Measurement and analysis of atmospheric aerosol optical thickness and Angstrom exponent of 1998-2000 over the Beijing area

Abstract

The quasi-continuous measurements of direct solar and sky scattered spectrum over Beijing have been conducted since September 1998 with an automatic moderate resolution solar spectroradiometer (MORSAS) developed by the Institute of Atmospheric Physics, Chinese Academy of Sciences. The measurements of direct solar spectrum under cloud free conditions, including clear and turbid skies, were used to derive atmospheric aerosol optical thickness. During the period of Asian-Pacific Regional Aerosol Characterization Experiment (ACE-Asia) in spring 2001, a spectral radiometer CIMEL CE-318 in AERONET (owned by US NASA/GSFC) was operated at the same time and the same place with MORSAS. Comparing the observed results from the two instruments, they are consistent with each other. In this paper we present the variation of atmospheric aerosol optical thickness and Angstrom exponent which symbolizes the width of particle spectrum in Beijing during recent three years. In contrast with the middle of 1990’s, the atmospheric aerosol optical thickness in autumn and winter in recent years decreased slightly, indicating that Beijing air quality has been improved by certain local environmental management, whereas in spring in the latest 2 years the atmospheric aerosol optical thickness has evidently increased as the increase of the dust weather events, and the Angstrom exponent tends to be lower. This reveals that the ratio of larger particles especially the large dust-sand particles in the air has increased. So it is very important to enhance dust source management for those upstream and local arid and semi-arid regions.