Transformation and ageing of biomass burning carbonaceous aerosol over tropical South America from aircraft in situ measurements during SAMBBA
Transformation and ageing of biomass burning carbonaceous aerosol over tropical South America from aircraft in situ measurements during SAMBBA
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DOI：
10.5194/acp-20-5309-2020
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发表时间：
2019-02
影响因子：
6.3
通讯作者：
W. Morgan;J. Allan;S. Bauguitte;E. Darbyshire;M. Flynn;James D. Lee;Dantong Liu;B. Johnson
中科院分区：
文献类型：
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作者：
W. Morgan;J. Allan;S. Bauguitte;E. Darbyshire;M. Flynn;James D. Lee;Dantong Liu;B. Johnson
抽象。我们提出了一系列的空中原位观测的生物质燃烧的含碳气溶胶在热带南美洲，包括一个大型的热带森林野火和一系列的区域调查飞行横跨巴西亚马逊和塞拉多的案例研究。该研究是2012年9月至10月期间进行的南美生物质燃烧分析（SAMBBA）项目的一部分。我们发现有限的证据表明，通过大气老化结合有机气溶胶（OA）的化学性质的重大变化，气溶胶质量的净增加。根据我们的案例研究分析，OA的氧化在2.5-3小时的范围内显着且快速增加，并且与二次有机气溶胶的产生一致。观察到OA的净增加有限，再加上化学成分的这种变化，意味着OA的蒸发也在发生，以平衡这些变化。我们观察到显着的涂层黑碳颗粒在源，但随着老化的颗粒核心尺寸和涂层厚度的变化有限。我们量化的变化在我们的研究中的OA与一氧化碳的比例作为一个关键参数，代表初始火灾条件和净气溶胶产生与大气老化的指标。我们在研究区域西部的亚马逊热带森林中观察到0.075-0.13 µgsm-3 ppbv-1的比值，受降水影响较小，在东部的塞拉多环境中观察到0.095 µgsm-3 ppbv-1的值（其中sm-3是指标准立方米）。这些数值与数值模型用来代表生物质燃烧有机酸排放的排放系数是一致的。黑碳颗粒核尺寸通常在250至290 nm的平均质量直径范围内，而在受沉淀影响较小的空气质量中，涂层厚度在40至110 nm范围内。我们观察到的变异性的主要驱动因素似乎与初始火源的变化有关。从我们的研究中得到的一个关键教训是，由于区域气溶胶及其驱动因素的复杂性，由于存在许多合并和竞争因素，简单地将我们的观测结果汇总为大气老化的函数会产生误导。我们的研究探讨和量化的关键不确定性，在近场和区域尺度的生物质燃烧气溶胶的演变。我们的研究结果表明，除了大气老化过程中OA的显着氧化外，火灾的初始条件是南美洲热带地区碳质气溶胶物理和化学性质的主要驱动因素。这些研究结果意味着，气溶胶负担的大小及其对天气、气候、健康和自然生态系统的影响的不确定性很可能在于量化排放源，以及大气扩散、迁移和清除，而不是化学物质的质量增强。
Abstract. We present a range of airborne in situ observations of biomass burning carbonaceous aerosol over tropical South America, including a case study of a large tropical forest wildfire and a series of regional survey flights across the Brazilian Amazon and Cerrado. The study forms part of the South American Biomass Burning Analysis (SAMBBA) project, which was conducted during September and October 2012. We find limited evidence for net increases in aerosol mass through atmospheric ageing combined with substantial changes in the chemical properties of organic aerosol (OA). Oxidation of the OA increases significantly and rapidly on the scale of 2.5–3 h based on our case study analysis and is consistent with secondary organic aerosol production. The observations of limited net enhancement in OA coupled with such changes in chemical composition imply that evaporation of OA is also occurring to balance these changes. We observe significant coatings on black carbon particles at source, but with limited changes with ageing in both particle core size and coating thickness. We quantify variability in the ratio of OA to carbon monoxide across our study as a key parameter representing both initial fire conditions and an indicator of net aerosol production with atmospheric ageing. We observe ratios of 0.075–0.13 µgsm-3ppbv-1 in the west of our study region over the Amazon tropical forest in air masses less influenced by precipitation and a value of 0.095 µgsm-3ppbv-1 over the Cerrado environment in the east (where sm−3 refers to standard metre cubed). Such values are consistent with emission factors used by numerical models to represent biomass burning OA emissions. Black carbon particle core sizes typically range from mean mass diameters of 250 to 290 nm, while coating thicknesses range from 40 to 110 nm in air masses less influenced by precipitation. The primary driver of the variability we observe appears to be related to changes at the initial fire source. A key lesson from our study is that simply aggregating our observations as a function of atmospheric ageing would have been misleading due to the complex nature of the regional aerosol and its drivers, due to the many conflating and competing factors that are present. Our study explores and quantifies key uncertainties in the evolution of biomass burning aerosol at both near-field and regional scales. Our results suggest that the initial conditions of the fire are the primary driver of carbonaceous aerosol physical and chemical properties over tropical South America, aside from significant oxidation of OA during atmospheric ageing. Such findings imply that uncertainties in the magnitude of the aerosol burden and its impact on weather, climate, health and natural ecosystems most likely lie in quantifying emission sources, alongside atmospheric dispersion, transport and removal rather than chemical enhancements in mass.