Ambient sulfur dioxide, nitrogen dioxide, and ammonia at ten background and rural sites in China during 2007–2008

We present two years (January 2007–December 2008) of atmospheric SO2, NO2 and NH3 measurements from ten background or rural sites in nine provinces in China. The measurements were made on a monthly basis using passive samplers under careful quality control. The results show large geographical and seasonal variations in the concentrations of these gases. The mean SO2 concentration varied from 0.7 ± 0.4 ppb at Waliguan on Qinghai Plateau to 67.3 ± 31.1 ppb at Kaili in Guizhou province. The mean NO2 concentration ranged from 0.6 ± 0.4 ppb at Waliguan to 23.9 ± 6.9 ppb at Houma in southern Shanxi. The mean NH3 concentration ranged from 2.8 ± 3.0 ppb at Shangdianzi in northeastern Beijing to 13.7 ± 8.4 ppb at Houma. At most sites, SO2 and NO2 peaked in winter and reached minima in summer, while NH3 showed maximum values in summer and lower values in cold seasons. On the whole, the geographical distributions of the observed gas concentrations are consistent with those of emissions. The ground measurements of SO2 and NO2 are contrasted to the SCIAMACHY SO2 and OMI NO2 tropospheric columns, respectively. Although the satellite data can capture the main features of emissions and concentrations of SO2, they do not reflect the variations of SO2 in the surface layer. The situation is better for the case of NO2. The OMI NO2 columns capture the geographical differences in the ground NO2 and correlate fairly well with the ground levels of NO2 at six of the ten sites.