Spatial and seasonal variations of atmospheric sulfur concentrations and dry deposition at 16 rural and suburban sites in China

AbstractThe large emissions of sulfur dioxide (SO2) in China have raised worldwide concerns due to its contribution to acid rain and particulate pollution. Monitoring sulfur (S) concentrations and estimating its deposition are important for evaluating air quality and its effects on ecosystems and human health. To date atmospheric dry S deposition in China remains unclear due to the paucity of measurements, especially in rural regions where the ecosystems are sensitive to acid deposition. In this study, we monitored both SO2 and particulate SO42− (pSO42−) concentrations at 8 sites south and 8 sites north of the Huai River in rural and suburban parts of China between 2010 and 2012. The measured concentration of SO2 and pSO42− were combined with GEOS-Chem modeled dry deposition velocities to estimate dry S deposition inputs to the surfaces. SO2 and pSO42− concentrations were high from October/November to next March/April and they (esp. SO2) decreased sharply since March/April at the northern sites, reflecting elevated SO2 emissions by winter heating (which normally starts in October/November and ends in March/April in the north of the Huai River). However the southern sites did not show this trend. Annual dry deposition of SO2 plus pSO42− in this study ranged from 3.1 to 27.1 kg S ha−1 across all the sites in the year 2011 (except one site from May 2011 to April 2012) and showed large spatial variation. The sites in northern China had greater dry deposition due to the higher S concentrations compared with sites in southern China. We also found relatively low pSO42−/pNO3- ratios at most sites, reflecting NOx emissions had a larger influence than SO2 emissions on particle composition during the 2010–2012 period at the measurement sites. Our results suggest that dry S deposition is still important input to ecosystems in spite of slow reduction of Chinese national SO2 emissions since 2005. More research on both wet and dry S deposition and their impacts on the environment and human health should be carried out following the introduction of policies to reduce SO2 emissions