acm.aqrc.ucdavis.edu · Web viewdetermine the levels of selected organic flame retardants (FRs) in...
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Dimitrios K. Papanastasiou CIRES/CU and CSD/NOAA [email protected] Atmospheric Chemistry of c-C5HF7 and c-C5F8: OH Reaction Rate Coefficients and Oxidation Products Perfluorocyclopentene (c-C5F8) and 1H-Heptafluorocyclopentene (c- C5HF7) are unsaturated cyclic compounds used as etching agents in the Si semiconductor industry. Both compounds are potent greenhouse gases and their environmental impact should be evaluated. Here, we present a thorough laboratory study of their OH radical reactivity, their atmospheric degradation mechanism, and their radiative properties and global warming potential. Finally, this study aims to expand our knowledge on the atmospheric reactivity and degradation mechanism of cyclic unsaturated fluorinated compounds. The rate coefficients for the gas-phase reaction of OH with c-C5HF7 and c-C5F8 were measured over a range of temperature (242–370 K) and pressure (50–100 Torr, He) using pulsed laser photolysis laser induced fluorescence and relative rate techniques. The reaction rate coefficients were found to have a positive temperature dependence, for the temperature range employed in this study, with no pressure dependence observed. The OH radical and Cl-atom initiated degradation of c-C5F8 and c- C5HF7, in the presence of O2, resulted in the formation of F(O)CCF2CF2CF2CH(O) for c-C5HF7 and F(O)CCF2CF2CF2CF(O) for c-C5F8 as the major stable end-products, which implies that the cyclic alkoxy radicals formed in this system ring open, predominantly, on the original C-C double bond. Insights derived from the kinetic and product studies will be presented along with a comparison of the present work with previous studies. Tomasz Gierczak (CIRES/CU and CSD/NOAA), Francois Bernard (CIRES/CU and CSD/NOAA), and James B. Burkholder (CSD/NOAA)
Transcript of acm.aqrc.ucdavis.edu · Web viewdetermine the levels of selected organic flame retardants (FRs) in...
Dimitrios K. Papanastasiou CIRES/CU and CSD/NOAA
Atmospheric Chemistry of c-C5HF7 and c-C5F8: OH Reaction Rate Coefficients and Oxidation Products
Perfluorocyclopentene (c-C5F8) and 1H-Heptafluorocyclopentene (c-C5HF7) are unsaturated cyclic compounds used as etching agents in the Si semiconductor industry. Both compounds are potent greenhouse gases and their environmental impact should be evaluated. Here, we present a thorough laboratory study of their OH radical reactivity, their atmospheric degradation mechanism, and their radiative properties and global warming potential. Finally, this study aims to expand our knowledge on the atmospheric reactivity and degradation mechanism of cyclic unsaturated fluorinated compounds.
The rate coefficients for the gas-phase reaction of OH with c-C5HF7 and c-C5F8 were measured over a range of temperature (242–370 K) and pressure (50–100 Torr, He) using pulsed laser photolysis laser induced fluorescence and relative rate techniques. The reaction rate coefficients were found to have a positive temperature dependence, for the temperature range employed in this study, with no pressure dependence observed.
The OH radical and Cl-atom initiated degradation of c-C5F8 and c-C5HF7, in the presence of O2, resulted in the formation of F(O)CCF2CF2CF2CH(O) for c-C5HF7 and F(O)CCF2CF2CF2CF(O) for c-C5F8 as the major stable end-products, which implies that the cyclic alkoxy radicals formed in this system ring open, predominantly, on the original C-C double bond.
Insights derived from the kinetic and product studies will be presented along with a comparison of the present work with previous studies.
Tomasz Gierczak (CIRES/CU and CSD/NOAA), Francois Bernard (CIRES/CU and CSD/NOAA), and James B. Burkholder (CSD/NOAA)
Jabir Syed COMSATS University Islamabad
Title: E-waste driven pollution in Pakistan: First evidence of atmospheric exposure to flame retardants (FRs) in Karachi city
Pakistan has been identified as one of the major importers of e-waste among developing countries with a domestic e-waste generation of 317 kt in 2015. Karachi being a seaport receives tons of imported old and obsolete electronics and electrical equipment (EEE) from all around the world which, in turn, is traded from vendors to scrap dealers to dismantlers who recycle the e-waste at the possible expense of their health to extract valuable materials from the waste. The main objective of this study was to
determine the levels of selected organic flame retardants (FRs) in the areas with intensive informal e-waste recycling activities in Karachi, Pakistan. Dechlorane Plus (DP), “novel†� brominated flame retardants (NBFRs) and phosphorus-based FRs (OPFRs) were often detected in high concentrations in atmospheric samples. Therefore, the possibility exists of increased contamination of FRs with increased exposure to laborers as well as nearby populations. Further investigations of contamination and exposure to human are needed to take appropriate steps by the authorities for environmentally sound management of e-waste recycling in the country. Our study confirms findings from other developing countries which implicates informal e-waste recycling activities as potential major emission sources of FRs. Further research into this topic could help to inform and thereby support future regulatory efforts to minimize negative impacts of informal e-waste recycling on environmental health.
Iqbal Ma, Syed JHb, Knut Bc,d, Chaudhry MJIe, Li Jb, Zhang Gb, Malik RNa
aEnvironmental Biology and Ecotoxicology Laboratory, Department of Environmental Sciences, Faculty of Biological Sciences, Quaid-I-Azam University, Islamabad 45320, Pakistan
bCOMSATS University, Islamabad 45550, Pakistan
cNorwegian Institute for Air Research, Box 100, NO-2027 Kjeller, Norway
dUniversity of Oslo, Department of Chemistry, Box 1033, NO-0315 Oslo, Norway
eWWF-Pakistan, Ferozpur Road, PO Box 5180, Lahore 54600, Pakistan
Jakub Kubecka University of Helsinki
Configurational sampling of atmospheric molecular clusters
The main aim of this work is the development of a theoretical approach for the effective configurational sampling of atmospheric molecular clusters. Currently used configurational sampling methods are mainly based on random distributing of molecules in space, combined with molecular dynamic simulations at a low level of theory. We suggest to use rigid molecular dynamics combined with force field methods instead of randomly distributed molecules. This approach is illustrated using molecular clusters containing sulphuric acid and guanidine in different ratios. Since this pair of molecules often undergoes proton transfer, its configurational sampling is challenging. Nevertheless, we are presenting an approach which can be used even for this case, and compare our results with some already existing sampling methods.
Hanna Vehkamäki, Theo Kurtén
Lin He Leibniz Institute for Tropospheric Research
A Kinetic Study of the Atmospheric Aqueous-Phase Reactions of OH Radicals with Methoxyphenolic Compounds
Methoxyphenols, which are emitted from biomass burning, are important species in atmospheric multiphase chemistry. In the present study, the temperature-dependent OH radical reactions with six methoxyphenol compounds in the aqueous phase have been investigated by laser flash photolysis for the first time. The competition kinetics method using SCN- has been used to determine the rate constants. The following rate constants (in unit of L mol-1 s-1) have been obtained: 2-methoxyphenol, k298k = (1.0 ± 0.1) * 10^10, 3-methoxyphenol, k298k = (1.4 ± 0.1) * 10^10, 2,6-dimethoxyphenol, k298k = (1.7 ± 0.1) * 10^10, 3-methoxycatechol, k298k = (1.9 ± 0.1) * 10^10, 2-methoxy-4-methylphenol, k298k = (1.7 ± 0.1) * 10^10, 4-(2-methoxyethyl)phenol, k298k = (1.7 ± 0.1) * 10^10. With the obtained rate constant and their T-dependencies, the Arrhenius parameters of these reactions have been derived. Meanwhile, the rate constant for fully diffusion controlled reaction of each case have been calculated based on the well-known Smoluchowski equation and, furthermore by DFT calculations. Moreover, the Hammett plots of phenolic compounds have been established with our measurement result, which could be used for predicting the unknown rate constants of other phenolic compounds. All of the findings are expected to enhance the predictive capabilities of models such as the chemical aqueous-phase radical mechanism (CAPRAM).
Lin He, Thomas Schaefer and Hartmut Herrmann
Qi Chen Peking University
Formation of Highly Oxygenated Organic Molecules from the Photooxidation of Aromatic Compounds
Oxidation flow reactors have been widely used to study the formation and evolution of secondary organic aerosol (SOA) over time scales ranging from hours to multiple days of equivalent atmospheric exposure. We deployed an Aerodyne Potential Aerosol Mass (PAM) flow reactor in the laboratory to study the formation of highly oxygenated organic molecules (HOMs) from the photooxidation of aromatic compounds. Precursors include benzene, toluene, xylene, mesitylene, and naphthalene. Both low and high NOx regimes are studied. HOMs are detected by using a nitrate-ion chemical ionization time-of-flight mass spectrometer (TOF-CIMS). Non-refractory particle chemical components are detected by using a high-performance time-of-flight aerosol mass spectrometer (LTOF-AMS). We show
that the oxidation of aromatics with OH radicals leads to subsequent autooxidation reactions that form HOMs. The laboratory data are compared to the ambient observations in urban Beijing.
