The Concentration Variation Property And Extinction Characteristics Of Aerosols In Winter Of Nanjing

Air pollution, visibility degradation, and many other environmental problems have become increasingly significant and urgent with the advancement of urbanization. Haze is a particular phenomenon of visibility degradation.Characteristics of aerosol particle size distribution and extinction as well as the relationship between light extinction coefficient and aerosol mass concentration in haze days are analyzed so as to explore the characteristics and factors of visibility degradation.In this way, environmental problems in the urban region can be solved more properly.Aerosol concentration variation, aerosol scattering coefficient, black carbon mass concentration, NO2 volume concentration, PM2.5 mass concentration, visibility and meteorological data in January 2015 in Nanjing were analyzed. Log-normal distribution and other correlative nonlinear fitting methods were used in order to get the variation characteristics of aerosol particle size distribution,gaseous pollutants,scattering and absorption coefficients, meanwhile, aerosol scattering and absorption coefficients’ contribution to atmospheric extinction, relationship between visibility and aerosol number concentration, PM2.5 mass concentration and relative humidity were analyzed.The data of haze during the observation was classified and characteristics of low visibility were analyzed.Causes of visibility degradation in this observation can be summarized with methods presented above.The results indicated that aerosol particle number and volum concentration with diameter between 0.1 μm and 10.0 μm are (2784.2±937.6) cm-3 and (16.9±7.1)μm3/cm3. Diurnal variations of aerosol particle number concentrate and size distribution with 2 peaks at morning time and night were observed. Aerosol particle size distribution managed by log-normal method shows 4 geometric mean diameter of corresponding models which are 0.11 μm, 0.15 μm, 0.22 μm, 1.16 μm. The conclusion also indicates that particles in accumulation mode take a more contribution in particle size distribution. Aerosol scattering and absorption coefficients were (423.4±265.3) Mm-1 and (24.5±14.3) Mm-1, and their contribution to the atmospheric extinction were 89.2 % and 5.2 % respectively. The atmospheric extinction was mainly contributed to the aerosol scattering during observation period.The visibility decreased exponentially with particle number concentration and PM2.5 mass concentration, and showed a negative correlation with relative humidity. The mean visibility during the observation period was 4.3 km,and low visibility episodes(<2 km) frequently happened.Haze had a frequency of 83.3 % during the observation,aerosol particle number concentration, light extinction coefficient and PM2.5 mass concentration during haze episodes were evidently higher than those of non-haze periods with the highest values during haze episodes reached 6227.8 cm-3, 1471.2 Mm-1 and 358μg/m3 respectively,aerosol size distribution varied obviously in thses conditions. Local sources and particular weather conditions carry a significant impact on formation of haze. The visibility degradation was contributed to the influences of particles and relative humidity.