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Concentrations of gaseous elemental mercury (GEM) were continuously monitored from May 2011 to May 2012 at the Wuzhishan State Atmosphere Background Monitoring Station (109°29′30.2″ E, 18°50′11.0″ N) located in Hainan Island. This station is an ideal site for monitoring long-range transport of atmospheric pollutants from mainland China and Southeast Asia to South China Sea. Annual average GEM concentration was 1.58 ± 0.71 ng m during the monitoring period, which was close to background values in the Northern Hemisphere. GEM concentrations showed a clear seasonal variation with relatively higher levels in autumn (1.86 ± 0.55 ng m) and winter (1.80 ± 0.62 ng m) and lower levels in spring (1.16 ± 0.45 ng m) and summer (1.43 ± 0.46 ng m). Long-range atmospheric transport dominated by monsoons was a dominant factor influencing the seasonal variations of GEM. The GEM diel trends were related to the wind speed and long-range atmospheric mercury transport. We observed 30 pollution episodes throughout the monitoring period. The analysis of wind direction and backward trajectory suggested that elevated GEM concentrations at the monitoring site were primarily related to the outflows of atmospheric Hg from mainland China and the Indochina peninsula. The △GEM/△CO values also suggested that GEM was significantly affected by the long-range transport from the anthropogenic sources and biomass burning in Asia and Indochina peninsula. [ABSTRACT FROM AUTHOR]

Coupling air pollutants with particular meteorological conditions can induce air pollution episodes. To our knowledge, how typhoons influence mercury (Hg) as an extreme weather phenomena has not been reported. Gaseous elemental Hg (GEM) was measured during a time period (from September 16, 2011 to October 9, 2011) that included three typhoons (Haitang, Nesat, and Nalgae) at the Wuzhishan National Atmospheric Background Station. The GEM concentration during these typhoons ranged from 1.81 to 4.73 ng/m (2.97 ± 0.58 ng/m), 1.27 to 4.42 ng/m (2.69 ± 0.83 ng/m), and 1.43 to 2.99 ng/m (2.47 ± 0.32 ng/m), which was higher than for the non-typhoon period (1.14-2.93 ng/m, 1.61 ± 0.52 ng/m). Simultaneously, the three typhoon periods exhibited a significant positive correlation between the GEM concentration and wind speed. These results differ from the common belief that lower pollutant concentrations will occur due to a typhoon accelerating pollutant diffusion. Changes in the wind direction and long range pollutant transport from the Chinese mainland can reasonably account for this abnormality. There was a significantly positive correlation between the GEM and SO, NO, CO, and O levels during the three typhoons periods, which indicates they came from the same sources or areas. A backward trajectory analysis and the concentration weighted field at our monitoring site indicated that clean air masses mainly came from Southeast Asia or the southeast and northeast sea surfaces during non-typhoon periods, while polluted air masses came from the Chinese mainland during the three typhoon periods. The results implied that the increased GEM concentrations in the Wuzhi Mountain were caused by the long-range atmospheric transport of Hg from the Chinese mainland during the typhoon periods. The combustion of coal may be the main emission sources. [ABSTRACT FROM AUTHOR]

This paper retrieves the bidirectional polarization distribution functions (BPDFs) of the distinct urban cover in the Pearl River Delta (PRD) region employing the high spatial resolution of multi-angle polarized measurements made by the Directional Polarimetric Camera (DPC). The BPDF operational products of MICROPOL and POLDER measurements were used to validate the BPDF products of the DPC, with the results demonstrating that the BPDF product of the DPC measurements accurately expresses the surface polarized reflectance. The polarized reflectance of distinct surface types in the PRD region was studied using the DPC measurements. The results demonstrate that the polarized reflectances of different surface types differ and decrease as the normalized difference vegetation index increases. The polarized reflectance of a distinct surface type in the PRD region decreases with increasing scattering angle. The basic theory of investigating surface properties using multi-angle polarized measurements is proposed. [ABSTRACT FROM AUTHOR]