Qi Chen* (1), Yongjie Li (2), Xi Cheng (1), Yan Zheng (1), Keren Liao (1), Ying Liu (3), Tong Zhu (1,3)
(1) State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing, China
(2) Department of Civil and Environmental Engineering, Faculty of Science and Technology, University of Macau, Taipa, Macau, China
(3) Beijing Innovation Center for Engineering Science and Advanced Technology (BIC-ESAT), Peking University, Beijing, China
Steve White CSIRO
SAPRC16 chemical mechanism performance against smog chamber experiments
In 2016, CSIRO Energy was tasked as one of the reviewers of the updated SAPRC-16 mechanism. As the mechanism has been generated and refined using smog chamber experiments, we assessed against a new set of experiments that had not been used previously. The ability of the mechanism to fit experimental data from these chamber experiments will be presented. The majority of these experiments were undertaken using aromatic hydrocarbons, with a small number of experiments conducted using alkenes or dialkenes. A small number of new experiments have been completed with either added carbon monoxide, or in the absence of added NOx.
The results in general were consistent with SAPRC-11, with most experiments predicting ozone formation accurately, with some under-prediction in total hydrocarbon reacted. Variation in the types of blacklights used for different experiments showed no variation. There were potentially some light-intensity dependent issues with ozone predictions for p xylene oxidation, however these impacts were minor. Prediction of the dialkenes was not as accurate as the aromatic hydrocarbons in predicting oxidation in the presence of NOx, and further work is required to understand the reasons why.
We also intend to present some limited results investigating the oxidation of simple amines in the presence of a hydrocarbon surrogate mixtures will be presented. The implications on aerosol formation will be addressed.
Steve White, Merched Azzi, Brendan Halliburton, Yanyan Zhou, Kangwei Li, Ian Campbell
Theodora Nah
School of Energy and Environment, City University of Hong Kong
Ammonia, Particle pH and the Partitioning of Inorganic and Organic Species
The implementation of stringent emission regulations has resulted in the decline of SO2, NOx and CO. In contrast, NH3 emissions are largely unregulated, with emissions projected to increase in the future. Results from a field study conducted in an agricultural-intensive region in the SE US are presented to investigate how NH3 affects particle acidity and SOA formation via the gas-particle partitioning of semi-volatile organic acids. Particle water and pH were determined using the ISORROPIA-II thermodynamic model. We find that despite the high NH3 concentrations (average 8.1 ± 5.2 ppb), PM1 were highly acidic with pH values ranging from 0.9 to 3.8, and an average pH of 2.2 ± 0.6. Measured particle-phase water-soluble organic acids were on average 6 % of the total non-refractory PM1 organic aerosol mass. The measured molar fraction of oxalic acid in the particle phase ranged between 47 and 90 % for PM1 pH 1.2 to 3.4. The measured oxalic acid gas-particle partitioning ratios were in good agreement with their corresponding thermodynamic predictions, calculated based on oxalic acid’s physicochemical properties, ambient temperature, particle water and pH. For this study, higher NH3 concentrations relative to what has been measured in the region in previous studies had minor effects on PM1 organic acids and their influence on the overall organic aerosol and PM1 mass concentrations.
Hongyu Guo (Department of Chemistry, University of Colorado at Boulder)
Amy P. Sullivan (Atmospheric Science Department, Colorado State University)
Yunle Chen (School of Earth and Atmospheric Sciences, Georgia Institute of Technology)
David J. Tanner (School of Earth and Atmospheric Sciences, Georgia Institute of Technology)
Athanasios Nenes (Schools of Earth and Atmospheric Sciences and Chemical and Biomolecular Engineering, Georgia Institute of Technology)
Armistead G. Russell (School of Civil and Environmental Engineering, Georgia Institute of Technology)
Nga Lee Ng (Schools of Earth and Atmospheric Sciences and Chemical and Biomolecular Engineering, Georgia Institute of Technology)
L. Gregory Huey (School of Earth and Atmospheric Sciences, Georgia Institute of Technology)
Rodney J. Weber (School of Earth and Atmospheric Sciences, Georgia Institute of Technology)
Carmen Tovar Institute for Atmospheric and Environmental Research, University of Wuppertal, 42097 Wuppertal, Germany
Kinetic and mechanistic investigations of the reactions of trans-2, 3-epoxybutane and cis-2, 3-epoxybutane with Cl atoms and OH radicals
Epoxy compounds (EC) are cyclic oxygenated hydrocarbons widely distributed in the atmosphere from anthropogenic sources.
Herewith we report the rate coefficient measurements for the gas phase reactions of chlorine atoms and OH radicals with trans-2,3-epoxybutane (tEB) and cis-2,3-epoxybutane (cEB) at 298 K and 1 atm in synthetic air. Using the relative rate method with two reference compounds and the FTIR technique in the QUAREC chamber, the obtained rate coefficients were (in cm3 molecule-1 s-1): ktEB = (6.99 2.09) × 10-11, kcEB = (6.92  2.15) x 10-11 for reaction with chlorine atoms and ktEB =(1.63±0.66) ×10-12, kcEB = (1.62±0.62) ×10-12 for reaction with OH radicals, respectively.
Investigations performed to assess the degradation mechanism of the OH radical initiated oxidation of tEB and cEB in air using FTIR analysis showed the formation of peroxy acetyl nitrate (PAN) and other degradation products. The reaction mechanisms of cEB and tEB with Cl atoms have been also investigated and the reaction products will be presented. Pathways for the formation of these products and atmospheric implications will be discussed.
To our knowledge this is the first reported kinetic study for the reaction of these compounds with Cl atoms and OH radicals. Obviously there are also no prior measurements of the products generated from these reactions.
Peter Wiesen, Institute for Atmospheric and Environmental Research, University of Wuppertal, 42097 Wuppertal, Germany.
Iustinian Bejan, Alexandru Ioan Cuza" University of Iasi, Faculty of Chemistry and Integrated Center of Environmental Science Studies in the North-Eastern Region – CERNESIM, 700506, Iasi, Romania.
Frank Winiberg Jet Propulsion Lab/Caltech
Does water complexation affect the reaction of the β-hydroxyethylperoxy radical with NO?
Formation of organic nitrates from the oxidation hydrocarbons in the troposphere is a significant loss pathway for nitrogen oxides (NOx) and HOx radicals (OH and HO2). Unsaturated hydrocarbons are emitted in large quantities into the atmosphere. They are primarily oxidized by OH, producing β-hydroxyperoxy radicals. One major loss process for these radicals is reaction with NO, producing organic nitrates or NO2. Organic nitrates are a sink for NOx through deposition and formation of secondary
organic aerosols, whereas NO2 can photolyse to produce tropospheric ozone. Formed from the oxidation of ethene, β-hydroxethylperoxy (β-HEP) serves as a model molecule for studying more complex systems, such as isoprene. Both experimental and theoretical works in the literature support the formation of a β-HEP H2O complex, and a 6 fold increase in the β-HEP self-reaction rate coefficient has been observed as a function of relative humidity (0 – 50 %) and temperature (270 – 298 K). In the upper troposphere up to 14% of RO2 radicals could be complexed with H2O and there are currently no chemical mechanisms for these reactions global models. Here we present results from an experimental study of the reaction of β-HEP + NO over a range of water concentrations and temperatures, using Multiplexed-Photoionization Mass Spectrometry (MPIMS). Results will be discussed along with the mechanistic developments and atmospheric implications.
Copyright 2018, California Institute of Technology
Aileen Hui,[1,2] Kristen Zuraski,[1] Matthew D. Smarte,[2] Rebecca L. Caravan,[3] Greg Jones,[2] Joseph Messinger,[2] Mitchio Okumura,[2] David Osborn,[3] Carl. J. Percival,[1] Craig Taatjes,[3] Stanley P. Sander.[1]
[1] Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 USA
[2] Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125 USA
[3] Combustion Research Facility, Mailstop 9055, Sandia National Laboratories, Livermore, California, 94551 USA
Guillaume Chossiere Massachusetts Institute of Technology
Sensitivity of present and future aviation-related air quality impacts to changing background conditions
The past decades have seen significant growth in commercial aviation traffic and fuel burn, averaging 3.7% per year, and traffic is projected to double again by 2035. This growth has resulted in significant increases in aviation emissions, even while emissions of pollutants from most other major sectors in developed countries are stable or falling. This will change the chemical background and pathways encountered by aviation emissions once released into the atmosphere, changing their air quality impacts and the sensitivity of surface conditions to these growing aviation emissions. Furthermore, uncertainties present in current-day non-aviation emissions are rarely quantified or propagated into calculations of air quality impacts, but could affect air quality impact pathways for the same reason. We produce a global estimate of the sensitivity of aviation-attributable air quality impacts to changes and uncertainty in current and future non-aviation emissions inventories. We quantify uncertainty in current and future surface-level NOx, SOx, and NH3 emissions, and use the GEOS-Chem chemistry-transport
model adjoint to evaluate its effect on the pathways linking aviation emissions to air quality impacts. Our results provide a new, quantitative estimate of a major source of modeling uncertainty, and can be used to inform decision makers and the public regarding which aviation emissions should be targeted in order to achieve maximum benefits in terms of public health.
