The size distribution of particulate was analyzed by the FA-3 9 stage sampler in Northern-suburb of Nanjing from January to November in 2014. First, the monitoring result from FA-3 was compared with the results of the same period obtained from a medium flow size grading sampler (KC-120H) and online monitoring instrument of the Environmental Protection Agency. The data correlation coefficients were all greater than 0.95. The fine particle concentration from FA-3 was lower by 13.9% and 16.6%, while PM10 concentration was higher by 15.2% and 13.3% respectively. However, the deviations were in the acceptable range of atmospheric sampling which could indicate the accurate classification and sampling of particulate for FA-3. Particulate pollution in Northern-suburb Nanjing was serous in which the annual average concentrations of PM1.1, PM2.1 and PM10 were(65.6±37.6), (91.0±54.7) and (168.0±87.0) μg·m-3 respectively; fine particles dominated and most of them had a diameter of less than 1.1 μm. Particle size distribution was bimodal with peaks at 0.43-0.65 and 9-10 μm; the median diameter was 1.83 μm which was in the accumulation mode. In winter, the concentration of fine particle size was higher and in spring the coarse particle size was higher; in summer, the fine particle size concentration was not significantly reduced but coarse particle size was obviously lower than those in other seasons. The differences of particle size distribution in day and at night were very small in coarse segment and in fine segment, the nocturnal concentrations were mostly higher than diurnal concentrations. The precipitation had cleaning effect for each size range of particulate except in summer and the effect was more distinct in fine particle size. In haze days, with the aggravation of haze level, the particle concentration in the diameter range of 0.43-2.1 μm increased gradually while in this segment the particle concentration was significantly negatively correlated with visibility. Using relative humidity of 70% as the demarcation, the particle size distribution changed significantly:when humidity was greater than 70%, mass concentration of particle with a diameter of less than 0.43 μm reduced significantly but that with diameter range of 0.43-2.1 μm increased obviously which should be related to the particle hygroscopic growth. The air mass sources could be divided into four categories in northern-suburb of Nanjing. Air mass from the northwest with rapid transport velocity was the cleanest in which the fine particle size concentration was significantly lower than those in other directions; the air mass from local and surrounding was the most severely polluted with high concentrations in both fine and coarse segment, its transmission distance was short and wind speed was small which contributed greatly to air pollution of Nanjing with probability of occurrence of pollution reaching 73.9%.
Keywords: aerosol; air mass sources; comparison of samplers; haze; particle hygroscopic growth; particle size distribution; precipitation scavenging.