Seasonal Variations Of Aerosol Optical Properties In Qingdao

Aerosol has much influence on the climate through direct and indirect ways, and has significant effect on atmospheric quality and humans'health. In order to study the atmospheric aerosol's environmental and climate effects, the volume size distribution of aerosol particles spectrum, chemical composition and optical properties of aerosol must be fully understood. In which the direct observation of atmospheric aerosol optical properties are regarded as the most urgent problem, because the results could be used to provide necessary parameters for estimating and forecasting model of aerosol radiation force on climate changing and aerosol's environmental effects. Lying on the south of Shandong peninsula and surrounded on three sides by the sea, Qingdao is the most important coastal cities, and it's the transition area of subtropical and temperate zones which has the characteristic of monsoon climate and ocean climate. Because of the unique geographical location and climate environment, atmospheric aerosol in Qingdao is commonly influenced by the continent and ocean. Therefore, study on the seasonal variations of aerosol optical properties in Qingdao has great significance on effects aerosol made on climate and environment of the land and sea border area.Based on the direct and scattered radiation data measured in 156 sunny days by Sky radiometer settled on the Baguanshan hill, Aerosol Optical Depth (AOD), Single Scattering Albedo (SSA), ?ngstr?m turbidity coefficient, wavelength index, complex refractive index and the volume size distribution in spring, summer, autumn and winter weather from April 2002 to December 2006 are calculated, and the seasonal variations of aerosol optical properties as well as the impact factors are discussed. The results show that seasonal variations of aerosol optical properties in Qingdao have some commonness: AOD increases with the decrease of wavelength, and a majority of values are smaller than 0.7. In addition, the diurnal variations are mostly lower in the morning and higher in the afternoon. The seasonal averaged SSA shows strong scattering effect, and it has obvious positive correlation with relative humidity. Seasonal variations of the real and imaginary part of complex refractive index are not very evident, and they are approximately considered fixed with the change of wavelength according to the MIE scattering theory. Seasonal averaged complex index is m~ = 1.51?0.01i. Under the Aitken nuclei mode, the volume size distribution in every season rapidly grows with size increase and achieves the first peak value during 0.1-0.3μm under the accumulation mode. AOD and visibilities have opposite change trend. When AOD at 500nm wave band is lager than 1.0 or smaller than 0.5, visibilities are below 10.0km or above 10.0km, respectively. The negative relationship between relative humidity and visibilities is apparent at eight and fourteen o'clock in four seasons.The results indicate that seasonal variations of aerosol optical properties have more differences: In spring, diurnal variation styles are rich and daily mean AOD ranges from 0.3 to 0.5 under most weather. Influenced by dust and transport of continent pollutions, seasonal averaged AOD is lager than other seasons except the value of June. Seasonal averaged SSA has decreasing trend with the increase of wavelength, and SSA at 500nm wave band is 0.909 which is nearly equal to summer and winter's value. Seasonal averaged turbidity coefficient is the biggest in four seasons, and the frequency peak of daily mean values occurs between 0.2 and 0.3. Seasonal mean wavelength index is smaller than any other season with value of 0.862, and not a few of values are between 1.1 and 1.2, or between 0.8 and 0.9. In addition, dimensions of particles are various. Seasonal mean real part of complex refractive index is bigger than summer and autumn, yet smaller than winter. In the meanwhile, the imaginary part is the smallest in four seasons. Volume size distribution presents three peaks besides the first peak is lower than the second and third. The result shows that, fine and coarse mode particles are richer than the accumulation mode with the influence of local or external dust. Under the dust weather, peaks of volume size distribution under accumulation mode shift to the lager particle size as well as the content of fine and coarse mode particles increases. These two factors make lager AOD and smaller wavelength index.Except one day of July, the other 13 days'data are all of June, so the summer result mostly reflects monthly mean result of June. The AOD and wavelength index maximum are caused by a build-up of pollutant aerosol in the coast, the secondary aerosol formation by gas-to-particle conversion, hygroscopic growth of hydrophilic aerosols in the lower troposphere and the frequent occurrence of biomass burning emissions in eastern coastal regions of China, and daily mean AOD ranges from 0.5 to 0.7. SSA at 500nm wave band is 0.910. ?ngstr?m turbidity coefficient is about 0.2 ~0.4 which is smaller than spring and daily mean wavelength ranges from 1.1 to 1.6. The real part of complex refractive index is the smallest in the four seasons, and the imaginary part is just smaller than autumn. Volume size distribution presents three peaks besides the first peak is higher than the second and third. It indicates that the accumulation mode particles are more than fine mode and coarse mode particles.The air is clean in autumn and winter, and the seasonal averaged AOD is smaller than spring and summer. Daily mean AOD is lower than 0.7, and most values are smaller than 0.3. Seasonal averaged SSA is the lowest in four seasons with the value of 0.886, and the aerosol particles have lower scattering ability than the other seasons. Most of the ?ngstr?m turbidity coefficient is lower than 0.2, and wavelength index is always between 1.3 and 1.4. The real part of complex refractive index is smaller than spring and winter, yet the imaginary part is the biggest in all seasons. The characteristic of volume size distribution is some like summer.The seasonal mean AOD is the smallest in winter, and daily mean values are almost lower than 0.5 as well as the ?ngstr?m turbidity coefficient with most values lower than 0.2. SSA at 500nm wave band has the value equal to spring and summer. The same as autumn, seasonal mean wavelength is almost between 1.3 and 1.4. The fact that real part of complex refractive is bigger than summer and autumn, yet imaginary part smaller than those two seasons indicates that the scattering ability of winter is stronger than summer and autumn. Volume size distribution presents two peaks besides the first peak is lower than the second. It shows that fine and coarse mode particles are richer than the accumulation mode, and this may have some relation with the fuel burning such as coal in winter.