Sebastian D. Eastham (MIT)
Steven R. H. Barrett (MIT)
Marie Camredon LISA, UMR CNRS/INSU
Speciation and properties of gaseous organic compounds: an explicit modeling of organic species sources and sinks
Thousands of organic compounds are present in the atmosphere. Either directly emitted by natural and anthropogenic sources, or formed in situ by photochemical reactions, these organic compounds are nowadays known to largely impact air quality and climate. The speciation and the properties of individual organic species remain however largely unknown. Theirs environmental impacts are therefore difficult to quantify.
This study aims at exploring the speciation and the physico-chemical properties of gaseous organic compounds in the troposphere, representing explicitly theirs sources and sinks. Scenario were developed in a box model for typical forest, rural and urban environments in winter and summer conditions. A very detailed speciation was considered for volatile organic compound emissions, considering around 160 primary organic species. The quasi-explicit gaseous oxidation mechanisms of these emitted species were generated using GECKO-A (Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere), leading to the formation of more than 5 hundred thousand secondary organic species. Deposition was considered for all primary and secondary gaseous organic compounds.
The simulated results were used to examine the major organic species, their physico-chemical properties (kinetic constants, saturation vapor pressure, Henry's law coefficient) and their impact on air quality (HOx concentrations, NOx budget and potential transfers towards the condensed phases).
G. Siour, R. Valorso, B. Aumont (LISA, UMR CNRS/INSU 7583, Universités Paris-Est Créteil et Paris Diderot, IPSL, 94010 Créteil CEDEX, France)
Ningxin Wang UC Davis
Correlating aerosol chemical composition and optical properties using 7-year co-located measurements at the ARM Southern Great Plains (SGP) site
Understanding the correlation between aerosol composition, size distribution and its optical and hygroscopic properties helps elucidate the aerosol's direct and indirect effects on our climate. Long-term, co-located measurements of aerosol composition and size distribution, cloud condensation nuclei (CCN), aerosol optical properties (e.g., aerosol absorption/scattering coefficient) together with meteorological conditions are available at the DOE Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site near Lamont, Oklahoma. The non-refractory submicrometer aerosol (NR-PM1) chemical composition from 2011-2018 are monitored using an Aerosol Chemical Speciation Monitor (ACSM). Measurements show that the NR-PM1 mass concentration at SGP is dominated by organics most of the time with ammonium nitrate increasing during winter months. Positive Matrix Factorization (PMF) analysis of the ACSM measurements reveal that the organic aerosol (OA) at SGP are composed of oxygenated OA with episodes of enhanced biomass burning OA (BBOA). We explore the correlations between BBOA with aerosol absorption measurements from a Particle Soot Absorption Spectrometer (PSAP) and CCN measurements from a Cloud Condensation Nuclei Counter (CCNC). We also use aerosol compositional information to explore the effect of photochemical aging and RH on aerosol optical properties.
Ningxin Wang (a), Thomas Watson (b), Qi Zhang (a)
(a) Department of Environmental Toxicology, University of California, 1 Shields Ave., Davis, CA, 95616, USA
(b) Brookhaven National Laboratory, Upton, NY, 11973, USA
Pius Lee NOAA
Potential Performance differences of the National Air Quality Forecasting Capability when upgrading the Chemical Transport Model
The National Oceanic and Atmospheric Administration (NOAA) National Air Quality Forecasting Capability (NAQFC) is a vital service that NOAA provides to safeguard public health as well as environmental resilience through information-driver mitigation, and remedial and adaptation actions. The NAQFC system is under a study to potentially upgrade its Chemical Transport Modeling component from using the Community Multiscale Air Quality Model (CMAQ) version 5.0.2 to version 5.2. This is a major upgrades in chemistry and their corresponding emission sciences. The following lists the major science upgrades: (a) upgrade of the gas chemistry for the Carbon-Bond Mechanism version 5 (CB05) to version 5 Revision1 (CB05R1); (b) Inclusion of Halogen chemistry; (c) Employment of more explicit speciation for isoprene and monoterpenes from biogenic sources; (d) Upgrade of the aerosol module
using a more sophisticated secondary aerosol production suite of multi-generational oxidation mechanism; and (e) Application of a fuller set of National Emission Inventory (NEI) that aligns better with CMAQ version 5.2 from the base year of 2014. Their performance statistical metrics were compared and ranked to provide a basis for implementation recommendation.
Youhua Tang1,2, Daniel Tong1,2,3, Barry Baker1,2 , Jeff McQueen4, Jianping Huang4,5,
1 NOAA/Air Resources Laboratory, College Park, MD,
2 UMD/Cooperative Institute for Climate and Satellites, College Park, MD,
3 Center for Spatial Information Science and Systems, George Mason University, Fairfax, VA
4 National Oceanic and Atmospheric Administration (NOAA), National Centers for Environmental Prediction (NCEP), College Park, MD
5 I.M. Systems Group Inc., Rockville, MD
Rasmus V. Otkjær Department of Chemistry, University of Copenhagen
Trends in Peroxy Radical Hydrogen Shift Rate Constants
Unimolecular hydrogen shift reactions in peroxy radicals have been shown to be important in the atmospheric oxidation of isoprene and α-pinene. [P. Wennberg et al., Chem. Rev. 118, 3337-3390 (2017); T. Berndt et al. Nature Comm., 7, 13677 (2016)] These studies also report the efficient generation of highly oxidized organic molecules known to contribute to particle formation and growth. Unimolecular hydrogen shifts are also known to be important in the combustion of organic materials. The role of these reactions in the oxidation of organics in the atmosphere has received less attention due, in part, to the lack of kinetic data at relevant temperatures.
Here we use an experimentally verified theoretical approach based on Multi-Conformer Transition State Theory (MC-TST) to calculate rate constants for a systematic set of H-shifts. [Submitted to J. Phys. Chem. A] Our results show that substitution at the abstraction site, with OH, OOH, OCH₃, C=C or C=O leads to increases in the rate constant by factors of up to ~1000. In addition, reactions leading to secondary carbon radicals (alkyl substituent) are 100 times faster than those leading to primary carbon radicals, and those leading to tertiary carbon radicals a factor of 30 faster again. When the ring size in the TS is 6, 7 or 8 atoms (1,5; 1,6 or 1,7 H-shift), the H-shift reactions rate constants can reach 1 sâ»Â¹� . Thus H-shift reactions are likely much more prevalent in the atmosphere than previously considered.
Henrik G. Kjaergaard, Department of Chemistry, University of Copenhagen
Rodrigo G. Gibilisco
Bergische Universität Wuppertal, Institute for Atmospheric and Environmental Research
Product distribution and reaction kinetics of 3-methyl-3-penten-2-one initiated by OH radicals and Cl atoms.
Unsaturated carbonyls are present in the atmosphere from biogenic and anthropogenic sources. They are potential contributors for SOA formation. Therefore, investigations on the major photooxidation pathways of those compounds are important to assess their environmental impacts and effects on human health.
Gas-phase rate coefficients of the reaction of 3-methyl-3-penten-2-one (3M3P2O) with hydroxyl radicals (OH) and chlorine atoms (Cl) have been studied for the first time. The relative kinetic technique has been employed in these studies. Experiments have been performed in a simulation chamber at (298 ± 3) K and 1 atm of synthetic air using in situ FTIR technique for reactants monitoring decay. Rate coefficients obtained in this study were (10-11cm3 molec-1 s-1): kOH= (6.2 ±0.6) and kCl= (28.8 ±2.4)
In addition, quantification of the main degradation products for the reaction of 3M3P2O with OH and Cl were performed. The reaction pathways leading to the formation of the identified product species, consistent with our understanding of the atmospheric chemistry of organic peroxy and alkoxy radicals, are presented. Atmospheric implications are also discussed.
Acknowledgements
The authors acknowledge financial support of their work by the Deutsche Forschungsgemeinschaft (DFG). R. G. Gibilisco is very grateful to the Alexander von Humboldt Foundation for providing a Georg Forster postdoctoral fellowship. I. Bejan acknowledges support provided by PN-III-P4-ID-PCE-2016-0807 project.
Ian Barnes (a), Iustinian G. Bejan (b), Peter Wiesen (a)
(a) Bergische Universität Wuppertal, Institute for Atmospheric and Environmental Research, 42097 Wuppertal / Germany.
(b) Faculty of Chemistry and CERNESIM research center, “Alexandru Ioan Cuza†� University of Iasi, Romania
Zixu (Tiffany) Zhao UC Riverside
Heterogeneous Ozonolysis of Endocyclic Organic Aerosol Model Compounds: Chemical Mechanisms and Implication for Criegee Intermediate Dynamics
Unsaturated low-volatile organic compounds have been observed in atmospheric aerosol particles (e.g., aerosols from plants, cooking and biomass burning) and human skin. Understanding their chemical fates through reaction with ozone at the relevant surfaces is crucial to elucidating the multiphase chemical mechanisms and predicting environmental and health impacts. In this work, heterogeneous ozonolysis of two endocyclic organic aerosol model compounds (shikimic acid and 4-cyclohexene-1,2-diacid) were studied in a flow tube reactor. Reaction kinetics and reaction products were characterized by multiple techniques including GC-MS, TOF-CIMS, and UV-Vis. Using different relative humidity (30%, 60%, and 90%) and mixing with glutaric acid resulted in changes of the particle viscosity and Criegee Intermediate dynamics. Hence, different reaction kinetics and product distributions were observed. For both pure endocyclic compounds, the reactive uptake coefficients are higher under higher relative humidity; but upon mixing with glutaric acid, the ozone reactive uptake coefficients increased substantially only for shikimic acid. The oxidation products suggest that Criegee Intermediates reaction with water is a more dominant pathway for shikimic acid. In both systems, hydroperoxides are important products. Different from gas-phase ozonolysis of endocyclic VOC, the “hydroperoxide channel†� that produces peroxy radicals and OH through the heterogeneous ozonolysis was found to be minimal.
