Lightning Talks & Poster Presentations

Lightning Talks & Poster Presentations

NO3 Initiated Oxidation of Furan Compounds: Rate Coefficients, Gas-Phase Chemical Mechanisms and SOA Formation

Poster Competition

Presented by: Fatima AL ALI, Université du Littoral Côte d'Opale

Lightning Talk & Poster Display: Furan compounds are emitted in substantial quantities from biomass burning, greatly participating in OH and NO3 reactivity. In this work, we investigate the NO3 reaction of furan, 2-methylfuran, 3-methylfuran, 2,5-dimethylfuran, and 2,3,5-trimethylfuran. Experiments were performed in CHARME simulation chamber at 294 ± 2 K, atmospheric pressure and under dry conditions (RH  2%). Rate coefficients were measured using the relative rate method and PTR-ToF-MS for monitoring of furan and reference compound concentrations vs. time. Oxidation product characterization and quantification were done using spectrometric (PTR-ToF-MS, TD-GC-MS, GC-MS, LC-MS-MS) and spectroscopic (FTIR) techniques allowing mechanism elucidation. SOA formation was followed by SMPS. Hence, the nighttime atmospheric removal of furan compounds upon reaction with NO3 is an important sink, with rate coefficients of 1.91 to 16.7 × 10-11 cm3 molecule-1 s-1. The mechanistic studies show that two major reaction pathways drive the NO3 reaction with methylated-furan: NO3 addition to carbon-2/5 of the ring and H-abstraction from the methyl(s) group(s).

Additional Authors: Cécile COEUR, ULCO, Nicolas HOUZEL, ULCO, Alexandre TOMAS, IMT NORD EUORPE, Manolis N. ROMANIAS, IMT NORD EUROPE.

Secondary Organic Aerosol (SOA) formation from the gas-phase reaction of guaiacol with NO3 radicals

Presented by: Fatima AL ALI, Université du Littoral Côte d'Opale

Poster Display Only: Guaiacol (2-methoxyphenol) is a major representative compound emitted by wood combustion consequently to the pyrolysis of lignin. With an atmospheric lifetime of 1 min with NO3, guaiacol has a high reactivity during night and is the main degradation pathway with the hydroxyl reactivity during day time. In this work, we investigate the SOA formation from the NO3 reaction of guaiacol. Experiments were performed in CHARME and LPCA-ONE atmospheric simulation chamber at 294 ± 2K, atmospheric pressure and under dry conditions (RH < 2%). Guaiacol gas concentration was measured using a PTR-ToF-MS and SOA formation was followed by a SMPS. After the full oxidation of gaseous guaiacol, SOA were collected on quartz filters and analyzed on a ESI-LC-QToF-MSMS to determine the aerosol chemical composition and the relative abundance. Experiments in both chambers showed good agreement for SOA formation from guaiacol and NO3 with yield values ranging from 0.01 and 0.21. Nineteen organic compounds (86 including isomers) have been identified in the SOA mainly represented by nitro-aromatic compounds confirming previous studies on NO3 reactivity with guaiacol derivatives. Nevertheless, and to our knowledge, it’s the first work concerning guaiacol to show compounds with molecular structures with one, two or three aromatic rings. A mechanism has been proposed to explain the formation of most compounds, especially the multiple aromatic rings compounds.

Additional Authors: Paul Genevray, ULCO, Lingshuo Meng, ULCO, Alexandre TOMAS, IMT Nord Europe, Cécile Cœur, ULCO

Development and evaluation of an improved mechanism for the oxidation of dimethyl sulfide in the UKCA model

Presented by: Alexander Archibald, University of Cambridge

Lightning Talk & Poster Display: Dimethyl sulfide (DMS) is an important trace gas emitted from the ocean. The oxidation of DMS is important for global climate through the role DMS plays in setting the sulfate aerosol background in the troposphere. However, the mechanisms of DMS oxidation are very complex and have proved elusive to accurately determine in spite of decades of research. As a result the representation of DMS oxidation in global chemistry-climate models is often greatly simplified. Recent field observations and laboratory studies have prompted renewed efforts in constraining the uncertainty in the oxidation mechanism of DMS as incorporated in global chemistry-climate models. Here we build on recent laboratory and observational evidence and develop a new DMS mechanism for inclusion in the UKCA chemistry-climate model. We compare our new mechanism to the existing UKCA mechanism and to a range of recently developed mechanisms reported in the literature through a series of global and box model experiments. Our box model experiments highlight that there is significant variance in simulated secondary oxidation products of DMS across mechanisms used in the literature, with divergence in the sensitivity of these products to temperature exhibited. Our global model studies show that our updated and improved DMS scheme performs better than the current scheme when compared against observations. However, sensitivity studies underscore the need for further laboratory and observational constraints.

Additional Authors: B. A. Cala, University of Cambridge and NIOZ Royal Netherlands Institute for Sea Research, Scott Archer-Nicholls University of Cambridge, James M. Weber University of Cambridge and Sheffield University, N. Luke Abraham, University of Cambridge, Paul T. Griffiths, University of Cambridge, Y.M. Shin, University of Cambridge, Matthew Woodhouse, CSIRO

Trace H2S Promotes Organic Aerosol Production and Organosulfur Compound Formation in Planetary Haze Photochemistry Experiments

Presented by: Eleanor Browne, University of Colorado Boulder & Cooperative Institute for Research in Environmental Sciences

Poster Display Only: Trace sulfur gases and planetary organic haze, produced by CH4 photochemistry, are ubiquitous in planetary atmospheres of the solar system and likely exoplanets. Their respective chemistries are also thought to be key in the understanding of the early Earth atmosphere. Investigation of sulfur chemistry has largely focused on the production of inorganic sulfur and has neglected the formation of organosulfur compounds. However, evidence from present-day studies shows that organosulfur contribute substantially to haze. Here, we performed laboratory studies to explore how the addition of trace amounts of H2S (0.5-5 ppmv) affects haze analogs produced from the ultraviolet photochemistry of CH4 and CO2/CH4 gas mixtures in N2. We analyzed the aerosol product composition and size in real time using a quadrupole aerosol mass spectrometer (Q-AMS) and a scanning mobility particle sizer (SMPS). We find that the inclusion of trace amounts of H2S in the precursor mixture significantly enhances the formation of organic aerosol mass, particle effective density, and leads to the formation of organosulfur compounds. Thiol-ene chemistry is proposed as a possible organosulfur formation mechanism. The altering of organic haze particle amount, size, and composition further suggests that trace amounts of H2S can impact how an organic haze affects climate, habitability, and prebiotic chemistry.

Additional Authors: Nathan W. Reed, CU Boulder & CIRES, Boswell A. Wing, CU Boulder, Margaret A. Tolbert, CU Boulder & CIRES

First Direct Kinetic Studies of Four-Carbon, Resonance-Stabilized Criegee Intermediates Formed from Isoprene Ozonolysis

Presented by: Rebecca Caravan, Argonne National Laboratory

Poster Display Only: Isoprene is the most abundant non-methane hydrocarbon emitted into Earth’s atmosphere. Ozonolysis of isoprene produces MVK-oxide ((CH2=CH)(CH3)COO) and MACR-oxide ((CH2=C(CH3))CHOO) – four-carbon, resonance-stabilized Criegee intermediates. We have utilized the novel photolytic schemes of the Lester group to conduct the first direct experimental kinetic studies of these intermediates. We will present results from experimental and theoretical studies of the reactions of MVK-oxide and MACR-oxide with atmospherically pertinent species, and discuss how these results impact our understanding of their role in Earth’s lower atmosphere. We will also compare their reactivity with that of MECI ((CH3CH2)(CH3)COO), which has the same carbon-backbone as MVK-oxide but lacks resonance stabilization. This material is based upon work supported by the Division of Chemical Sciences, Geosciences and Biosciences, Office of Basic Energy Sciences (BES), U.S. Department of Energy (USDOE) under contract no. DE-AC02-06CH11357 (Argonne), DE-FG02-87ER13792 (U Penn), DE-AC02-05CH11231 (ALS, LBNL). Sandia is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. This research was carried out in part by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA, supported by the Upper Atmosphere Research and Tropospheric Chemistry program © 2022, California Institute of Technology.

