Airborne Measurements of Optical Properties of Tropospheric Aerosols over an Urban Area

摘要

Aircraft measurements of aerosol sizes, intensities of direct-solar and circumsolar (aureole) radiations, and upward and downward fluxes of solar radiation were carried out over Nagoya, a typical urban area in Japan, using an optical particle counter, an aureolemeter and spectral pyranometers, respectively. Vertical profiles of optical thicknesses and volume spectra of aerosols have been successfully retrieved by inverting measured aureole intensities. The obtained values have been utilized to estimate the absorption indices of aerosols from the downward flux measurements. The results are summarized as follows:1) The concentration and the vertical stratification of tropospheric aerosols vary considerably day by day.2) Bimodal volume spectra of aerosols with radii smaller and larger than r∼0.5μm generally prevail in the troposphere. The former is more predominant than the latter in the haze layer, and viceversa above that layer.3) Estimated values of the imaginary index of refraction of tropospheric columnar aerosols are within the range of 0.005∼0.014 in the visible region and 0.008∼0.020 in the near infrared region. Corresponding values for the haze layer are slightly larger, i. e. 0.007∼0.018 and 0.011∼0.028 in the visible and near infrared regions, respectively.