Oxidant Budgets of the Northern Hemisphere Troposphere Since 1950

羟基自由基（OH）是对流层中的主要氧化剂，因此其浓度控制着大多数大气污染物的丰度和寿命，包括重要的温室气体甲烷（CH 4）。臭氧（O3）也是一种重要的氧化剂，本身也是一种温室气体。OH和O3的浓度是相互依赖的，两者都由涉及CH 4、一氧化碳（CO）、非甲烷挥发性有机化合物（NMVOC）和氮氧化物（NOX = NO + NO2）的一系列复杂反应决定。由于这些化合物的排放量自工业化前时代以来发生了很大变化，对流层中OH和O3的收支也将发生变化。然而，目前对这些过去变化的理解存在很大的不确定性，因此，预测未来变化和相关气候影响也存在很大的不确定性，过去趋势的这种不确定性大多来自缺乏观测，限制了研究。虽然有几个直接的观测数据集表明了O3浓度在整个世纪的变化，但没有OH。甲烷、非甲烷挥发性有机化合物、一氧化碳和氮氧化物的直接观测数据集最多可追溯到1980年代。这些时间序列可以通过分析被困在积雪（松散的雪）中的空气在时间上向后延伸。虽然CH 4的这种历史时间序列已经存在了一段时间，但CO和某些NMVOCs，特别是烷烃的历史时间序列最近才出现。此外，我们最近还确定，从积雪分析，硝酸烷基酯的历史时间序列。硝酸烷基酯是涉及NOX的化学反应的产物，因此可以用作NOX变化的诊断。这些新的（在硝酸烷基酯的情况下，独特的），历史性的时间序列提供了一个令人兴奋的机会，调查自1950年以来的观测约束条件下，北方半球对流层的OH和O3预算的变化。非常有趣的是，迄今为止对这些时间序列进行的简单分析表明，大气化学发生了重大变化。为了充分利用这些时间序列的价值，需要用一个全面的化学-气候模型进行详细的研究。在这里，我们提出了第一个这样的研究。这项研究的结果将是：1）更好地了解不断变化的人为排放对北方半球对流层OH和O3预算的影响; 2）改进的建模能力，预测未来的变化，更好地为气候政策提供信息。这项建议汇集了雪空气数据解释专家和化学气候建模专家。这两个小组在有机（包括烷基）硝酸盐化学方面也有相当多的专业知识。该提案特别建立在过去NERC资助的关于公司空气中烷烃和烷基硝酸盐趋势的工作基础上，使用简单的关系和模型。

The hydroxyl radical (OH) is the dominant oxidizing agent in the troposphere, as such its concentration controls the abundances and lifetimes of most atmospheric pollutants, including the important greenhouse gas methane (CH4). Ozone (O3) is also an important oxidant and is itself a greenhouse gas. The concentrations of OH and O3 are interdependent, both being determined by a complex series of reactions involving CH4, carbon monoxide (CO), non-methane volatile organic compounds (NMVOCs) and nitrogen oxides (NOX = NO + NO2). As emissions of these compounds have changed substantially since pre-industrial times, the tropospheric budgets of OH and O3 will also have changed. However, there are large uncertainties associated with current understanding of these past changes and consequently very large uncertainties in projected future changes and associated climate impacts.Most of this uncertainty in past trends comes from lack of observations to constrain studies. Whilst there are a few direct observational data sets which indicate how O3 concentrations changed through the 20th century, there are none for OH. Direct observational data sets of CH4, NMVOCs, CO and NOX, extend, at best, from the 1980s. These time series can be extended backward in time through the analysis of air trapped in firn (unconsolidated snow). Whilst such historic time series have been available for CH4 for some time, only recently have they become available for CO and for some NMVOCs, in particular alkanes. Furthermore, we have also recently determined, from firn analysis, historic time series of alkyl nitrates. Alkyl nitrates are products of the chemistry involving NOX and as such can be used as a diagnostic of the changes in NOX. These new (and in the case of the alkyl nitrates, unique), historic time series provide an exciting opportunity to investigate the changing OH and O3 budgets of the northern hemisphere troposphere since 1950 with observational constraints never available before. Very interestingly, the simple analyses carried out on these time series to date suggest that substantial changes in the atmospheric chemistry have occurred. To exploit the full value of these time series a detailed study is required with a comprehensive chemistry-climate model. Here we propose the first such study.The outcomes of this study will be: 1) a better understanding of the impact of changing anthropogenic emissions on the OH and O3 budgets of the northern hemisphere troposphere; 2) an improved modelling capability with which to project future changes and better inform climate policy.This proposal brings together experts in firn air data interpretation with experts in chemistry-climate modelling. Both groups also have considerable expertise in organic (including alkyl) nitrate chemistry. This proposal specifically builds on past NERC funded work on the trends of alkanes and alkyl nitrates in firm air using simply relationships and models.