Haofei Zhang, UC Riverside
Jesse Kroll MIT
Inferring reaction kinetics from complex atmospheric mass spectrometric datasets
Aileen Hui California Institute of Technology and Jet Propulsion Laboratory, California Institute of Technology
Kinetics and product yield studies of the HO2 + CH3C(O)O2 reaction: direct detection of OH by mid-IR spectroscopy
Organic peroxy radicals (RO2) are important intermediates in the atmosphere formed from the oxidation of volatile organic compounds (VOCs). In unpolluted regions, one of the primary loss processes of RO2 is reaction with HO2. Although HO2 + RO2 reactions were once thought to be exclusively radical terminating, for some more complex RO2 such as CH3C(O)O2, the reaction includes an additional product channel that generates OH.
The title reaction has three possible product channels: HO2 + CH3C(O)O2 → CH3C(O)OOH + O2 (R1a), CH3C(O)OH + O3 (R1b), OH + CH3 + CO2 + O2 (R1c). CH3C(O)O2 is formed from the photo-oxidation of various carbonyl compounds including isoprene, which has been linked to the disagreement
between modeled and measured OH profiles over remote, forested regions of the world. The atmospheric impact of the R1 depends on the overall rate constant (k1) and the branching ratios (α1a, α1b, and α1c); however, large uncertainties in previously reported values warrant further investigation of this reaction.
This work investigated the kinetics and product yields of R1 by directly detecting OH and HO2 using Infrared Kinetic Spectroscopy (IRKS). k1, α1a, α1b, and α1c were measured at 100 Torr over the temperature range of 230 - 296 K. This work reports the first temperature dependence measurements of α2a and extends by 20 K the lower limit of the range of temperatures over which R1 has been previously studied.
©2018 California Institute of Technology.
Mitchio Okumura (California Institute of Technology), Stanley Sander (Jet Propulsion Laboratory, California Institute of Technology)
Aleksandra Volkova California State University, Northridge
Atmospheric chemistry of (Z)-CF3CH=CHCl: Cl atom, OH radical and O3 reactions, and the role of isomerization
(Z)-1-chloro-3,3,3-trifluoropropene, (Z)-CF3CH=CHCl, is a haloolefin which has been developed as part of a new generation of CFC replacements. Previously, we have studied the atmospheric chemistry of the structural isomer, (E)-CF3CH=CHCl, and a significant body of literature now exists on the environmental impact of this species. (Z) to (E) isomerization has been shown to occur in some halogenated olefins. This process can impact the reactivities and lead to differences in the product distribution of (Z)-CF3CH=CHCl relative to (E)-CF3CH=CHCl. To access this effect, a combined experimental and computational study was undertaken.
We report on the kinetics and mechanism of the reactions of Cl atoms and OH radicals with (Z)-CF3CH=CHCl. Low pressure Cl atom kinetics measurements for both (Z)- and (E)-CF3CH=CHCl are presented. Evidence for isomerization and a significant chlorine atom elimination channel was observed experimentally and supported by computational results. Finally, the stable oxidation products of the reaction of O3 with (Z)-CF3CH=CHCl (and the (E)-isomer) were investigated. No isomerization was detected in the reaction of (Z)-CF3CH=CHCl with O3. The results are discussed with respect to the atmospheric chemistry and environmental impact of (Z)- and (E)-CF3CH=CHCl.
Theis I. Sølling, Lene Løffler Andersen, Ole John Nielsen, Mads P. Sulbaek Andersen
Ali Akherati Colorado State University
Carbon-, Oxygen-, and Size- Resolved Model to Simulate the Microphysics, Chemistry, and Thermodynamics of Biomass Burning Organic Aerosol
Biomass burning is an important source of organic aerosol (BBOA) to the atmosphere. Yet, there are large uncertainties in understanding the chemical evolution of BBOA and its consequent impacts on climate and human health. We will develop a state-of-the-science OA model that combines the two-dimensional statistical oxidation model (SOM) with the TwO-Moment Aerosol Sectional (TOMAS) model. The SOM uses a two-dimensional carbon-oxygen grid to track the gas- and particle-phase chemistry, gas/particle partitioning, and properties of gas- and particle-phase organic precursors and products. The TOMAS model uses two moments, that of number and mass, of the aerosol size distribution to model processes of nucleation, condensation, and coagulation. This updated model, resolved in dimensions of carbon number, oxygen number, and size, will simulate the microphysics, chemistry, and thermodynamics of BBOA and include the following processes: (a) semi-volatile POA, (b) SOA formation from semi-volatile, intermediate-volatility and volatile organic compounds, (c) multi-generational aging that includes functionalization and fragmentation reactions, (d) low-volatility SOA formation from autoxidation and oligomerization reactions, (e) influence of vapor wall losses encountered in chamber experiments, and (f) phase state of OA. The model will be evaluated against chamber and flow reactor experiments performed at the Fire Laboratory in Missoula, MT as part of the FLAME and FIREX campaigns.
Christopher Cappa, Civil and Environmental Engineering, UC Davis
Jeffrey R. Pierce, Atmospheric Science, Colorado State University
Shantanu Jathar, Mechanical Engineering, Colorado State University
Andrew Rickard Wolfson Atmospheric Chemistry Laboratories, Department of Chemistry, University of York
Mechanisms for Atmospheric chemistry: GeneratioN, Interpretation and FidelitY - MAGNIFY
Over the past decade the Master Chemical Mechanism (http://mcm.leeds.ac.uk/MCM) has been hugely influential on the atmospheric chemistry community, where it is extensively used in a wide variety of science/policy applications where chemical detail is required to assess issues related to air quality and atmospheric composition. The joint UK/French MAGNIFY Project provides a strategic framework for the sustainable development of the MCM into the future. This involves a complete overhaul of its
construction rules so that future generations can be auto-generated using the GECKO-A framework (Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere (http://geckoa.lisa.u-pec.fr)), and opening it up more to the community. Detailed updates include areas such as the ozonolysis of organic species and the chemistry of the resulting Criegee intermediates, photolysis and the chemistry of polyfunctional compounds. MAGNIFY builds upon the success of the MCM, maintaining it as the “gold standard†� benchmark mechanism for atmospheric chemistry.
Mathew Evans, Mike Newland, Peter Bräuer, Killian Murphy, Dan Ellis - National Centre for Atmospheric Science, Wolfson Atmospheric Chemistry Laboratories, Department of Chemistry, University of York, York, UK.
Bernard Aumont, Richard Valorso, Marie Camredon - Laboratoire Interuniversitaire des Systemes Atmospheriques (LISA) UMR 7583 CNRS Universites Paris-Est Creteil et Paris Diderot, Institut Pierre-Simon Laplace, Creteil Cedex, France.
Camille Mouchel-Vallon, Sasha Madronich - Atmospheric Chemistry Observations and Modelling, National Center for Atmospheric Research, Boulder, Colorado 80307, USA.
Michael Jenkin - Atmospheric Chemistry Services, Okehampton, Devon, UK.
Anna Shcherbacheva Institute for Atmospheric and Earth System Research/Physics
Parameter identification of molecular cluster enthalpies and entropies by Monte Carlo method
Recent development in design of mass spectrometers has enabled the detection
and quantification of ionic clusters from molecular scale upward.
However, measurements alone do not reveal characteristics of the proccesses,
such as clusters growth and evaporation. A Monte Carlo method
suggests an approach that enables identification of entropies and enthalpies
from time-dependent measurements of cluster concentrations, conducted at varying temperatures. In the present study the technique was tested by applying
the MCMC simulations to synthetic cluster concentrations generated using
Atmospheric Cluster Dynamic Code (ACDC). The results of MCMC simulations
are compared to synthetic measurements, such that entalpies and
entropies are treated as unknown parameters that vary within the procedure.
By using preliminary developed experimental design the minimal settings required for accurate identification of parameters have been detected. Although
the simulations have been conducted for a system of neutral cluster of sulphuric
acid and ammonia, similar procedure can be applied to ionic clusters
and real measurements, as the instrumentation allows measuring cluster concentrations at high time-resolution.
Hanna Vehkamäki (Institute for Atmospheric and Earth System Research/Physics) , Heikki Haario (Lappeenranta University of Technology)
David Hanson Augsburg University
Modeling of OH, HO2 and RO2 reactions in atmospheric pressure flow reactors
Vertically-aligned photooxidation flow reactors have been used to study RO2 reactions [Hanson et al. 2004; Noziere et al. 2017] and to form H2SO4 in particle formation experiments [Abdullahi et al. 2015]. Presented here are simulations of the photo-oxidation chemistry in these experiments. A two-dimensional model has been developed to simulate OH, NO, HO2 etc. radical reactions forming H2SO4 and these simulations provide insight into the oxidation conditions within the particle flow reactor. An additional chemistry module is presented that tracks the oxidation products of the Cl-initiated oxidation of cyclohexane and cyclopentane. These simulations facilitate RO2 sensitivity determinations of proton-transfer mass spectrometry as well as the detection of the end products by that instrument.
