Missing peroxy radical sources within a summertime ponderosa pine forest
Missing peroxy radical sources within a summertime ponderosa pine forest
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DOI：
10.5194/acp-14-4715-2014
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发表时间：
2014-05
影响因子：
6.3
通讯作者：
G. Wolfe;C. Cantrell;S. Kim;R. Mauldin;T. Karl;P. Harley;A. Turnipseed;W. Zheng;F. Flocke;E. Apel;R. Hornbrook;S. Hall;K. Ullmann;S. Henry;J. Digangi;E. S. Boyle;L. Kaser;R. Schnitzhofer;A. Hansel;M. Graus;Yoshihiro Nakashima;Y. Kajii;A. Guenther;F. Keutsch
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作者：
G. Wolfe;C. Cantrell;S. Kim;R. Mauldin;T. Karl;P. Harley;A. Turnipseed;W. Zheng;F. Flocke;E. Apel;R. Hornbrook;S. Hall;K. Ullmann;S. Henry;J. Digangi;E. S. Boyle;L. Kaser;R. Schnitzhofer;A. Hansel;M. Graus;Yoshihiro Nakashima;Y. Kajii;A. Guenther;F. Keutsch
抽象的。有机过氧 (RO2) 和氢过氧 (HO2) 自由基是光化学过程中的关键中间体，可在整个对流层产生臭氧、二次有机气溶胶和活性氮库。在生物碳氢化合物丰富的地区，过氧自由基化学的丰富性和复杂性对当代模型提出了重大挑战，特别是考虑到在这种环境中缺乏测量。我们展示了 2010 年夏季在美国黄松林中获得的过氧自由基观测结果，其中包括能量、气溶胶、碳、水、有机物和氮的生物-水-大气相互作用——落基山有机碳研究 (BEACHON-ROCS)。总过氧自由基混合比高达 180 pptv（体积万亿分之一），是迄今为止有记录以来的最高混合比之一。使用综合测量套件来约束近乎明确的 0 维盒模型，我们研究了森林冠层下方过氧自由基的来源、汇和分布。基本化学机制低估了总过氧自由基多达 3 倍。由于过氧自由基的主要反应伙伴要么被测量（NO），要么被低估（HO2 和 RO2，即自反应），因此缺少来源是这一结果最可能的解释。模型输出与观测结果的密切比较揭示了至少两个不同的源特征。第一个缺失的来源，其特征是中午峰值急剧上升并且对太阳辐射的强烈依赖，与光解产生的 HO2 一致。第二个缺失源的昼夜曲线在下午达到峰值，表明存在一个独立于太阳驱动的光化学（例如反应性碳氢化合物的臭氧分解）产生 RO2 的过程。这些缺失源的最大幅度（分别约为 120 和 50 pptv min−1）与之前的观察结果一致，暗示森林内发生了意外的强烈氧化。我们的结论是，类似的机制可能是许多此类观察结果的基础。
Abstract. Organic peroxy (RO2) and hydroperoxy (HO2) radicals are key intermediates in the photochemical processes that generate ozone, secondary organic aerosol and reactive nitrogen reservoirs throughout the troposphere. In regions with ample biogenic hydrocarbons, the richness and complexity of peroxy radical chemistry presents a significant challenge to current-generation models, especially given the scarcity of measurements in such environments. We present peroxy radical observations acquired within a ponderosa pine forest during the summer 2010 Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics and Nitrogen – Rocky Mountain Organic Carbon Study (BEACHON-ROCS). Total peroxy radical mixing ratios reach as high as 180 pptv (parts per trillion by volume) and are among the highest yet recorded. Using the comprehensive measurement suite to constrain a near-explicit 0-D box model, we investigate the sources, sinks and distribution of peroxy radicals below the forest canopy. The base chemical mechanism underestimates total peroxy radicals by as much as a factor of 3. Since primary reaction partners for peroxy radicals are either measured (NO) or underpredicted (HO2 and RO2, i.e., self-reaction), missing sources are the most likely explanation for this result. A close comparison of model output with observations reveals at least two distinct source signatures. The first missing source, characterized by a sharp midday maximum and a strong dependence on solar radiation, is consistent with photolytic production of HO2. The diel profile of the second missing source peaks in the afternoon and suggests a process that generates RO2 independently of sun-driven photochemistry, such as ozonolysis of reactive hydrocarbons. The maximum magnitudes of these missing sources (~120 and 50 pptv min−1, respectively) are consistent with previous observations alluding to unexpectedly intense oxidation within forests. We conclude that a similar mechanism may underlie many such observations.