Airborne aerosols over central Africa during the Experiment for Regional Sources and Sinks of Oxidants (EXPRESSO)
Airborne aerosols over central Africa during the Experiment for Regional Sources and Sinks of Oxidants (EXPRESSO)
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DOI：
10.1029/1999jd900804
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发表时间：
1999-12
影响因子：
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通讯作者：
S. Ruellan;H. Cachier;A. Gaudichet;P. Masclet;J. Lacaux
中科院分区：
文献类型：
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作者：
S. Ruellan;H. Cachier;A. Gaudichet;P. Masclet;J. Lacaux
作为1996年11月在非洲中部进行的区域氧化剂源和汇实验的一部分，获得了24个气溶胶样品，并进一步分析了黑碳和有机碳（BC和OC）、水溶性有机碳（WSOC）、多环芳烃（PAH）、可溶性离子、元素组成和形态。粒子收集在不同的大气层以上的热带森林或热带辐合带附近的非洲中部的稀树草原。发现所有大气层中的粒子数浓度（直径10- 14，000纳米）都很高（3，100 ± 2，060 cm−3，n = 24）。土壤来源的颗粒物比预期的要少（20±18 μg m−3，n = 21），它们的存在主要被评估为火灾的再次夹带。另一方面，热解颗粒丰富，在森林边界层（3.8±2.3 μg m−3，n = 6）、稀树草原边界层（9.8±3.9 μg m − 3，n = 6）或Harmattan层（8.7±1.6 μg m −3，n = 3）中发现了高水平的黑碳（BC）浓度。其他火灾示踪剂（如钾，草酸盐，或多环芳烃）证实了热带草原火灾在区域对流层的压倒性影响。另一个结果是，不同层之间和通过热带对流带可能发生垂直和水平交换。在我们的样品中测量的WSOC平均占总颗粒有机碳的46±9%（n = 11）。在Harmartan层中发现了高值，其中平均WSOC占总颗粒有机碳的85± 18%（n = 3），指出生物质燃烧颗粒作为云凝结核（CCN）的潜力。使用不同的化学指标，产生收敛的信息，生物质燃烧颗粒的老化。在这些指标中，发现WSOC/OC的比率从地面到Harmartan层增加了2至3倍。这项工作的一个产品也是高浓度的有机酸（甲酸盐，乙酸盐，草酸盐）在森林边界层的存在，这表明这些化合物的一个强大的生物源。最后，在EXPRESSO实验，这发生在旱季开始时，热带草原火灾盛行在区域范围内，而灰尘输入哈麦丹气流仍然很低。我们的研究结果表明，在这些条件下，硝酸盐主要保持在气相中，因此氮营养物质的转运仅限于该地区。
As part of the Experiment for Regional Sources and Sinks of Oxidants (EXPRESSO) conducted over central Africa in November 1996, 24 airborne aerosol samples were obtained and further analyzed for black and organic carbon (BC and OC), water-soluble organic carbon (WSOC), polycyclic aromatic hydrocarbons (PAHs), soluble ions, elemental composition, and morphology. Particles were collected in the different atmospheric layers either above the tropical forest or the savanna of central Africa near the Intertropical Convergence Zone. Particle number concentrations (10–14,000 nm diameter) were found to be high in all atmospheric layers (3100±2060 cm−3, n = 24). Soil-derived particles were less abundant than expected (20±18 μg m−3, n = 21), and their presence was assessed mainly to reentrainment by fires. On the other hand, pyrogenic particles were abundant, and high levels of black carbon (BC) concentrations were found either in the forest boundary layer (3.8±2.3 μg m−3, n = 6), the savanna boundary layer (9.8±3.9 μg m−3, n = 6), or in the Harmattan layer (8.7±1.6 μg m−3, n = 3). Other fire tracers (such as K, oxalate, or PAHs) confirmed the overwhelming impact of savanna fires in the regional troposphere. Another result is the possible occurrence of vertical and horizontal exchanges between the different layers and through the ITCZ. WSOC was measured in our samples representing on average 46±9% (n = 11) of the total particulate organic carbon. High values were found in the Harmattan layer, where on average WSOC accounts for 85±18%, (n = 3) of the total particulate organic carbon, pointing out the potential of biomass burning particles to act as cloud condensation nuclei (CCN). Different chemical indicators were used, which produce convergent information on the aging of biomass burning particles. Among these indicators, the ratio WSOC/OC was found to increase by a factor of 2 to 3 from the ground to the Harmattan layer. A product of this work is also the presence of high concentrations of organic acids (formate, acetate, and also oxalate) in the forest boundary layer suggesting a strong biogenic source for these compounds. Finally, during the EXPRESSO experiment, which took place at the beginning of the dry season, savanna fires were prevailing at a regional scale, whereas dust inputs by Harmattan airflow were still low. Our results suggest that in these conditions nitrate primarily remains in the gaseous phase, and thus the translocation of nitrogen nutrients is confined to the region.