| PAHs are one kind of persistent organic pollutants (POPs) and are formed from the incompleted combustions of fossil fuels. There has been a great concern about PAHs for their carcinogenic, teratogenic and mutagenic effects. PAHs are semivolatile compounds and exit in particle and gas-phases in atmosphere. Rain and fog play a significant role in leaching the PAHs existing in the atmosphere, and this leaching is mainly through the dissolution of gaseous PAHs or the adsorption of particulate PAHs. Then PAHs in dry and wet deposition is an important source of the PAHs in water, soil and some other environmental mediums. Research on the PAHs in rain and fog helps us understand the air pollution situation in different regions, and provides strong support for developing reasonable and effective policies and regulations.Current research focuses on the PAHs in the atmosphere, water, sediment and other environmental mediums. However, rain and fog as PAH important mode of exchange between the earth surface and atmosphere, not only in Shanghai, even in the nationwide the study on PAHs of rain and fog is scarce. The objective of this work is to determine the concentration, distribution and sources of PAHs in rain and fog water collected from Shanghai, China. There are three main contents in this work, as following:(1) To choose and optimize the extraction method. We use solid phase microextraction (SPME), which is simple, solvent-free, time-saving, high sensitivity and good selectivity. Parameters affecting the collection of efficiencies of PAHs were assessed according to the extraction efficiencies, and the best and simple conditions of SPME were confirmed to extract PAHs from rain and fog water. The characterization of extracts was carried out by gas chromatography with mass detector (GC/MS).(2) Rain water samples collected from six rain sample sites in urban area of Shanghai during May to September 2009 were fully and systematically investigated in terms of the concentration, deposition flux, distribution and sources. The average concentration and deposition of total PAHs per event were 481 ng L-1 and 24.23 mg m-2. The annual deposition flux of PAHs in rainwater was estimated to be 590μg m-2, and there will be 4148 kg PAHs landed in the Shanghai area, suggesting rainfall as a major possible pathway for removing PAHs from the atmosphere. Diagnostic analysis by the ratios of Ant/(Phe+Ant) and Flu/(Flu+Pyr) suggested that combustion of fossil fuels, grass and wood 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.(3) The concentration and source of PAHs in fog water collected in Shanghai from March to December 2009 were investigated. The total PAH concentration in fog water ranges from 0.03 to 6.67μg L-1 (mean of 1.06μg L-1), and is much higher in winter. Concentration of PAHs in fog or rain water reduces after pre-rain or pre-fog events due to scouring impact. Average concentration of PAHs in fog is higher than in rain. Diagnostic ratios analysis suggests that petroleum and combustion are the dominant contributors to PAHs in urban Shanghai. Backward trajectories are calculated to determine the origin of the air masses, showing that air masses are mostly from the northeast territory. |
PDF Full Text Request