干旱区生态环境知识资源中心

Aerosol optical properties over a southern sub-tropical site Skukuza, South Africa were studied to determine the variability of the aerosol characteristics using CIMEL Sunphotometer data as part of the AErosol RObotic NETwork (AERONET) from December 2005 to November 2006. Aerosol optical depth (ACID), Angstrom exponent (alpha), and columnar water vapor (CWV) data were collected, analyzed, and compiled. Participating in this network provided a unique opportunity for understanding the sources of aerosols affecting the atmosphere of South Africa (SA) and the regional radiation budget. The meteorological patterns significantly (p < 0.05) influenced the amount and size distribution of the aerosols. Results showed that seasonal variation of ADD at 500 nm (AOD(500)) over the observation site were characterized by low values (0.10-0.13) in autumn, moderate values (0.14-0.16) in summer and winter seasons, and high to very high values (0.18-0.40) during the spring, with an overall mean value of 0.18 +/- 0.12. Angstrom exponent alpha(440-870), varied from 0.5 to 2.89, with significant (p < 0.0001) seasonal variability. CWV showed a strong annual cycle with maximum values in the summer and autumn seasons. The relationship between AOD, Angstrom exponent (alpha), and CWV showed a strong dependence (p < 0.0001) of alpha on AOD and CWV, while there was no significant correlation between AOD and CWV. Investigation of the adequacy of the simple use of the spectral AOD and Angstrom exponent data was used in deriving the curvature (a(2)) showed to obtain information for determining the aerosol-particle size. The negative a(2) values are characterized by aerosol-size dominated by fine-mode (0.1-1 mu m), while the positive curvatures indicate abundance of coarse particles (>1 mu m). Trajectory cluster analyses revealed that the air masses during the autumn and winter seasons have longer advection pathways, passing over the ocean and continent. This is reflected in the aerosol properties that are derived from the ocean, desert, and anthropogenic activities that include biomass burning and industrial pollution. (C) 2013 Elsevier B.V. All rights reserved.