Exchange rate of mercury between atmosphere and different kinds of Earth’s surfaces on the east slope of Mt. Gongga

Abstract

Seasonal mercury flux measurements (three sampling periods: 2005 autumn, 2005 winter, and 2006 spring) were conducted at two soil sites, two grasslands and a cornfield on the east slope of Nit. Gongga, located in the southwest of Sichuan Province, China. The mercury flux was monitored using a dynamic flux chamber (DFC) method, and mercury concentrations in the air were measured with a TEKRAN 2537A Mercury Vapor Analyzer. Mercury exchange rates show a distinctly seasonal pattern and vary from-18.7• ng .m -2 "h "1 in winter to 19.2:L26.5 ng *m "2 .h "1 in spring, Hg exchange flux is a bidirectional process, however, it is dominated by dry deposition in winter and emission of mercury is the main process in some other seasons, besides the climate influence on mercury exchange rates. Atmosphere gaseous mercury concentration is anther important factor, high atmosphere mercury concentration (7.6 ng 9 m -a, nearly two times higher than in the spring, 3.2 ng 9 m "3 ) in winter caused by anthropogenic sources bated mercury emission from land surfaces and enhanced Hg deposition. According to our research, vegetation cover can lower mercury flux and increase dry deposition, and this may imply that plants in the background site are the sink of atmosphere mercury. Hg fluxes showed a clear diurnal pattern when the conditions were both sunny and overcast that Hg emission rate reached the maximum at noon and fell to the minimum at night. The daytime mercury flux rate peak is obviously related to solar radiation. The flux also significantly correlates with air temperature, and negatively correlates with air relative humidity.