Characteristics of Gaseous Pollutants at a Regional Background Station in Southern China

Measurements of gaseous pollutants (O-3, NOx, SO2, and CO) were conducted at Dinghushan background station in southern China from January to December 2013. The levels and variations of O-3, NOx, SO2, and CO were analyzed and their possible causes discussed. The annual average concentrations of O-3, NOx, SO2, and CO were 24.6 +/- 23.9, 12.8 +/- 10.2, 4.0 +/- 4.8, and 348 +/- 185 ppbv, respectively. The observed levels of the gaseous pollutants are comparable to those at other background sites in China. The most obvious diurnal variation of O3 was observed in autumn, with minima in the early morning and maxima in the afternoon. The diurnal variations of SO2 showed high values during the day. The diurnal cycles of NOx showed higher values in the morning and lower values during the night. Higher CO concentrations were observed in spring followed by winter, autumn, and summer. Biomass burning, in combination with the transport of regional pollution, is an important source of CO, SO2, and NOx in spring and winter. Backward trajectories were calculated and analyzed together with corresponding pollutant concentrations. The results indicate that air masses passing over polluted areas are responsible for the high concentrations of gaseous pollutants at the Dinghushan background station.