| High resolution instruments were used to investigate the relationship between aerosol size distribution characteristics and meteorological factors，and its possible influence on visibility in urban Nanjing from November to December 2009. Results show that the size distribution of aerosol number concentration showed a bimodal shape with the main peak value concentrating at particle sizes of 0.04-0.1 μm. Mass concentration distribution presented a bimodal shape with the two peak values concentrating at particle sizes of 0.5-0.7 μm and 2.7 μm, and the surface area concentration distribution presented two peaks from 0.1 to 0.5μm and from 0.5 to 0.9μm. It is found that the diurnal and interdiurnal variations of particle concentrations are obvious. Human activities and variation of atmospheric stability had great effect on daily variation of particle concentrations, while meteorological conditions such as precipitation, wind, relative humidity and so on had strong influence on interdiurnal variation. The aerosol size distribution was significantly affected by relative humidity. When RH was lower than 54%, number concentration of aerosol particles less than 1 μm in diameter increased gradually as RH increased, and concentration of particles with diameter larger than 1 μm almost had no change. When RH was higher than 54%, number concentration of aerosol particles ranging from 0.01 to 0.2 μm and from 2.7 to 10 μm decreased with the increase of RH, in contrast, concentration of aerosol particles between 0.5 and 1.5 μm in diameter increased. In addition, the particle number size distributions were different in rainy, foggy, sunny and haze weather conditions. Compared to sunny day, concentration of particles with different sizes all decreased in rainy day. In foggy weather, The number concentration of aerosol particles ranging from 0.01 to 0.3 μm and from 2.7 to 10 μm decreased, and aerosol particles between 0.3 and 2.7 μm increased in comparison with sunny day. Scavenging action of rain and fog to particles of different sizes from high to low was that coarse particles> nuclei mode particles> accumulation mode particles. In haze day, the peak of number concentration distribution moved toward a higher value. Compared to sunny day, the number concentration of aerosol particles ranging from 0.03 to 0.1 μm decreased, and aerosol particles between 0.1 and 2.7 μm increased in haze day. Based on Mie theory, the correlation between visibility and surface area concentration with different particle sizes indicated that particles between 0.1 and 2 μm in diameter shows a good correlation with visibility, which was the major contributor to visibility degradation in Nanjing. |
