatile organic compounds (VOCs) inside smoke-impacted homes within days after the fire and these continued for about five weeks. We found that levels of VOCs gradually decreased until February, when they had become indistinguishable from levels that are normally observed inside homes. The Marshall Fire was largely fueled by building materials, furniture, vehicles, and other man-made materials rather than by vegetation. As a result, VOCs that are non-typical for biomass burning can be expected and some evidence is reported. People were advised to increase ventilation and add filtration by activated carbon to their homes, and the effectiveness of these measures is illustrated. We also made measurements before, during and after professional home restoration efforts and will present how these impacted indoor VOC concentrations.

Additional Authors: William Dresser, University of Colorado Boulder; Abigail Koss, Tofwerk; Evan Coffey, University of Colorado Boulder; Avery Hatch, University of Colorado Boulder; Caroline Frischmon, University of Colorado Boulder; Helen Pliszka, University of Colorado Boulder; Jonathan Silberstein, University of Colorado Boulder; Bart Croes, University of Colorado Boulder; Christine Wiedinmyer, University of Colorado Boulder; Marina Vance, University of Colorado Boulder; Michael Hannigan, University of Colorado Boulder


A Better Representation of VOC chemistry from VCP and Cooking emissions in WRF-Chem

By: Qindan Zhu, Cooperative Institute for Research in Environmental Sciences and the NOAA Chemical Sciences Laboratory

Invited Presentation: Volatile organic compounds (VOCs) fuel the production of air pollutants like ozone and particulate matter (PM) through reactions with hydroxyl radicals (OH) and nitrogen oxides (NOx). The representation of VOCs chemistry remains challenging in reduced chemical mechanisms due to its complexity in speciation and reactions. We are developing a chemical mechanism compatible with WRF-Chem that better represents VOC chemistry in urban areas such as Los Angeles. This chemical mechanism, RACM2_BERK_VCP, is based on RACM2_Berkeley mechanism and includes more complex oxygenated VOC chemistry to address the impact of VCP and cooking emissions. We then incorporate the TUV photolysis scheme, a more complex SOA_VBS scheme, and aerosol uptake reactions to better represent photolysis, aerosol, and ozone. We also add five new species, D4 siloxane, D5 siloxane, p-Dichlorobenzene, and PCBTF as VCP tracers and nonanal as a cooking emission tracer. We evaluate how well this RACM2_BERK_VCP mechanism simulates VOC chemistry and ozone in WRF-Chem by comparing it against the airborne VOC measurements during RECAP-CA field campaign, as well as surface ozone (O3) monitors from Airnow network in June 2021, LA. We discuss how O3 changes due to different VOC emission sectors and provide insights on VOC emission control strategy for ozone regulations. We also show that adding missing VOC reactivity is important for models to accurately represent OH.

Additional Authors: Rebecca Schwantes, NOAA Chemical Sciences Laboratory, Boulder, CO Brian McDonald, NOAA Chemical Sciences Laboratory, Boulder, CO Matthew Coggon, NOAA Chemical Sciences Laboratory, Boulder, CO Colin Harkins, Cooperative Institute for Research in Environmental Sciences - University of Colorado Boulder and NOAA Chemical Sciences Laboratory, Boulder, CO Jian He, Cooperative Institute for Research in Environmental Sciences - University of Colorado Boulder and NOAA Chemical Sciences Laboratory, Boulder, CO Meng Li, Cooperative Institute for Research in Environmental Sciences - University of Colorado Boulder and NOAA Chemical Sciences Laboratory, Boulder, CO Chelsea Stockwell, Cooperative Institute for Research in Environmental Sciences - University of Colorado Boulder and NOAA Chemical Sciences Laboratory, Boulder, CO Bryan Place, Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720, now at U.S. Environmental Protection Agency Eva Y. Pfannerstill, Department of Environmental Science, Policy, and Management, University of California, Berkeley, Berkeley, CA 94720 Clara M. Nussbaumer, Department of Atmospheric Chemistry, Max Planck Institute for Chemistry, 55128 Mainz, Germany Paul Wooldridge, Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720 Benjamin, C. Schulze, Department of Environmental Science and Engineering, California Institute of Technology, Pasadena, CA 91125, USA Caleb Arata, Department of Civil and Environmental Engineering, University of California, Berkeley, Berkeley, CA 94720 Anthony Bucholtz, Department of Meteorology, Naval Postgraduate School, Monterey, CA 93943, USA John H. Seinfeld, Department of Environmental Science and Engineering, California Institute of Technology, Pasadena, CA 91125, USA Allen H. Goldstein, Department of Civil and Environmental Engineering, University of California, Berkeley, Berkeley, CA 94720; Department of Environmental Science and Policy Management, University of California, Berkeley, Berkeley, CA 94720 Ron C. Cohen, Department of Earth and Planetary Sciences, University of California, Berkeley, Berkeley, CA 94720; Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720


