Optical properties of haze in Seoul using ground-based and satellite observations

To define the quantitative optical properties of haze in Seoul, we made use the ground-based (skyradiometer) and satellite (MODIS, CALIPSO) observation data. Aerosol optical thickness (AOT), Angström exponent (Alpha), and volume-size distribution were retrieved at five spectral channels of skyradiometer. And fine mode fraction (FMF) and vertical profile of aerosol layer were obtained from MODIS and CALIPSO products. AOT500nm in haze was 0.80±0.32 while this on clear day was 0.20±0.15. On the other hands, Alpha was found to be little different value both in haze and on clear day, 1.00±0.36 and 1.04±0.35, respectively. The volume size distribution show a general bimodal behavior with two peaks, called as fine mode and coarse mode. In haze, the maximum value of fine mode increased, but the maximum value of coarse mode slightly decreased in comparison with these on clear day. Moreover, FMF retrieved from MODIS was found to be 0.59±0.13 and large value not only in Seoul but also in the Korean peninsula and Eastern region of China. The particle-size information clearly proves that small size particles are dominant in haze. In CALIPOSO-derived aerosol layer profile, much of aerosol layers of haze are located below altitude of 2km in troposphere. It is because anthropogenic fine particles are emitted near the surface by human activities.