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Abstract Title: Impacts of Meteorology and Size-Resolved Ionic Composition on Gas-Particle Partitioning of Atmospheric Reactive Mercury
Presenter Name: Hangtian Zhou
Company/Institution: Nanjing University
Session: Special Session - New developments in understanding reactive mercury concentrations and chemistry
Co-Authors: Hangtian Zhou,Lei Zhang,Weikang Zhang,Guichen Zhang,Yu Zhao

Abstract Information :

Atmospheric reactive mercury (RM) includes gaseous oxidized mercury (GOM) and particulate-bound mercury (PBM). Gas-particle partitioning of RM plays a key role in atmospheric mercury behaviors. In this study, GOM and PBM were measured by the Tekran 2537X/1130/1135 system and the Reactive Mercury Active System (RMAS) as a part of the STAMP campaign at NJU, a suburban site in eastern China. The size-resolved concentrations of PBM and ions were also measured using the Micro-Orifice Uniform Deposit Impactor (MOUDI). The effects of temperature (T), relative humidity (RH) and ionic composition on the gas-particle partitioning coefficient (Kp) for RM were investigated. To compare with existing studies, the Tekran data were firstly used to calculate Kp. An empirical linear correlation between log(1/Kp) and 1/T was obtained. No significant correlations were found based on the overall dataset and the seasonal data, except for summer. The summer correlation had a high absolute value of slope (~12000), which was much higher than most existing studies (with a lower mean temperature) but similar to a summer case at a high-altitude background site in east Asia. This indicated that Kp is more sensitive to T at a higher temperature level. To further examine the impacts of meteorology, RH was introduced into the correlation analysis as conducted in recent studies. A multiple linear regression was performed following: log(Kp)=a+bT+cRH. Although the correlations were slightly improved, the coefficients for seasons other than summer were still low, indicating that other factors, such as ionic composition, might have stronger contributions to the variation of Kp at a polluted site like NJU. Although Tekran could underestimate GOM, correlation between log(1/Kp) and 1/T based on the RMAS data exhibited a similar slope as Tekran in summer, which could be attributed to the good linear relationship between the GOM concentrations measured by the two methods. Results from MOUDI showed that log(1/Kp) increases with SO42? at ultra-fine particle segment and with NO3? at coarse particle segment. Sulfate and nitrate contribute significantly to the nucleation and growth of particles, respectively. The replacement of Cl? with SO42? and NO3? on particles induces RM transfer from particles to the gaseous phase due to the higher vapor pressure of HgCl2, resulting in a higher value of log(1/Kp).

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