Investigating Key Uncertainties in Models of Tropospheric Photochemistry

我们对大气成分对气候和空气质量影响的理解依赖于大气化学和运输数值模型的模拟。这种模式的光化学成分是不确定的，由于减少详细的化学机制，以满足计算需求，也由于在其表示的光化学中使用的化学衍生动力学参数的不确定性。通过与观测结果进行比较来验证模型中的臭氧光化学成分是很困难的，因为臭氧在自由对流层中的寿命很长（约20天），这意味着大气中某一特定点的臭氧浓度变化通常是由传输而不是光化学决定的。然而，验证我们对臭氧光化学的理解对于我们预测未来气候和空气质量至关重要，特别是在臭氧前体来源未来发生变化以及对流层臭氧收支其他部分（如平流层输入和表面沉积）发生任何变化的情况下。该提案利用了ITCT拉格朗日-2K4（洲际运输和化学转化）实验期间的一组独特观测结果。这些提供了一套微量气体和气溶胶在单一的空气质量在多个阶段，在其平流横跨北大西洋从北美到欧洲的测量。这些关联的观测允许臭氧光化学被检查在一个“流量相对”，伪拉格朗日参考框架，消除平流对观测到的臭氧变化的影响。使用拉格朗日化学传输模型（CTM）模拟观测到的气团内的臭氧变化，将首次允许在几天的时间尺度上评估模型光化学的不确定性。将受模式不确定性干扰的蒙特-卡罗型模式模拟与观测到的气团内成分变化进行比较，将检验模式光化学与观测的一致性。将获得关于哪些不确定性对臭氧光化学影响最大的信息。然后将提出建议，说明应集中努力减少实验室或大气测量中的不确定性。该提案设想了一个为期一年的短期项目，利用现有的工具来调查这些问题，这些问题对我们对空气质量和气候模型的信心至关重要。该模型框架已经开发，可在利兹本地运行，全套观测结果可立即使用。该项目将受益于英国领先的大气建模小组之一的专业知识，以及与化学学院小组密切联系的动力学不确定性和参数化方面的当地专业知识。

Our understanding of the impacts of atmospheric composition on climate and air quality relies on simulations from numerical models of atmospheric chemistry and transport. The photochemical components of such models are uncertain, due to the reductions of detailed chemical mechanisms introduced to meet computing demands, and also due to uncertainties in empirically-derived kinetic parameters used in their representations of photochemistry. Validation of the ozone photochemistry component of models by comparison with observations is difficult, since the long lifetime of ozone in the free troposphere (~20 days), means that variability in its concentration at a given point in the atmosphere is generally dominated by transport rather than photochemistry. However, validation of our understanding of ozone photochemistry is critical to our predictions of future climate and air quality, particularly under future changes to ozone precursor sources, and any changes to other parts of the tropospheric ozone budget, such as stratospheric input and surface deposition. This proposal exploits a unique set of observations made during the ITCT Lagrangian-2K4 (Intercontinental Transport and Chemical Transformation) experiment. These provide measurements of a suite of trace gases and aerosol in single air masses at multiple stages during their advection across the North Atlantic from North America to Europe. These linked observations allow ozone photochemistry to be examined in a 'flow-relative', pseudo-Lagrangian frame of reference, removing the influence of advection on the observed ozone change. Simulations of ozone change within the observed air masses using a Lagrangian chemical transport model (CTM) will for the first time allow uncertainties in model photochemistry to be assessed over a timescale of several days. Comparison of Monte-Carlo type model simulations, perturbed by model uncertainties, with observed composition changes within air masses, will test the consistency of model photochemistry with observations. Information will be gained on which uncertainties have the largest impacts on ozone photochemistry. Recommendations will then be made of where effort should be focused in reducing uncertainties in laboratory or atmospheric measurement. The proposal envisages a short 1-year project, using existing tools to investigate these issues, which are of central importance to our confidence in models of air quality and climate. The model framework has already been developed to run locally in Leeds, and the full set of observations is available for use immediately. The project will benefit from expertise from one of the leading atmospheric modelling groups in the UK, in addition to local expertise in kinetic uncertainties and parameterisations from close links with groups in the School of Chemistry.