Barbara Noziere, CNRS/IRCELYON, Villeurbanne, France
Emma D'Ambro University of Washington, Seattle
Δ3-carene photoxidation SOA: identifying particle-phase products and the first steps of oxidation
While α-pinene is the most abundantly emitted monoterpene and thus the most widely studied, Δ3-carene reacts more rapidly with common atmospheric oxidants. Thus, a similar quantity can be oxidized in the same time frame and potentially be a substantial contributor to secondary organic aerosol (SOA). However, much is unknown about the oxidation products and mechanism of SOA formation. We present
chamber measurements examining SOA formation from the reaction of Δ3-carene and OH, compared to α-pinene + OH. A Filter Inlet for Gases and AEROsols (FIGAERO), coupled to an iodide Chemical Ionization Mass Spectrometer (CIMS), measured the oxidize products in both the gas and particle phases. We observed similar aerosol mass yields from Δ3-carene OH oxidation and α-pinene + OH oxidation, however, initial results suggest Δ3-carene + OH SOA has a lower oligomer content relative to that of α-pinene. To understand the products and SOA formed, we focus on developing a mechanism of the first steps of Δ3-carene oxidation. Previous work examined some of the first steps of Δ3-carene + OH, which we expand upon here using a quantum chemical calculation methodology to calculate the rates of intramolecular H-shifts primarily from RO2, as well as RO. We find that, in agreement with previous measurements, a major fate of Δ3-carene is caronaldehyde. Additionally, we identify pathways that may lead to the formation of highly oxygenated material (HOM) and compounds identified in our mass spectra.
Emma L. D’Ambro, University of Washington
Kristian H. Møller, University of Copenhagen
Noora Hyytinen, University of Helsinki
Rasmus V. Otkjær, University of Copenhagen
Siddharth Iyer, University of Helsinki
Joel A. Thornton, University of Washington
Henrik G. Kjærgaard, University of Copenhagen
Theo Kurtén, University of Helsinki
Haichao Wang Peking University
Heterogeneous hydrolysis of dinitrogen pentoxide in Beijing during winter haze episode
The nature of dinitrogen pentoxide (N2O5) heterogeneous hydrolysis is important to understand the regional NOx removal and particulate nitrate pollution. The gap between the prediction and observation of the coefficient reflects the N2O5 heterogeneous uptake mechanism still not well understand. A field campaign was conducted at the suburban site in Beijing from January to March 2016. The N2O5 uptake coefficient, γ(N2O5), was determined by the observation data in polluted winter haze episodes, and show strong dependence on particulate nitrate and aerosol liquid water content. The observed γ(N2O5) is variable and lower than currently implemented parameterizations predicted, even take the organic coating-inorganic core theory into consideration. Volatile organic compound in these haze episodes was characterized with low organic carbon oxidization state (O: C ratio was 0.48 on average), which was suggested inhibiting diffusivity and/or solubility efficiently. The performance of prediction was improved
after including this effect. The results have implications for the suppression of coating by the organic with low O: C in N2O5 heterogeneous hydrolysis is underestimated in North China in wintertime as well as other similar regions.
Haichao Wang1, Keding Lu1*, Xiaorui Chen1, Zhaofeng Tan1#, Xuefei Ma1, Zhijun Wu1, Xin Li1, Yuhan Liu1, Dongjie Shang1, Yusheng Wu1, Limin Zeng1, Min Hu1, Sebastian Schmitt2, Astrid Kiendler-Scharr2, Wahner Andreas2 and Yuanhang Zhang1,3
1State Key Joint Laboratory or Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing, China.
2Institute of Energy and Climate Research, IEK-8: Troposphere, Forschungszentrum Jülich GmbH, Jülich, Germany
3CAS Center for Excellence in Regional Atmospheric Environment, Chinese Academy of Science, Xiamen, China
#Now at the Institute of Energy and Climate Research, IEK-8: Troposphere, Forschungszentrum Jülich GmbH, Jülich, Germany
Hendrik Fuchs Forschungszentrum Jülich
Investigation of the oxidation of methyl vinyl ketone (MVK) by OH radicals in the atmospheric simulation chamber SAPHIR
The photooxidation of methyl vinyl ketone (MVK) was investigated in the SAPHIR chamber for high and low NO conditions. Measurements of trace gas concentrations were compared to concentration time series calculated using the MCM. Comparison of measured and modeled OH radical concentrations showed the need for enhanced OH radical production under low NO conditions. Product yields, including methylglyoxal and glycolaldehyde, as well as OH observations were consistent with assumptions of additional RO2 plus HO2 reaction channels as proposed in the literature. However, HO2 radical concentrations were also underestimated by the model, suggesting that additional OH is not directly produced from RO2 radical reactions, but indirectly via increased HO2. Quantum chemical calculations show that HO2 could be produced from a fast 1,4-H shift of the second most important MVK derived RO2 species. However, this channel was not large enough to bring modelled HO2 radical concentrations into agreement with measurements due to the small yield of this RO2 species. An additional reaction channel of the major RO2 would be required that produces HO2 radicals to achieve model-measurement agreement. A set of H-migration reactions for the main RO2 radicals were investigated by quantum chemical and theoretical kinetic methodologies, but did not reveal a contributing route to HO2 radicals.
Sascha Albrecht, Forschungszentrum Jülich
Ismail-Hakki Acir, Forschungszentrum Jülich
Birger Bohn, Forschungszentrum Jülich
Martin Breitenlechner , Harvard University
Hans-Peter Dorn, Forschungszentrum Jülich
Georgios I. Gkatzelis, Forschungszentrum Jülich
Andreas Hofzumahaus, Forschungszentrum Jülich
Frank Holland, Forschungszentrum Jülich
Martin Kaminski, Forschungszentrum Jülich
Frank N. Keutsch, Harvard University
Anna Novelli, Forschungszentrum Jülich
David Reimer, Forschungszentrum Jülich
Franz Rohrer, Forschungszentrum Jülich
Ralf Tillmann, Forschungszentrum Jülich
Luc Vereecken, Forschungszentrum Jülich
Robert Wegener, Forschungszentrum Jülich
Alexander Zaytsev, Harvard University
Astrid Kiendler-Scharr, Forschungszentrum Jülich
Andreas Wahner, Forschungszentrum Jülich
Iustinian Bejan "Alexandru Ioan Cuza" University of Iasi
Kinetic investigations of the OH-initiated oxidation of a series of alkylfurans at 298 K and atmospheric pressure
Furans are emitted in the atmosphere from anthropogenic and biogenic sources. The reactivity of furans with hydroxyl radicals (OH) in atmospheric conditions could lead to photooxidant and SOA formation.
The aim of this study was to determine rate constants for the reaction of the alkylfurans with OH radicals to assess the relative importance of these reactions as atmospheric loss processes. Kinetics of
the OH radical reactions with furan (FN), 2-methylfuran (2-MF), 3-methylfuran (3-MF), 2,3-dimethylfuran (2,3DMF), 2,5-dimethylfuran (2,5DMF), 2,3,5-trimethylfuran (TrMF) and tetramethylfuran (TeMF), respectively, have been investigated in the present work.
Long path FTIR analysis was used to monitor the decay of the alkylfurans and the reference compounds in the ESC-Q-UAIC photoreactor. Using the relative rate method the following rate constants (10-11 cm3 molecule-1 s-1): k(FN) = (2.70±0.78), k(2MF) = (7.16±2.51), k(3MF) = (9.05±2.59), k(2,3DMF) = (13.50±3.84), k(2,5DMF) = (13.59±4.94), k(TrMF) = (25.47±7.33) and k(TeMF) = (42.22±8.71) were obtained. These are first reported rate coefficients for the OH radical reactions with TrMF and TeMF.
The atmospheric implications of the cited reactions were estimated through the kinetic data obtained in this work. The reactivity trends will be discussed.
Acknowledgement: The financial support provided by UEFISCDI within the PN-III-P4-ID-PCE-2016-0807 (IGAC-CYCLO) and by EUROCHAMP-2020 projects is gratefully acknowledged.
