Direct Measurements of the Local Ozone Production Rate in the Pollution Outflow from a Megacity

Abstract:

Tropospheric ozone (O₃) is major secondary air pollutant that is formed in the atmosphere through the complex oxidation of volatile organic carbon compounds (VOCs) in the presence of nitrogen oxides (NO_x) and sunlight. In order to effectively implement control measures to reduce O₃ levels, it is necessary to understand the chemical processes that in part govern O₃ concentration, and to disaggregate local chemical O₃ production from transport. To address this issue, a major field campaign was organised at the Weybourne Atmospheric Observatory (WAO), a coastal site in the UK that is regularly within the pollution outflow from London and Western Europe. As part of this campaign, a novel approach to directly measure in situ the rate of local O₃ production was employed along with a range of instrumentation to measure concentrations of different radical species as well as with detailed VOC and NO_x speciation. We will present preliminary findings from a major O₃ pollution event (~120 ppb) that occurred during the campaign as a case study for investigating the contributing factors influencing O₃ formation at a NO_x limited site. Direct measurements of local chemical O₃ production rates are compared with those inferred from a range of indirect approaches.