Total gaseous mercury in a coastal city (Qingdao, China): Influence of sea-land breeze and regional transport

Abstract

Abstract Atmospheric mercury cycling in coastal urban areas in East China is complex due to the combined influence of both intensive inland anthropogenic emission sources and marine air masses. In this study, continuous measurements of total gaseous mercury (TGM) concentrations were conducted from December 2017 to December 2018 at a coastal site, Shilaoren, in Qingdao, East China. Concentrations of TGM ranged from 0.59 ng m−3 to 24.46 ng m−3 with a mean value of 2.28 (±0.87) ng m−3. TGM exhibited a distinct diurnal cycle mostly with an early morning peak and an afternoon minimum. The daily minimum and mean TGM concentrations with the occurrence of sea-land breeze circulation were higher than those without. In addition, TGM concentrations exhibited a strong dependence on wind direction with an average value of 2.41 ng m−3 in air masses from inland, ~24% higher than that from the ocean. Correlation analysis suggested that mobile combustion was a major anthropogenic emission source to TGM at Shilaoren, and coal-fired power plants became a significant contributor in winter. Potential source contribution function analysis and episodic studies attributed high TGM concentrations (>90th percentile value = 3.28 ng m−3) to regional transport from anthropogenic emission sources in the neighboring cities or provinces in eastern China. Frequently occurring typhoons contributed to the high TGM episodes in summer. Prior to the arrival of a typhoon, TGM concentrations rose sharply due to transport from polluted regions in East Asia as well as downdrafts at the front and lateral edges of a typhoon, whereas dropped to a mean concentration of 1.57 ng m−3, comparable to the globally background value, as the typhoon arrived. This study contributes to a better understanding of the effects of meteorological processes including sea-land breeze and typhoons as well as regional transport on atmospheric mercury cycling in eastern China's coastal environments.