Claudiu Roman1, Cecilia Arsene1,2, Romeo-Iulian Olariu1,2, Iustinian Gabriel Bejan1,2*
1Department of Chemistry, †�Alexandru Ioan Cuza†� University of Iasi, 11 Carol I, 700506 Iasi, Romania
2Integrated Center of Environmental Science Studies in the North Eastern Region - CERNESIM, †�Alexandru Ioan Cuza†� University of Iasi, 11 Carol I, 700506 Iasi, Romania
John Orlando Atmospheric Chemistry Observations and Modeling Laboratory, National Center for Atmospheric Research
Steady State Continuous Flow Chamber for the Study of Atmospheric Hydrocarbon Oxidation Chemistry under Daytime and Nighttime Conditions – Chamber Characterization and First Results
We present here the development and characterization of the NCAR Atmospheric Simulation Chamber, a 10 m3 Teflon chamber that can be operated in a continuous flow mode that accurately represents realistic mid-latitude tropospheric oxidant concentrations in either daytime or nighttime conditions. Steady-state “daytime†� conditions are obtained by photolysis of an OH precursor (H2O2), which is continuously flowing into the chamber along with NO and the VOC under study (with constant sampling out of the chamber). This allows chemistry to be studied at controlled and constant levels of NO (about 100 ppt – 10 ppb) where peroxy radical (RO2) lifetimes can be as long as about 1 min, allowing diverse unimolecular and bimolecular reaction pathways to be explored. Similarly, nighttime conditions can be achieved by continuous flow of NO and O3 into the chamber, producing steady-state levels of NO3 in the presence of sub-ppb levels of NO. In this presentation, an overview of the chamber capability is presented, along with results from ‘proof-of-concept’ experiments involving daytime, OH-initiated
isoprene oxidation. Specifically, yields of methacrolein and methyl vinyl ketone (MACR/MVK) from OH-initiated oxidation of isoprene are presented over a range of RO2 lifetimes and compared with box model simulations using recently developed chemical mechanisms (Leeds MCM and CalTech). In addition, the implications of this new chemistry for global MVK/MACR distributions are examined using CAM-Chem.
Xuan Zhang, John Ortega, Stephen Shertz, Rebecca H. Schwantes, Louisa K. Emmons, Siyuan Wang, Andrew J. Weinheimer, Denise D. Montzka, Geoffrey S. Tyndall, and John J. Orlando, all Atmospheric Chemistry Observations and Modeling Laboratory, National Center for Atmospheric Research, Boulder CO
Juliane Fry Reed College
Oxidation products and aerosol production from NO3 oxidation of isoprene
Isoprene is a key biogenic trace gas in the troposphere, constituting the majority of global non-methane hydrocarbon emissions. Its oxidation mechanisms are therefore important drivers of biogenic secondary organic aerosol (BSOA) and ozone production. Although isoprene is mainly emitted during daytime and oxidized photochemically, dark reactions with O3 and NO3 constitute a non-negligible fraction of isoprene oxidation and may play a dominant role in production of isoprene derived organic nitrogen and SOA, especially in regionally polluted areas. At the NO3Isop campaign at the atmospheric simulation chamber SAPHIR in the Forschungszentrum Jülich, Germany (30. July - 24. August 2018), we conducted a series of experiments to comprehensively investigate gas- and aerosol-phase products of NO3 + isoprene. These experiments were deisgned to mimic conditions observed in the residual layer, under varying conditions of dominant RO2 bimolecular fate, RO2 lifetime, humidity, and seed aerosol. Instruments participating in the chamber study included optical and mass spectrometric measurements of gaseous and aerosol phase molecules and compound classes, including measurements of key radical species. Selected experiments focused on later-generation chemistry, day-to-night and night-to-day transitions, seed acidity, and BVOC mixtures. This presentation will show preliminary results from this comprehensive study of NO3 + isoprene chemistry.
Author team: Researchers from the NO3Isop campaign at atmospheric simulation chamber SAPHIR in Jülich Germany (30. July - 24. August 2018)
Lavinia Onel University of Leeds
Kinetic study of the reaction of the simplest Criegee intermediate with ozone
A significant fraction of unsaturated volatile organic compounds are oxidised by ozone producing highly reactive Criegee intermediates (CI), such as the simplest CI, CH2OO, in the atmosphere. Some of the CI generated by ozonolysis may be collisionally stabilised and then react with other species. The reaction of the stabilised CH2OO with O3 is potentially important in atmospheric oxidation and chamber studies of ozonolysis. However, the reaction has been little studied and there are large uncertainties in the value of its rate coefficient at 298 K: the only one previous experimental study (Chang et al. 2018) found 7 x 10-14 cm3 s-1 and the theoretical studies are in discrepency, e.g. 10-18 - 10-16 cm3 s-1 (Kjaergaard et al. 2013) and 4 x 10-13 cm3 s-1 (Vereecken et al. 2015). We have started a kinetic study of the reaction at 296 K and two different pressures, 80 and 300 Torr, using a novel flash photolysis experiment coupled with time-resolved multipass broadband UV absorption spectroscopy. CH2OO has been generated by photolysing CH2I2/O2 at 248 nm. The broadband UV absorption experiments enable to choose the concentrations of the reagents to avoid aerosol formation in the system on the time scale of the kinetic measurements. The measurements use gaseous mixtures containing 98% O2 to instantaneously regenerate O3 after photolysis at 248 nm. Results will be presented and implications for chamber studies of ozonolysis and modelling of atmospheric composition will be discussed.
Mark A. Blitz (University of Leeds), Paul Seakins (University of Leeds), Dwayne Heard (University of Leeds) and Daniel Stone (University of Leeds)?
Lu Xu California Institute of Technology
Unimolecular Reactions of Peroxy Radicals Formed in the Oxidation of α-pinene and β-pinene by Hydroxyl Radical
Roughly 150 Tg of monoterpenes is emitted into Earth’s atmosphere every year. The oxidation of monoterpenes plays an important role in NOx cycle and formation of organic aerosol. However, the oxidation mechanisms of monoterpenes are still uncertain, largely due to the incomplete understanding on the roles of peroxy radical (RO2) in the oxidation process. The unimolecular reactions of RO2 are typically overlooked, but their importance has been pointed out in recent studies. The unimolecular reactions of monoterpene RO2 have been proposed to lead to the formation of highly oxidized molecules (HOMs), which could nucleate to form new particles and hence affect Earth’s radiation balance. The rates of unimolecular reactions of monoterpene RO2 have not been measured. In this study, we perform laboratory experiments to determine the unimolecular reactions rate of α-pinene and β-pinene RO2. We deployed a Gas-Chromatography Chemical Ionization Mass Spectrometer (GC-CIMS) to conduct isomer-specific measurements of the oxidation products, based on which the RO2 chemistry is probed. We find that the unimolecular reaction rate depends on RO2 isomers and the unimolecular reaction of the ring-opened RO2 is highly competitive with its bimolecular reactions in the atmosphere. The implications of the fast RO2 unimolecular reactions on the formation of HOMs and organic aerosol will also be discussed.
Kristian H. Møller, University of Copenhagen
John D. Crounse, California Institute of Technology
Rasmus V. Otkjær, University of Copenhagen
Henrik G. Kjaergaard, University of Copenhagen
Paul O. Wennberg, California Institute of Technology
Michael Link Colorado State University, Chemistry Department
Constraining the summertime chemical production of organic acids in forested environments with measurements and modeling
Organic acids comprise a significant fraction of reactive atmospheric carbon and are critical to the growth of secondary organic aerosol, influence the acidity of precipitation and participate in multiphase oxidation processes. Specific mechanisms for organic acid formation from atmospheric oxidation are not well resolved because their abundances are not well known, but also because they are thought to have primary and secondary sources. We have constrained the chemical production of organic acids during the summertime from two forested environments by combining ambient measurements with results from laboratory experiments while working toward organic acid carbon closure through box modeling. We find that in Alabama during SOAS organic acids were produced during the day and removed from the atmosphere at night on rapid timescales. In contrast, slow daytime production and a potential nighttime source characterized the pattern of organic acid abundance measured from a forest in Colorado during the summer of 2016. Organic acid measurements from the Focused Isoprene eXperiments suggest that isoprene oxidation by OH is the strongest contributor to organic acid carbon observed at SOAS with much weaker contributions from monoterpene oxidation. Most organic acid carbon is observed to be produced from oxidation chemistry at SOAS whereas evidence of varied oxidation processes and potential emission contribution is observed from the forest in Colorado.
Ryan Fulgham, Patrick Brophy, Trey Murschell, Delphine Farmer (Colorado State University, Chemistry Department)
Mixtli Campos-Pineda University of California, Riverside
Low pressure yields of stabilized Criegee intermediates produced from ozonolysis of a series of alkenes
Cavity ring-down spectroscopy (CRDS) was utilized in combination with chemical titration with sulfur dioxide (SO2) to quantify stabilized Criegee intermediates (sCIs) produced at low pressures (4-20 Torr) in ozonolysis reactions of cis-2-butene, trans-2-butene, 2-methyl-2-butene, 2,3-dimethyl-2-butene, cyclopentene, and cyclohexene. The yield of stabilized sCI, acetaldehyde oxide (CH3CHOO), from trans-2-butene ozonolysis decreased with decreasing pressure and reached a nascent yield of zero at the zero-pressure limit, in agreement with a previous study based on the measurement of H2SO4 formation. The yield of stabilized CH3CHOO from cis-2-butene ozonolysis had the same trend and reached a nascent yield of 0.05 ± 0.04 at the zero-pressure limit. The yield of stabilized acetone oxide, (CH3)2COO, from 2,3-dimethyl-2-butene decreased with decreasing pressure and reached 0.12 ± 0.05 at the zero-pressure limit, in agreement with a previous study. The nonsymmetric alkene 2-methyl-2-butene produced two stabilized sCIs, CH3CHOO and (CH3)2COO, and their total yield decreased with decreasing pressure and reached 0.01 ± 0.03 at the zero-pressure limit. For cyclopentene and cyclohexene, the sCI yields were essentially constant near zero, as expected from endocyclic alkenes. The nascent yields of sCI of various alkenes are compared, and their correlations with the alkene structures are discussed.
