Sources and Dynamic Processes Controlling Background and Peak Concentrations of TGM in Nanjing, China

Casey Hall,Zhuyun Ye,Huiting Mao,Tijian Wang,Yang Zhang,Xiuqun Yang,Jialei Zhu,Che-Jen Lin,Congbin Fu,Robert Talbot,Aijun Ding

doi:10.3390/atmos5010124

Abstract

Total gaseous mercury (TGM) data from urban Nanjing, at the western edge of the Yangtze River Delta (YRD) region in China, over nine months, were analyzed for peak and background mercury concentrations. The background concentration of TGM was found to be 2.2 ng∙m−3. In examining episodic influences of free tropospheric air masses on the surface TGM concentrations in Nanjing, we hypothesize heterogeneity in the global distribution of TGM concentrations in the free troposphere. The nine-month averaged diurnal cycles of TGM indicate a strong co-emission with SO2 and an underestimation of greater than 80% TGM emissions in current inventories. Regular peak concentrations of mercury were investigated and the major causes were YRD emissions, transport from rural areas, and monsoonal transport. Transport of rural emissions is hypothesized to be from illegal artisanal small-scale gold mining that are currently missing in the emission inventories. Enhancement of TGM associated with summer monsoon contributed to a maximum TGM concentration in mid-May–early June, an inverse seasonality in comparison to most other observations in China, North America, and Europe.

Highlights

Mercury is a persistent pollutant with long-term health consequences for both humans and ecosystems
This study aims to investigate the factors controlling temporal variability of Total gaseous mercury (TGM) concentrations in Nanjing and more broadly the Yangtze River Delta (YRD)
Nine months of TGM data was collected in Nanjing, China in 2011

Summary

Introduction

Mercury is a persistent pollutant with long-term health consequences for both humans and ecosystems. Winds during the February episode came from the west while the average direction was northerly, in July the average modeled wind direction at 850 hPa was southwesterly, while the low concentration air mass came from the southeast at 2000 m AGL, and during September the seasonal winds came from the east southeast at ground level while the low concentrations coincided with northerlies and all were coincident with increased wind speed. These features indicate fast widespread ventilation over the YRD by mixing of clean, free tropospheric air masses leading to relatively unpolluted conditions

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