Despite recent efforts to investigate the distribution and fate of polycyclic aromatic hydrocarbons （PAHs） in air, water, and soil, very little is known about their temporal change in wet deposition. As a result of increased attention to public health, a large-scale survey on the deposition flux and distribution of PAH contamination in rainwater was urgently conducted in Shanghai, China. In this study, 163 rainwater samples were collected from six sites, and 15 PAH compounds were detected by the use of a simple solid phase microextraction （SPME） technique coupled with gas chromatography-mass spectrometry. The dominant PAH species monitored were naphthalene, phenanthrene, anthracene, and fluoranthene. The concentration of total PAHs per event was between 74 and 980 ng/L, with an average value of 481 ng/L, which is at the high end of worldwide figures. The annual deposition flux of PAHs in rainwater was estimated to be 4148 kg/yr in the Shanghai area, suggesting rainfall as a major possible pathway for removing PAHs from the atmosphere. Diagnostic analysis by the ratios of An/178 and Fl/Fl＋Py suggested that combustion of grass, wood, and coal was the major contributor to PAHs in the Shanghai region. Back trajectory analysis also indicated that the pollutant sources could be from the southern part of China.
Lili YanXiang LiJianmin ChenXinjun WangJianfei DuLin Ma
The hygroscopicity of atmospheric aerosols significantly influences their size distribution, cloud condensation nuclei ability, atmospheric residence time, and climate forcing. In order to investigate the hygroscopic behavior of aerosol particles and serious haze in China, a Hygroscopic Tandem Differential Mobility Analyzers （HTDMA） system was designed and constructed at Fudan University. It can function as a scanning mobility particle sizing system to measure particle size distribution in the range of 20-1000 nm in diameter, as well as a hygroscopicity analyzer for aerosol particles with diameters between 20-400 nm in the range of 20%-90% RH （relative humidity）. It can also measure the effect of uptake of inorganic acids or semiVOCs on the hygroscopic behavior of aerosols, such as typical inorganic salts in atmospheric dust or their mixtures. The performance tests show that the system measured particle size of the standard polystyrene latex spheres （PSLs） is 197 nm, which is in excellent agreement with the certified diameter D=199±6 nm, as well as a standard deviation of the repeated runs SD=8.9×10^-4. In addition, the measured hygroscopic growth factors of the model compounds, （NH4）2SO4 and NaNO3, agree with the Kohler theoretical curves. The results indicate that the HTDMA system is an excellent and powerful tool for studying the hygroscopic behavior of submicron aerosols and meets the demand required for laboratory research and fieldwork on atmospheric aerosols in China.
UV-induced degradation of odorous dimethyl sulfide （DMS） was carried out in a static White cell chamber with UV irradiation. The combination of in situ Fourier transform infrared （FT-IR） spectrometer, gas chromatograph-mass spectrometer （GC-MS）, wide-range particle spectrometer （WPS） technique, filter sampling and ion chromatographic （IC） analysis was used to monitor the gaseous and potential particulate products. During 240 min of UV irradiation, the degradation efficiency of DMS attained 20.9%, and partially oxidized sulfur-containing gaseous products, such as sulfur dioxide （SO2）, carbonyl sulfide （OCS）, dimethyl sulfoxide （DMSO）, dimethyl sulfone （DMSO2） and dimethyl disulfide （DMDS） were identified by in situ FT-IR and GC-MS analysis, respectively. Accompanying with the oxidation of DMS, suspended particles were directly detected to be formed by WPS techniques. These particles were measured mainly in the size range of accumulation mode, and increased their count median diameter throughout the whole removal process. IC analysis of the filter samples revealed that methanesulfonic acid （MSA）, sulfuric acid （H2SO4） and other unidentified chemicals accounted for the major non-refractory compositions of these particles. Based on products analysis and possible intermediates formed, the degradation pathways of DMS were proposed as the combination of the O（1D）- and the OH- initiated oxidation mechanisms. A plausible formation mechanism of the suspended particles was also analyzed. It is concluded that UV-induced degradation of odorous DMS is potentially a source of particulate pollutants in the atmosphere.
