<title>Aerosol optical depth and its seasonal variations in Kwangju</title>

Abstract

The seasonal variation of aerosol optical depth have been studied using solar radiation data from the multi-filter rotating shadow-band radiometer (MFRSR) from July 1998 to July 2000 in Kwangju, Korea. The MFRSR is a ground-based instrument that measures the global and diffuse components of solar irradiance at seven wavelengths, 415, 500, 610, 665, 862, 940 and total band. The channels were used to measure aerosol optical depth (AOD) except 940 nm. Langley plot of the natural log of the direct irradiance versus air mass was used to determine optical depth from the slope and the solar irradiance at the top of the atmosphere at each wavelength. The variation of total atmospheric optical depth (TOD) shows seasonal characteristics with maxima in spring and winter and minima in summer. Aerosol optical depth (AOD) was determined by subtracting the effects of molecular scattering and absorption by ozone and water vapor from the TOD. Angstrom coefficient was also determined from the slope of aerosol optical depth spectra. The annual value of aerosol optical depth varied from 0.02 to 0.87 at a wavelength 672 nm during the measurement period. In spring the AOD values were affected by long range transport aerosol from China. Increased local anthropogenic aerosols in the region have also significantly affected the AOD value in fall.