The Mechanism Analysis Of Atmospheric Aerosol Affecting Visibility In Tianjin Region

Using2009-2011observation data of visibility, aerosol mass and number concentrations, the aerosol scattering and absorption properties and number concentration spectrum distribution feature are analyzed. In addition, aerosol complex refractive index is calculated taking use of Mie theory. The major influencing factors of atmospheric visibility in Tianjin and their contribution rates on extinction are analyzed. Then the major influencing factors are determined. We eventually established an atmospheric visibility forecast model based on this basis. The results indicated that the mean atmospheric visibility in Tianjin is11.12km with the minimum value in summer and maximum value in winter. The diurnal variation of visibility shows single-peak distribution. The average scattering coefficient and absorption coefficient is0.485km-1and0.0489km-1, respectively. Spectrum distribution of aerosol number concentration fits well with Junge-spectrum distribution and the correlation coefficients between the observation and formula is0.988. The number concentration of fine particles that smaller than1μm is highest in winter and lowest in spring. And the number concentration of particles larger than1μm has minimum value in summer and small variation among other seasons. The equivalent complex refractive index of aerosol at0.55μm wave length in Tianjin urban is calculated using Mie theory and of the result is1.649-0.0257i. Tianjin urban aerosol contributes95%to the extinction, while scattering accounts for86%and absorption accounts for9%respectively. The contribution in scattering of small particles is far larger than large particles. Aerosol particles smaller than0.5μm have the largest contribution on scattering coefficient which is about75%. The spectrum distribution of scattering coefficient contribution rate show single-peak distribution and the peak shows around0.4μm. Both of particles smaller than1μm and large particles are important to the absorption. The spectrum distribution of absorption show multi-peak distribution and the peaks occur around0.4μm、4μm、9μm and20μm.The analysis of the atmospheric visibility and its influencing factors in2009shows that, When RH is lower than60%, there is significant nonlinear correlation between concentration of PM2.5and the visibility, then is the correlation between concentration of PMio and the visibility, the correlation between the concentration of PM10minus PM2.5and the visibility is the worst of all. Whereas when RH is greater than60%, the nonlinear correlation between the concentration of PM10and the visibility is the better, then is the correlation between PM2.5and the visibility. The nonlinear correlation coefficients between RH and the visibility are higher than their corresponding linear correlation coefficients. Using the atmospheric visibility data from2009to2011and conventional meteorological elements such as temperature, relative humidity, pressure and wind speed, the visibility forecast formula is fitted, which indicate that meteorological parameters can better forecast atmospheric visibility.