Factors controlling variability in the oxidative capacity of the troposphere since the Last Glacial Maximum
Factors controlling variability in the oxidative capacity of the troposphere since the Last Glacial Maximum
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DOI：
10.5194/acp-14-3589-2014
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发表时间：
2014-01-01
影响因子：
6.3
通讯作者：
Alexander, B.
中科院分区：
文献类型：
--
作者：
Murray, L. T.;Mickley, L. J.;Alexander, B.
过去大气的氧化能力是高度不确定的。我们在这里提出了一个新的气候-生物圈-化学建模框架，以确定氧化剂水平在现在和过去的对流层。我们使用GEOS-Chem化学传输模型，该模型由NASA戈达德空间研究所（GISS）ModelE的气象场驱动，并具有来自动态全球植被模型的土地覆盖和火灾排放。我们目前的时间片模拟的今天，后期前工业时代（公元1770年），和末次冰期最大值（LGM，19-23 ka），我们测试的灵敏度模型结果的不确定性在闪电和火灾排放。我们发现，大多数工业化前和古气候模拟产生的氧化剂水平相对于今天减少。与以前的研究相反，对流层平均OH在我们的合奏显示在末次冰期相对于工业化前时代（0.5 +/-12%）的变化不大，尽管甲烷浓度大幅减少。我们发现对流层平均臭氧光解率，水蒸气，氮氧化物和活性碳的总排放量之间存在一个简单的线性关系，解释了72%的全球平均OH的变化在11个不同的模拟在上一次冰期-间冰期的时间间隔和工业时代。控制对流层氧化能力的关键参数包括平流层臭氧、对流层水汽和闪电氮氧化物排放。全球平均OH的变化，因为LGM对火灾排放不敏感。我们的模拟结果与前工业时代的δ O-17在末次冰期的硫酸盐和硝酸盐以及CO、HCHO和H2 O2中的冰芯记录基本一致。我们的研究结果表明，在冰芯中观察到的大气甲烷的冰川间冰期变化主要是由其源的变化驱动的，而不是其汇与OH。
The oxidative capacity of past atmospheres is highly uncertain. We present here a new climate-biosphere-chemistry modeling framework to determine oxidant levels in the present and past troposphere. We use the GEOS-Chem chemical transport model driven by meteorological fields from the NASA Goddard Institute of Space Studies (GISS) ModelE, with land cover and fire emissions from dynamic global vegetation models. We present time-slice simulations for the present day, late preindustrial era (AD 1770), and the Last Glacial Maximum (LGM, 19-23 ka), and we test the sensitivity of model results to uncertainty in lightning and fire emissions. We find that most preindustrial and paleo climate simulations yield reduced oxidant levels relative to the present day. Contrary to prior studies, tropospheric mean OH in our ensemble shows little change at the LGM relative to the preindustrial era (0.5 +/- 12 %), despite large reductions in methane concentrations. We find a simple linear relationship between tropospheric mean ozone photolysis rates, water vapor, and total emissions of NOx and reactive carbon that explains 72% of the variability in global mean OH in 11 different simulations across the last glacial-interglacial time interval and the industrial era. Key parameters controlling the tropospheric oxidative capacity over glacial-interglacial periods include overhead stratospheric ozone, tropospheric water vapor, and lightning NOx emissions. Variability in global mean OH since the LGM is insensitive to fire emissions. Our simulations are broadly consistent with ice-core records of Delta O-17 in sulfate and nitrate at the LGM, and CO, HCHO, and H2O2 in the preindustrial era. Our results imply that the glacial-interglacial changes in atmospheric methane observed in ice cores are predominantly driven by changes in its sources as opposed to its sink with OH.