Sulfur deposition in the Beijing-Tianjin-Hebei region, China: Spatiotemporal characterization and regional source attributions

Elevated atmospheric sulfur (S) deposition, which can affect ecosystems and human health, is a severe environment problem in the Beijing-Tianjin-Hebei (BTH) region. Here we investigated the spatiotemporal characteristics of S deposition and its regional sources in January (winter) and July (summer), 2015 in BTH using the CMAQ model coupled with the Integrated Source Apportionment Method (CMAQ-ISAM). The results showed that S deposition in high ecological risk areas (regions with S deposition significantly exceeding the critical load) of BTH was higher in summer (1.99 kg S ha(-1) mon(-1)) than in winter (1.18 kg S ha(-1) mon(-1)), with 82% (18% for winter) attributed to wet deposition and the rest to dry deposition. The daily variation of S dry deposition was mainly dependent on sulfur dioxide (SO2) dry deposition velocity in winter while S concentration in summer. SO2 dry deposition velocity was mainly caused by the change of resistance to surface resistance (R-c). In summer, during the periods of significant wet deposition due to precipitation, S concentration decreased significantly by similar to 70%. The results of the regional source appointment suggested that local emissions (inside BTH) contributed similar to 65% to dry deposition but only 8% and 28% to wet deposition in January and July respectively. For the contribution from non-local emission (outside BTH), Shandong contributed most to S dry deposition (17% on average). The contributions from Shandong (23%) and Shanxi (12%) to S wet deposition were higher in July than in January (10% and 3%, respectively). Analysis of daily contributions suggests that the contribution from nonlocal emissions to dry deposition could be enhanced by the southwest background wind. Local emissions took an important part in S total deposition (similar to 70%) during dry days while non-local emissions contributed significantly (similar to 65%) to total deposition during wet days. For seasonally, S total deposition was contributed more by local emissions (56%) in January but was dominated by non-local emissions (65%) in July. It demonstrates the need for a comprehensive strategy on local and non-local emissions for pollutant control against ecological risk caused by deposition.

Automated summary

This study investigated the spatiotemporal characteristics of sulfur deposition and its regional sources in the Beijing-Tianjin-Hebei region. The results showed higher sulfur deposition in summer than in winter, with the majority attributed to wet deposition. Local emissions had a larger contribution to dry deposition, while non-local emissions had a larger contribution to wet deposition. A comprehensive strategy on both local and non-local emissions is needed to control the ecological risk caused by deposition.