Additional Authors: Michael F. Vansco, Argonne National Laboratory & University of Pennsylvania, Kristen Zuraski, NASA Jet Propulsion Laboratory, Frank A. F. Winiberg, NASA Jet Propulsion Laboratory & California Institute of Technology, M. Anwar H. Khan, University of Bristol Tianlin Liu, University of Pennsylvania, Meijun Zou, University of Pennsylvania, Kendrew Au, Sandia National Laboratories, Charles A. Marcus, NASA Jet Propulsion Laboratory & California Institute of Technology, Nisalak Trongsiriwat, University of Pennsylvania, Yu-Lin Li, Academia Sinica & National Taiwan University, Yen-Hsiu Lin, Academia Sinica & National Taiwan University, Wen Chao, Academia Sinica, Jim Jr-Min Lin, Academia Sinica & National Taiwan University, Patrick J. Walsh, University of Pennsylvania, Dudley E. Shallcross, University of Bristol, Leonid Sheps, Sandia National Laboratories, David L. Osborn, Sandia National Laboratories & UC Davis, Carl J. Percival, NASA Jet Propulsion Laboratory Stephen J. Klippenstein, Argonne National Laboratory, Craig A. Taatjes, Sandia National Laboratories, Marsha I. Lester, University of Pennsylvania Rebecca L. Caravan, Argonne National Laboratory & NASA Jet Propulsion Laboratory & Sandia National Laboratories

Modeling the atmospheric fate of Per- and Polyfluoroalkyl Substances (PFAS)

Presented by: Emma D'Ambro, US EPA, ORD

Poster Display Only: Per- and polyfluoroalkyl substances (PFAS) are a class of human-made compounds that have received attention due to their presence in drinking water and resulting human exposure. More recently, air emissions, transport, and deposition have been identified as a likely pathway contributing to their water concentration. However, few studies have examined the air concentration and deposition of PFAS. One of the major impediments is the lack of emissions information since they are not a designated criteria or hazardous air pollutant and thus are not reported to regulatory agencies. Therefore, most modeling studies have focused on individual compounds and very few have investigated atmospheric chemical transformations. We present results from the Community Multiscale Air Quality (CMAQ) model applied to a case study of a fluoropolymer manufacturer in North Carolina. Emission rates of 53 speciated compounds were obtained for this point source, the most detailed emissions information from a point source to-date. Previously, we investigated the air concentrations and deposition extending up to ~150km from the facility. Here, we test the sensitivity of our previous results to different model inputs and find the level of chemical speciation is the most important factor for accurately predicting transport and deposition. Future work will implement the suite of PFAS and their known atmospheric oxidation reactions into a box model framework to understand PFAS chemistry and partitioning.

Additional Authors: Benjamin Murphy, US EPA, Havala Pye, US EPA

Atmospheric Chemical Reaction Mechanism Dependence on the Environment and Stellar Radiation

Poster Competition

Presented by: Alexandra Deal, CU Boulder/CIRES

Lightning Talk & Poster Display: Chemical mechanisms relevant to planetary atmospheres, including the contemporary and ancient Earth, are highly susceptible to the environment. For example, water is considered a necessary precursor for life yet many biotically relevant reactions are thermodynamically forbidden in bulk water (the “water paradox”). However, recent evidence shows that water-air interfaces are auspicious reaction environments for these reactions. Organic molecules concentrate at these interfaces, forming films with distinct compositions, morphologies, and optical and chemical properties, potentially resulting in a novel array of products. Furthermore, water-air interfaces and organic films would have ample access to starlight which provides a driving force for chemistry via energy transduction from stellar radiation to high energy chemical bonds. However, this chemistry is extremely sensitive to the environment and the stellar radiation spectrum, making fundamental mechanistic studies important to understand chemical reactions in all atmospheres. We use examples from the dark chemistry and photochemistry of α-oxoacids and α-hydroxyacids to illustrate the similarities and differences in their reaction mechanisms in different phases and under various stellar irradiative environments. By examining fundamental chemical reaction mechanisms of these molecules in atmospherically relevant environments, we begin to build a more general understanding of the available processes in diverse atmospheres.

Additional Authors: Veronica Vaida, CU Boulder/CIRES

Multi-day Evolution of Organic Aerosol Mass and Composition from Biomass Burning Emissions

Presented by: Abraham Dearden, Colorado State University

Poster Display Only: Biomass burning is an important source of primary organic aerosol (POA) and volatile organic compounds (VOCs) to the atmosphere. Yet there are uncertainties surrounding the oxidation chemistry of POA and VOCs leading to SOA formation. Lim et al. (2019) performed 50+ photooxidation experiments on biomass burning emissions using a small environmental chamber (~150 L) at the Fire Sciences Laboratory in Missoula MT. In this work, we used a kinetic model, SOM-TOMAS (Statistical Oxidation Model-TwO Moment Aerosol Sectional), to simulate the physicochemical evolution of organic aerosol (OA) in 15 of these chamber experiments. SOM-TOMAS simulates the oxidation chemistry, thermodynamics, and microphysics of OA, in addition to accounting for rapid dilution and wall losses. For most experiments the model was able to simulate the time-dependent evolution of the OA mass concentration but systematically underestimated the change in the OA O:C ratio with time. Simulations indicated that the same VOC classes that have previously been found to be important for SOA formation in smoke (oxygenated aromatic, heterocyclic, and semi-volatile compounds) at shorter photochemical ages (<12 hours) are also relevant at longer photochemical ages (~1 day to ~1 week). Heterogeneous oxidation, oligomerization, and assumptions about phase state modestly influenced the OA mass evolution. Ongoing work is focused on linking these laboratory insights to aircraft-based field measurements (e.g., WE-CAN, FIREX-AQ).

Additional Authors: Ali Akherati, UC Davis, Charles He, CSU, Christopher Lim, MIT, David Hagan, QuantAQ, Christopher Cappa, UC Davis, Jesse Kroll, Jeffrey Pierce, , CSU,Shantanu Jathar, CSU

Multi-scale modeling of air quality and mechanism comparison with MUSICA

Presented by: Louisa Emmons, NCAR

Poster Display Only: One of the key features in the design of the MUlti-Scale Infrastructure for Chemistry and Aerosols (MUSICA) is the ability to easily change chemical mechanisms within an earth system model such as the Community Earth System Model (CESM). This capability is being developed with the Model Independent Chemistry Model (MICM), which is currently available in a box model (MusicBox) and being coupled to CESM. Another key design feature of MUSICA is the ability to simulate local-to-global scales within a single model. MUSICAv0 is a configuration of the CAM-chem global chemistry climate model with variable resolution refined over arbitrary regions of the globe. This presentation will illustrate these two components of MUSICA. Results from MusicBox with MICM will show the comparison of complex and simplified mechanisms, quantifying their ability to predict atmospheric composition and air quality metrics. Results from MUSICAv0 simulations with refined regions over the U.S., Asia and Africa will illustrate the value of integrating regional scale modeling in a global model.

Additional Authors: Mary Barth, NCAR, Gabriele Pfister, NCAR, John Orlando, NCAR, Matthew Dawson, NCAR, Kyle Shores, NCAR, Kelley Barsanti, NCAR, Duseong Jo, NCAR, Wenfu Tang, NCAR

Investigation of nighttime chemistry of trans-2-hexene in the atmospheric simulation chamber SAPHIR

Poster Competition

Presented by: Michelle Färber, Forschungszentrum Jülich

Lightning Talk & Poster Display: Investigations of nighttime chemistry of selected alkenes such as trans-2- hexene, performed in the atmospheric simulation chamber SAPHIR at Forschungszentrum Jülich, Germany, revealed a discrepancy between measured and modelled HO2 and RO2 radical concentrations at high and medium levels of nitrogen dioxide (NO2, 40 ppbv) and ozone (O3, 25 ppbv), respectively. Such chemical conditions have been observed in cities characterised by high pollution such as London, UK, and Beijing, China. To further investigate the chemistry of organic peroxy radicals (RO2) from trans- 2-hexene at these conditions, we performed a series of O3+NO2 experiments in the atmospheric simulation chamber SAPHIR. The experiments were conducted for a range of NO2 concentrations and temperatures (0 to 40 ppbv and 5 to 35 °C, respectively) to test the chemistry between the RO2 radical and NO2 which is the main reaction partner for RO2 at these experimental conditions. For the ozonolysis (NO2=0) of trans-2-hexene, we find a good agreement between measured and modelled radical concentrations. However, with increasing NO2 concentration discrepancies appear due to the lack of RO2+NO2 reaction paths for most of the implemented RO2 in the model used. Due to the limited knowledge about both forward and backward reaction rates for the RO2+NO2 reaction, we derived a backward reaction rate obtained from our results and its impact on the modelled radical concentrations will be discussed in the presentation.

