Preindustrial to present-day changes in tropospheric hydroxyl radical and methane lifetime from the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP)
Preindustrial to present-day changes in tropospheric hydroxyl radical and methane lifetime from the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP)
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DOI：
10.5194/acp-13-5277-2013
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发表时间：
2013-01-01
影响因子：
6.3
通讯作者：
Zeng, G.
中科院分区：
文献类型：
--
作者：
Naik, V.;Voulgarakis, A.;Zeng, G.
我们分析了时间片模拟从17个全球模式，参加了大气化学和气候模式相互比较项目（ACCMIP），探讨当今（2000年）的羟基自由基（OH）浓度和甲烷（CH 4）寿命相对于工业化前的时间（1850年）和1980年的变化。模拟和观测衍生的甲烷和甲基氯仿的寿命的比较表明，目前的全球多模式平均OH浓度被高估了5%至10%，但在不确定性的范围内。该模型一贯模拟较高的OH浓度在北方半球（NH）相比，南半球（SH）的今天（2000年;半球间的比例为1.13至1.42），在基于观测的方法，一般表明较高的OH在SH，虽然不确定性很大。模拟的一氧化碳（CO）浓度的评估，OH的主要汇，对地面和卫星观测表明，低偏差的NH，可能有助于高南北OH不对称的模型。这些模型在当今OH浓度的区域分布方面差异很大（高达34%）。尽管区域变化很大，但多模式全球平均值（质量加权）OH浓度变化不大，在过去的150年，由于同时增加的因素，提高OH（湿度、对流层臭氧、氮氧化物（NOx）排放和平流层臭氧减少引起的紫外线辐射），由OH汇的增加补偿（甲烷丰度、一氧化碳和非甲烷挥发性有机碳（NMVOC）排放）。工业化前到现在OH变化的符号和幅度的巨大模型间差异（从减少12.7%到增加14.6%）表明，我们对OH和甲烷寿命的长期趋势的理解仍然存在不确定性。我们发现，这种多样性在很大程度上解释了不同的比例的变化，在全球平均对流层CO和NOx的负担（Δ CO/Δ NOx，大约代表的OH汇的变化与OH源的变化）在模型中，指出需要更好地约束自然前体排放和化学机制，在当前一代的化学气候模型。对于1980年至2000年期间，我们发现气候变暖和平均OH（3.5 +/-2.2%）的轻微增加导致甲烷寿命减少4.3 +/- 1.9%。通过分析10个模型进行的敏感性模拟，我们发现，工业化前到今天的气候变化减少了约4个月的甲烷寿命，对气候系统的负反馈。此外，我们分析了归因实验的一个子集的模型相对于2000年的条件下，只有一个前体的时间设置为1860年的水平。我们发现，全球平均OH增加了46.4 +/- 12.2%，以响应工业化前到今天的人为氮氧化物排放量的增加，并减少了17.3 +/-2.3%，7.6 +/-1.5%，和3.1 +/- 3.0%，由于甲烷负担，人为CO和NMVOC排放量的增加，分别。
We have analysed time-slice simulations from 17 global models, participating in the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP), to explore changes in present-day (2000) hydroxyl radical (OH) concentration and methane (CH4) lifetime relative to preindustrial times (1850) and to 1980. A comparison of modeled and observation-derived methane and methyl chloroform lifetimes suggests that the present-day global multi-model mean OH concentration is overestimated by 5 to 10% but is within the range of uncertainties. The models consistently simulate higher OH concentrations in the Northern Hemisphere (NH) compared with the Southern Hemisphere (SH) for the present-day (2000; inter-hemispheric ratios of 1.13 to 1.42), in contrast to observation-based approaches which generally indicate higher OH in the SH although uncertainties are large. Evaluation of simulated carbon monoxide (CO) concentrations, the primary sink for OH, against ground-based and satellite observations suggests low biases in the NH that may contribute to the high north-south OH asymmetry in the models. The models vary widely in their regional distribution of present-day OH concentrations (up to 34 %). Despite large regional changes, the multi-model global mean (mass-weighted) OH concentration changes little over the past 150 yr, due to concurrent increases in factors that enhance OH (humidity, tropospheric ozone, nitrogen oxide (NOx) emissions, and UV radiation due to decreases in stratospheric ozone), compensated by increases in OH sinks (methane abundance, carbon monoxide and non-methane volatile organic carbon (NMVOC) emissions). The large inter-model diversity in the sign and magnitude of preindustrial to present-day OH changes (ranging from a decrease of 12.7% to an increase of 14.6 %) indicate that uncertainty remains in our understanding of the long-term trends in OH and methane lifetime. We show that this diversity is largely explained by the different ratio of the change in global mean tropospheric CO and NOx burdens (Delta CO/Delta NOx, approximately represents changes in OH sinks versus changes in OH sources) in the models, pointing to a need for better constraints on natural precursor emissions and on the chemical mechanisms in the current generation of chemistry-climate models. For the 1980 to 2000 period, we find that climate warming and a slight increase in mean OH (3.5 +/- 2.2 %) leads to a 4.3 +/- 1.9% decrease in the methane lifetime. Analysing sensitivity simulations performed by 10 models, we find that preindustrial to present-day climate change decreased the methane lifetime by about four months, representing a negative feedback on the climate system. Further, we analysed attribution experiments performed by a subset of models relative to 2000 conditions with only one precursor at a time set to 1860 levels. We find that global mean OH increased by 46.4 +/- 12.2% in response to preindustrial to present-day anthropogenic NOx emission increases, and decreased by 17.3 +/- 2.3 %, 7.6 +/- 1.5 %, and 3.1 +/- 3.0% due to methane burden, and anthropogenic CO, and NMVOC emissions increases, respectively.