AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
An Improved Volatility Basis Set for Modeling Organic Aerosol in both CAMx and CMAQ
BONYOUNG KOO, Greg Yarwood, Eladio Knipping, ENVIRON International Corporation
Abstract Number: 418 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Due to the complex nature of atmospheric organic aerosol (OA), it is impractical to explicitly simulate evolution of thousands of atmospheric organic compounds in photochemical grid models (PGMs). Therefore, PGMs adopt some kind of simplified representation where organic compounds with similar properties and/or origin are lumped together. The first generation volatility basis set (VBS) approach grouped OA compounds by volatility and provided a unified framework for gas-aerosol partitioning of both primary and secondary OA and their chemical aging. However, a VBS approach with one dimension of variation (volatility) is unable to describe observed variations in OA oxidation state (i.e., O:C ratio) at a fixed volatility level. A two-dimensional VBS approach was recently introduced where degree of oxidation is also tracked in addition to volatility but further study is needed to fully parameterize the 2-D VBS model.
In this study, a new OA module based on the VBS approach is implemented in two widely-used PGMs. Our scheme uses four basis sets to model ambient OA with different oxidation state: two sets for oxygenated OA (anthropogenic and biogenic) and two for freshly emitted OA (from anthropogenic sources and biomass burning). Each basis set has five volatility bins including a zero-volatility bin for essentially non-volatile compounds. The scheme adjusts both carbon number and oxidation state in response to chemical aging by simplifying the 2-D VBS scheme. The new organic PM module is implemented in both the CAMx and CMAQ PGMs and evaluated with a modeling database that simulates a 2005 summer episode over the entire continental US.