| This study synchronously collects PM10 at suburban and urban sites in Nanjing and analyzes 16kinds of PAHs by the GC-MS, to understand the characteristics of distribution and the influences of meteorological conditions. Samples were collected by FA-3 sampler in each season(November 2009:autumn, January 2010:winter,April 2010:spring,July 2010:summer). The characteristics of distribution of PAHs were analyzed with meteorological data, O3 concentration, boundary data and HYSPLIT. The conclusions were as follows:The concentrations of total PAHs at the urban and suburban are in the ranges of 32.84?245.35ng/m3 and 21.43-225.72ng/m3 in PM10, respectively, and 19.11 ?111.57ng/m3 and 19.69?125.21ng/m3 in PM2.1. PAHs are mainly concentrated in fine fraction, especially in the ultrafine particles (< 1.1 ?m) in spring, summer,winter, however PAHs are more in coarse ones in autumn. PAHs concentrations at the two sites are close to each other, and show similar seasonal variation with the winter concentrations larger than those in the summer. There are two peaks at size diameters of 0.43-0.65?m and 4.7-5.8?m in both seasons. The size concentration peak in fine mode remained higher than in coarse mode in spring and winter, and in summer and autumn the peak in coarse mode is higher.PAHs mainly compose of 4-, 5- and 6-ring PAHs that have mass fractions (to total PAH mass) of 78.7%?83.1% in PM10 and 80.5%?87.1% in PM2.1,and the fraction of 4-rings PAHs in winter is clearly larger than those of other seasons. For 2?4 ring PAHs,the fine mode is lower than coarse mode, and the opposite for 5?6ring PAHs. The PAHs at two sites shows different diurnal variations. At the urban site, the concentration in the daytime is higher than that in the nighttime, whereas values in the nighttime become larger at the suburban site. The concentration of PAHs in fine mode in the daytime is lower than that in the nighttime, and in coarse mode it is similar in the daytime and nighttime. The peak in fine mode shifts in large size at night in winter.Among the various meteorological parameters, the PAH concentration shows clearly negative correlations to both temperature and relative humidity, and a positive correlation is noticed between the PM10 and PAHs. The influence of meteorological parameters is more significant in warm seasons (summer and autumn)than that in cold seasons (winter and spring). Ozone concentration also has a negative correlation to the 5- and 6-ring PAHs concentration. The precipitation had cleaning effect for each size range of PAHs in autumn, and for coarse mode PAHs in summer and summer. For each size range in spring, for fine mode in summer and winter the precipitation has concentration on increasing of PAHs.The results from air mass back-trajectory model show that the accumulation of PAHs is mainly influenced by local emission, and polluted airs from southwest and southeast of Nanjing are also an important source of the PAHs through shout-range transport. |
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