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Modeling the Impact of CINO2 on Ozone Formation in the Houston Area
Citation:
SIMON, H., Y. Kimura, G. McGaughey, D. ALLEN, S. S. Brown, H. D. Osthoff, J. M. Roberts, D. W. BYUN, AND D. Lee. Modeling the Impact of CINO2 on Ozone Formation in the Houston Area. JOURNAL OF GEOPHYSICAL RESEARCH: ATMOSPHERES. American Geophysical Union, Washington, DC, 114(D00F03):1-17, (2009).
Impact/Purpose:
National Exposure Research Laboratory′s (NERL′s) Atmospheric Modeling Division (AMD) conducts research in support of EPA′s mission to protect human health and the environment. AMD′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. AMD 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 AMD 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:
During the summer of 2006, nitryl chloride (ClNO2) mixing ratios of over 1 ppb were measured in the Houston urban area. Nitryl chloride is potentially important to atmospheric chemistry in urban environments because its photolysis products include both NO2 and chlorine atoms. Chlorine atoms have previously been shown to significantly increase ozone formation in urban Houston. Photochemical modeling was performed using the Comprehensive Air quality Model with extensions (CAMx) to estimate the effects of observed nitryl chloride concentrations on local chemistry in Southeast Texas. CAMx was modified to include a formation mechanism for nitryl chloride as well as its photolysis reaction. Comparisons between model predictions and ambient measurements showed that the model predicted ClNO2 concentrations were within the range of observed data. Model simulations predict that ClNO2 increases total reactive chlorine mass by 20-40% in the atmosphere of Southeast Texas. Despite the high reactivity of chlorine, nitryl chloride caused only modest increases in ozone concentrations (up to 1.0 - 1.5 ppb when baseline 1-hr average ozone concentrations were between 60 and 85 ppb). The chemistry and physical processes which affect ozone formation were further investigated using box model simulations and a Lagrangian Process Analysis tool (LPA) within the gridded photochemical modeling simulations. These analyses showed that vertical dispersion and local atmospheric composition moderated the effect of nitryl chloride on ozone mixing ratios.
