Temporal trend and sources of speciated atmospheric mercury at Waliguan GAW station, Northwestern China

Abstract

Abstract. Measurements of speciated atmospheric mercury were conducted at a remote mountain-top station (Waliguan (WLG) Baseline Observatory) at the edge of northeastern part of the Qinghai-Xizang Plateau, Western China. Mean concentrations of total gaseous mercury (TGM), particulate bound mercury (PBM), and gaseous oxidized mercury (GOM) during the whole sampling campaign were 1.98 ± 0.98 ng m −3 , 19.4 ± 18.1 pg m −3 , and 7.4 ± 4.8 pg m −3 , respectively. Levels of speciated Hg at WLG were slightly higher than those reported from remote areas of North America and Europe. Both regional sources and long-rang transport played important roles in the distribution of atmospheric TGM and PBM at WLG, whereas GOM showed major links to the regional sources, likely as well as the in-situ productions via photochemical processes. Regional sources for speciated Hg were mostly located to the east of WLG, which is the most industrial and urbanized areas of Qinghai province. Potential source contribution function (PSCF) results showed that eastern Gansu, western Ningxia and Shanxi Province were likely the potential source regions of WLG, with good accordance with locations of urban areas and industrial centers. Moreover, we found that Northern India may be a significant source region for WLG during the sampling campaign, and this is the first published evidence suggesting long-range transport of atmospheric Hg from India to the Northeastern Tibetan Plateau. Seasonal and diurnal variations of TGM were in contrast to most of the previous studies in China, with relatively higher levels in warm seasons and night, respectively. The temporal trend of TGM also highlighted the impact of long-range transport on the distribution of TGM in ambient air at WLG.

Characteristics and potential sources of atmospheric mercury at a subtropical near‐coastal site in East China

“…The GOM/PBM concentrations in winter and in spring were not significantly different from each other (t test). Using the same speciation measurements, the concentrations of GOM at DAO are similar to those observed elsewhere, while the concentrations of PBM at DAO are much higher than the concentrations measured at remote sites and urban/suburban areas [Choi et al, 2008;Engle et al, 2010;Fu et al, 2012a;Sigler et al, 2009]. The GOM and PBM concentrations are possibly influenced by local anthropogenic Hg sources during the sampling period.…”

“…The TGM concentration was 3.3 ± 1.4 ng m À3 , higher than the concentrations observed at most remote sites in Europe and U.S. (<2 ng m À3 ) [Choi et al, 2008;Engle et al, 2010;Kock et al, 2005;Sigler et al, 2009] and in SW and NW China (1.6-2.6 ng m À3 ) [Fu et al, 2010[Fu et al, , 2012a[Fu et al, , 2012b, but lower than the concentrations observed at urban sites in China (e.g., 4.9-8.3 ng m À3 in Beijing, 13.5 ± 7.1 ng m À3 in Guangzhou, 5.4 ± 4.1 ng m À3 in Yangtze River Delta, and 3.8 ± 1.3 ng m À3 in Ningbo) [Wang et al, 2007;Nguyen et al, 2011]. The elevated mean concentration suggests the influence from local and regional Hg emissions, with possible contributions from industrial processes (including power plants, steel plants, and cement plants) and domestic heating in industrial/urban areas in Eastern China.…”

“…TGM was measured every 5 min using a Tekran Model 2537B Hg vapor analyzer at 0.75 L min À1 sampling flow rate [Fu et al, 2012a;Lindberg et al, 2000;Rutter et al, 2011;Zhang et al, 2015]. This analyzer was housed in a laboratory with temperature controlled at 24-26°C.…”

“…GOM and PBM measurements were conducted in winter (December 14-19, 2012) and spring (March 13-19, 2013) using a methodology developed in our group [Fu et al, 2012a;Landis et al, 2002;Zhang et al, 2015]. The sampling period (winter and spring) of GOM and PBM was selected to coincide with the period when anthropogenic Hg emission is higher with smaller influence from clean marine air.…”

“…The endpoints of the backward trajectories were applied in Potential Source Contribution Function (PSCF) analysis [Choi et al, 2008;Fu et al, 2012a;Kim et al, 2005]. The geophysical region centered by DAO (101°t o 141°E, 9°to 49°N) was divided into 160,000 grid cells of 0.1 × 0.1 latitude and longitude.…”