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Published August 4, 2010 | Supplemental Material + Published
Journal Article Open

Role of aldehyde chemistry and NO_x concentrations in secondary organic aerosol formation


Aldehydes are an important class of products from atmospheric oxidation of hydrocarbons. Isoprene (2-methyl-1,3-butadiene), the most abundantly emitted atmospheric non-methane hydrocarbon, produces a significant amount of secondary organic aerosol (SOA) via methacrolein (a C_4-unsaturated aldehyde) under urban high-NO_x conditions. Previously, we have identified peroxy methacryloyl nitrate (MPAN) as the important intermediate to isoprene and methacrolein SOA in this NO_x regime. Here we show that as a result of this chemistry, NO_2 enhances SOA formation from methacrolein and two other α, β-unsaturated aldehydes, specifically acrolein and crotonaldehyde, a NO_x effect on SOA formation previously unrecognized. Oligoesters of dihydroxycarboxylic acids and hydroxynitrooxycarboxylic acids are observed to increase with increasing NO_2/NO ratio, and previous characterizations are confirmed by both online and offline high-resolution mass spectrometry techniques. Molecular structure also determines the amount of SOA formation, as the SOA mass yields are the highest for aldehydes that are α, β-unsaturated and contain an additional methyl group on the α-carbon. Aerosol formation from 2-methyl-3-buten-2-ol (MBO232) is insignificant, even under high-NO_2 conditions, as PAN (peroxy acyl nitrate, RC(O)OONO_2) formation is structurally unfavorable. At atmospherically relevant NO_2/NO ratios (3–8), the SOA yields from isoprene high-NO_x photooxidation are 3 times greater than previously measured at lower NO_2/NO ratios. At sufficiently high NO_2 concentrations, in systems of α, β-unsaturated aldehydes, SOA formation from subsequent oxidation of products from acyl peroxyl radicals+NO_2 can exceed that from RO_2+HO_2 reactions under the same inorganic seed conditions, making RO_2+NO_2 an important channel for SOA formation.

Additional Information

© Author(s) 2010. This work is distributed under the Creative Commons Attribution 3.0 License. Received: 7 April 2010 – Published in Atmos. Chem. Phys. Discuss.: 19 April 2010. Revised: 13 July 2010 – Accepted: 16 July 2010 – Published: 4 August 2010. This research was funded by US Department of Energy Biological and Environmental Research Program DE-FG02-05ER63983, US Environmental Protection Agency STAR grant RD-83374901, US National Science Foundation grant ATM-0432377, and the Electric Power Research Institute. This publication has not been formally reviewed by the EPA. The views expressed in this document are solely those of the authors and EPA does not endorse any products mentioned in this publication. The authors would like to thank K. E. Kautzman and A. J. Kwan for experimental assistance, and F. Paulot for helpful discussion. Edited by: M. Gysel.

Attached Files

Published - Chan2010p11330Atmos_Chem_Phys.pdf

Supplemental Material - acp-10-7169-2010-supplement_1_.pdf


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