Relations between optically derived aerosol parameters, humidity, and air-quality data in an urban atmosphere

Abstract

Multiwavelength correlation analysis between aerosol optical depth and precipitable water indicators (surface vapor pressure or vertically integrated precipitable water) yielded a systematic, inverse-wavelength type of dependency in the extracted slopes (apparent attenuation coefficients) that was suggestive of a simple correlation between precipitable water and the accumulation-mode number density of the aerosols. On a diurnal basis, increasing trends in aerosol optical depth were negatively correlated with surface relative humidity and thus resulted either from variations in the nature or abundance of dry aerosol or possibly from convection-induced increases in relative humidity at higher altitudes in the aerosol scattering layer. The diurnal trend in aerosol optical depth plus the limited correlation between surface volume extinction coefficients derived from visibility measurements and relative humidity indicated that the aerosol optical scale height, on a diurnal basis, varied in an inverse fashion with surface relative humidity. -from Authors