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NOx emission reduction co-benefits for secondary organic aerosol formation
Citation:
Pye, H. AND R. Mathur. NOx emission reduction co-benefits for secondary organic aerosol formation. 2018 CMAS Conference, Chapel Hill, NC, October 22 - 23, 2018.
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 aerosol is a significant component of PM2.5 and is an increasing fraction of the total in many locations. Organic aerosol is largely secondary in nature and forms from the gas to particle conversion of low volatility or semi-soluble species. In the southeast US, monoterpene oxidation is responsible for half of the total organic particulate matter. In this work, we examine an efficient pathway to organic aerosol that is expected to account for an increasing fraction of monoterpene chemistry as NOx declines. This unimolecular pathway to secondary organic aerosol (SOA) poses a potential penalty in terms of PM2.5 for reducing NOx. Using ambient observations downwind of Atlanta, an explicit mechanism, and CMAQ model calculations, we show that this NOx penalty can be fully offset by reductions in oxidants that come with reducing NOx. As a result, we predict a positive coupling between anthropogenic NOx and regional biogenic SOA from unimolecular monoterpene oxidation pathways.
