Pollution Characteristics of Aerosol Number Concentration in Winter and Spring in a Northern Suburb of Nanjing

: Using APS-3321, the atmospheric aerosol number concentrations (0.5-20 μm) were continuously monitored to analyze the characteristics of winter and spring pollution in 2014 in a northern suburb of Nanjing. The average number concentrations were (364.8±297.8) cm-3 and (79.6±62.4) cm-3 in winter and spring, respectively; fine particles (0.5-1.0 μm) accounted for 87.8% and 86.6% of the total, respectively. There were significant variations in number concentration at different periods. The diurnal variations in number concentrations were evident with high concentrations at night and low concentrations during the day. The early peaks were at 07:00 and 09:00, and number concentrations began to increase rapidly starting at 17:00 and 18:00 in winter and spring, respectively. The distribution of the number concentrations was unimodal, with peak sizes between 0.583 and 0.626 μm in winter and less than 0.542 μm in spring. With the increase in relative humidity, aerosol number concentrations increased gradually; at the same time, the peak size moved to a larger diameter which reflected the influence of hygroscopic growth of aerosols. During the total observation period, it reached 83.3% of the proportion of hazy days. The number concentration of particles less than 2.0 μm increased significantly with the increase in the haze pollution level, which was more obvious in winter. In spring, the proportion of fine particles increased with the increase in the haze level but in winter, it decreased during hazy days due to a significant increase in particle size caused by aging. The analysis of the typical pollution process in January indicated that there was a strong correlation between the source of air mass and the surface wind direction. Pollutants transmitted from the northern Jiangsu Province and the accumulation of pollutants due to slow winds were important causations of the pollution process.