The Influence of Atmospheric Conditions on the Production of Ozone during VOC Oxidation

Abstract:

Tropospheric ozone is a short-lived climate forcing pollutant that is detrimental to human health and crop growth. Reactions involving volatile organic compounds (VOC) and nitrogen oxides (NO_x) in the presence of sunlight produce ozone. Ozone production is a non-linear function of the concentrations of both NO_x and VOC, with VOC acting as the “fuel” for ozone production and NO_x as the “catalyst”. Different VOC, due to their differing structure and carbon content, have different maximum potential to produce ozone. Due to different degrees of reactivity, VOC also differ in the time taken to reach this maximum ozone production potential under ideal conditions. Ozone production is also influenced by meteorological factors such as radiation, temperature, advection and mixing, which may alter the rate of ozone production, and the degree to which VOC are able to reach their maximum ozone production potential. Identifying the chemical and meteorological processes responsible for controlling the degree to which VOC are able to reach their maximum ozone production potential could inform decisions on emission control to efficiently tackle high levels of tropospheric ozone.

In this study we use a boxmodel to determine the chemical processes affecting ozone production under different meteorological and chemical conditions. The chemistry scheme used by the boxmodel is “tagged” for each initial VOC enabling attribution of ozone production to its VOC source. We systematically vary a number of meteorological parameters along with the source of NO_x within the box model to simulate a range of atmospheric conditions. These simulations are compared with a control simulation done under conditions of maximum ozone formation to determine which parameters affect the rate at which VOC produce ozone and the extent to which they reach their maximum potential to produce ozone. We perform multi-day simulations in order to examine whether these processes can influence ozone production over timescales relevant to regional-scale ozone production.