Additional Authors: Luc Vereecken, Institute of Energy and Climate Research, Troposphere (IEK-8), Forschungszentrum Jülich, Germany, Hendrik Fuchs, Institute of Energy and Climate Research, Troposphere (IEK-8), Forschungszentrum Jülich, Germany, Georgios Gkatzelis, Institute of Energy and Climate Research, Troposphere (IEK-8), Forschungszentrum Jülich, Germany, Franz Rohrer, Institute of Energy and Climate Research, Troposphere (IEK-8), Forschungszentrum Jülich, Germany, Sergej Wedel, Institute of Energy and Climate Research, Troposphere (IEK-8), Forschungszentrum Jülich, Germany, Andreas Wahner, Institute of Energy and Climate Research, Troposphere (IEK-8), Forschungszentrum Jülich, Germany, Astrid Kiendler-Scharr, Institute of Energy and Climate Research, Troposphere (IEK-8), Forschungszentrum Jülich, Germany, Anna Novelli, Institute of Energy and Climate Research, Troposphere (IEK-8), Forschungszentrum Jülich, Germany

Detection of Ambient Concentrations of Hydroxyl Radical using Broadband Cavity-Enhanced Absorption Spectroscopy

Presented by: Callum Flowerday, Brigham Young University (BYU)

Poster Display Only: The hydroxyl radical (OH) is responsible for the initiation of formation of a range of secondary pollutants in the atmosphere such as ozone and secondary organic aerosols. As such, it is a species of interest in monitoring and modelling of both biogenic and anthropogenic emissions. While methods of OH monitoring do exist, they tend to involve large, non-portable instruments and often do not measure OH directly but involve chemical ionization or the measurement of known products of reaction with OH. This work describes the development of a spectrometer utilizing broadband cavity-enhanced absorption spectroscopy (BBCEAS) to directly measure OH in the atmosphere. BBCEAS uses a high finesse optical cavity with highly reflective mirrors (>99.8% reflectivity) to create a long pathlength that provides the ability of in situ sampling. This portable BBCEAS spectrometer was made with an open cavity giving it the ability to directly measure ambient concentrations of OH radical. The instrument currently has a 3-sigma limit of detection for OH, determined using an environmental chamber, of 5 × 10^8 molecules cm^-3 using a 2.5 m base length cavity and a 30 min averages. Further improvements are being made to improve resolution and base pathlength to lower the detection limit to ambient atmospheric concentration levels.

Additional Authors: Callum E. Flowerday, BYU, Ryan Thalman, Snow College, Matthew C. Asplund, BYU, Samuel A. Badstubner, BYU, Adam K. Cook, BYU, Philip Lundrigan, BYU, Jaron C. Hansen, BYU

Unimolecular reactions of hydroxy-substituted Criegee Intermediates

Poster Competition

Presented by: Lauri Franzon, University of Helsinki

Lightning Talk & Poster Display: The chemistry of stabilized Criegee intermediates (sCI) is a subject of great interest to atmospheric chemistry as these form from ozonolysis, one of the most common atmospheric oxidation reactions. Studies on sCI reactions have however mainly focused on sCI:s formed from the ozonolysis of pure hydrocarbons. Unsaturated alcohols are the most common heteroatom-including alkenes in the atmosphere, and thus the unimolecular reactions of OH-substituted sCI:s are worth studying. This work is a computational investigation of thermal reaction rates for six simple OH-substituted sCI:s. Intramolecular H-shifts from the OH to the carbonyl oxide (COO) are compared to the most likely unimolecular reactions of the corresponding non-substituted sCI:s. Conformer analysis was performed for the sCI:s using Molecular Mechanics, and all conformers were characterized based on the relative positions of the OH and COO. The geometries of important conformers were optimized using wB97X-D/aug-cc-pVTZ, and electronic energy corrections were calculated using CCSD(T)-F12/VDZ-F12. CCSDT(Q) corrections were calculated for a select small molecules to better account for multi-configurational character. Reaction rates were calculated using the Eyring equation with Eckart tunneling corrections. Our results indicate that the H-shift from the OH is the main reaction pathway for all sCI:s with a suitable conformer, and that unimolecular reactions are likely to dominate for most simple OH-substituted sCI:s.

Additional Authors: Theo Kurtén, University of Helsinki

Atmospheric oxidation of imine derivative of piperazine initiated by OH radical.

Poster Competition

Presented by: Thomas Golin Almeida, University of Helsinki

Lightning Talk & Poster Display: Piperazine is a widely used amine as a solvent in carbon-capture (CC) technologies, which seek to mitigate the impact of fossil-fueled energy production on the climate. Concerned with the impact on air quality that atmospheric emissions of such amine may have, studies have observed the cyclic imine 1,2,3,6-tetrahydropyrazine (THPyz) to be its major photo-oxidation product. However, almost nothing is known about the fate of this imine. In fact, very few studies have focused on the atmospheric chemistry of imines in general, despite consistently appearing as major products of amine oxidation. In the presented work, we explored the reaction mechanism of THPyz oxidation initiated by OH radical, as well as the fate of the first-generation products, with quantum chemistry and theoretical kinetics methods. We predict that the major initial channels involve H-abstraction from a α-amino carbon, leading to subsequent formation of a second imine function. Typically carcinogenic compounds, nitrosamines are expected to have low but non-negligible yields, with a maximum value of ~3% under high NOx regimes. Pathways involving attack of the OH radical on the imine group are minor but still relatively competitive. One of these pathways (H-abstraction from the imine C) leads to the formation of an isocyanate function, potentially also imparting toxicity to the product. Even though it is a minor channel for THPyz, it could be more competitive in the atmospheric oxidation of other imines.

Additional Authors: Theo Kurtén, University of Helsinki

Acetonyl peroxy and hydro peroxy self- and cross- reactions: Temperature-dependent kinetics parameters, branching fractions, and chaperone effects

Presented by: Fred Grieman, NASA JPL

Poster Display Only: Acetone, one of the most abundant OVOCs in the atmosphere, leads to the formation of CH3C(O)CH2O2 radicals. The cross-reaction between CH3C(O)CH2O2 and HO2 is either a temporary reservoir reaction forming CH3C(O)CH2OOH or a radical propagation pathway forming OH + CH3C(O)CH2O. In this study, we have determined the temperature dependent kinetics parameters, branching fractions, and chaperone effects of the cross- and self-reactions between CH3C(O)CH2O2 and HO2 using Infrared Kinetic Spectroscopy (IRKS). As in our previous room temperature study, the IRKS system employed two tunable diode lasers, and a near-UV probe to measure three species (OH, HO2 and CH3C(O)CH2O2) independently and simultaneously on the µs time scale. The radical temporal profiles were analyzed to determine rate coefficients and uncertainties using the Markov Chain Monte Carlo (MCMC) algorithm to systematically determine the rate coefficients and their uncertainties. The acetone chaperone effect on the HO2 self-reaction was determined for the first time.

Additional Authors: Kristen Zuraski, Jet Propulsion Laboratory, Aileen O. Hui, Caltech, Julia Cowen, Pomona College, Frank A. F. Winiberg, Jet Propulsion Laboratory, Carl J. Percival, Jet Propulsion Laboratory, Mitchio Okumura, Caltech, Stanley P. Sander, Jet Propulsion Laboratory

Chemical surrogate modeling with uncertainty quantification using a Bayesian Neural ODE

Poster Competition

Presented by: Lin Guo, University of Illinois at Urbana-Champaign (UIUC)

Lightning Talk & Poster Display: Neural Ordinary Differential Equations (N-ODE) have shown promise in emulating models of atmospheric chemistry. Here we create a probabilistic (Bayesian) N-ODE to create a chemical mechanism with uncertainty quantification. We emulate a photochemical box model of atmospheric ozone formation with 10 reactions, 13 species, and external inputs of solar radiation, emission, and deposition. We use Stochastic Gradient Langevin Dynamics (SGLD) for model training. For cases where the solar radiation is constant and emission/deposition are disabled, the posterior mean gives accurate predictions with validation error (RMSE) 5.6 x 10-2 ppm and testing error (RMSE) 6.1 x 10-2 ppm (trained on 300 simulations of 30 min duration, validated on 100 simulations of 30 min duration and tested on 40 min duration). For cases with variable solar radiation and emission and deposition enabled, the model can probabilistically capture the periodicity of the system when trained on a single 4-day simulation and projected to its 7-day extension. Model performance remains good when trained on up to ~250 simulation examples. Future work will focus on scaling our training workflow to larger datasets.

Additional Authors: Xiaokai Yang, UIUC, Zhonghua Zheng, The University of Manchester, Nicole Riemer, UIUC, Christopher W. Tessum, UIUC.

