Aerosol optical properties and direct radiative effect over Gobabeb, Namibia

Clean Air Journal

article

Joseph A. Adesina¹  Stuart J. Piketh¹  Paola Formenti²  Gillian Maggs-Kölling³  Brent N. Holben⁴  Mikhail G. Sorokin⁵ 

[1] School of Geo- and Spatial Science, Unit for Env. Sc. and Management, North-West University;Laboratoire Interuniversitaire des Systèmes Atmosphériques, Universités Paris-Est- Créteil andParis Diderot, Institut Pierre Simon Laplace;Gobabeb Research and Training Centre;Laboratory for Terrestrial Physics, NASA Goddard Space Flight Center;Science Systems and applications Inc. NASA Goddard Space Flight Center

关键词: Aerosol Optical Depth;    Volume Size Distribution;    Radiative Forcing;    Single Scattering Albedo;    MODIS;   

DOI  :  10.17159/caj/2019/29/2.7518

学科分类：土木及结构工程学

来源: National Association for Clean Air

【 摘 要 】

Atmospheric aerosols contribute significantly to the uncertainty in radiative forcing effects that influence the climate as well as posing a significant health risk to humans. The climatic implications of aerosols are dependent on many variables, including aerosol size, shape, chemical composition, and position in the atmospheric column. The radiative impact of aerosols transported over the west coast of southern Africa has been found, in particular, to be complicated by the aforementioned aerosol properties. This study investigated the columnar optical properties of aerosols over Gobabeb, Namibia (23.5621° S, 15.0409° E, 405 m asl) using sunphotometer data between December 2014 and November 2015. Aerosol mean optical depth AOD500 had its maximum and minimum values in 2015 August (0.37±0.30) and June (0.06±0.02), respectively. The Angström parameter was mostly above unity during the study period and indicated the prevalence of fine particles for the most part of the year with maximum and minimum values observed in August 2015 (1.44±0.19) and December 2014 (0.57±0.19), respectively. The columnar water vapor was highest in January (2.62±0.79) and lowest in June (0.76±0.27). The volume size distribution showed the fine particles having a mean radius of about 0.16 µm and the coarse mode had variation in sizes with a radius ranging between 3 µm and 7 µm. The single scattering albedo at visible wavelengths ranged between 0.83 and 0.91. The phase function was high at small angles but minimum at about 140° in all seasons. The radiative forcing showed a heating effect in all seasons with maximum and minimum in winter (9.41 Wm-2) and autumn (3.64 Wm-2), respectively. Intercomparison of the sunphotometer data with the Moderate Resolution Imaging Spectroradiometer (MODIS) showed that the satellite sensor overestimates the aerosol loading compared to the ground-based sunphotometer measurements. Both sets of observations were better correlated during the spring and winter seasons than for the summer and autumn.

【 授权许可】

CC BY