Effects of local pollution and environmental humidity on aerosol-size spectra and light-scattering coefficients in southern Taiwan

Atmospheric aerosols were intensively studied in Tainan in southern Taiwan from February to March 1995. The time-series data showed that variations of hourly aerosol light-scattering coefficients (sigma(scat)) and aerosol volume concentrations were consistent with a squared correlation coefficient at 0.87. For comparisons with the measured sigma(scat), the aerosol light-scattering coefficient was calculated (sigma(scat, c)) using the Mie theory and aerosol size spectra. A linear regression analysis showed that the squared correlation coefficient between sigma(scat, c) and sigma(scat) was at 0.89. During the study period, certain events were observed which might result from variations of either meteorology or source emissions. The morning fog was found to have the most progressive growth in the range of 0.8 to 0.9 mu m, with a minor contribution from a size interval of 1 to 2 mu m. In contrast, other activities showed the most progressive size interval was from 0.35 to 0.6 mu m. In this study, two cases affected predominantly by the variations in relative humidity (RH) were chosen to investigate the sigma(scat, c) across aerosol sizes. In an ascending RH environment, the sigma(scat) increased from 0.35 to 0.50 km(-1) with an increasing sigma(scat, c) in the range from 0.2 to 0.9 mu m. For a descending RH environment, the sigma(scat) reduced from 0.75 to 0.14 km(-1) with a significant reduction in sigma(scat, c) for the range from 0.45 to 2.0 mu m. (C) 1999 Elsevier Science Ltd.