| With urban haze occurring frequently, atmospheric fine particulate matter(PM2.5) has recently drawn a great deal of concern. Taiyuan is one of the highest PM2.5 pollution cities in China, where coal-fired heating results in more serious particulate air pollution, especially in winter. In this study, firstly, PM2.5 samples were collected in the heating season of 2009, 2011, 2012 and 2013 at the roof of a building near Yingze Bridge in Taiyuan; secondly, PAHs, OC and EC were analyzed in the laboratory; and the PAHs, OC and EC concentration levels, variation, health risk and potential sources were discussed and estimated finally. The results were of great significance to assess the environmental and human health risk and source of carbonaceous aerosols in Taiyuan in recent years, and provide a scientific evidence for the air particles pollution prevention and control measures. The main conclusions were as followed:1. The average mass concentrations were 268.7 μg/m3, 167.3 μg/m3, 218.5 μg/m3 and 181.4 μg/m3 for PM2.5; 826.2 ng/m3, 915.7 ng/m3, 658.3 ng/m3 and 420.8 ng/m3 for Σ16-PAHs; 53.0 μg/m3, 41.6 μg/m3, 41.8 μg/m3 and 30.0 μg/m3 for OC, and 21.0 μg/m3, 6.5 μg/m3, 15.8 μg/m3 and 6.1 μg/m3 for EC, in the heating season of 2009, 2011, 2012 and 2013, respectively. Generally, the PM2.5, PAHs, OC and EC level in Taiyuan were all yearly decreased, which may be related to the decrease of the emission sources and increase of central heating. Compared with many domestic and foreign cities, concentrations of PM2.5 and its PAHs, OC and EC in Taiyuan were all at higher levels.2. The Fla was the most abundant PAH species for all samples in the investigated years, followed by Pry, Phe and Chr. Middle rings of species accounted for the most in all of the 16 PAHs, indicating that sources of PAHs in Taiyuan were primarily from coal combustion. The toxicity equivalence concentrations(BaPeq) based on benzo[a]pyrene(BaP) as the primary representative for PAHs were 42.7 ng/m3, 87.8 ng/m3, 36.2 ng/m3 and 41.1 ng/m3, respectively, which were all higher than the BaP limit value proposed by China and WHO(2.5 ng/m3 and 1 ng/m3), indicating the potential risk to the local human health in Taiyuan. Results from the diagnose ratios and principal component analysis showed that the PAHs in Taiyuan were mainly emitted by coal combustion, vehicle exhaust and biomass combustion, and small part deriving from coke emissions and petroleum.3. OC and EC in atmospheric PM2.5 in Taiyuan was significantly correlated in all samples, which showed that OC and EC were from the same emission sources, but there also existed secondary organic carbon in ambient air. Principal component analysis indicated OC and EC in Taiyuan were primarily emitted from coal combustion, biomass burning and vehicle exhaust. Road dust was another source for the samples of 2013 in Taiyuan due to the large-scale and prolonged urban construction.4. At some extent, the carbonaceous aerosols was affected by meteorological factors such as ambient temperature, relative humidity, wind speed. Generally, PM2.5, PAHs, OC and EC were negatively correlated with temperature, wind speed, and positively proportional to relative humidity. At high temperature vertical convection strengthened, which can promoted the diffusion of pollutants. As to PAHs, temperature also can affect the distribution of PAHs in vapor and particle phase. Higher wind speed helped dilution and diffusion of pollutants in horizontal direction, which led to lower level of pollutants. When relative humidity was high, the particles can not only absorb water but also organic matter, resulting in higher concentration of pollutants. Elevated concentrations of PM2.5 and the carbon component can increase the light absorption and scattering effect in the atmosphere and decrease the atmospheric visibility, which might be the main cause of haze formation. |
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