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Predicting SOA from organic nitrates in the southeastern United States
Citation:
Pye, H., D. Luecken, AND L. Xu. Predicting SOA from organic nitrates in the southeastern United States. American Geophysical Union AGU Fall Meeting, San Francisco, CA, December 14 - 18, 2015.
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:
Organic nitrates have been identified as an important component of ambient aerosol in the Southeast United States. In this work, we use the Community Multiscale Air Quality (CMAQ) model to explore the relationship between gas-phase production of organic nitrates and their subsequent aerosol-phase partitioning for the Southern Oxidants and Aerosol Study (SOAS) 2013 time period.Current chemical transport models may underestimate the role of particulate organic nitrates (pON), and aerosol parameterizations are generally not connected to later generation gas-phase species. Explicit predictions of pON from gas-phase intermediates is challenging as gas-phase mechanisms need verification. We highlight areas where further information is needed. During the morning and evening transition hours, reactions of monoterpenes with ozone, OH, and nitrate radicals are predicted to contribute to organic nitrate formation. During the night, organic nitrate formation is primarily due to nitrate radicals and RO2+HO2 reactions with high yields of organic nitrates, above what has been observed in many chamber experiments. We find that the CMAQ model overestimates total gas-phase alkyl nitrates, particularly at night, and that uptake to the particle followed by hydrolysis can improve model predictions of both the gas and aerosol phase components.
