Comparative Analysis Of Polycyclic Aromatic Hydrocarbons In Fine And Coarse Particulates In Nanjing On Their Characteristics And Sources

Synchronous sampling of particulate matter was conducted in the urban and suburban sites in Nanjing to understand the PAHs in particulates on their characteristics, sources and the influences of meteorological conditions in each season(November2009:autumn, January2010: winter, April2010:spring, July2010:summer). PAHs in fine(PM2.1) and coarse(PM2.1-10) particles in different sites and seasons were comprehensively and comparatively analysed. The conclusions were as follows:(1) The concentrations of PM2.1-PAHs in the urban and suburban sites ranged from25.92to90.80ng/m3and30.76to102.26ng/m3respectively, and PM2.1-10-PAHs were in the ranges of30.15-89.15ng/m3and31.81-89.18ng/m3respectively. PAHs in the two sites displayed similar daily variation trend, the concentrations and profiles of16PAHs from different sites were nearly the same, all of which meant that PAHs in the two sites had the same sources and pollution process. Seasonal variations of PAHs concentrations and profiles were found at both sites, indicated the seasonality of sources and meteorological influences. The concentrations of PM2.1-PAHs of the two sites were in the order of winter>spring>autumn>summer, while PM2.1-10-PAHS were autumn>winter>spring>summer. Generally, PAHs in Nanjing distributed more in fine particulates than coarse ones and the mean proportion of PM2.1/PM2.1+PM2.1-10was55%. The proportion values in autumn, winter, spring and summer were41%、66%、61%、50%respectively. Different from other seasons, PAHs in autumn were more abundant in coarse particulates, which may be attributed to the distinctive source types and unique pollution form of local emission in this season.(2) Negative correlations were found between temperature and PAHs in fine and coarse particulates, with a higher correlation coefficient with fine ones. Wind speed also negatively correlated with PAHs, and more remarkably with coarse ones. Precipitation could remove PAHs to some extent. PM2.1-PAHs were found to be significantly and exponentially associated with visibility within different ranges of relative humidity and no similar phenomenon was found on PM2.1.10-PAHs.Regional transport of air masses contributed much to the PAHs concentrations in Nanjing. In autumn, local emission dominated the abundance of PAHs and the air masses influenced coarse particles were more local. The PAHs in summer were influenced by local sources as well as the dilution by clean air from southwest, the pollution forms for fine and coarse particles were similar. In spring, the polluted air masses from ENE-S contributed to the accumulation of PAHs in fine and coarse particles, and the effect on fine particles was more serious than on coarse particles. In winter, the polluted air masses from NNW-NE and local emission equally contributed to the accumulation of PAHs, and regional transport had greater impact on fine particles.(3) Source apportionment by PCA showed that different seasons had different source types. The main sources for PM2.1-PAHs in spring and winter were both vehicle exhaust(spring:78.23%, winter:74.09%) and coal/coke (spring:15.64%, winter:18.63%), for PM2.1-10-PAHs in these two seasons, there existed another source of wood combustion. In summer, there was only one source type for PM2.1-PAHs:vehicle exhaust(87.24%), for PM2.1-10-PAHs, there were two source types:vehicle exhaust(79.27%) and biomass burning(9.64%). For autumn, the sources of PM2.1-PAHs were vehicle exhaust(72.93%), biomass burning(10.58%) and coal/coke(10.02%). The first source for PM2.1-10-PAHs was a mixed source:biomass burning and coal/coke(46.53%), the second one was vehicle exhaust(44.28%), whose contribution rate was smaller than for PM2.1-PAHs. Combined with the results of CMB, the main sources of PAHs in particulates in Nanjing were vehicle exhaust, coke and coal burning.