Clear Air Aerosol Microphysics Features in the Lower Troposphere in Beijing

Clear air aerosol number concentration and its number/size spectrum distribution in the lower troposphere were observed by a airborne instruments in Beijing etc. during April—July in 1982. Results show that the aerosol number concentration of the air coming from west, northwest and north are rather low (10-1—100cm-3 on the average). The number/size distribution has been fitted by =C/DA, with the correlation significance level α≤0.01, most exponential A values are less than 3. Because of the importance of the diameter 0.5 to 2μm particles in the atmosphere, its number/size distribution has also been by =C/DB. It is found that the correlation significance level isα≤0.01 for the most observations, andα≤0.05 for a small parts. The values of A, B and smaller particles (0.5≤D≤1μm) relative number concentration f1 are fairly uniform and steady both is horizontal and vertical direction. When effected by city, the aerosol number concentration in the mixing layer increase evidently, the number/size spectrum distribution is steeper and especially for the smaller particles (D~1μm) the concentration is very remarkable, therefore city effect is a important cause for high aerosol concentration, steep number/size distribution, strong local air pollution and low visibility in mixing layer