Characterization of the optical properties of biomass burning aerosols in Zambia during the 1997 ZIBBEE field campaign
Characterization of the optical properties of biomass burning aerosols in Zambia during the 1997 ZIBBEE field campaign
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DOI：
10.1029/2000jd900555
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发表时间：
2001-02
影响因子：
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通讯作者：
T. Eck;B. Holben;D. Ward;O. Dubovik;J. Reid;A. Smirnov;M. Mukelabai;N. C. Hsu;N. O'Neill;I. Slutsker
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文献类型：
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作者：
T. Eck;B. Holben;D. Ward;O. Dubovik;J. Reid;A. Smirnov;M. Mukelabai;N. C. Hsu;N. O'Neill;I. Slutsker
1997年8 - 9月在赞比亚国际生物质燃烧排放实验（ZIBBEE）期间进行的测量，生物质燃烧气溶胶在中南非洲（赞比亚）的热带草原地区的物理和光学特性进行了分析。由于非洲稀树草原的空间范围大，每年旱季发生燃烧的频率高，因此，表征生物质燃烧气溶胶的光学特性对于研究这些地区的大气辐射过程和遥感地表和大气特性非常重要。气溶胶机器人网络利用太阳天空辐射计对太阳直接观测和定向天空辐射的光谱测量来推断光谱气溶胶光学厚度（τa）、气溶胶尺寸分布和单次散射散射。在ZIBBEE的主要研究期间，这与该地区的生物质燃烧的高峰期相吻合，有一个高度的相关性和总柱水蒸气或可降水量（PWV），这表明烟雾气溶胶的输送从具有较高的PWV的区域。尺寸分布检索的生物质燃烧烟雾显示，积累模式占主导地位，并与亚马逊（玻利维亚）的烟雾比较显示，向更小的颗粒，非洲稀树草原烟雾的转变。这可能是燃烧方式（燃烧与阴燃）、燃料类型和水分含量以及气溶胶老化过程差异的结果。用几种方法反演了气溶胶的单次散射ω0，得到了ZIBBEE期间在λ 550 nm处ω0的平均值，范围为λ 0.82 ~ λ 0.85，因此在这些方法的反演不确定度λ 0.03内显示出良好的一致性。一般来说，ω0相对恒定，是气溶胶负载的函数，440 nm处的τa变化很小，范围为0.7至1.7。非洲热带稀树草原的烟雾比亚马逊森林地区的烟雾具有更高的吸收率，并且ω0随波长的增加而降低的速率也更大。埃波长指数的光谱变化的变化也进行了研究相对于气溶胶吸收的程度和积累模式的尺寸分布的变化。
The physical and optical properties of biomass burning aerosols in a savanna region in south central Africa (Zambia) were analyzed from measurements made during the Zambian International Biomass Burning Emissions Experiment (ZIBBEE) during August-September 1997. Due to the large spatial extent of African savannas and the high frequency of occurrence of burning in the annual dry seasons, characterization of the optical properties of the resultant biomass burning aerosols is important for the study of atmospheric radiative processes and for remote sensing of both surface and atmospheric properties in these regions. Aerosol Robotic Network Sun-sky radiometer spectral measurements of direct Sun observations and directional sky radiances were utilized to infer spectral aerosol optical depths (τa), aerosol size distributions, and single-scattering albedos. During the primary ZIBBEE study period, which coincided with the peak period of biomass burning in the region, there was a high correlation between the measured τa and the total column water vapor or precipitable water vapor (PWV), suggesting transport of smoke aerosol from regions with higher PWV. Size distribution retrievals of the biomass burning smoke show that the accumulation mode dominated and a comparison with smoke from Amazonia (Bolivia) shows a shift toward smaller particles for African savanna smoke. This may be the result of differences in mode of combustion (flaming versus smoldering), fuel type and moisture content, and the aging processes of the aerosol. The single-scattering albedo (ω0) of the aerosols were retrieved using several approaches, yielding average values of ω0 at ∼550 nm during ZIBBEE varying from ∼0.82 to ∼0.85, thus showing good agreement within the retrieval uncertainty of ∼0.03 of these methods. In general, ω0 was relatively constant as a function of aerosol loading, with very little change occurring for τa at 440 nm ranging from 0.7 to 1.7. African savanna smoke exhibits significantly higher absorption than smoke from Amazonian forested regions and also a greater rate of decrease of ω0 with increasing wavelength. Variations in the spectral change of the Angstrom wavelength exponent were also investigated with respect to the degree of aerosol absorption and changes in the accumulation mode size distributions.