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- Title
Highly Oxygenated Molecules from Aromatic Compounds and Their Role in Formation of Secondary Organic Aerosols.
- Authors
Zaytsev, Alexander; Breitenlechner, Martin; Koss, Abigail R.; Nihill, Kevin J.; Lim, Christopher Y.; Lerner, Brian M.; Krechmer, Jordan; Rowe, James C.; Roscioli, Joseph R.; Franklin, Jonathan P.; Cox, Joshua L.; Shutter, Joshua D.; Moss, Joshua; Canagaratna, Manjula; Worsnop, Douglas R.; Kroll, Jesse H.; Keutsch, Frank N.
- Abstract
Aromatic hydrocarbons, primarily emitted by anthropogenic sources, account for abig fraction of the volatile organic compounds in the urban atmosphere and play asignificant role in the formation of secondary organic aerosols (SOA). However, thedetailed gas-phase oxidation mechanism of multiple aromatic compounds is not fullyunderstood. In this work, we investigate hydroxyl radical (OH) multigeneration oxidation chemistryof three aromatic hydrocarbons: toluene, 1,2,4-trimethylbenzene (1,2,4-TMB) and1,3,5-trimethylbenzene (1,3,5-TMB) under moderate, urban-relevant NOx levels (30-70ppbv). Laboratory experiments were conducted at the MIT environmental chamber overapproximately 1 day of atmospheric-equivalent oxidation. We used a comprehensive suite ofchemical ionization mass spectrometry (CIMS) techniques to characterize and quantifyoxidation products including two proton-transfer reaction time-of-flight MS (PTR3 andVOCUS PTR) and two high-resolution time-of-flight chemical-ionization MS (NH4+-CIMSand I−-CIMS) for the gas-phase measurements. As for measuring particle-phase organics, wedeployed an aerosol mass spectrometer (AMS), a FIGAERO-I−-CIMS and a secondNH4+-CIMS equipped with an aerosol inlet comprising a gas-phase denuder and a thermaldesorption unit. Additional measurements were taken using optical, gas chromatographic, andmass spectrometric techniques. Using this extensive suite of instrumentation, we wereable to quantify a large fraction of the reactive carbon in multiple generations ofoxidation. Hydroxyl radicals are known to react with aromatic hydrocarbons to form peroxy (RO2)radicals which can isomerize by intramolecular hydrogen abstraction and lead to theformation of highly oxygenated molecules (HOMs). Here, we report the elementalcomposition and concentration of HOMs in the gas and condensed phases. We show thatunder urban conditions, in the presence of NO, the reaction of RO2 radicals with NOcompetes with the autooxidation pathway and leads to the formation of highly oxygenatednitrates which we quantify in the gas and particle phases. We also determine the kinetics ofthe formation of HOMs and other major oxidation products using a best-fit kineticparametrization which can provide information on the generation and reactivity of products.We show that although HOMs comprise only a small portion of the gas phase oxidationproducts, they contribute to a significant fraction of SOA mass. Information on the molecularlevel provided by the particle phase NH4+-CIMS and FIGAERO-I−-CIMS reveals insightsinto the range of volatilities and oxidation states of the compounds in the condensed phase.
- Subjects
AROMATIC compounds; AEROSOLS; VOLATILE organic compounds; OXIDATION states; CONDENSED matter; TOLUENE; GAS chromatography
- Publication
Geophysical Research Abstracts, 2019, Vol 21, p1
- ISSN
1029-7006
- Publication type
Article