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

Abstract

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 (Rc). In summer, during the periods of significant wet deposition due to precipitation, S concentration decreased significantly by ∼70%. The results of the regional source appointment suggested that local emissions (inside BTH) contributed ∼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 non-local emissions to dry deposition could be enhanced by the southwest background wind. Local emissions took an important part in S total deposition (∼70%) during dry days while non-local emissions contributed significantly (∼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.