Observations of Chlorinated Amines in an Urban Atmosphere in Summer and Winter

By: Jon Abbatt, University of Toronto

Invited Presentation: In this work, we present the first quantified analyses of chlorinated amines – monochloramine (NH2Cl), dichloramine (NHCl2), trichloramine (NCl3) – in the outdoor atmosphere. In particular, we used both proton-transfer-reaction mass spectrometry and iodide ion chemical ionization mass spectrometry to detect these molecules in downtown Toronto during campaigns in the summer of 2020 and the winter of 2021. Mixing ratios were especially high in the summer, repeatedly approaching ppbv levels during the nighttime for both NH2Cl and NHCl2. Mixing ratios during the daytime and in the winter were generally quite a bit lower, at the pptv level. The mixing ratios of NCl3 were at the 1 to 10 pptv level for most time periods. It is likely that NCl3 readily photolyses in sunlight, most likely forming Cl atoms which are able to initiate oxidation reactions in the atmosphere. We demonstrate that the daytime measurements of NCl3 imply that it is a photolytic Cl-atom source of comparable strength to more traditional Cl-atom sources, such as ClNO2. The primary sources of the chloramines detected at this sampling location are not known. Whereas they can be released by water purification facilities and swimming pools, the transient nature of the NCl3 signals and its short calculated photolytic lifetime suggest a highly local source, perhaps due to chlorine-related cleaning and disinfection activities.

Additional Authors: Chen Wang, Southern University of Science and Technology


Sulfur Oxidation Advancements – Improving mechanisms and modelling


Assessing and improving the DMS oxidation mechanism in the MCM and CRI-Strat

By: Lorrie Jacob, University of Cambridge

Presentation: Dimethyl sulfide (DMS), which originates from phytoplankton, is the major natural source of sulfur compounds in the atmosphere. The oxidation products of DMS can form aerosols, which contribute to the formation of clouds, making them important for rain and the radiative balance of the planet. Additionally, due to DMS naturally occurring above oceans, an oxidation product of DMS, methanesulfonic acid (MSA), has been used to determine sea ice extent in ice cores up to 300 years in the past. However, due to gaps in the oxidation pathway of DMS, there are large uncertainties in the modelling of MSA formation. This project works with the box model BOXMOX, an extension to the KPP, incorporating the Master Chemical Mechanism (MCM) and CRI-Strat, to assess the mechanisms in light of gas-phase experiments, both in NOx and NOx-free conditions. Additionally, the effect of additional reactions to CRI-Strat was explored. Through comparing the model outputs with the experiments, the models were found to have similar results in the NOx-free conditions, and accurately modelled dimethyl sulfoxide (DMSO) and sulfur dioxide (SO2). In the experiments with NOx, the model outputs differed from each other, and the experiments. MSA was overestimated, and SO2 was both over and underestimated by the models. The addition of a DMSO2 formation reaction had the biggest effect on the model runs, allowing CRI-Strat to model the experiment more closely.

Additional Authors: Chiara Giorio, University of Cambridge, Alex Archibald, University of Cambridge


Sulfur radical formation from the tropospheric irradiation of aqueous sulfate aerosols

By: Kelvin Bates, University of California, Davis

Presentation: The sulfate anion radical (SO4•–) is known to be formed in the autoxidation chain of sulfur dioxide, and from minor reactions when sulfate or bisulfate ions are activated by OH radicals, NO3 radicals, or iron. Here we report a new source of SO4•–, from the irradiation of the liquid water of sulfate-containing organic aerosol particles under natural sunlight and laboratory ultraviolet radiation. Irradiation of aqueous sulfate mixed with a variety of atmospherically relevant organic compounds degrades the organics well within the typical lifetime of aerosols in the atmosphere. Products of the SO4•– + organic reaction include surface-active organosulfates and small organic acids, alongside other products. Scavenging and deoxygenated experiments indicate that SO4•– radicals, instead of OH, drive the reaction. Ion substitution experiments confirm that sulfate ions are necessary for organic reactivity, while the cation is nearly irrelevant. The reaction proceeds at pH 1-6, implicating both bisulfate and sulfate in the formation of photoinduced SO4•–. Certain aromatic species may further accelerate the reaction through synergy. This new reaction may impact our understanding of atmospheric sulfur reactions, aerosol properties, and organic aerosol lifetimes when inserted into aqueous chemistry model mechanisms.

