Aerosol Size Distribution Measurement Under Different Pollution Types In Nanjing Area

High concentrations of aerosol particles in the atmosphere can directly or indirectly affect environment problem like decrease of visibility and haze day increased, it could cause respiratory and cardiovascular disease which do harm to human health. The characteristics of composition, size, physical and chemical properties of aerosol particles are essential to the overall understanding of the behavior and effects of ambient particles. Especially, the measurement of particle number size distribution, analyze the sources of aerosols and chemical, dynamic processes, help to improve atmospheric environment and explore the basis of other characteristics of aerosol particles.First of all, the study compared and evaluated the performances of three major instruments for aerosol measurement, APS(Aerodynamic Particle Sizer), SMPS(Scanning Mobility Particle Sizer) and WPS(Wide-range Particle Spectrometer). Aerosol size distribution of0.01～10μm was observed in northern Nanjing, combined with surface meteorological observations, air pollution index, satellite remote sensing of fire hot spots data, back trajectory model and methods of cluster analysis were used to talk about sources, transport paths and spectral distribution characteristics of aerosol particles under different weather condition like clean background, haze background (from local secondary pollution and crop residue burning in upwind areas) and dust background.The results showed that the variation trends of the particle concentration measured by the three instruments were in good agreement. But differences in absolute values of number concentration measured by the three instruments were also evident with SMPS providing the highest values, followed by WPS. APS showed the lowest concentration in the three instruments. There was a very good correlation between the values measured by SMPS and WPS in the size range between0.02-0.2um. In comparison with WPS, APS provided more available size spectra measurements. Bimodal distributions in diurnal variation were captured by all the three instruments, but the peak concentration and the size range measured by SMPS were higher than that by WPS. The differences among the three instruments were not sensitive to meteorological conditions and precipitation.The number concentration of accumulation mode is higher than any other aerosol modes in the two pollution processes. The peak value of aerosol particle number concentrations shifted to large particle size compare with other previously studies in this area. The ratio of SO42-/NO3-was 1.30and0.99indicating stationary sources were more important than traffic sources in the first event, but the second process is quite the reverse. Affected by the local sources from east and south, the particle counts below0.1μm gradually accumulate in the first process. The second process is mainly affected by a short distance transport from northeast and local sources from southwest, especially south, the concentration of aerosol particles is higher than other directions, indication that the sources of crop residue burning mainly from this direction.With a focus on a dust process originated in southern Mongolia and central Inner Mongolia, it shows that Nanjing affected by a long distance transport from northeast in May2011. The ultrafine particle≤0.08μm shows a high concentration because Local pollution is serious before dust process. During and after process the coarse mode of≤0.5μm providing the highest values. The aerosol number concentration of dust and local contaminated background is five times higher than that of clean background. Bimodal distributions in diurnal variation were captured under the influence of local pollution with the two peaks at10:00am and20:00pm which is much affected by dust weather and precipitation.The aerosol number concentration and size distribution have noticeable seasonal variation. The high values of aerosol concentration were captured in coarse mode in spring, nucleation mode in summer, accumulation mode in autumn and≤0.1μm in winter. It is significantly influenced by the meteorological parameters. Aerosol spectrum shows unimodal distributions in spring, summer and winter, with the peak between0.02～0.05μm. But differences in fall the spectrum shows bimodal distributions with the two peaks at0.05μm and0.1μm. By the boundary layer changes and human actives the aerosol number concentration of0.01～10μm shows bimodal distributions of diurnal variation with differences in each mode. Generally speaking, the peak of daytime emerges at12:00in spring and summer,10:00in fall and winter; the night peak general at18:00.