Impacts of Low-Level Jets on Surface Temperature

Presented by: Jonathan Hale, UC Davis

Poster Display Only: Low-Level Jets (LLJs) are a nocturnal event, where concentrated high wind speeds flow together in the low levels of the atmosphere. They exist from a few hundred feet to five thousand feet above ground level. LLJs are formed by a difference in temperature and elevation between the West and East geographical locations in the United States. This research provides a new perspective by focusing on the influence of LLJs on local temperature. LLJs drive the transportation of air from the Southeastern U.S. to the mid-Atlantic. With this research, temperature changes due to the LLJ that occurred the night before will become visualized through curtain plots and temperature time series. In the work conducted, three different cities were chosen in the state of Maryland, during the day a LLJ occurred. The surface temperature and wind speeds of the LLJ was gathered through RADAR wind profiler data and the Automated Surface Observing System (ASOS) Network. With this data, subplots were created to highlight the effect of the wind speeds on the temperature at a given time. All in all, it was found that the greater the magnitude of the wind speed was, the greater the temperature increased by. This is due to the warm, moist air that is traveling from up the Gulf Stream to the mid-Atlantic U.S.

Additional Authors: Kylie Hoffman, University of Maryland Baltimore County, Dr. Ruben Delgado, University of Maryland Baltimore County

Computational Investigation of the Reaction Routes for 3(RO···OR′) Intermediates Formed in Peroxy Radical Self- and Cross-Reactions

Presented by: Galib Hasan, University of Helsinki

Lightning Talk & Poster Display: Gas phase dimer (accretion product) formation is regarded as a significant reaction in the atmosphere because it can lead to the formation of very-low volatility highly oxygenated organic molecules (HOMs), which later form aerosol particles. On the other hand, organic peroxy radical (RO2) are the key intermediates in the chemistry of the atmosphere. One of the main sink reactions of RO2 is the recombination reaction RO2 + R’O2 . This reaction goes through an intermediate complex (RO…3O2…OR’) and three major reaction channels: 1) R_H=O + R’OH 2) ROOR’, and 3) RO2+ R’O2. In our study, we performed a systematic conformation search on the 3(RO…R’O) cluster and tried to estimate the kinetics of the three channels. We have found that all these channels are indeed competitive (with typical rates of at least greater than 10^6 s-1, and many have rates exceeding 10^10 s-1) in the atmosphere. This suggests that the computationally proposed novel RO2 + RO2 reaction mechanism is qualitatively compatible with experimental results on accretion product formation and may thus play a key role in the formation of organic aerosols.

Additional Authors: Rashid R. Valiev, University of Helsinki, Vili-Taneli Salo, University of Helsinki, Theo Kurten, University of Helsinki

Influence of application method on disinfection byproduct formation during indoor cleaning: an example of phenol chlorination during bleach cleaning

Presented by: Leif Jahn, University of Texas at Austin

Poster Display: Large-scale disinfection methods that have become increasingly common following the COVID-19 pandemic utilize techniques such as electrostatic precipitators, foggers, or "no touch devices” that generate and disperse disinfectant-laden droplets. These devices are designed to work with a variety of disinfectants including those based on peroxides, reactive chlorine species, and quaternary ammonium compounds. Compared to traditional disinfection techniques such as mopping, the dispersal of droplets may alter disinfection byproduct formation and the partitioning of compounds away from or to the disinfectant. In this work we applied bleach within an environmental chamber containing several tables and chairs using a high-volume spraying device or an ultrasonic humidifier. Gas-phase species were measured using a Vocus 2R PTR-ToF-MS. We observe gas-phase phenol concentrations to decrease as bleach is applied, indicating partitioning of phenol to the disinfectant, which is accompanied by the formation of a variety of multi-generation polychlorinated phenolic disinfection byproducts that volatilize from airborne droplets. Greater byproduct formation was observed during experiments with a larger phenol background. The byproducts identified have been observed during prior wastewater disinfection work but primarily under slightly acidic to near neutral pH conditions, not representative of bulk bleach with a pH ~11-12, suggesting unique aspects to these reactions within airborne droplets.

Additional Authors: Nirvan Bhattacharyya, UT Austin, Daniel Blomdahl, UT Austin, Mengjia Tang, UT Austin, Pearl Abue, UT Austin, Atila Novoselac, UT Austin, Lea Hildebrandt Ruiz, UT Austin, Pawel Misztal, UT Austin

Volatile Chemical Product Contributions to the Urban Secondary Organic Aerosol Burden in the United States

Presented by: Shantanu Jathar, Colorado State University

Lightning Talk & Poster Display: Volatile chemical products (VCPs) are a large source of oxygenated volatile organic compound (OVOC) emissions into the urban atmosphere, yet the oxidation chemistry of OVOCs leading to SOA formation remains uncertain. In this work, we leveraged high NOx environmental chamber data gathered at the University of California Riverside to develop parameters to represent SOA formation from a suite of VCP OVOCs. These VCP OVOCs included glycols, glycol ethers, oxygenated aromatics, and acetates. The SOA parameters were developed using SOM-TOMAS, a kinetic model that simulates the oxidation chemistry, thermodynamic properties, and microphysics of SOA. The SOA parameters were able to reproduce time-dependent SOA mass concentrations and oxygen-to-carbon (O:C) ratios observed in the chamber experiments. These parameters for OVOCs along with historical parameters for volatile hydrocarbons were used to develop a box model to study urban SOA formation. Consistent with recent work, the box modeling results confirmed that VCPs account for more than half of all urban SOA formed from anthropogenic sources in Los Angeles, CA and New York City, NY. Of the SOA attributed to VCP use, more than three quarters of it arose from oxidation of VCP hydrocarbons (alkanes, aromatics, monoterpenes being dominant) and less than a quarter came from VCP OVOCs (terpenoids, glycol ethers being dominant). Ongoing work is focused on understanding fossil fuel contributions to anthropogenic SOA in other US cities.

Additional Authors: Sreejith Sasidharan, Colorado State University, Yicong He, Colorado State University, Qi Li, University of California Riverside, David Cocker, University of California Riverside, Karl Seltzer, US Environmental Protection Agency, Brian McDonald, National Oceanic and Atmospheric Administration, Jeffrey R. Pierce, Colorado State University

Ions diffuse slower than water in mixed organic/inorganic aerosol particles

Presented by: Liviana Klein, ETH Zurich

Poster Display Only: Internally mixed organic/inorganic aerosols have been the focus of numerous studies in recent years. Nevertheless, ion diffusivities, important for calculations of evaporation rates and gas-to-particle partitioning in these systems, are still poorly understood. In this study, we determine the ion and water diffusivities of an atmospherically relevant surrogate system containing sucrose and NH4NO3 – a ubiquitous semi-volatile inorganic compound. We measure evaporation rates of single particles, levitated in an electrodynamic balance (EDB), in an environment of varying relative humidity (RH). We further fit the experimental results with a particle-shell model to determine diffusion coefficients of water molecules and of the inorganic ions. At elevated and rapidly changing RH, water quickly evaporates such that mass transfer limitations are not easily detected. In contrast, at dry conditions (< 30% RH) the evaporation rates of NH3 and HNO3 are significantly lower compared to what is expected for internally well-mixed particles. Our modeling results show that at low humidities the diffusion coefficients of the ions are orders of magnitude lower than that of water. This is an interesting finding which has not been reported in the literature to date and has implications on our understanding of gas-to-particle partitioning.

Additional Authors: Beiping Luo, ETH Zurich, Nir Bluvshtein, ETH Zurich, Merete Bilde, Aarhus University, Thomas Peter, ETH Zurich, Ulrich K. Krieger, ETH Zurich

WiFEX: Walk into the warm fog over Indo Gangetic Plain region

Presented by: Rachana Kulkarni, self

Poster Display Only: The presence of persistent heavy fog in northern India during winter creates hazardous situations for transportation systems and disrupts the lives of about 400 million people. The meteorological factors responsible for its genesis and predictability are not yet completely understood in this region. WiFEX is a first-of-its-kind multi-institutional initiative dealing with intensive ground-based measurement campaigns for developing a suitable fog forecasting capability under the aegis of the smart cities mission of India. Between the 2015–2020 winters, measurement campaigns were conducted at the Indira Gandhi International Airport, New Delhi, covering more than 90 dense fog events. The field experiments involved extensive suites of in-situ instruments and gathered simultaneous observations of micro-meteorological conditions, radiative fluxes, turbulence, droplet/aerosols microphysics, aerosol optical properties, fog water-chemistry, and vertical thermodynamical structure to describe the environmental stability in which fog develops. These field observations helped to interpret the strengths and deficiencies in the numerical modeling framework. Four scientific objectives were pursued: (a) life cycle of optically thin and thick fog, (b) microphysical properties in the polluted boundary layer, (c) fog water chemistry, gas/aerosol partitioning during fog life-cycle, and (d) numerical prediction of fog.

