An Investigation of Ozone Formation Through Its Precursors Co Nox VOC and its Loss Processes at a Sub Urban Site of Agra

Abstract

Ozone (O3) is a secondary pollutant which influences air quality, climate change and atmospheric chemistry. Being secondary in origin, tropospheric ozone formation is influenced by its precursors levels and meteorological variables, therefore, the present study was undertaken to identify complex chemistry of ozone formation, role of its precursors and meteorological variables during 2014-2016. In addition, the study also estimates various loss processes of ozone. Modelling of ozone levels has also been attempted using various statistical methods. The average concentration of surface O3 was 32.3 ± 22.7 ppb during the study period and that of NO, NOx* and CO was 6.5 ± 8.2 ppb, 12.1 ± 7.8 ppb and 527.3 ± 482.7 ppb, respectively. The positive rate of change of ozone was the maximum in April (12.2 ppbh-1) while minimum in January (2.4 ppbh-1), however, the negative rate of change was the maximum in November (-15.1 ppbh-1). Although several studies have been conducted on ozone and its precursors (NOx, CO and VOCs), however, there are no reports which simultaneously present ozone forming processes and ozone breakdown reactions. The present study is an attempt to bridge this gap. The present thesis consists of four chapters according to the four objectives proposed. The first chapter includes diurnal and seasonal variation of ozone, NOx and CO. Relationship of ozone with its precursor and meteorological parameters, vertical profile of CO, contribution of photostationary steady state towards ozone levels and high ozone episode analysis are also included. The second chapter includes the study of aromatic hydrocarbons, their seasonal variation and their role in ozone formation. The third chapter includes loss processes of ozone through particulate matter, carbonaceous aerosol and formation of carboxylic acids. The last chapter includes modelling of ozone levels using statistical models. newline