Abstract
Abstract. Multi-generational gas-phase oxidation of organic vapors can influence the abundance, composition and properties of secondary organic aerosol (SOA). Only recently have SOA models been developed that explicitly represent multi-generational SOA formation. In this work, we integrated the statistical oxidation model (SOM) into SAPRC-11 to simulate the multi-generational oxidation and gas/particle partitioning of SOA in the regional UCD/CIT (University of California, Davis/California Institute of Technology) air quality model. In the SOM, evolution of organic vapors by reaction with the hydroxyl radical is defined by (1) the number of oxygen atoms added per reaction, (2) the decrease in volatility upon addition of an oxygen atom and (3) the probability that a given reaction leads to fragmentation of the organic molecule. These SOM parameter values were fit to laboratory smog chamber data for each precursor/compound class. SOM was installed in the UCD/CIT model, which simulated air quality over 2-week periods in the South Coast Air Basin of California and the eastern United States. For the regions and episodes tested, the two-product SOA model and SOM produce similar SOA concentrations but a modestly different SOA chemical composition. Predictions of the oxygen-to-carbon ratio qualitatively agree with those measured globally using aerosol mass spectrometers. Overall, the implementation of the SOM in a 3-D model provides a comprehensive framework to simulate the atmospheric evolution of organic aerosol.
Highlights
Fine-mode organic particulate matter or organic aerosol (OA) accounts for roughly half of the dry ambient aerosol mass yet it remains one of its least understood constituents (Jimenez et al, 2009)
Higher concentrations of secondary organic aerosol (SOA) were predicted on the coast northwest of the Los Angeles metropolitan area due to the partitioning of near-coast biogenic SOA into the marine primary organic aerosol (POA) emitted in the surf zone
We integrated the statistical oxidation model (SOM) with the gas-phase chemical mechanism SAPRC-11 (Carter and Heo, 2013) in the UCD/CIT air quality model and used it to model the multigenerational oxidation and gas/particle partitioning of SOA in the South Coast Air Basin (SoCAB) and the eastern United States (US)
Summary
Fine-mode organic particulate matter or organic aerosol (OA) accounts for roughly half of the dry ambient aerosol mass yet it remains one of its least understood constituents (Jimenez et al, 2009). Ambient OA exists as a complex mixture of thousands of compounds with very different physical and chemical properties that arise from a host of sources and reaction pathways (Goldstein and Galbally, 2007). This OA and the organic vapors in equilibrium with it together form a dynamic system in which their mass, chemical composition and environmental properties are constantly evolving as a result of gas-, surface- and particle-phase reactions coupled to condensation and evaporation. OA is either directly emitted as primary organic aerosol (POA) or formed in the atmosphere from the oxidation of volatile organic compounds (VOC) as secondary organic aerosol (SOA). It is widely recognized that gas-phase VOC oxidation products (or more generically organic vapors) can undergo multi-generational oxidation, given sufficient time in the at-
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