Additional Authors: James Cope, UC Davis, Lillian Tran, UC Davis, Karizza Abellar, UC Davis, Tran Nguyen, UC Davis


Chamber studies of the oxidation of DMS, DMDS, and DMSO: Mechanism and aerosol formation

By: Matthew Goss, Massachusetts Institute of Technology

Presentation: The use of chemical ionization mass spectrometry has enabled recent advances in our understanding of the oxidation of dimethyl sulfide (DMS), which is central to the atmospheric sulfur cycle and secondary aerosol formation over the oceans. Here we apply these same approaches to study the oxidation of two related compounds, dimethyl disulfide (DMDS) and dimethyl sulfoxide (DMSO). DMDS and DMSO are themselves atmospherically-relevant organosulfur compounds, and due to the presence of common intermediate species, they can also shed light on the DMS oxidation mechanism. Using chamber studies monitored with chemical ionization mass spectrometry and aerosol mass spectrometry, this work examines total gas- and particle-phase product distribution from the low- and high-NO oxidation of DMDS and DMSO. The evolving concentrations of reactants and products give new insight into the oxidation mechanisms of these two compounds, while also offering clues into the aerosol formation channels of the DMS oxidation mechanism.

Additional Authors: Qing Ye, National Center for Atmospheric Research, Yaowei Li, Harvard University, Frank Keutsch, Harvard University, Jesse Kroll, Massachusetts Institute of Technology


Investigation of the OCS formation from the oxidation of DMS in marine-like conditions.

By: Anna Novelli, Institute of Energy and Climate Research, IEK-8: Troposphere, Forschungszentrum Jülich

Invited Presentation: Carbonyl sulfide (OCS) is the most abundant sulfur-containing gas in the Earth’s atmosphere playing a pivotal role as precursor to sulfate aerosol in the stratosphere. In the troposphere, dominant sources of OCS are oceans and anthropogenic emissions while consumption by the terrestrial biosphere is the largest sink. The marine environment is the dominant source region for OCS with comparisons between observations and models indicating that there is either an over-estimation of the terrestrial OCS sink or an unaccounted source over the tropical oceans. New chemical paths have been found for the peroxy radical formed from the oxidation of DMS by the OH radical that may impact the yield of OCS. We performed experiments in the atmospheric simulation chamber SAPHIR to elucidate the DMS oxidation chemical mechanisms focusing on the paths leading to the formation of OCS. The experiments were performed at atmospherically relevant conditions initiating the DMS oxidation with OH and Cl radicals and with measurements of precursors, radicals, OCS and oxidation products. An unexpected high yield of 7% for OCS was found for all experimental conditions. Concentrations of measured species were compared to results from a detailed chemical mechanism, which includes new chemical paths derived a-priori from theoretical calculations with the observed OCS being underestimated. We suggest additional paths and adjustment of rate coefficients to bring measurements and model results into agreement.

Additional Authors: Luc Vereecken, IEK-8: Troposphere, Forschungszentrum Jülich, Marc Von Hobe, IEK-7: Stratosphere, Forschungszentrum Jülich, Fred Stroh, IEK-7: Stratosphere, Forschungszentrum Jülich, Chenxi Qiu, IEK-7: Stratosphere, Forschungszentrum Jülich, Yun Li, IEK-8: Troposphere, Forschungszentrum Jülich, Franz Rohrer, IEK-8: Troposphere, Forschungszentrum Jülich, Hendrik Fuchs, IEK-8: Troposphere, Forschungszentrum Jülich, Hans-Peter Dorn, IEK-8: Troposphere, Forschungszentrum Jülich, Sergey Gromov, Max Plank Institute for Chemistry, Mainz, Sergej Wedel, IEK-8: Troposphere, Forschungszentrum Jülich, Martin Riese, IEK-7: Stratosphere, Forschungszentrum Jülich, Andreas Wahner, IEK-8: Troposphere, Forschungszentrum Jülich,Astrid Kiendler-Scharr IEK-8: Troposphere, Forschungszentrum Jülich, and Domenico Taraborrelli, IEK-8: Troposphere, Forschungszentrum Jülich