A Large Underestimate of Formic Acid from Tropical Fires: Constraints from Space-Borne Measurements
A Large Underestimate of Formic Acid from Tropical Fires: Constraints from Space-Borne Measurements
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DOI：
10.1021/acs.est.5b06385
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发表时间：
2016-06-07
影响因子：
11.4
通讯作者：
Shephard, M. W.
中科院分区：
文献类型：
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作者：
Chaliyakunnel, S.;Millet, D. B.;Shephard, M. W.
甲酸 (HCOOH) 是最丰富的羧酸之一，也是大气酸度的主要来源。最近的研究表明，HCOOH 预算存在重大缺口，大气浓度远高于已知来源的预期。在这里，我们利用对流层发射光谱仪最近的天基观测和 GEOS-Chem 大气模型来更好地量化生物质燃烧产生的 HCOOH 来源，并评估火灾排放是否有助于弥补该物种的巨大预算缺口。天基数据揭示了 HCOOH 模型严重低估了热带燃烧地区最突出的情况，表明火灾中有机酸的主要来源缺失。我们开发了一种方法来推断火灾对环境 HCOOH 的贡献分数，并根据对非洲的测量发现，热解 HCOOH:CO 增强比率远高于仅直接排放的预期，揭示了火羽流中产生了大量的二次有机酸。目前的模型严重低估（10 +/- 5 倍）非洲火灾的主要和次要 HCOOH 来源总量。如果将 10 倍偏差扩展到其他地区的火灾，则生物质燃烧在热带地区每年可产生 14 Tg/a 的 HCOOH，在全球范围内可产生 16 Tg/a。然而，即使这样的增加也仅占所需 HCOOH 来源总量的 15-20%，这意味着存在其他更大的缺失来源。
Formic acid (HCOOH) is one of the most abundant carboxylic acids and a dominant source of atmospheric acidity. Recent work indicates a major gap in the HCOOH budget, with atmospheric concentrations much larger than expected from known sources. Here, we employ recent space-based observations from the Tropospheric Emission Spectrometer with the GEOS-Chem atmospheric model to better quantify the HCOOH source from biomass burning, and assess whether fire emissions can help close the large budget gap for this species. The space-based data reveal a severe model HCOOH underestimate most prominent over tropical burning regions, suggesting a major missing source of organic acids from fires. We develop an approach for inferring the fractional fire contribution to ambient HCOOH and find, based on measurements over Africa, that pyrogenic HCOOH:CO enhancement ratios are much higher than expected from direct emissions alone, revealing substantial secondary organic acid production in fire plumes. Current models strongly underestimate (by 10 +/- 5 times) the total primary and secondary HCOOH source from African fires. If a 10-fold bias were to extend to fires in other regions, biomass burning could produce 14 Tg/a of HCOOH in the tropics or 16 Tg/a worldwide. However, even such an increase would only represent 15-20% of the total required HCOOH source, implying the existence of other larger missing sources.