Additional Authors: Sachin Ghude, IITM Pune, India; Sandip Wagh, IITM Pune, India; Ismile Gultepe, ECCC Ontario, Canada; Mrinal Biswas, NCAR Co, USA

Decoding VOC Photooxidation on a Molecular Level – A Novel Ensemble of Methods to Generate, Analyze, and Characterize Multifunctional Oxidation Products in the Gas and Particle Phase

Presented by: Finja Löher, University of Bayreuth

Poster Display Only: Tropospheric photooxidation of volatile organic compounds (VOCs) is closely associated with the formation of secondary organic aerosols (SOAs) and ground-level ozone. To elucidate underlying reactions, a molecular view on evolving multifunctional oxidation products is as useful as it is demanding. Here, we report first results from a newly integrated set-up enabling i) the controlled generation of photooxidation products, ii) their isomer-resolved analysis, and iii) assessments of their yields, gas-particle partitioning coefficients, and OH rate constants. For studying the photooxidation of anthropogenic and biogenic model VOCs (e.g. toluene, α-pinene), we performed experiments in a Teflon bag and a glass flow reactor at different temperatures, humidity levels, and NOx concentrations. The oxidized products were determined by SPME-GC-MS using a two-step derivatization scheme (Borrás et al. 2021) which extended the analytical range towards traditionally challenging compounds like aldehydes, ketones, carboxylic acids, and alcohols. Gas-phase products were monitored on-line while SOAs were collected and separated with cascade impactors prior to off-line analysis. As supplement, the relative rate method (Kato et al. 2011) provides an effective and coherent approach to assess the reaction of the emerging compounds with OH radicals. Jointly, these methods enable observations of the production and fate of atmospheric photooxidation products as key indicators of prevalent mechanisms.

Additional Authors: Elisabeth Eckenberger, University of Bayreuth, Esther Borrás, Fundación Centro de Estudios Ambientales del Mediterráneo (CEAM), Amalia Muñoz, Fundación Centro de Estudios Ambientales del Mediterráneo (CEAM), Anke C. Nölscher, University of Bayreuth

Comparison of Common Vapor Pressure Estimation Methods through Modeling of Alkene OH/NOx Systems

Poster Competition

Presented by: Emmaline Longnecker, Univeristy of Colorado, Boulder - Chemisty Department

Lightning Talk & Poster Display: Modeling of atmospheric reactions is an important tool in understanding the current and future impacts of human activity on the environment. Vapor pressure is a key parameter in modeling these reactions, as it largely determines the ability of a species to transition from the gas to particle phase. However, the vapor pressures of many atmospherically relevant molecules are still poorly constrained. To aid modeling efforts, several group contribution methods have been developed for estimating compound vapor pressures. The current study evaluates how four of these methods: SIMPOL, EVAPORATION, SPARC, and Nannoolal, impact the modeled predictions of secondary organic aerosol (SOA) yields for the reactions of C8-C14 1-alkenes and C9-C15 2-methyl-1-alkenes with OH radicals in the presence of NOx. The models were created in the kinetics modeling software KinSim and include rate constants measured by Atkinson and co-workers, quantitative reaction mechanisms developed by our research group from several previous environmental chamber studies of product yields, as well as gas-particle and gas-wall partitioning. The modeled SOA yields were compared to the measured values, and the large range of agreement exemplifies the impact of vapor pressure in modeling atmospheric reactions and indicates the need for further development of estimation methods.

Additional Authors: Julia G. Bakker-Arkema, Metropolitan Museum of Art, Paul J. Ziemann, CU Boulder

Investigating the Chemistry of Isoprene Nitrates and Nitrooxyorganosulfates Under Polluted Urban Conditions

Presented by: Alfred Mayhew, University of York

Poster Display Only: Isoprene is the most emitted non-methane volatile organic compound, and the chemistry of isoprene in the atmosphere can have large impacts on air quality, climate, and public health. Isoprene nitrates and nitrooxyorganosulfates are important due to their potential to contribute to secondary organic aerosol (SOA). This investigation involves a series of chamber experiments performed at the European PHOtoREactor (EUPHORE) designed to investigate the oxidation of isoprene, with a focus on oxidation by the nitrate radical (NO3). Experiments were designed to reproduce and contrast conditions observed in Beijing in 2017 where high ozone concentrations resulted in low NO concentrations and in NO3 playing a significant role in the formation of isoprene nitrates and nitrooxyorganosulfate aerosol in the late afternoon. All of the experiments were designed to reproduce a range of NO concentrations, photolysis conditions, and were performed both with and without seed aerosol in an effort to identify particle-specific reaction pathways. A comparison of filter samples taken during the chamber experiments with ambient measurements made in Beijing and other cities, alongside box modelling of the experiments, allows for a detailed investigation into the formation pathways of isoprene nitrates and nitrooxyorganosulfates. The findings from this work will have implications for our understanding of the oxidation of isoprene under urban low-NO conditions similar to those observed in Beijing.

Additional Authors: Esther Borrás, Fundación Centro de Estudios Ambientales del Mediterráneo (CEAM) Daniel Bryant, University of York Wolfson Atmospheric Chemistry Laboratories (WACL) Sri Budisulistiorini, University of York Wolfson Atmospheric Chemistry Laboratories (WACL) Amalia Muñoz, Fundación Centro de Estudios Ambientales del Mediterráneo (CEAM) Mike Newland, University of York Wolfson Atmospheric Chemistry Laboratories (WACL) Marvin Shaw, University of York Wolfson Atmospheric Chemistry Laboratories (WACL) Rubén Soler, Fundación Centro de Estudios Ambientales del Mediterráneo (CEAM) Milagros Ródenas, Fundación Centro de Estudios Ambientales del Mediterráneo (CEAM) Teresa Vera, Fundación Centro de Estudios Ambientales del Mediterráneo (CEAM) Andrew Rickard, University of York Wolfson Atmospheric Chemistry Laboratories (WACL) Peter Edwards, University of York Wolfson Atmospheric Chemistry Laboratories (WACL) Jacqueline Hamilton, University of York Wolfson Atmospheric Chemistry Laboratories (WACL)

Structure-activity relationship to predict Arrhenius parameters of OH addition to unsaturated volatile organic compounds under atmospheric conditions

Poster Competition

Presented by: Lisa Michelat, ICARE-CNRS Orleans

Lightning Talk & Poster Display: Hydrofluoroolefins (HFOs) and related haloalkenes are a family of man-made compounds replacing ozone-depleting substances that are increasingly emitted to the atmosphere as a result of their numerous industrial applications. Electrophilic OH addition in the gas phase represents the main environmental sink for these unsaturated compounds, where the degree and type of halogenation strongly affects their chemical reactivity. This leads to a diversity of behavior that has been a challenge for structure-activity relationships (SARs). In this work, we investigate and extend the potential of existing SARs to estimate OH rate coefficients under atmospheric conditions. Starting from the position of substituents across the double bond, our SAR-based approach coupled with theoretical calculations provides predictions of the temperature-dependent OH addition rate coefficient, k(T), of haloalkenes over a temperature range of 200–400K. We present improvements in accuracy and diversity upon existing approaches for estimating these kinetic data. We will investigate the potential for this method to be applied towards other substitutions, e.g., nitrates or carbonyls, to provide a general tool that can be easily used to predict the reactivity of most atmospheric compounds of interest.

Additional Authors: A. Mellouki, ICARE-CNRS, A. R. Ravishankara, Colorado State University, M. R. McGillen, ICARE-CNRS.

Atmospheric Chemistry Classics: Exploring Recent Trends in Surface Ozone

Presented by: Anke C. Noelscher, University of Bayreuth

Poster Display Only: With the aim to reduce tropospheric production rates of ozone and hence improve air quality, its precursors nitrogen oxides and aromatic volatile compounds have been regulated in many states worldwide since several decades. Despite the successful reduction of these precursors’ emissions, tropospheric ozone levels in many urban and suburban areas exhibit positive, rising trends (e.g. Yan et al., 2019). This highlights the complexity and non-linearity of the mechanisms leading to photochemical ozone production. Here, we present our analysis of the temporal and spatial trends of ozone along with its regulated precursors. We selected contrasting sites in Southern Germany with various degrees of air pollution: For example, at a site in Munich with high traffic nitrogen monoxide decreased at a rate of 2.2 µg/m³ per year over the course of the last 30 years, whereas ozone concentrations increased by about 0.6 µg/m³ annually (data source: UBA). In contrast, at a site located remotely within a spruce forest, we observed stagnating low levels of nitrogen oxides and persistent high levels of ozone reaching more than 100 µg/m³, therefore exceeding WHO air quality guidelines, during the summer of 2022. For further analysis, we combined spatial and temporal scales to bridge over long-term trends (decades), seasons, weekly and diurnal variability, and to highlight dependencies on the underlying chemical mechanisms regarding regional and local contributions to ozone production.

