Atmospheric PAH Contamination In The Western Watershed Of Bohai Sea, China

Atmospheric PAH contamination is a matter of great public health concern of scientists and policy makers in China. The Western Watershed of Bohai Sea, a area with large population, highly developed agriculture and industry, was recently identified as one of the areas in China with very high emission density of PAHs. Using both traditional active sampling and passive sampling technique developed in our lab, atmospheric PAH concentrations in gaseous and particulate phases were measured for the Western Watershed of Bohai Sea. Air-to-surface deposition depositions were also measured and atmospheric transport was addressed. The individual PAHs analyzed in this study were 16 USEPA priority PAHs except naphthalene.Atmospheric PAH concentrations in the study area were 54~1000 ng/m(3298±425 ng/m3)based on 24h active sampling, or 237~1500 ng/m3(752±337 ng/m3)based on the full season passive sampling, which were several times higher than those in many cities in developed countries. In fact, the Western Watershed of Bohai Sea was one of the regions with highest atmospheric PAH levels in the world. Interestingly, there was no significant difference in atmospheric PAHs between urban and rural sites with urban/rural ratio of only 1.24 in this study. This urban-rural pattern was quite different from all the other reports which revealed much higher PAHs levels in urban than rural areas. For the high PAH levels in the rural atmosphere in this area, low combustion efficiencies of coal/biomass were the major reasons, which resulted in very high PAHs emission factors.The Gas/Particulate ratio (G/P) of atmospheric PAHs in the study area was less than 2 for both active and passive sampling results, which was rather lower compared to the other reports in temperate zone. The regression slopes of partitioning coefficient log KPM10 and log pl0 were steeper than -1, out of the range of -0.6 ~ -1 often observed in other places, which provided an evidence for the EC adsorption domination in G-P partitioning.The PAH levels were highest in winter but lowest in summer and spring. The winter/summer ratios were ~2 and ~10 for gaseous and particulate PAHs, respectively. The seasonal variation of consumption of coal/biomass and meteorological conditions were major driven factors for the seasonality of gaseous PAHs, and temperature-dependent gas-particulate partitioning played a more important role in the seasonal variation of particulate PAHs. Relative higher atmospheric PAH concentrations were observed in southwest and northeast parts of Hebei province, and lower values were found in west of Hebei and northwest of Shandong. The spatial distributions of atmospheric PAHs were positive correlated with local emission, population density and GDP significantly.Diagnostic ratios of FLA/(FLA+PYR)和IcdP/(IcdP+BghiP) were applied for qualitative source apportionment. The combustions of coal and biomass were the major sources of atmospheric PAHs and petroleum combustion was important in non-heating season. Using PMF model provided by USEPA, four sources, namely industrial coal/vehicular, straw, domestic coal, and wood/coke oven, contributed 16.7%, 18.1%, 24.0% and 41.2% of the total emission, respectively. Roughly, the apportionment results were in agreement with the PAHs emission inventory of this area.The atmospheric deposition flux of PAHs was 8.5±6.2μg/(m2.d), higher than those of UK cities observed in early 1990s. Similar PAH deposition fluxes were found between urban and rural sites with a urban/rural ratio of 1.29, but approximately 6 times lower than those at baseline sites. The urban-rural trends of PAH deposition were in line with the pattern of atmospheric PAH concentrations. Different spatial distribution patterns in the depositions were revealed between high-molecular-weight (≥202) and low-molecular-weight (< 202) PAHs. The former followed similar spatial distribution pattern of atmospheric PAH concentrations, while relative higher fluxes of the latter were observed in northwest of Hebei. The possibilities of atmospheric outflow of PAHs were highest in winter based on the results of calculation of air mass trajectories.