Concentration and deposition of air pollutants over the South China Sea in summer 2004

This study presents our measurements on meteorological variables, radiations, and the concentrations of airborne pollutants over the South China Sea (SCS). The observations were conducted in the summer 2004 by a research vessel. The mean concentrations of SO2 and CO were 1.5 ppbv and 0.7 ppmv, respectively. Nonetheless, the spatial variations of the concentrations of SO2 and CO were lower than the detection limits of their instruments. In contrast, CO2, O3, NO and NO2 had apparent spatial variation. The mean concentrations of surface water pCO2, O3, NO and NO2 were 387 ± 16 ppmv, 15 ± 6 ppbv, 2.9 ± 2.7 ppbv and 6 ±3 ppbv, respectively. The highest concentrations of CO2, NO and NO2 and the lowest concentration of O3 occurred at the outlet of Pearl River.

A one-column ocean model is used to determine aerodynamic resistance and top 10m-water temperatures. The simulated water temperatures agree well with the observation with correlation > 0.52, and the correlation of 15m-water temperatures as low boundary was 0.99. The simulated aerodynamic resistance and observed concentration are used to determine the deposition fluxes of various air pollutants to the ocean surface. The derived deposition velocity of CO2 between the atmosphere and the ocean surface ranges from 2.6×10-4 to 9.4×10-3 m/s. It is found that the deposition velocities, determined by this study under various stability conditions, are close to those determined under neutral conditions, commonly assumed in the community. Their discrepancies are within 3 %, of which the largest discrepancy occurs while wind speed was low.