Additional Authors: Julia David, University of Bayreuth

Use of OH/VOC ‘site-specific’ rate coefficient data to test, train and constrain structure-activity relationships.

Presented by: John Orlando, Atmospheric Chemistry Observations and Modeling Laboratory, NCAR

Lightning Talk & Poster Display: Fully explicit models (e.g., GECKO-A, MechGen, MCM) operate in part on structure-activity relationships (SARs), rules that are used to generate rate coefficient (k) data for reactions that have not been experimentally studied. For OH/VOC reactions, the most popular form is the ‘Atkinson-type’ SAR in which each unique site of attack on a VOC is parameterized as a ‘base k’ multiplied by additional parameters that account for neighboring group effects, and the full set of parameters is optimized using available (total) k’s from lab studies. However, until now, while these parameterizations have proved useful for predicting total k’s, they have not been tested for their ability to predict branching ratios (or ‘site-specific’ k’s) for OH attack on a VOC. Our group has already published a comprehensive, digital, freely available, ‘living’ compilation of evaluated k’s for gas-phase reactions of OH with about 1350 VOC. Here we collect an additional 175 branching ratios (based on lab-derived quantitative product data) for inclusion in the database. These are predominantly obtained for OH/VOC abstraction reactions where unique products are formed from reaction at a particular site in the parent VOC. Comparisons will be made between these branching ratios (or site-specific k’s) and those predicted by the SARs used in developing GECKO-A and MechGen. The results of these comparisons will be used to the extent possible to suggest improvements to currently existing SARs.

Additional Authors: Bernard Aumont, LISA Univ. Paris, William P.L. Carter, UC Riverside, Max R. McGillen, CNRS Orleans, Abdelwahid Mellouki, CNRS Orleans, Benedicte Picquet-Varrault, LISA Univ. Paris, Timothy J. Wallington, Ford Motor Company,

Vibrational Photochemistry and Dissociation of Peroxyformic Acid Initiated by Visible Light

Presented by: Josue Perez, University of California San Diego

Poster Display Only: Peroxyformic acid (PFA) is an organic hydroperoxide formed in the atmosphere through several different pathways including the gas phase reaction of O3with chloroethene and the photo-oxidation of hydrocarbons. It is also a common industrial disinfectant used in both the food and medical industries. Photodissociation through the absorption of visible light is an important loss mechanism for atmospheric hydroperoxides (R-O-OH) at high solar zenith angles, where UV light is unavailable. Photodissociation of PFA leads to the production of OH radicals via the rupture of the weak hydroperoxide O-O bond. Here we present results from the visible light induced unimolecular dissociation of peroxyformic acid initiated by exciting the molecule in the vicinity of its fifth OH stretching overtone state (6νOH) in the vicinity of 620nm. Using laser induced fluorescence (LIF), we have detected the resulting OH fragments from these near thresholds unimolecular dissociation experiments and have determined the partitioning of the available energy into its internal and translational degrees of freedom. Using available literature data for the heat of formation of the parent PFA molecule and the resulting OH +HCO2 fragments, the O-O bond dissociation energy (D0) in PFA is estimated to be ~45.1 kcal/mol. Thus, excitation of room temperature PFA molecules in the region of 620nm leaves the OH + HCO2 fragments with roughly 3 kcal/mol of available energy.

Additional Authors: Josue E. Perez, UC San Diego, Madhusudan Roy, UC San Diego, Amitabha Sinha, UC San Diego

Nonisothermal nucleation in the gas phase is driven by cool subcritical clusters

Presented by: Bernhard Reischl, University of Helsinki

Poster Display Only: The classical view of nucleation in the gas phase assumes isothermal conditions where the nucleating clusters are in thermal equilibrium with their surroundings. However, in all first-order phase transitions, latent heat is released, potentially heating the clusters and suppressing the nucleation. The question of how the released energy affects cluster temperatures during nucleation as well as the growth rate remains controversial. To investigate the nonisothermal dynamics and energetics of homogeneous nucleation, we have performed molecular dynamics simulations of a supersaturated vapor in the presence of thermalizing carrier gas. The results obtained from these simulations are compared against kinetic modeling of isothermal nucleation and classical nonisothermal theory. For the studied systems, we find that nucleation rates are suppressed by two orders of magnitude at most, despite substantial release of latent heat. Our analyses further reveal that while the temperatures of the entire cluster size populations are elevated, the temperatures of the specific clusters driving the nucleation flux evolve from cold to hot when growing from subcritical to supercritical sizes and resolve the apparent contradictions regarding cluster temperatures. Our findings provide unprecedented insight into realistic nucleation events and allow us to directly assess earlier theoretical considerations of nonisothermal nucleation.

Additional Authors: Valtteri Tikkanen, University of Helsinki, Hanna Vehkamäki, University of Helsinki, Roope Halonen, Tianjin University

Investigating fundamental structures in atmospheric chemical reaction mechanisms

Presented by: Sam Silva, The University of Southern California

Lightning Talk & Poster Display: Techniques from the discrete mathematical field of graph theory can provide a potential new set of tools for quantifying the structure and dynamics of the atmospheric chemical system. This has been shown by prior work, which demonstrated that mechanism analyses through the lens of graph theory reproduces existing knowledge in the field. Here, we go beyond reproduction of existing knowledge to explore what graph theoretical analysis can tell us about mechanism structure and dynamics. We present new structural analysis of atmospheric chemical mechanisms focused on so-called “graph motifs” in mechanisms of varying complexity. Motifs in reaction mechanisms are repeat patterns of interactions between compounds. The prevalence of all possible connection patterns for a given number of compounds are explored and compared to a random baseline. This analysis technique allows us to characterize the basic building blocks of atmospheric chemical mechanisms and relate them to mechanism dynamics. Our work indicates key differences in motif prevalence across mechanisms. For example, a subset of motifs related reciprocal reactions (reactions where at least one of the reactants and the products are the same) are much more common in reduced form mechanisms. We additionally explore the implications of these motifs on the dynamics of the chemical system to enable further insight into mechanism behavior.

Additional Authors: Mahantesh Halappanavar, Pacific Northwest National Laboratory

Explicit and reduced chemical mechanisms for indoor air quality models

Presented by: Roberto Sommariva, University of Birmingham

Poster Display Only The air quality inside homes and workplaces is an important human health issue as most people spend the majority of their time indoors. The emissions, formation and removal of pollutants in indoor settings are significantly different than the equivalent processes in outdoor settings and require bespoke modelling tools to study and assess exposure and health impacts. We present two chemical mechanisms, designed for use in indoor air quality models: 1) a highly detailed chemical mechanism which can be used in a flexible multi-box model (MBM-Flex) to study inter-room air quality variability, and 2) a reduced chemical mechanism derived from the Master Chemical Mechanism (MCM, Saunders et al., 2003; Jenkin et al., 2003) which can be used in a large eddy simulation model (Chem-LES) to investigate intra-room dynamics, ventilation effects and formation of pollutant hotspots within a room. The two chemical mechanisms are compared to each other, to the INCHEM-Py indoor chemistry mechanism (Shaw & Carslaw, 2021), and to the MCM (used as reference standard) under a variety of chemical conditions and a range of indoor-outdoor exchange settings. We examine how well chemical mechanisms of different complexity are able to reproduce the concentrations of selected target species (e.g. O3, NOx, CO) within the timeframe of the simulations. This work is part of the project "Indoor Air Quality Emissions & Modelling System (IAQ-EMS)", funded by the Met Office and UK Research and Innovation.

Additional Authors: James G. Levine, University of Birmingham; David Shaw, University of York; Nicola Carslaw, University of York; Christian Pfrang, University of Birmingham; William J. Bloss, University of Birmingham.

