Secondary Organic Aerosol Study: Model Development and Applications for the ICARTT Period

Secondary organic aerosol (SOA) forms in the atmosphere. Gas-phase reactive organic species undergo atmospheric oxidation and produce compounds with low enough vapor pressure that makes them semi-volatile, therefore able to partition between gas and aerosol phases. These semi-volatile compounds partition to the aerosol phase in the atmosphere to form SOA.

A SOA model, combined with the 3-D regional chemical transport model – STEM 2K3 – is being developed to predict the SOA concentrations during ICARTT experiment period. The chemical mechanism is based on SAPRC-99 of W.P.L. Carter (http://pah.cert.ucr.edu/ftp/pub/carter/SAPRC99/) to include the detailed and representative organic chemistry that leads to the formation of SOA. Model results will be compared with observed data from ICARTT aircraft to measure the performance of the model. The ambient organic aerosol concentrations will be used to infer the level of SOA during the experiment period. For specific locations, elementary carbon (EC) and organic carbon (OC) ratio can also be used to determine the SOA level of that area, by subtracting primary OC emissions from the measured OC concentrations. The EC concentrations, not directly available in ICARTT data set, will be derived from the aerosol optical absorption.