Measurements of Singlet Oxygen and Organic Triplet Excited States in Aqueous Aerosols in Hong Kong, South China
THEODORA NAH, Yuting Lyu, Yin Hau Lam, Yitao Li, Nadine Borduas-Dedekind,
City University of Hong Kong Abstract Number: 95
Working Group: Aerosol Chemistry
AbstractPhotooxidants in the atmospheric aqueous phase, such as triplet excited states (
3C*) and singlet oxygen (
1O
2), play important roles in the formation and transformation of secondary organic aerosols (SOA). In order to elucidate the importance of these aqueous reactions in SOA formation and transformation, it is necessary to quantify the quantum yields and steady-state concentrations of these aqueous photooxidants. However, measurements of aqueous photooxidants in atmospheric samples are still scarce. In this study, using the chemical probe technique, we show that the illumination of aqueous aerosols in Hong Kong leads to the efficient production of
3C* and
1O
2. Experiments were conducted using PM2.5 and size-fractionated aerosols collected during different seasons in two urban and one semi-rural locations in a year-round study. We observed that
3C* and
1O
2 production were the highest in the winter and the lowest in the summer for all three locations. Differences in the locations (urban vs. semi-rural) did not have noticeable effects on
3C* and
1O
2 formation. The seasonal trends of
3C* and
1O
2 production were observed to be due to seasonal variations in the long-range air mass transport. [
1O
2]ss and [
3C*]ss were observed to correlate with the concentration and absorbance of water-soluble organic carbon in both PM2.5 and size-fractionated aerosols. We also attempt to correlate
3C* and
1O
2 production to the composition and measurable optical properties of the PM2.5 and size-fractionated aerosols. This is the first investigation of aqueous photooxidant production in atmospheric aerosols in a South China city, and our findings will help the modeling of aqueous organic aerosol photochemistry in the South China region.