Developing methods for efficient transport and chemistry calculations in forecasting applications

Poster Competition

Presented by: Obin Sturm, NASA GMAO

Lightning Talk & Poster Display: The Goddard Earth Observing System Composition Forecast (GEOS-CF) produces global predictions of atmospheric chemical constituents using the GEOS-Chem chemistry module at a resolution of 0.25 degrees. Due to its multiple dimensions of complexity, i.e., chemical detail and high spatial resolution, GEOS-CF is computationally demanding. We explore various strategies for accelerating GEOS-CF model simulations, including (1) reducing chemical complexity in transport calculations, (2) reducing spatial detail in chemistry calculations, and (3) pre-conditioning the chemical solver. Timing experiments indicate that though advecting a reduced set of chemical species lessens the computational burden of transport calculations, this strategy has limited potential to shorten the wall time of GEOS-CF runs. Instead, the largest speedup potential is in the reduction of the load imbalance in chemistry calculations. Load imbalances are primarily driven by chemistry calculations in twilight regions, where grid cells far from chemical pseudo-equilibrium transition to new regimes. We explore methods to accelerate chemistry computations under twilight conditions, including running stratospheric chemistry at a coarser resolution or feeding an initial solution to the chemical solver (pre-conditioning). We find that these strategies can reduce wall time substantially while retaining most of the chemical complexity in the system. Such solutions are particularly attractive for forecasting applications.

Additional Authors: Christoph Keller, NASA GMAO

Atmospheric Photolysis of CF3CHO: A Source of HFC-23?

Presented by: Mads Sulbaek Andersen, California State Univeristy

Lightning Talk & Poster Display: CF3CHO is an atmospheric degradation product of several chlorofluorocarbon (CFC) alternatives, including some commercially important hydrofluoroolefins (HFOs). The photolysis of CF3CHO has three principal pathways: (1) CF3CHO + hν → CF3 + HCO, (2) CF3CHO + hν → CF3H + CO, (3) CF3CHO + hν → CF3CO + H There is conflicting information on the CF3CHO photolysis in the literature. Campbell et al. (DOI 10.21203/ recently announced that they have observed a 308 nm - quantum yield of Φ2 = 0.010 ± 0.005, meaning that actinic photolysis of CF3CHO would be a source of CF3H, HFC-23. CF3H has a large global warming potential of GWP100 =12,960 and could in effect present a significant additional secondary contribution to the radiative forcing of climate from the parent CFC alternative. We have investigated the photolysis kinetics and products of CF3CHO under photolysis conditions relevant to the troposphere and the stratosphere. Experiments show that actinic photolysis produces CF3 radicals, which under atmospheric conditions gives dominantly COF2. No formation of CF3H was observed under these conditions in contradiction to results published most recently. Photolysis using 254 nm radiation gives CF3H in a significant yield, in addition to CF3 radicals. The photochemical lifetime of CF3CHO and the CF3H yields are discussed with respect to troposphere and stratospheric conditions and in context of the environmental impact of important CFC substitutes.

Additional Authors: Ole John Nielsen, University of Copenhagen

Chekimomi: a tool for enabling FAIR kinetic models

Presented by: Luc Vereecken, Forschungszentrum Jülich GmbH

Poster Display Only: Chemical kinetic modeling is a critical tool in atmospheric chemistry research, where it is used in many applications such as the design and interpretation of experiments, or regional and global modelling. The kinetic models are build from experimental data, theoretical predictions, and structure-activity relationships, and thus reflect our current knowledge on the studied chemical system. Many kinetic solvers exist for the kinetic coupled differential equations, each with their own notational style and capabilities, and integrated in (locally developed) tool chains for e.g. handling experimental data, analyzing model results, parameter optimization, or visualization. However, these different notational styles and tool chains are not directly interoperable, and literature model data is typically not reproducible in another tool chain without significant (manual) effort. We have developed an open source modularized model handler, Chekimomi, which is able to help in the transcription of chemical models. It supports differences in notational styles, rate coefficient equations, chemical identifiers, photochemistry, etc., and can support local variations in the tool chains. By simplifying exchange of kinetic data, Chekimomi is a useful tool for publishing chemical models and rate data in a FAIR way (Findable, Accessible, Interoperable, Reproducible). Efforts are ongoing to expand the supported styles, tool chains, chemical identifiers and human-readable export formats.

Additional Authors: Yat Sing Pang, Forschungszentrum Jülich GmbH, Andreas Wahner, Forschungszentrum Jülich GmbH, Astrid Kiendler-Scharr, Forschungszentrum Jülich GmbH

The gas-phase formation mechanism of iodic acid: a catalytic role of iodine in particle formation

Presented by: Rainer Volkamer, University of Colorado Boulder

Poster Display Only: Iodine is a micronutrient, and a reactive trace element in atmospheric chemistry that destroys ozone and nucleates particles. Iodine oxoacids (e.g., iodic acid, HIO3) and higher iodine oxide polymers (IxOy) present viable pathways to iodine particle formation. While much research has investigated the formation of IxOy species, the formation mechanism of iodic acid is missing. The lack of an understanding about iodic acid formation makes it difficult to assess the relevance of both pathways in iodine particle formation in the atmosphere. This presentation discusses chamber experiments at CLOUD, box modeling, and quantum chemical calculations to investigate the formation mechanism of iodic acid. A mechanism is proposed, and tested against field observations. The new mechanism provides a missing link between iodine sources and particle formation in atmospheric models. Since particulate iodate is readily reduced, recycling iodine back into the gas-phase, our results suggest a catalytic role of iodine in aerosol formation.

Additional Authors: Henning Finkenzeller, CU Boulder, Sid Iyer, Tuni, Finland, Matti Rissanen, Tuni, Finland, Theo Kurten, UHelsinki, and the CLOUD collaboration

Reduction strategies for the automatic generation of SOA mechanism using GENOA

Presented by: Zhizhao Wang, CEREA, ENPC

Lightning Talk & Poster Display: The degradation of volatile organic compounds (VOC) in the troposphere leads to the formation of secondary organic aerosols (SOA) and is therefore crucial to 3D air quality modeling (AQM). Although detailed VOC mechanisms like MCM can accurately describe the influence of VOC chemistry on SOA formation, they cannot be directly applied to SOA simulations in AQM due to the overwhelming computational costs. Thus, we developed GENOA (GENerator of the reduced Organic Aerosol mechanism), which automatically reduces complex SOA mechanisms into smaller mechanisms with fewer species. The GENOA training involves searching for potential reduction attempts using predefined reduction strategies (e.g., lump species, remove species/reactions), and evaluating their effects on SOA concentrations under selected representative atmospheric conditions (e.g., conditions under different chemical regimes). Automatically, the process can be conducted serially (search/evaluate one reduction at a time) or parallelly (search/evaluate multiple reductions and select the best one). It can also be customized by user-specified parameters and tracked explicitly. GENOA has been applied to the degradation mechanisms of sesquiterpene, toluene, and monoterpene, reducing the number of condensable species from 356 to 6, 103 to 10, and 738 to 43, respectively, with an average error increase of less than 4% in the 0D testing on more than 10,000 conditions. Their performances in 3D modeling are currently investigated.

Additional Authors: Florian Couvidat, INERIS France, Karine Sartelet, CEREA ENPC

New Measurements of Glyoxal Yields from Acetaldehyde Oxidation

Presented by: James Warman, University of Leeds

Poster Display Only: Volatile organic compounds (VOCs) introduced into the atmosphere either through primary emissions or secondary chemistry play a crucial role in air quality and climate change. Whilst satellite measurements of VOCs are desirable for advancing our understanding of the chemistry and emissions both locally and globally, the large quantity and broad, overlapping spectra of the majority of VOCs make observations of direct VOC emissions impossible. Glyoxal (GL) and formaldehyde (FA) are two notable exceptions; ratios of GL:FA can provide information on primary emissions if the chemistry of GL and FA formation is understood. One such precursor, acetaldehyde, particularly relevant to the marine boundary layer (MBL), is thought to produce GL through a minor OH abstraction channel from the methyl site. Modelled GL mixing ratios in the MBL consistently under predict experimental values, indicating a missing source of GL that may be mitigated through acetaldehyde chemistry. Measurements conducted within the University of Leeds HIRAC (Highly Instrumented Reactor for Atmospheric Chemistry) apparatus provide evidence for the production of GL, however demonstrate a significantly lower yield (0.11 ± 0.02 %) than expected from the Master Chemical Mechanism (2.6 %). These results suggest an increased discrepancy between modelled and measured GL mixing ratios, providing a need for further investigation into the missing GL source in the MBL.