Prof. Jingsong Zhang (University of California, Riverside)
Nanna Myllys UC Irvine
What is required to form stable clusters at atmospheric conditions?
Using quantum chemistry and cluster formation simulations we have studied what properties molecules should have in order to enhance sulfuric acid-driven particle formation. Among oxidized monoterpene products multi-carboxylic acids are the most prominent candidates to enhance particle formation. However, it is very unlikely that multi-carboxylic acids and sulfuric acid, even together with common stabilizing compounds, can drive new-particle formation via clustering mechanisms. Since experimental studies have shown that oxidized organic compounds participate in the initial steps of particle formation some other mechanisms or compounds are needed to explain experimental evidences. One possible reason for the discrepancy between experimental and theoretical results might be the formation of covalently-bound dimers. The formed dimer products very likely have a lower saturation vapor pressure than the reacting monomers due to a higher molecular mass and a larger number of functional groups, and thus these clusters are more stable against evaporation. Furthermore, we have demonstrated that strong organobases, such as guanidine, might significantly enhance the initial steps of particle formation even at low concentrations. Due to a mech-like cluster structures and high stability against evaporation, sulfuric acid–guanidine clusters could act as seeds for further growth via the uptake of other vapor molecules such as oxidized organic compounds.
Jonas Elm, Aarhus University
Tinja Olenius, Stockholm University
Rebecca Schwantes National Center for Atmospheric Research/Atmospheric Chemistry Observations and Modeling Laboratory
Exploring the Importance of Horizontal Resolution versus Chemical Resolution in CESM/CAM-chem
Global climate and chemical transport models are increasingly adding capability for finer horizontal resolution, but the significance of increased chemical resolution has received less attention. This work using the Community Earth System Model/Community Atmosphere Model with chemistry (CESMTM/CAM-chem) quantifies and compares the importance of finer horizontal and chemical resolution. Four different horizontal resolutions were tested (1.9° x 2.5°, 0.9° x 1.25°, 0.47° x 0.63°, 0.23° x 0.31° against three different chemical mechanisms (MOZART-TS1 (default in CESM2.0), MOZART-TS1 with more complex isoprene chemistry, and MOZART-TS1 with more complex isoprene and terpene chemistry). The recently completed isoprene and terpene updates to MOZART-TS1 have been designed to better represent mixed chemical regimes by including more descriptive later-generation chemistry. CESM/CAM-chem simulations were evaluated with field campaign observations collected in the Southeast U.S. during the summer of 2013. During the summer in the Southeast U.S., anthropogenic and biogenic emissions are noticeably spatially segregated, so the interactions between model resolution and complexity of chemical mechanism are of particular importance. This work tests whether the advantages of enhanced chemical resolution are different at finer resolution and assesses the relative computational cost and the accuracy of simulated surface ozone with both increasing horizontal and chemical resolution.
Rebecca Schwantes, Louisa Emmons, Forrest Lacey, John Orlando (National Center for Atmospheric Research)
Rishabh Shah Center for Atmospheric Particle Studies, Carnegie Mellon University
Contrasting SOA Formation in Urban and Rural Locations using an Oxidation Flow Reactor
We present direct and oxidized measurements of atmospheric aerosol in remote and urban case locations. The remote location is Finokalia village on Crete island, Greece. Finokalia is characterized by highly oxidized organic aerosol, with air masses coming from different sources (marine aerosol over the Mediterranean Sea, urban pollution from mainland Europe).
An oxidation flow reactor (OFR) is used for oxidized sampling. Size distribution and chemical composition of ambient and oxidized aerosol particles are measured using a scanning mobility particle
sizer and high-resolution time-of-flight aerosol mass spectrometer. We find that ambient aerosol on all days of sampling is highly oxidized (indicated by elemental O/C=0.9 and H/C=1.5 ratios). Using National Oceanic and Atmospheric Administration’s trajectory model, we find that when the air parcels are received from mainland Europe, the oxidation state of particles increases upon processing in the OFR – a behavior not observed when air parcels are transported completely from marine environments.
The contrasting urban case locations are Pittsburgh and New York. We studied SOA formation from vehicular emissions and VOCs emitted from personal care products and paint products. SOA formed in the OFR is enhanced by 2 μgm-3 when sampling adjacent to a freshly-painted parking lot. Elemental analysis of the AMS data will inform how the oxidation of these urban emissions differs from the oxidation of aerosols at the remote location.
Albert A. Presto, Center for Atmospheric Particle Studies, Carnegie Mellon University
Andrew Rickard University of Birmingham/University of Leicester
AtChem, an open source box-model for the Master Chemical Mechanism
Box-models are important tools for the study of atmospheric chemistry,
used to design, simulate and interpret laboratory and chamber
experiments as well as ambient measurements. At its core an
atmospheric chemistry box-model consists of a chemical mechanism and a
numerical integrator to solve the corresponding system of ordinary
differential equations. Assembling the model components may prove
challenging for a non-experienced user, hence the need for an
easy-to-use tool. Access to well documented scientific code is
increasingly considered a necessity within the scientific community
both to improve the reliability of research outcomes and to ensure the
traceability and reproducibility of the results.
AtChem has been designed to address these concerns and, more
specifically, to facilitate the use and evaluation of the Master
Chemical Mechanism (MCM), a quasi-explicit chemical mechanism which
describes in detail the gas-phase oxidation of methane and 142
non-methane hydrocarbons. AtChem can be used as an online service for
relatively simple simulations (e.g., laboratory and chamber
experiments) and as offline software for more complicated and longer
simulations (e.g., field campaigns). AtChem allows direct use of
MCM-based mechanisms and includes an easy implementation of model
constraints. The model is released as open source, under MIT licence,
and adopts a number of programming best practices, including strict
adherence to language standards and an extensive testing regime.
R. Sommariva (University of Birmingham/University of Leicester), S. Cox (University of Leicester), C. Martin (University of Leeds), K. Boronska (University of Leeds), J. Young (University of Leeds), P. Jimack (University of Leeds), M.J. Pilling (University of Leeds), W.J. Bloss (University of Birmingham), P.S. Monks (University of Leicester), A.R. Rickard (NCAS/University of York)
Ryan Thalman Snow College
Development of a UV inlet-less Broadband Cavity Enhanced Absorption Spectrometer (BBCEAS) for detection of HCHO, HONO, NO2 and O4
An instrument for measuring nitrous acid (HONO), a short-lived reactive trace component of the atmosphere was developed using Broadband Cavity Enhanced Absorption Spectroscopy (BBCEAS). Light is bounced back between two highly reflective mirrors to achieve very long path lengths (2-5 km) over a short (0.5-2m) base length. The path length enhancement enables sensitive detection of trace compounds at the pptv and ppbv level depending on the compound. HONO absorbs strongly in the near UV (350-400 nm) with a structured absorbance pattern allowing for the application of Differential Optical Absorption Spectroscopy (DOAS) fitting to retrieve the concentrations of narrow band absorbers. Measurement of HONO also suffers from contamination and line loss due to the reactivity of the HONO with surfaces. The prototype instrument developed and tested operates without an air sampling inlet, in an “open path†� configuration. Several LEDs were tested which allowed the instrument measurement window to extend from either 320 – 350 nm or 350 – 390 nm. The instrument also is able to measure other compounds that absorb between 355 and 390 nm such as formaldehyde, BrO, NO2, and O4. Initial instrument performance and field deployment is assessed along with feasibility for eddy-flux measurements.
Jaron Hansen, Brigham Young University
Taekyu Joo Georgia Institute of Technology
Secondary Organic Aerosol Formation and the Oxidation Mechanism of Methylfuran by Nitrate Radical Oxidation
Biomass burning contributes significantly to both primary and secondary organic aerosol (SOA). Recent studies demonstrate that a large fraction of SOA is produced from precursors emitted during biomass burning, such as furan derivatives. Methylfurans are important furan derivatives that show an increase in concentration in biomass burning plumes. Our current understanding of SOA formation from methylfurans is extremely limited, and even less attention has been paid to nighttime oxidation of this class of compounds. In this work, we investigate SOA formation and the reaction mechanism of 2- and 3-methylfuran by nitrate radical (NO3) oxidation at the Georgia Tech Environmental Chamber (GTEC) facility. We injected N2O5 as the source of NO3, and the VOC:N2O5 ratio was set ~1:4 to ensure peroxy radicals react with NO3. We compared the proposed oxidation mechanism with the compounds observed using a High Resolution Time-of-Flight Chemical Ionization Mass Spectrometer (HR-ToF-CIMS) coupled with a Filter Inlet for Gases and AEROsols (FIGAERO). In the gas-phase we identified multiple 2nd generation products in addition to nitrated compounds, though we were not able to detect the main 1st generation product (1,4-dicarbonyl). The compounds in the particle-phase included high MW oligomers as well as low volatility 1st and 2nd generation products.
