Application of the Statistical Oxidation Model (SOM) to Secondary Organic Aerosol formation from photooxidation of C&amp;lt;sub&amp;gt;12&amp;lt;/sub&amp;gt; alkanes

C D Cappa,C L Loza,J H Seinfeld,J S Craven,L D Yee,X Zhang

doi:10.5194/acp-13-1591-2013

Abstract

Abstract. Laboratory chamber experiments are the main source of data on the mechanism of oxidation and the secondary organic aerosol (SOA) forming potential of volatile organic compounds. Traditional methods of representing the SOA formation potential of an organic do not fully capture the dynamic, multi-generational nature of the SOA formation process. We apply the Statistical Oxidation Model (SOM) of Cappa and Wilson (2012) to model the formation of SOA from the formation of the four C12 alkanes, dodecane, 2-methyl undecane, cyclododecane and hexylcyclohexane, under both high- and low-NOx conditions, based upon data from the Caltech chambers. In the SOM, the evolution of reaction products is defined by the number of carbon (NC) and oxygen (NO) atoms, and the model parameters are (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 molecules. Optimal fitting of the model to chamber data is carried out using the measured SOA mass concentration and the aerosol O:C atomic ratio. The use of the kinetic, multi-generational SOM is shown to provide insights into the SOA formation process and to offer promise for application to the extensive library of existing SOA chamber experiments that is available.

Highlights

M and oxygen (NO) atoms, and the model parameters are (1) only is the precursor secondary organic aerosol (SOA) species the number of oxygen atoms added per reaction, (2) the de- reactive towards OH, but so are the oxidation products
The time-evolution of the observed wall-loss corrected SOA mass concentrations (COA) and the particle-phase O:C atomic ratios are shown in Fig. 1, along with the tuned model results obtained using both Pfrag parameterizations and after fitting simultaneously to both COA and O:C
As oxidation proceeds, the observed COA increases until the parent [HC] decays to around 10 % of its initial value

Summary

Introduction

M and oxygen (NO) atoms, and the model parameters are (1) only is the precursor SOA species (i.e. the parent organic) the number of oxygen atoms added per reaction, (2) the de- reactive towards OH, but so are the oxidation products. Optimal fitting of the model to chamber data is carried out using the measured SOA mass concentration and the aerosol O:C atomic ratio. Laboratory chamber experiments are the main source of data on the mechanism of oxidation and theSScOieAnfocremsing potential of multi-generational SOM is shown to provide insights into the a parent organic. Organic aerosol (OA) comprises a major fraction of the atmospheric sub-micron aerosol burden (Zhang et al, 2007; Jimenez et al, 2009), and the dominant portion of OA is tion, as they generally treat SOA formation as a one-step process from precursor to prSodouclitds.

Methods

Results

Discussion

Conclusion