| Abstract: |
Secondary organic aerosols (SOA) probably make substantial contributions to aerosol direct and indirect climate forcing, yet their origin and evolution is currently not well understood, and models severely underpredict atmospheric observations. The precursors of SOA are believed to be the extremely complex oxidation intermediates of gas phase hydrocarbon chemistry. We have developed the most detailed atmospheric organic mechanism (the NCAR/U.Paris Self-Generating Master Mechanism) that is being applied to calculating organic gas-aerosol partitioning, including calculation of aerosol properties such as mass, composition, and spectral absorption. The model will be evaluated using the comprehensive data set from the MILAGRO field campaign (March 2006, Mexico), and will be used collaboratively to develop simplified organic mechanisms for estimating thermodynamic properties (e.g. vapor pressures, solubility, activity coefficients) in mixed-phase (hydrophobic and hydrophilic) aerosols (e.g. with U.C./Davis AIM model), coupling to inorganic aerosol chemistry (e.g. with PNNL’s MOSAIC model, and implementation in a three-dimensional regional chemistry-transport model (e.g. NCAR/NOAA/PNNL WRF-Chem.
We have made important advances in reducing the complexity of the chemical representation without significant loss of accuracy, by applying mechanism truncations based on a combination of minimum saturation vapor pressures, a hierarchal lumping of similar isomers, and minimum branching ratios. These advances allow us to model the organic photochemistry of even relatively large compounds (20 carbon atoms or more) that are thought to contribute to SOA formation. |
