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Rapid production of highly oxidized molecules in isoprene aerosol via peroxy and alkoxy radical isomerization pathways in low and high NOx environments: Combined laboratory, computational and field studies.
Jaoui, Mohammed; Piletic, Ivan R; Szmigielski, Rafal; Rudzinski, Krzysztof J; Lewandowski, Michael; Riedel, Theran P; Kleindienst, Tadeusz E.
Afiliação
  • Jaoui M; Center for Environmental Measurement & Modeling, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, United States of America. Electronic address: jaoui.mohammed@epa.gov.
  • Piletic IR; Center for Environmental Measurement & Modeling, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, United States of America.
  • Szmigielski R; Environmental Chemistry Group, Institute of Physical Chemistry, Polish Academy of Sciences, 01-224 Warsaw, Poland.
  • Rudzinski KJ; Environmental Chemistry Group, Institute of Physical Chemistry, Polish Academy of Sciences, 01-224 Warsaw, Poland.
  • Lewandowski M; Center for Environmental Measurement & Modeling, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, United States of America.
  • Riedel TP; Center for Environmental Measurement & Modeling, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, United States of America.
  • Kleindienst TE; Center for Environmental Measurement & Modeling, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, United States of America.
Sci Total Environ ; 775: 145592, 2021 Jun 25.
Article em En | MEDLINE | ID: mdl-34380608
Recently, we identified seven novel hydroxy-carboxylic acids resulting from gas-phase reactions of isoprene in the presence of nitrogen oxides (NOx), ozone (O3), and/or hydroxyl radicals (OH). In the present study, we provide evidence that hydroxy-carboxylic acids, namely methyltartaric acids (MTA) are: (1) reliable isoprene tracers, (2) likely produced via rapid peroxy radical hydrogen atom (H) shift reactions (autoxidation mechanism) and analogous alkoxy radical H shifts in low and high NOx environments respectively and (3) representative of aged ambient aerosol in the low NOx regime. Firstly, MTA are reliable tracers of isoprene aerosol because they have been identified in numerous chamber experiments involving isoprene conducted under a wide range of conditions and are absent in the oxidation of mono- and sesquiterpenes. They are also present in numerous samples of ambient aerosol collected during the past 20 years at several locations in the U.S. and Europe. Furthermore, MTA concentrations measured during a year-long field study in Research Triangle Park (RTP), NC in 2003 show a seasonal trend consistent with isoprene emissions and photochemical activity. Secondly, an analysis of chemical ionization mass spectrometer (CIMS) data of several chamber experiments in low and high NOx environments show that highly oxidized molecules (HOMs) derived from isoprene that lead to MTAs may be produced rapidly and considered as early generation isoprene oxidation products in the gas phase. Density functional theory calculations show that rapid intramolecular H shifts involving peroxy and alkoxy radicals possess low barriers for methyl-hydroxy-butenals (MHBs) that may represent precursors for MTA. From these results, a viable rapid H shift mechanism is proposed to occur that produces isoprene derived HOMs like MTA. Finally, an analysis of the mechanism shows that autoxidation-like pathways in low and high NOx may produce HOMs in a few OH oxidation steps like commonly detected methyl tetrol (MT) isoprene tracers. The ratio of MTA/MT in isoprene aerosol is also shown to be significantly greater in field versus chamber samples indicating the importance of such pathways in the atmosphere even for smaller hydrocarbons like isoprene.
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Texto completo: 1 Coleções: 01-internacional Base de dados: MEDLINE Assunto principal: Laboratórios Idioma: En Revista: Sci Total Environ Ano de publicação: 2021 Tipo de documento: Article

Texto completo: 1 Coleções: 01-internacional Base de dados: MEDLINE Assunto principal: Laboratórios Idioma: En Revista: Sci Total Environ Ano de publicação: 2021 Tipo de documento: Article