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Mayorga R, Chen K, Raeofy N, Woods M, Lum M, Zhao Z, Zhang W, Bahreini R, Lin YH, Zhang H. Chemical Structure Regulates the Formation of Secondary Organic Aerosol and Brown Carbon in Nitrate Radical Oxidation of Pyrroles and Methylpyrroles. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2022; 56:7761-7770. [PMID: 35675110 DOI: 10.1021/acs.est.2c02345] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Nitrogen-containing heterocyclic volatile organic compounds (VOCs) are important components of wildfire emissions that are readily reactive toward nitrate radicals (NO3) during nighttime, but the oxidation mechanism and the potential formation of secondary organic aerosol (SOA) and brown carbon (BrC) are unclear. Here, NO3 oxidation of three nitrogen-containing heterocyclic VOCs, pyrrole, 1-methylyrrole (1-MP), and 2-methylpyrrole (2-MP), was investigated in chamber experiments to determine the effect of precursor structures on SOA and BrC formation. The SOA chemical compositions and the optical properties were analyzed using a suite of online and offline instrumentation. Dinitro- and trinitro-products were found to be the dominant SOA constituents from pyrrole and 2-MP, but not observed from 1-MP. Furthermore, the SOA from 2-MP and pyrrole showed strong light absorption, while that from 1-MP were mostly scattering. From these results, we propose that NO3-initiated hydrogen abstraction from the 1-position in pyrrole and 2-MP followed by radical shift and NO2 addition leads to light-absorbing nitroaromatic products. In the absence of a 1-position hydrogen, NO3 addition likely dominates the 1-MP chemistry. We also estimate that the total SOA mass and light absorption from pyrrole and 2-MP are comparable to those from phenolic VOCs and toluene in biomass burning, underscoring the importance of considering nighttime oxidation of pyrrole and methylpyrroles in air quality and climate models.
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Affiliation(s)
- Raphael Mayorga
- Department of Chemistry, University of California, Riverside, California 92507, United States
| | - Kunpeng Chen
- Department of Environmental Sciences, University of California, Riverside, California 92507, United States
| | - Nilofar Raeofy
- Department of Environmental Sciences, University of California, Riverside, California 92507, United States
| | - Megan Woods
- Department of Chemistry, University of California, Riverside, California 92507, United States
| | - Michael Lum
- Department of Environmental Sciences, University of California, Riverside, California 92507, United States
| | - Zixu Zhao
- Department of Chemistry, University of California, Riverside, California 92507, United States
| | - Wen Zhang
- Department of Chemistry, University of California, Riverside, California 92507, United States
| | - Roya Bahreini
- Department of Chemistry, University of California, Riverside, California 92507, United States
- Department of Environmental Sciences, University of California, Riverside, California 92507, United States
- Environmental Toxicology Graduate Program, University of California, Riverside, California 92507, United States
| | - Ying-Hsuan Lin
- Department of Environmental Sciences, University of California, Riverside, California 92507, United States
- Environmental Toxicology Graduate Program, University of California, Riverside, California 92507, United States
| | - Haofei Zhang
- Department of Chemistry, University of California, Riverside, California 92507, United States
- Department of Environmental Sciences, University of California, Riverside, California 92507, United States
- Environmental Toxicology Graduate Program, University of California, Riverside, California 92507, United States
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Tovar CM, Haack A, Barnes I, Bejan IG, Wiesen P. Experimental and theoretical study of the reactivity of a series of epoxides with chlorine atoms at 298 K. Phys Chem Chem Phys 2021; 23:5176-5186. [PMID: 33624654 DOI: 10.1039/d0cp06033j] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Evaluating the reactivity of epoxides in the gas phase is very important due to their wide distribution in the atmosphere, potential health implications and atmospheric impact. The kinetic rate constants for the oxidation of epoxides have been very little studied until now. From the experimental data obtained in this work has been observed that there is an increase in reactivity towards chlorine atoms as a CH2 group is added to the hydrocarbon chain. The Structure Activity Relationship (SAR) method usually provides a good approximation of the rate constant for a wide series of compounds especially for those without complex structure and multiple organic functions. However, a good determination of the factors included in SAR estimations depends largely on the database of these compounds, which in the case of epoxides is very limited. The SAR estimation method also does not take into account other possible factors that could affect reactivity, such as the geometry of the molecule. The aim of this work is to further evaluate the reactivity of epoxides with chlorine atoms using experimental determinations, theoretical calculations and SAR estimations. For this, rate coefficients have been measured at 298 ± 2 K and 1000 ± 4 mbar pressure of synthetic air in a 1080 l Quartz Reactor (QUAREC) and a 480 l Duran glass reactor for the reaction of chlorine atoms with cyclohexene oxide (CHO), 1,2-epoxyhexane (12EHX), 1,2-epoxybutane (12EB), trans-2,3-epoxybutane (tEB) and cis-2,3-epoxybutane (cEB). Theoretical calculations for the reactions studied are in good agreement with our experimental findings and provide insights about the position of the H atom abstraction and reactivity trends for a series of epoxides. The importance of taking into consideration the geometrical distribution and the ring influence to improve SAR calculations is discussed.
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Affiliation(s)
- Carmen M Tovar
- Institute for Atmospheric and Environmental Research, University of Wuppertal, 42097 Wuppertal, Germany.
| | - Alexander Haack
- Physical and Theoretical Chemistry, University of Wuppertal, 42097 Wuppertal, Germany
| | - Ian Barnes
- Institute for Atmospheric and Environmental Research, University of Wuppertal, 42097 Wuppertal, Germany.
| | - Iustinian Gabriel 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.
| | - Peter Wiesen
- Institute for Atmospheric and Environmental Research, University of Wuppertal, 42097 Wuppertal, Germany.
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