Atmos. Chem. Phys. Discuss., 13, 21961-21988, 2013
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Sensitivities of NOx transformation and the effects on surface ozone and nitrate
H. Lei and J. X. L. Wang
National Oceanic and Atmospheric Administration (NOAA), Air Resource Laboratory, College Park, Maryland, USA

Abstract. As precursors for tropospheric ozone and nitrate aerosols, Nitrogen oxides (NOx) in present atmosphere and its transformation in responding to emission and climate perturbations are studied by CAM-Chem model and air quality measurements including National Emission Inventory (NEI), Clean Air Status and Trends Network (CASTNET) and Environmental Protection Agency Air Quality System (EPA AQS). It is found that not only the surface ozone formation but also the nitrate formation is associated with the relative emissions of NOx and volatile organic compounds (VOC). Due to the availability of VOC and associated NOx titration, ozone productions in industrial regions increase in warmer conditions and slightly decrease against NOx emission increase, which is converse to the response in farming region. The decrease or small increase in ozone concentrations over industrial regions result in the responded nitrate increasing rate staying above the increasing rate of NOx emissions. It is indicated that ozone concentration change is more directly affected by changes in climate and precursor emissions, while nitrate concentration change is also affected by local ozone production types and their seasonal transfer. The sensitivity to temperature perturbations shows that warmer climate accelerates the decomposition of odd nitrogen (NOy) during the night. As a result, the transformation rate of NOx to nitrate decreases. Examinations on the historical emission and air quality records on typical pollution areas further confirm the conclusion drawn from modeling experiments.

Citation: Lei, H. and Wang, J. X. L.: Sensitivities of NOx transformation and the effects on surface ozone and nitrate, Atmos. Chem. Phys. Discuss., 13, 21961-21988, doi:10.5194/acpd-13-21961-2013, 2013.
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