Improving our understanding of the role of biogenic emissions on urban air quality

Secondary organic aerosol (SOA), formed from the atmospheric oxidation of volatile organic compounds has known adverse effects on air quality and human health. However, the contributions of biogenic SOA to organic aerosol in urban areas, with high levels of anthropogenic pollutants, is poorly understood. In this study, biogenic SOA markers are identified and quantified using liquid chromatography coupled to mass spectrometry. Time resolved samples were collected across several Asian mega cities and represent good case studies for anthropogenic-biogenic interactions to be investigated. Difficulties surrounding accurate quantification of these markers is addressed, and new methods proposed to start to overcome these challenges. Significant concentrations of biogenic organosulfates and nitrooxy-organosulfates were identified across the megacities of Beijing, Guangzhou and Delhi. Local isoprene emissions and high levels of anthropogenic pollutants, in particular NOx and particulate SO4 2– , led to significant formation of isoprene organosulfates and nitrooxy-organosulfates under both high- and low-NO oxidation conditions, with significant heterogeneous transformations of isoprene-derived oxidation products to particulate species. Local isoprene emissions were found to be highly influenced by local temperatures, with higher temperatures promoting higher concentrations, an important observation for a warming climate. Monoterpene derived organosulfates and nitrooxy-organosulfaes were observed to have strong diurnal variations using high time resolution filter sampling, but were observed in much lower concentrations than those formed from isoprene. Due to a significant lack of authentic standards, accurate quantification of markers is a challenge. A new method for the prediction of ionisation efficiencies was developed, and for the first time applied to biogenic SOA markers. This prediction allowed for the differences in ionisation efficiencies to be considered, leading to more reliable quantification. This method was then applied to the quantification of biogenic organic acids across Beijing, Delhi and Guangzhou and are some of the first observations of their kind for these species.