AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Hygroscopicity Trends of Secondary Organic Aerosol Generated from Ozonolysis of 1-Alkenes
RYAN SULLIVAN, Markus Petters, Aiko Matsunaga, Sarah Suda, Lorena Minambres, Annelise Faulhaber, Paul Ziemann, Sonia Kreidenweis, Carnegie Mellon University
Abstract Number: 249 Working Group: Aerosols, Clouds, and Climate
Abstract Secondary organic aerosol (SOA) can potentially influence cloud properties and climate by absorbing water and contributing to cloud condensation nuclei populations. Alkenes are gaseous precursors of SOA that are emitted from a variety of anthropogenic and biogenic sources. We produced SOA from the oxidation of a series of 1-alkene homologs to investigate the relationships between the alkene precursor structure, the measured aerosol hygroscopicity, and the chemical composition of the chamber-generated aerosol. The effect of Criegee radical scavenger structure and polarity on the resulting aerosol properties was explicitly investigated through the addition of water vapor, alcohols, aldehydes, or inorganic acids to the chamber. The observed aerosol hygroscopicity was found to decrease with increasing precursor chain length and increasing product molecular volume, as expected from Köhler theory. Shorter-chain and more polar Criegee scavengers increased the hygroscopicity of the aerosol compared to longer-chain and less polar scavengers, also as expected. A new analysis method coupled HPLC polarity-based separation of organic compounds with scanning flow rapid CCN analysis to determine the hygroscopicity of individual compounds in the complex organic aerosol. This provided new insights into the distribution of compound hygroscopicity and composition as a function of chamber reaction conditions. This new tandem method revealed that the aerosol was composed of two modes of compound hygroscopicity, characterized by a hygroscopicity parameter (kappa) of ~0.02 and ~0.2. We present an analysis of the measured net hygroscopicity as well as the relative fractions of each hygroscopicity mode, and compare these to expected values based on known reaction mechanisms and rates. We anticipate that these results will help improve our ability to accurately predict SOA hygroscopicity from known precursors.