Additional Authors: Paul Seakins, University of Leeds, Daniel Stone, University of Leeds, Graham Boustead, University of Leeds

Probing the DMS Oxidation Mechanism Through Measurements of the OH Radical

Presented by: Frank Winiberg, Jet Propulsion Laboratory

Poster Display Only: Dimethyl sulfide (DMS) is the largest contributor of natural sulfur to the atmosphere. The oxidation of DMS results in the formation of sulfate aerosols that can affect Earth’s radiative balance by scattering solar radiation and serving as cloud condensation nuclei. Hydroperoxymethyl thioformate (HPMTF), is a newly identified major oxidation product of DMS and could potentially have a major impact on the atmospheric budget of sulfur. In a recent study modeling study, we have shown that accounting for HPMTF chemistry results in a significant decrease in boundary layer levels of SO2 and H2SO4 and increases in sulfate aerosol in the upper troposphere, with an associated 110% increase in sulfate aerosol nucleation rate. We will present the preliminary results from the investigation of the formation kinetics of HPMTF by examining the hydroxyl radical (OH) co-product. The HPMTF formation rate coefficient will be studied using the Pulsed Laser Photolysis-Laser Induced Fluorescence apparatus from the chlorine-initiated oxidation of DMS under relevant temperature and pressure conditions for the troposphere. Analysis of the data will be completed by fitting the time dependent OH signals with a comprehensive chemical simulation model that will be developed as part of this work. The measured rate coefficients and atmospheric implications will be discussed.

Additional Authors: Carl J. Percival, Jet Propulsion Laboratory, and Stanley P. Sander, Jet Propulsion Laboratory

Automated Mechanism Reduction Algorithm Applied to Isoprene Chemistry

Presented by: Forwood Wiser, Columbia University

Poster Display Only: Automated chemical mechanism reduction has been applied to complex combustion mechanisms in order to reduce the computational effort needed to run them. The isorpene atmospheric chemical mechanism is highly complex and is a good candidate for automated reduction due to the extensive use of reduced isoprene mechanisms, but no automated reduced mechanisms have been tested so far. In this work, the Caltech isoprene mechanism was reduced using an automated reguction algorithm. After additional manual adjustments, the resulting mechanism outperformned the published RACM isoprene mechanism while containing only 9 isoprene species and 17 reactions. This method shows significant promise in the development of mechanism reduction algorithms for atmospheric chemistry.

Additional Authors: V. Faye McNeill, Columbia University, Daniel Westervelt, Columbia University, Arlene Fiore, MIT, Daven Henze, University of Columbia Boulder, Siddhartha Sen, Microsoft Research, Havala Pye, EPA, Bryan Place, EPA

Kinetic Studies of the Pressure and Temperature Dependence of OH+SO2 in the Presence of Water Vapor

Poster Competition

Presented by: Megan Woods, California Institute of Technology

Lightning Talk & Poster Display: The oxidation of sulfur dioxide (SO2) by the hydroxy radical (OH) is the dominant pathway in the formation of sulfate particles. The formation of these particles is a foundation for aerosol growth, formation, and cloud droplet nucleation. These processes play a critical role in our tropospheric radiation budget and therefore our climate. As a result, it is imperative to accurately characterize the kinetics of the title reaction to understand its influence on our troposphere and climate. Currently, there is only one study which explores the temperature range of OH+SO2 and observes the collisional efficiency of atmospherically relevant bath gasses nitrogen (N2 , 50-750 Torr, 230-333K), and water vapor (H2O 50 Torr total pressure, 273-333 K). In consequence, it is essential to further expand on this work and investigate the influence of N2 and H2O on the reaction rate constant at temperatures and pressures relevant to the troposphere. To elucidate knowledge gap, laser photolysis-laser induced fluorescence (LP-LIF) will be employed to observe OH+SO2+M at the temperature range 230-293 K and a pressure range of 50 – 750 Torr of N2 and 273-298K and 50-500 Torr total pressure with fractional H2O =(0-4)×〖10〗^17 molec/cm^3. The collected data may provide new insight into the enhancement of the rate coefficient for OH+SO2 in the presence of H2O that have been previously reported. The potential tropospheric impact will be discussed.

Additional Authors: Carl J. Percival, JPL, Stanley P. Sander, JPL, Mitchio Okumura, Caltech, Frank A.F Winiberg,JPL

Low-pressure yields of stabilized Criegee intermediates produced from ozonolysis of a series of alkenes

Poster Competition

Presented by: Lei Yang, UC Riverside

Lightning Talk & Poster Display: Ozonolysis of alkenes is an important oxidation pathway of alkenes in the troposphere because it is involved in the production of organic aerosol and OH radicals. The mechanism of ozonolysis of alkenes involves the formation of a primary ozonide (POZ), which then decomposes into a carbonyl and a carbonyl oxide (Criegee intermediate). Criegee intermediates are produced with a broad internal energy distribution. High-energy Criegee intermediates decompose into atmospherically important compounds (e.g. vinoxy, OH radical). Stabilized Criegee intermediates (sCIs) undergo reactions to produce secondary ozonides and organic aerosols. Cavity ring-down spectroscopy (CRDS) is utilized in combination with chemical titration with sulfur dioxide to quantify sCIs. The reactions are carried out under various flow and low-pressure conditions. Reference cross-sections of the products and reactants are fitted with spectral features to obtain product number densities. The yields of sCIs are measured at different low pressures, and the nascent yields are determined by extrapolation to zero pressure. Endocyclic alkenes show no sCI production at the pressures studied. Acyclic alkenes show pressure-dependent sCI yields. Formaldehyde oxide from the 1-alkenes studied has a high nascent yield than larger CIs due to its relatively high energy barrier for dissociation. The information on the low-pressure yields from the current studies can be used as a benchmark for theoretical calculations.

Additional Authors: Mixtli Campos-Pineda, UC Riverside, Jingsong Zhang, UC Riverside

Understanding How Representative Laboratory Simulation is for Ambient Chemical Processes through a Compound-Specific Approach

Presented by: Lindsay Yee, UC Berkeley

Poster Display Only: Organic aerosols (OA) contain a myriad of individual chemical constituents. Their chemical composition varies based on many factors including sources of primary OA as well as the chemical and environmental conditions under which secondary OA are formed. This creates a significant challenge to chemically characterize all the potential compounds that arise in ambient OA, as most of these compounds are uniquely created in the atmosphere and few authentic standards are available. We have obtained laboratory and field samples of OA on quartz filters representing a variety of sample types and chemical regimes (e.g. biomass burning, terpene oxidation, natural, rural, and urban environments). We resolved thousands of unique compounds among samples analyzed using two-dimensional gas chromatography with high-resolution time-of-flight mass spectrometry. We are curating over 24,000 mass spectra to be added to the open-access electron impact mass spectral database known as the University of California, Berkeley, Goldstein Library of Organic Biogenic and Environmental Spectra (UCB-GLOBES). Analyses of this database show thus far that laboratory oxidation experiments are far more chemically diverse than our ambient datasets, yet to date we still only see at most ~40% of ambient dataset overlap with laboratory datasets. Our analysis provides additional insight into how representative laboratory simulation may be for ambient chemical processes.

Additional Authors: Lindsay D. Yee, UC Berkeley, Emily B. Franklin, UC Berkeley, Robin J. Weber, UC Berkeley, Yutong Liang, Georgia Tech, Coty N. Jen, Carnegie Mellon University, Haofei Zhang, UC Riverside, and Allen H. Goldstein, UC Berkeley

High time resolution ambient measurements of gas- and particle-phase perfluorocarboxylic acids (PFCAs): Implications for sources and fate

Presented by: Cora Young, York University

Poster Display Only: Per- and polyfluoroalkyl substances (PFAS) are widely used in numerous consumer and industrial products, including non-stick materials and firefighting foams. Perfluorocarboxylic acids (PFCAs) are a class of PFAS and are found ubiquitously in the environment, including in remote regions far from sources. While PFCAs can be directly emitted into the atmosphere through production and use of fluoropolymers, they can also be formed by atmospheric oxidation of volatile PFAS. A complete understanding of PFCA sources, fate, and transport requires atmospheric PFCA measurements. Current atmospheric sampling methods primarily rely on offline sampling techniques with timescales of several hours to days. Because atmospheric processes that drive production and fate of PFCAs occur on shorter timescales, faster measurement techniques are needed to provide insight into these processes. Here, we describe two new approaches to high time resolution atmospheric PFCA measurements, as well as their application to ambient measurements in Toronto, Canada. The ambient ion monitor-ion chromatograph-mass spectrometer (AIM-IC-MS) provides in situ hourly measurements of gas- and particle-phase PFCAs. The time-of-flight chemical ionization mass spectrometer (ToF-CIMS) measures in situ gaseous PFCAs at a timescale of 10 seconds. Data from the AIM-IC-MS and ToF-CIMS, along with co-located meteorological and air quality parameters will be used to describe new insights into PFCA sources, fate, and transport.

Additional Authors: Shira Joudan, York University, Jessica Clouthier, York University, Trevor VandenBoer, York University, Jeremy Wentzell, Environment and Climate Change Canada, John Liggio, Environment and Climate Change Canada