| To recognize the pollution characteristics and sources of PM2.5 in Guanzhong, PM2.5 were sampled in Xi’an, Baoji, Weinan and Qinling from March 2012 to February 2013, and then PM2.5 mass, elements, water soluble inorganic ions and carbon compositions were analyzed. Finally, PMF and CMB were used to analyze the contribution of different sources to PM2.5. The main results are as follows:During the sampling period, the annual concentrations of PM2.5 in Xi’an, Baoji, Weinan and Qinling were(156.1±102.8) μg·m-3,(118.4±77.7) μg·m-3,(123.6±69.7) μg·m-3 and(109.3±82.9) μg·m-3, respectively. As to the seasonal variations, the highest concentration appeared in winter, lowest in summer, and medial in spring and autumn. In the view of spatial variations, Xi’an > Baoji > Weinan > Qinling in spring, Xi’an > Weinan > Baoji > Qinling in summer, Xi’an > Weinan > Qinling > Baoji in autumn, and Xi’an > Qinling > Baoji > Weinan in winter. Elements, water soluble inorganic ions and carbon compositions also showed spatial and temporal vatiations. Among the compositions, Al, Si, Ca, Fe and Zn were the major elements. The analysis of enrichment factor showed that Al, Si, Ca and Ti were mainly from natural sources, Cr and Mn were affected by natural and anthropogenic sources together, and Zn, As Br and Pb were mainly from anthropogenic sources. SO42-, NO3- and NH4+ were the major ions, and they accounted for 80%~90% of the total ions. The concentration of SO42-, NO3- and NH4+ were highest in winter, and SO42- also had high concentration in summer. The annual ratios of NO3-/SO42- were 0.73~0.76, which indicated that pollutants mainly came from stationary sources, especially coal combustion. OC showed the highest concentration in winter in all sites, however EC had little differences among seasons. As to the spatial variation, Xi’an had the highest OC and EC in all seasons, especially in winter, which showed the same variation with PM2.5.The analysis of material balance showed that OM, which accounted for 22.7%~31.7% of PM2.5, was the main component of PM2.5 in Guanzhong. In addition, SO42-、NO3- and GM also had high ratios, and they accounted for 5.2%~21.0%, 11.3%~15.3% and 10.1%~17.2%, respectively. As to the seasonal variation, GM and OM, which accounted for 18.7%~28.4% and 17.9%~28.6%, respectively, were the main components in spring; SO42- and OM, which accounted for 24.0%~36.1% and 14.5%~21.1%, respectively, were the main components in summer; OM, which accounted for 26.2%~34.8% and 22.9%~36.4%, respectively, were the main components in autumn and winter.The PMF results showed that the contribution of secondary nitrate, secondary sulfate, coal combustion, vehicle exhausts, biomass burning and geological material to the annual PM2.5 were 15.2%, 20.1%, 19.2%, 12.7%, 12.8% and 13.1%, respectively in Xi’an; 15.1%, 22.9%, 17.9%, 10.4%, 15.4% and 12.6%, respectively in Baoji; 14.7%, 22.7%, 18.6%, 10.8%, 14.8% and 12.2%, respectively in Weinan; 18.4%, 27.2%, 10.9%, 9.8%, 10.3% and 20.0%, respectively in Qinling. The CMB results showed that the contribution of secondary nitrate, secondary sulfate, coal combustion, vehicle exhausts, biomass burning and geological material to the annual PM2.5 were 13.3%, 16.1%, 22.9%, 9.8%, 14.9% and 15.8%, respectively in Xi’an; 12.3%, 17.8%, 21.0%, 8.6%, 16.2% and 16.0%, respectively in Baoji; 11.9%, 15.8%, 21.3%, 8.4%, 15.7% and 15.1%, respectively in Weinan; 13.5%, 18.5%, 14.4%, 7.5%, 15.1% and 18.1%, respectively in Qinling. In spring, geological material was the primary source; in summer, secondary sulfate was the primary source; in autumn, the contribution of biomass burning was important; in winter, biomass burning and secondary sulfate were equal important. As to geological material, construction dust was the most important source in cities, especially in Xi’an, however soil dust was the most important source in Qinling. For the coal combustion, the contribution of industry coal was larger than domestic coal, but smaller gap in winter. |
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