Secondary organic aerosol (SOA) is formed from partitioning of the oxidation products of volatile organic compounds (VOCs) onto pre-existing aerosols. This study estimates the secondary organic carbon (SOC) contribution from five individual VOC precursors, namely, isoprene, α-pinene, β-caryophyllene, toluene and naphthalene by applying the SOA tracer method developed by Kleindienst et al. [2007, 2012].

Samples collected at Guangzhou (GZ), Nansha (NS) and Tsuen Wan (TW) in 2009 were analyzed by methanol extraction followed with trimethylsilylation before GC-MS analysis. On an annual basis, the estimated SOC concentrations were comparable at GZ (2.35 μgC/m³, 16% to OC) and NS (1.99 μgC/m³, 17% to OC), and lowest at TW (1.47 μgC/m³, 14% to OC). Based on the combined information of...[ Read more ]

Secondary organic aerosol (SOA) is formed from partitioning of the oxidation products of volatile organic compounds (VOCs) onto pre-existing aerosols. This study estimates the secondary organic carbon (SOC) contribution from five individual VOC precursors, namely, isoprene, α-pinene, β-caryophyllene, toluene and naphthalene by applying the SOA tracer method developed by Kleindienst et al. [2007, 2012].

Samples collected at Guangzhou (GZ), Nansha (NS) and Tsuen Wan (TW) in 2009 were analyzed by methanol extraction followed with trimethylsilylation before GC-MS analysis. On an annual basis, the estimated SOC concentrations were comparable at GZ (2.35 μgC/m³, 16% to OC) and NS (1.99 μgC/m³, 17% to OC), and lowest at TW (1.47 μgC/m³, 14% to OC). Based on the combined information of backward trajectories, wind speed, wind direction, and spatial variations of criteria air pollutants, the origin of air masses was classified into two types, namely continental and marine origins. Generally, the SOC contributions at individual sites were more significant under the influence of continental air masses and their concentrations at GZ, NS and TW were estimated at 2.82, 2.80 and 2.09 μgC/m³, respectively while on marine days, they were estimated at 1.42, 0.65 and 0.57 μgC/m³, respectively.

The SOA tracer method also allows identification of relative importance of biogenic and anthropogenic SOA. On continental days, all three sites were under a greater SOC contribution from anthropogenic sources, ranging from 53 – 58 % of estimated SOC. On marine days, anthropogenic SOC was still dominant at GZ and only 45% of estimated SOC was from biogenic sources. NS and TW inversely had a more significant SOC contribution from biogenic sources, at 52% and 71% to estimated SOC, respectively. Results from this thesis work indicate that the few common anthropogenic and biogenic VOCs make significant contributions to SOA in this region.

The analytical protocol also allows quantification of 25 polar organic compounds. They include dicarboxylic acids, aromatic acids either from secondary formation or emitted during biomass burning), fatty acids, saccharides and anhydrosugars. Concentration variations of the six groups of polar organic compounds are examined in the thesis work. The concentrations of all species were found higher on continental days than marine days. Among the three sites, concentrations were consistently the highest at GZ. The physical and chemical processes underlying the spatial and temporal variations are discussed in the thesis.