Spatial And Temporal Distribution Of Gaseous Elemental Mercury And Emission From Anthropogenic Sources In Chongqing, China

Mercury, which exists mainly in liquid form at normal temperature with high vapour pressure, is one of the high-toxic and non-needful elements for human beings. Gaseous elemental mercury (GEM) is predominant in the atmosphere (more than 90%). Due to its low solubility and high stability, Hg⁰ has a residence time of 0.5-2 year and thus can undergo long range transport. Atmospheric mercury can adversely impact human health due to its deposition to, and biomethylation and bioaccumulation in terrestrial and aquatic systems. Therefore, it is important to conduct the research on the atmospheric mercury for understanding the status of mercury pollution, elucidating the biogeochemical cycling and developing the measure for prevention and remediation of mercury pollution.Recently, there were a certain research on atmospheric mercury in America and Europe, while just a few in China. Still, those were confined to one or several sites with short-term measurements. As the most important industry in southwest of China, Chongqing has a large consumption of energy, above 70% being coal. As widely recognized, the burning of fossil fuel was the biggest one of atmospheric mercury among the anthropogenic sources. In order to investigate the status of concentrations, the characteristics of spatial and temporal distribution, the impacting factors and the emission from the anthropogenic sources in Chongqing, the Lumex^? RA-915⁺ mercury analyzer was used to measure the concentration of GEM in the main district of Chongqing for a long time combined with the methods of emission factors and grey predicting.The conclusions as follows:Average concentrations of GEM during the study period ranged from 4.65-7.89 ng m^-3 with a mean value of 6.45±0.21 ng m^-3 in Chongqing, China. It was approximately 4 times of the accepted global background concentrations (1.5-2 ng m^-3). Previous studies from various city areas in the world showed that GEM concentrations ranged from 1.8 to 9.8 ng m^-3 with much higher GEM concentration in Asia than in North America, exception for Mexico. The GEM concentrations in the air of Chongqing were greatly influenced by the land-use and/or the ambient environment. The mean values of GEM decreased in order of Transport>Industrial>Commercial>Educational>Natural conservation area. The GEM had no differences among the transport (7.07), industrial (7.05) and commercial areas (6.71), but was significantly higher than in the educational (5.97) and natural conservation areas (4.65 ng m^-3), suggesting that mobile emission sources (cars, trucks, buses, etc.) and industrial sources (coal burning) may contribute to atmospheric Hg in urban regions. Our results showed that there was also serious atmospheric Hg pollution in the commercial areas, where the GEM concentration was very close to those in the transport and industrial areas. Relatively low GEM concentrations were expected in the educational and natural conservation areas with the lowest at the natural conservation area where no local anthropogenic sources existed.The GEM showed monthly and diurnal variation during the study period. The GEM gradually increased from Aug. to Nov. in 2006 and reached the peak values in Nov. The highest concentration (8.24 ng m^<sup>-3) was observed in November, whereas the lowest (5.36 ng m^-3) was observed in August. The similar trends were already observed in other studies. On the other hand, the characteristics of diurnal patterns of GEM were impacted by the ambient environment. At Jinyun Mountain site, GEM concentrations were distinctly higher during the day than at night for winter and summer months. On the contrary, the GEM were found to be higher at night at the site of Power Plant. The characteristics of diurnal variation of atmospheric mercury at Southwest University site were similar to those at the site of Power Plant. Moreover, the trend of diurnal variation at each site was consistent for winter and summer months. Additionally, the concentrations were typically lower and the range of variation was always stronger in Nov. than Jan.The concentrations of GEM in the air were correlated significantly with the meteorological parameters. However, such relationship obviously varied with areas. At Jinyun Mountain site, GEM concentrations were strongly positively correlated with air temperature and solar radiation, while GEM had negative correlation with both parameters at Power Plant and at Southwest University. There was positively significant relationship between relative humidity and GEM concentrations at all three sites, while there is no consistent relationship between barometric pressure and GEM during the measurements. Besides, the concentration of atmospheric mercury at Southwest University site declined from 6.64 through 4.34 ng m^-3 as the precipitation occurred. That showed the efficient removal effect of precipitation on mercury in the atmosphere. Additionally, the diurnal variation of mercury contents was not obvious, compared to that on the fine day.The GEM was greatly influenced by human activities in Chongqing. In the industrial area were located a great many enterprises including the Chongqing Power Plant and Chongqing Steel Plant, both of which have large consumption of coal. And sometimes there were always heavy traffic flows and jams, which can result in serious atmospheric pollution in the transport area. Additionally, in the commercial area the air could not flow well due to lots of markets and many people. All above mentioned contributed to the high concentrations of GEM in the atmosphere. By comparison, the GEM were low in the educational area with little Hg emission from the human activity and in the natural conservation area with nearly no human disturbance.The Hg emission from the anthropogenic sources was investigated using the method of emission factors and grey predicting. The Hg emission from anthropogenic sources was 9.47 t in Chongqing, in 2005. Among those, the coal burning, cement production and waste incineration, which were the largest contributors, accounted for 64.5%. 22.2% and 7.7%, respectively. The Hg emission increased annually and was from 4.65 t in 1995 to 9.47 t in 2005. Moreover, that will reach 13.79 t in 2010, if no efficient measures. In order to take control of Hg emission from the anthropogenic sources efficiently in Chongqing, the measures were suggested such as improving the efficiency of Hg removing using the existing equipments, the scientific management of waste and adopting the advanced the technology of incineration and improving the traffic condition and the technology of gas engine in vehicles.