Jean C. Rivera-Rios, Fobang Liu, Masayuki Takeuchi (Georgia Institute of Technology); Matthew J. Alvarado(Atmospheric and Environmental Research); Nga Lee Ng (Georgia Institute of Technology)
Yuhan Liu Peking University
A Comprehensive Test of the Recent Proposed HONO Sources in Field Measurements at Rural North China Plain
As HONO photolysis is an important source of OH radicals, apportionment of the ambient HONO sources is necessary to better understand atmospheric oxidation. It was found in summer 2014 in the Wangdu campaign (a rural site in North China Plain) that the importance of the various HONO sources changed according to the variable atmospheric and surface conditions, even within the same site. Using current literature parameterizations for the different processes, NO2 heterogeneous conversion, NO2 photoenhanced conversion, photolysis of adsorbed nitric acid and particulate nitrate and direct emissions from soil were all included in a box model. The simulation results reproduced the observed HONO production rates during noontime in general. Using existing parameterizations of the uptake coefficient, NO2 photoenhanced conversion, photolysis of particulate nitrate are the two major
mechanisms of HONO formation, which accounted for (169)% and (5325)% respectively. Soil emission is an important HONO source on fertilized days that accounted for (806)% of simulation HONO during noontime. For some of the biomass burning periods, the NO2 heterogeneous conversion to HONO were promoted significantly while the others not. In addition, the contributions from the other proposed production channels for HONO can be neglected for the conditions in Wangdu in general.
Keding Lu1*, Xin Li1*, Huabin Dong1, Rolf Haeseler2, Andreas Hofzumahaus2, Hendrik Fuchs 2, Frank Holland2, Zhaofeng Tan2, Haichao Wang1, Qi Zou1, Rohrer Franz2, Yusheng Wu1,b, Birger Bohn2, Limin Zeng1, Min Hu1, Kyung-Eun Min3, Steven Brown3,4, Alfred Wiedensohler5, Andreas Wahner2, Yuanhang Zhang1*
1.State Key Joint Laboratory of Environment Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing, 100871, China
2.Institute of Energy and Climate Research, IEK-8: Troposphere, Forschungszentrum Juelich GmbH, Juelich, Germany
3.Chemical Sciences Division, Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO, USA
4.Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80305 USA
5.Leibniz Institute for Tropospheric Research, Permoserstr. 15, 04318 Leipzig, Germany
Zhaofeng Tan IEK-8: Troposphere, Forschungszentrum Jülich, Jülich, Germany
Experimental budgets of OH, HO2 and RO2 radicals and implications for ozone formation in the Pearl River Delta (PRD) in China 2014
OH, HO2, and RO2 radicals and the OH reactivity were measured in the PRD in China, in autumn 2014. The completeness of the radical measurements offers to carry out an experimental budget analysis for all radicals (OH, HO2, and RO2) and their sum (ROx). The RO2 budget can only be closed when the missing OH reactivity is attributed to unmeasured VOCs. Thus, the existence of unmeasured VOCs is directly confirmed by the RO2 observations. Although the closure of the RO2 budget is to a great extent improved by the addition of unmeasured VOCs, a significant imbalance in the afternoon remains indicating a missing RO2 sink. In the afternoon, however, the OH budget indicates a missing OH source of (4-6) ppbv/h. The diurnal variation of this missing OH source shows a similar pattern as that of the missing RO2 sink so that both approximately compensate each other in the ROx budget. These observations suggest the existence of a chemical mechanism that converts RO2 to OH without the involvement of NO. The photochemical net ozone production rate calculated from the reaction of HO2
and RO2 with NO yields an integrated amount of 100 ppbv/day ozone in this campaign. An even larger integrated net ozone production of 140 ppbv/day would be calculated from the oxidation rate of VOCs with OH, if HO2 and all RO2 radicals would solely react with NO. However, the unknown RO2 loss (as evident in the RO2 budget) causes 30% less ozone production than would be expected from the VOC oxidation rate.
K. Lu / CESE, Peking University, Beijing, China
A. Hofzumahaus / IEK-8: Troposphere, Forschungszentrum Jülich, Jülich, Germany
H. Fuchs / IEK-8: Troposphere, Forschungszentrum Jülich, Jülich, Germany
B. Bohn / IEK-8: Troposphere, Forschungszentrum Jülich, Jülich, Germany
F. Holland / IEK-8: Troposphere, Forschungszentrum Jülich, Jülich, Germany
Y. Liu / CESE, Peking University, Beijing, China
F. Rohrer / IEK-8: Troposphere, Forschungszentrum Jülich, Jülich, Germany
M. Shao / CESE, Peking University, Beijing, China
K. Sun / CESE, Peking University, Beijing, China
Y. Wu / CESE, Peking University, Beijing, China
L. Zeng / CESE, Peking University, Beijing, China
Y.S. Zhang / CESE, Peking University, Beijing, ChinaUniversity,
Q. Zou / CESE, Peking University, Beijing, China
A. Kiendler-Scharr / IEK-8: Troposphere, Forschungszentrum Jülich, Jülich, Germany
A. Wahner / IEK-8: Troposphere, Forschungszentrum Jülich, Jülich, Germany
Y.H. Zhang / CESE, Peking University, Beijing, China
Zhonghua Ren Department of Chemical Engineering, The University of Melbourne
Atmospheric Oxidation of Piperazine Initiated by OH: A Theoretical Kinetics Investigation
Piperazine (PZ) mixed with other amines is a proposed carbon capture solvent, but there is concern about the impact of PZ on local air quality and the potential to produce toxic products. Here, the OH initiated oxidation of PZ has been investigated using ab initio calculations and RRKM / master equation kinetic modelling. The PZ + OH reaction is found to proceed at around the capture rate, consistent with
experiment, with abstraction predominantly from C—H sites. The subsequent reaction kinetics of carbon and nitrogen centred PZ radicals with O2 are also studied, so as to determine the first-generation oxidation products, which include imines, alkoxy radicals, nitrosamines and nitramines.
Gabriel da Silva, Department of Chemical Engineering, The University of Melbourne
Craig Stroud Environment Canada
Impact of Chemical Aging of Semi-volatile Vapours on Modelling Organic Aerosol Formation in the Athabasca Oil Sands Region
Rapid secondary organic aerosol formation (SOA) has been observed downwind of the Athabasca oil sand facilities in Northern Alberta, Canada. It has been proposed that the rapid formation is due to oxidation of intermediate volatile organic compounds (IVOCs) that are released from the open-pit mining facilities (Liggio et al, 2016). Environment and Climate Change Canada (ECCC) uses the GEM-MACH chemical transport model to predict the relationship between pollutant emissions and atmospheric concentrations. The standard SOA scheme in GEM-MACH uses the two-product fit to the gas/particle partitioning equation (Odum et al., 1996) and assumes that the POA emitted and SOA formed is non-volatile. GEM-MACH under-predicts SOA concentrations in the oil sands region when using bottom-up pollutant emissions, based on the facility emission inventories, and using the standard two-product SOA scheme (Stroud et al., 2018).
This work describes the incorporation of the volatility basis set (VBS) approach for predicting SOA into the high spatial resolution version of the GEM-MACH model (2.5-km grid spacing for nested domain). IVOC emissions from pollutant sources in the Canadian and U.S. national inventories are estimated, as well as IVOC emissions from the Athabasca oil sand open-pit mines. Two modern VBS parameterizations were evaluated. The first parameterization increases low yields by adding multi-generational oxidation aging reactions to increase SOA mass at lower volatilities (Tsimpidi et al., 2010). The second parameterization adjusts first-generation experimental SOA yields to correct for losses of vapours to smog chamber walls in experiments, which results in a larger increase in lower volatility organic mass after a single oxidation event (Ma et al., 2017). In this presentation, the model organic aerosol output is compared to aircraft observations in the oil sand region and to ground organic aerosol measurements from networks across North America. The statistical scores of month-long simulations will be compared to assess the two VBS approaches and the standard Odum et al. approach. The impact of the different VBS parameterizations on organic aerosol predictions will be assessed for the geographical regions of North America, with particular emphasis on the Canadian boreal forest and aged oil sand plumes.
Liggio, J. et al., Oil sands operations as a large source of secondary organic aerosols, (2016), Nature, 534 (7605), pp. 91-94, DOI: 10.1038/nature17646.
Stroud, C.A. et al., Improving air quality model predictions of organic species using measurement-derived organic gaseous and particle emissions in a petrochemical-dominated region, (2018), Atmospheric Chemistry and Physics, 18 (18), pp. 13531-13545, DOI: 10.5194/acp-18-13531-2018.
Odum, J.R. et al., Gas/particle partitioning and secondary organic aerosol yields, (1996), Environmental Science and Technology, 30 (8), pp. 2580-2585.
Ma, P.K. et al., Evaluating the impact of new observational constraints on P-S/IVOC emissions, multi-generation oxidation, and chamber wall losses on SOA modeling for Los Angeles, CA,(2017), Atmospheric Chemistry and Physics, 17 (15), pp. 9237-9259.
Tsimpidi, A.P. et al., Evaluation of the volatility basis-set approach for the simulation of organic aerosol formation in the Mexico City metropolitan area, (2010), Atmospheric Chemistry and Physics, 10 (2), pp. 525-546.
Jacob Sommers1,2, Patrick Hayes2, Ayodeji Akingunola1, Paul Makar1, Junhua Zhang1, Michael Moran1, Katherine Hayden1, John Liggio1, Shao-Meng Li1 and Craig Stroud1
