A systematic field measurement was conducted at an island site (Wanshan Island, WSI) over the South China Sea (SCS) in autumn 2013. It was observed that mixing ratios of O3 and its precursors (such as volatile organic compounds (VOCs), nitrogen oxides (NOx = NO + NO2) and carbon monoxide (CO)) showed significant differences on non-episode days and episode days. Additional knowledge was gained when a photochemical box model incorporating the Master Chemical Mechanism (PBM-MCM) was applied to further investigate the differences/similarities of O3 photochemistry between non-episode and episode days, in terms of O3-precursor relationship, atmospheric photochemical reactivity and O3 production. The simulation results revealed that, from non-O3 episode days to episode days, 1) O3 production changed from both VOC and NOx-limited (transition regime) to VOC-limited; 2) OH radicals increased and photochemical reaction cycling processes accelerated; and 3) both O3 production and destruction rates increased significantly, resulting in an elevated net O3 production over the SCS. The findings indicate the complexity of O3 pollution over the SCS. Elevation of maritime O3 and its precursors was attributable to the transport of polluted continental air, implying impact of human activities on atmospheric composition above the SCS.
Scopus Subject Areas
- Health, Toxicology and Mutagenesis
- Photochemical box model
- South China Sea