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Examining the impact of heterogeneous nitryl chloride production on air quality across the United States
Citation:
SARWAR, G., H. SIMON, P. BHAVE, AND G. Yarwood. Examining the impact of heterogeneous nitryl chloride production on air quality across the United States. Atmospheric Chemistry and Physics. Copernicus Publications, Katlenburg-Lindau, Germany, 12(14):6067-6677, (2012).
Impact/Purpose:
The National Exposure Research Laboratory′s (NERL′s) Atmospheric Modeling and Analysis Division (AMAD) conducts research in support of EPA′s mission to protect human health and the environment. AMAD′s research program is engaged in developing and evaluating predictive atmospheric models on all spatial and temporal scales for forecasting the Nation′s air quality and for assessing changes in air quality and air pollutant exposures, as affected by changes in ecosystem management and regulatory decisions. AMAD is responsible for providing a sound scientific and technical basis for regulatory policies based on air quality models to improve ambient air quality. The models developed by AMAD are being used by EPA, NOAA, and the air pollution community in understanding and forecasting not only the magnitude of the air pollution problem, but also in developing emission control policies and regulations for air quality improvements.
Description:
The heterogeneous hydrolysis of dinitrogen pentoxide (N2O5) has typically been modeled as only producing nitric acid. However, recent field studies have confirmed that the presence of particulate chloride can alter the reaction product to produce nitryl chloride (CINO2) which can undergo photolysis to generate chlorine atoms and nitrogen dioxide (NO2). Both chlorine and NO2 can affect atmospheric chemistry and air quality. We present an updated gas phase chlorine mechanism that can be combined with the Carbon Bond 05 mechanism and incorporate the combined mechanism into the Community Multiscale Air Quality modeling system. We then update the current model treatment of heterogeneous hydrolysis of 2O5 to include CINO2 as a product. The model, in combination with a comprehensive inventory of chlorine compounds, reactive nitrogen, particulate matter, and organic compounds, is used to evaluate the impact of the heterogeneous ClNO2 production on air quality across the United States for the months of February and September in 2006. The heterogeneous production increases ClNO2 in coastal as well as many in-land areas in the United States. Particulate chloride derived from sea-salts, anthropogenic sources, and forestfires activates the heterogeneous production of ClNO2. With current estimates of tropospheric emissions, it modestly enhances monthly mean 8-h ozone (up to 1–2 ppbv or 3–4 %) but causes large increases (up to 13 ppbv) in isolated episodes. This chemistry also substantially reduces the mean total nitrate by up to 0.8–2.0 µg m−3 or 11–21 %. Modeled ClNO2 accounts for up to 6 % of the monthly mean total reactive nitrogen. Sensitivity results of the model suggest that heterogeneous production of ClNO2 can further increase O3 and reduce TNO3 if elevated particulate-chloride levels are present in the atmosphere.
URLs/Downloads:
Examining the impact of heterogeneous nitryl chloride production on air quality across the United States (PDF, NA pp, 6285 KB, about PDF)Atmospheric Chemistry and Physics
