Nighttime observations of anomalously high levels of hydroxyl radicals above a deciduous forest canopy
Nighttime observations of anomalously high levels of hydroxyl radicals above a deciduous forest canopy
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DOI：
10.1029/2000jd900691
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发表时间：
2001-10
影响因子：
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通讯作者：
I. Faloona;D. Tan;W. Brune;J. M. Hurst;D. J. Barket;T. L. Couch;P. Shepson;E. Apel;D. Riemer-D.-Rieme
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文献类型：
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作者：
I. Faloona;D. Tan;W. Brune;J. M. Hurst;D. J. Barket;T. L. Couch;P. Shepson;E. Apel;D. Riemer-D.-Rieme
白天测量的羟基和氢过氧自由基（OH和HO 2）的氧化剂的研究计划：光化学，排放和运输（PROPHET）1998年夏季密集表明，这些气相大气氧化的关键组成部分持续在整个晚上在这个北方森林地区的显着金额。观察到的典型过夜OH水平为0.04 ppm（pptv）（1.1 × 106分子/cm 3），而HO 2浓度范围为1至4 pptv。在展开之前、之后和期间进行的诊断测试的结果表明，干扰测量的可能性很小。反应性生物烃异戊二烯的配置测量证实了观察到的OH水平，表现出显着的衰减以上的森林树冠过夜。所观察到的异戊二烯寿命范围从1.5至12小时在黑暗中，它们相关性很好，从化学氧化所测得的OH丰度。可能的暗反应，可以产生这种高水平的OH包括臭氧分解的活性极强的生物萜类化合物。然而，在稳态模型，其中包括这种假设的生产机制，HO 2自由基产生的数量比测量。尽管如此，如果测量值是代表中纬度温带森林的夜间边界层，这种观察到的夜间现象可能会大大改变我们对这种原始，低NOx环境中大气氧化的昼夜模式的理解。
Diurnal measurements of hydroxyl and hydroperoxy radicals (OH and HO2) made during the Program for Research on Oxidants: Photochemistry, Emissions, and Transport (PROPHET) summer intensive of 1998 indicate that these key components of gas phase atmospheric oxidation are sustained in significant amounts throughout the night in this northern forested region. Typical overnight levels of OH observed were 0.04 parts per trillion (pptv) (1.1 × 106 molecules/cm3), while HO2 concentrations ranged from 1 to 4 pptv. Results of diagnostic testing performed before, after, and during the deployment suggest little possibility of interferences in the measurements. Collocated measurements of the reactive biogenic hydrocarbon isoprene corroborate the observed levels of OH by exhibiting significant decays overnight above the forest canopy. The observed isoprene lifetimes ranged from 1.5 to 12 hours in the dark, and they correlate well to those expected from chemical oxidation by the measured OH abundances. Possible dark reactions that could generate such elevated levels of OH include the ozonolysis of extremely reactive biogenic terpenoids. However, in steady state models, which include this hypothetical production mechanism, HO2 radicals are generated in greater quantities than were measured. Nonetheless, if the measurements are representative of the nocturnal boundary layer in midlatitude temperate forests, this observed nocturnal phenomenon might considerably alter our understanding of the diurnal pattern of atmospheric oxidation in such pristine, low-NOx environments.