Biomass burning emission disturbances of isoprene oxidation in a tropical forest
Biomass burning emission disturbances of isoprene oxidation in a tropical forest
复制标题
DOI：
10.5194/acp-18-12715-2018
复制
发表时间：
2017-12
影响因子：
6.3
通讯作者：
F. Santos;K. Longo;A. Guenther;Saewung Kim;D. Gu;D. Oram;G. Forster;James D. Lee;J. Hopkins;J. Brito;S. Freitas
中科院分区：
文献类型：
--
作者：
F. Santos;K. Longo;A. Guenther;Saewung Kim;D. Gu;D. Oram;G. Forster;James D. Lee;J. Hopkins;J. Brito;S. Freitas
摘要。基于2012年9月南美生物质燃烧分析（SAMBBA）机载实验期间进行的微量气体测量，我们提出了巴西亚马逊雨林大气化学成分的表征。我们分析了主要的生物质燃烧排放示踪剂，即一氧化碳（CO）、氮氧化物（NOx）、臭氧（O3）、异戊二烯及其主要氧化产物甲基乙烯酮（MVK）、甲基丙烯醛（MACR）和异戊二烯羟基过氧化氢（ISOPOOH）。SAMBBA的重点主要是生物质燃烧排放，但也有几次飞行在亚马逊森林没有直接受到生物质燃烧影响的地区，揭示了由于非洲和亚马逊东部的生物质燃烧示踪剂的远距离运输，在化学成分中具有生物质燃烧特征的背景。采用[MVK + MACR + isoopooh]∕[异戊二烯]比值和羟基自由基（OH）间接计算法评价了亚马逊森林大气的氧化能力。我们比较了背景区域（CO < 150ppbv）、根据光化学年龄（[O3]∕[CO]）分类的新鲜烟羽和老化烟羽，以评估生物质燃烧排放对亚马逊森林大气氧化能力的影响。我们观察到，生物质燃烧排放干扰了异戊二烯氧化反应，特别是对于新鲜羽流（[MVK + MACR + ISOPOOH]∕[异戊二烯]= 7）顺风。在较低海拔（~ 500米）的新鲜烟羽中，异戊二烯的氧化比在老化的烟羽中要高，这预示着在地表附近可能发生一系列复杂的氧化反应，这可能与二次有机气溶胶（SOA）的形成有关。我们提出了一个基于顺序反应模型的OH计算的改进，该模型考虑了生物质燃烧制度和背景环境的垂直和水平输送。我们对[OH]估算的方法得出的值与最近在亚马逊雨林中观测到的[OH] × 106（分子cm−3）的值相同。在新烟柱时期，[OH]的垂直剖面和[MVK + MACR + isoopooh]∕[异戊二烯]比值表明，在从行星边界层向云层过渡（1000 ~ 1500 m）的过程中，氧化能力有所增强。这些高值的[OH] （1.5 × 106分子厘米−3）和[MVK + MACR + ISOPOOH]∕[异戊二烯]（7.5）表明，由于云层边缘对光解速率的影响，云层上方和云层内部发生了显著变化，这对OH的生成速率有重要影响。
Abstract. We present a characterization of the chemical composition of the atmosphere of the Brazilian Amazon rainforest based on trace gas measurements carried out during the South AMerican Biomass Burning Analysis (SAMBBA) airborne experiment in September 2012. We analyzed the observations of primary biomass burning emission tracers, i.e., carbon monoxide (CO), nitrogen oxides (NOx), ozone (O3), isoprene, and its main oxidation products, methyl vinyl ketone (MVK), methacrolein (MACR), and isoprene hydroxy hydroperoxide (ISOPOOH). The focus of SAMBBA was primarily on biomass burning emissions, but there were also several flights in areas of the Amazon forest not directly affected by biomass burning, revealing a background with a signature of biomass burning in the chemical composition due to long-range transport of biomass burning tracers from both Africa and the eastern part of Amazonia. We used the [MVK + MACR + ISOPOOH] ∕ [isoprene] ratio and the hydroxyl radical (OH) indirect calculation to assess the oxidative capacity of the Amazon forest atmosphere. We compared the background regions (CO < 150 ppbv), fresh and aged smoke plumes classified according to their photochemical age ([O3] ∕ [CO]), to evaluate the impact of biomass burning emissions on the oxidative capacity of the Amazon forest atmosphere. We observed that biomass burning emissions disturb the isoprene oxidation reactions, especially for fresh plumes ([MVK + MACR + ISOPOOH] ∕ [isoprene] = 7) downwind. The oxidation of isoprene is higher in fresh smoke plumes at lower altitudes (∼ 500 m) than in aged smoke plumes, anticipating near the surface a complex chain of oxidation reactions which may be related to secondary organic aerosol (SOA) formation. We proposed a refinement of the OH calculation based on the sequential reaction model, which considers vertical and horizontal transport for both biomass burning regimes and background environment. Our approach for the [OH] estimation resulted in values on the same order of magnitude of a recent observation in the Amazon rainforest [OH] ≅ 106 (molecules cm−3). During the fresh plume regime, the vertical profile of [OH] and the [MVK + MACR + ISOPOOH] ∕ [isoprene] ratio showed evidence of an increase in the oxidizing power in the transition from planetary boundary layer to cloud layer (1000–1500 m). These high values of [OH] (1.5 × 106 molecules cm−3) and [MVK + MACR + ISOPOOH] ∕ [isoprene] (7.5) indicate a significant change above and inside the cloud decks due to cloud edge effects on photolysis rates, which have a major impact on OH production rates.