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.