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Updating CMAQ secondary organic aerosol properties relevant for aerosol water interactions
Citation:
Pye, H., B. Murphy, T. Nguyen, A. Carlton, L. Xu, AND N. Ng. Updating CMAQ secondary organic aerosol properties relevant for aerosol water interactions. 2016 CMAS Conference, Chapel Hill, NC, October 24 - 26, 2016.
Impact/Purpose:
The National Exposure Research Laboratory (NERL) Computational Exposure Division (CED) develops and evaluates data, decision-support tools, and models to be applied to media-specific or receptor-specific problem areas. CED uses modeling-based approaches to characterize exposures, evaluate fate and transport, and support environmental diagnostics/forensics with input from multiple data sources. It also develops media- and receptor-specific models, process models, and decision support tools for use both within and outside of EPA.
Description:
Properties of secondary organic aerosol (SOA) compounds in CMAQ are updated with state-of-the-science estimates from structure activity relationships to provide consistency among volatility, molecular weight, degree of oxygenation, and solubility/hygroscopicity. These updated properties are used to predict interaction of organic aerosol with particle-phase liquid water. Model predictions are compared to observations over the southeast United States during the Southern Oxidant and Aerosol Study. Based on model-predicted OM/OC, SOA is frequently well-mixed with the inorganic phase throughout most of the Eastern US except in urban areas where POA concentrations are high and OM/OC is low. As a result, aerosol liquid water contributes to the partitioning medium for semivolatile organics. Including water in the partitioning medium of OA leads to overestimates in OC at night and reasonable performance during the daytime unless deviations in ideality are considered. Property updates discussed here will be available in CMAQ v5.2.
