Comparison of aerosol optical properties derived from radiometer data and direct measurement

Description

Aerosol optical properties are an important of the earth’s climate system and have an important effect on the earth’s radiation budget. In order to estimate the effect of aerosols on the earth’s surface radiation budget, JMA Meteorological Research Institute has continuously measured aerosol optical properties on ground based-measurement. Scattering and Absorption coefficients were measured directly using an integrating nephelometer (TSI model 3563) and a particle Soot/Absorption Photometer (PSAP3L). Aerosol optical properties were also retrieved from the radiometer data; a sky-radiometer (Prede POM-02), and direct and diffuse irradiance. In this study, we compared trend and seasonal variation of aerosol optical properties derived from direct measurement data and those derived from the radiometer data. The trend of aerosol optical thickness (AOT) from the sky-radiometer was the same trends of extinction coefficient (Cext) from the nephelometer and PSAP3L; AOT and Cext have decreasing trend. The trend of single scattering albedo (SSA) from the sky-radiometer was the same trend of SSA from the nephelometer and PSAP3L; SSA has increasing trend. These trends were significant in the confidence level 95%. Seasonal variation of AOT from the radiometers data had maximum value in summer. However, extinction coefficient from the nephelometer and PSAP3L did not show the clear seasonal variation and had maximum value in winter; this maximum value was caused by the accumulated aerosol particle in the temperature inversion layer. The seasonal variation of SSA from both the direct measurement and the retrieved one shows that SSA was high in summer and low in winter. There was a tendency that SSA (sky-radiometer) > SSA(nephelometer+PSAP3L) > SSA( direct and diffuse irradiance data). Ångström exponent from the radiometer data (sky-radiometer and irradiance data) was low in spring. However, Ångström exponent from nephelometer and PSAP3L did not have clear seasonal variation. Roughly speaking, though there were some differences, the trend and seasonal variation of aerosol characteristics estimated from direct measurement data were consistent with those derived from radiometer data.