| dc.description.abstract | Because the discriminations of aerosol’s chemical components, size distributions and morphology, optical variations of aerosols would influence solar radiation emitted on earth and further the climate change. In this thesis, aerosol size distribution and scattering coefficient datas continually monitored in Taiwan supersite sited in HSIN-CHUANG from March to September in 2002 and Air quality datas monitored synchronously in another site nearby setup by Taiwan Environmental Protection Agency was chosen to be analyzed particularly for aerosols’ optical effects.
Analysis revealed that aerosol scattering coefficient was highly positive- correlated(R2>0.80) with relative humidity from 14:00pm to 23:00pm and contribution of backward scattering coefficient in total scattering coefficient was reduced at the same period. When scattering coefficient was well correlated(R2>0.75) with relative humidity, it was also found that scattering coefficient was highly positive-correlated with concentration of nitrate, carbon monoxide, ozone and nitrogen dioxide. Beside, backward scattering coefficient was positive-correlated with variation of aerosol concentration. Aerosol concentration was very sensitive with variation of relative humidity especially with particle size within 0.1～0.5μm.
Detail analysis of episodes happened from March to September in 2002 has discovered that during the period of the second event of Yellow Dusts influencing Taiwan area, backward scattering of aerosols induced by different wave length light contributed total scattering convergently. It was observed that backward scattering contributed to total scattering induced by red light vary in small amplitude at some periods in that episode. Aerosol volume concentration was mainly due to particle size with 2.5～10μm during the period of Yellow Dusts.
From the regression of organic carbon(OC) and elemental carbon(EC) concentration monitored from 7:00am to 9:00am(the period of aerosol absorption effect contributed scattering effect most), it was found that OC/EC=2(R2=0.83) which represented that there existed secondly organic aerosol when OC/EC＞2. Also the regression of green light scattering coefficient and chemical components was formulated as
TG(Mm-1)=16Sulfate(μgm-3)+ 16Nitrate(μgm-3)+ 6Organic carbon(μgm-3)-14.
It was found the formula above could explain about 80% variations of scattering coefficient datas.
In HSIN-CHUANG area, scattering coefficient in spring was higher than that in summer. There was seasonal variations in the ratios of backward scattering to total scattering. The ratio was higher in summer than that in spring. Instead, it was not found that absorption coefficient varied seasonally.
By evaluating the radiative forcing, the critical single scattering albedo in HSIN-CHUANG area was about 0.82. It was obviously observed that the scattering rates varied seasonally. When aerosol scattering coefficient was above 99Mm-1, the existence of aerosols suspended would cool the atmospheric radiation. | en_US |