Gas-particle partitioning of atmospheric reactive mercury and its contribution to particle bound mercury in a coastal city of the Yangtze River Delta, China

Speciated atmospheric mercury including reactive gaseous mercury (RGM), particle bound mercury (PBM), and gaseous elemental mercury (GEM) were measured for a two-year period in Ningbo city, the Yangtze River Delta, China. Averaged concentrations of PBM and RGM were 316 +/- 377 pg m(-3) and 100 +/- 123 pg m(-3), respectively, with the highest RGM/PBM ratio in summer (0.73 +/- 1.31) and the lowest in winter (0.35 +/- 0.56). The relationship between RGM/PBM ratio and PM2.5 was nonlinear. When PM2.5 fell in the range of 15-100 mu g m(-3), the PBM increased, the RGM decreased, and the RGM/PBM ratio showed an obvious decreasing trend as PM2.5 increased. An empirical linear relationship between log(1/K-p) and 1/T was obtained for different seasons. The correlation coefficient and slope of the equation were highest in winter, suggesting that T explained more for K-p variation and RM transferred quickly to the particle phase in the cold season. The relationships between K-p and aerosol compositions show that K-p increased with increasing fractions of Organics (Org), nitrate (NO3), and chloride (Chl) and decreasing fractions of sulfate (SO4) and ammonium (NH4) in aerosols. Principle component analysis - multiple linear regression (PCA-MLR) was used to evaluate the relative contributions of gas-particle partitioning of RM and sectional primary emissions to PBM in different seasons. The results show that the contributions of RM partitioning to PBM were 28.0% in spring, 28.3% in summer, 31.2% in autumn, and 39.2% in winter, which was well explained by the seasonal variations of temperature and aerosol compositions.