EXAMINATION OF TROPOSPHERIC OZONE AND ITS PRECURSORS WITHIN AN AIR QUALITY MODEL AND IMPLICATIONS FOR AIR QUALITY AND CLIMATE

Abstract

Elevated levels of tropospheric ozone (O3) caused by emissions of NOx and VOCs negatively impact human health, crops, and ecosystems. Even if precursor emissions are reduced below current levels, predicted higher temperatures due to increased greenhouse gas emissions could impede resulting air quality benefits. Air quality models simulate the complex relationships that form O3 and are used to guide policy decisions directed at improving O3. The body of this work encompasses three projects related to improvements in the representation of O3 and precursors in air quality models. First, I examine the role of O3 and its precursors in air quality and climate change by evaluating ozone production efficiency (OPE) and O3 precursors within models. I modified a chemical mechanism and the emissions of NOx to accurately represent NOx, the reactivity of NOx with peroxy radicals, HCHO, isoprene, as well as organic and inorganic NOy reservoir species. Implementation of these modifications increased confidence in model simulations. Results indicate accepted inventories overestimated NOx emissions but underestimate total VOC reactivity and OPE. Second, I examined the dependence of surface O3 on temperature (climate penalty factor (CPF)) throughout a period of 11 years within an air quality model and measurements. Future increases in temperature could offset benefits from future reductions in the emission of O3 precursors. Determining and understanding the CPF is critical to formulating effective strategies to reduce future exceedances. I have demonstrated that the model can reproduce O3 sensitivity to temperature reasonably well. By controlling emissions specifically of NOx mankind has reduced its vulnerability. Third, I compare satellite-observed and modeled ammonia (NH3) under varying chemical environments over East Asia. Regulation of O3 precursor concentrations in the atmosphere has an indirect effect on NH3 concentrations. Air quality policy to reduce NOx and through that also nitric acid (HNO3) in the atmosphere can result in an increase in the concentration of NH3 because of its neutralizing ability. Therefore, a less acidic atmosphere sequesters less NH3. This preliminary work exposes different areas that need to be addressed to gain greater insight into NH3 emissions and chemistry.