Mechanisms responsible for the build-up of ozone over South East England during the August 2003 heatwave
Mechanisms responsible for the build-up of ozone over South East England during the August 2003 heatwave
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DOI：
10.1016/j.atmosenv.2011.04.035
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发表时间：
2011-12-01
影响因子：
5
通讯作者：
Fisher, B. E. A.
中科院分区：
文献类型：
--
作者：
Francis, X. V.;Chemel, C.;Fisher, B. E. A.
社区多尺度空气质量（CMAQ）模型用于量化2003年8月热浪期间英格兰东南部臭氧积聚的原因。与以往的研究不同，本研究定量地评估了个别气象和化学过程对事件时间演变的影响。对建模系统的性能进行了简要评价。模拟系统能够捕捉到这一事件的演变，在2003年8月1日至4日期间臭氧水平增加，之后达到最大值。对CMAQ模式结果的分析表明，三种机制是造成这一事件的主要原因：(i)来自欧洲大陆的长期高压系统的水平输送，（ii）西风和东风近地面风的辐合，以及（iii）来自自由对流层剩余层的富含臭氧的空气向下夹带。研究发现，早晨残留层向下夹带臭氧是白天臭氧水平提高的关键。该机制的相关性得到了模型臭氧垂直分布与光探测和测距（激光雷达）测量结果的良好一致性的支持。臭氧浓度变化率的过程分析表明，水平输送和垂直输送对解释臭氧的变率同样重要。模拟系统模拟的化学过程对臭氧浓度增加的贡献在接近地表的地方相对较小。然而，它对那里臭氧浓度下降的贡献与气象过程的贡献一样重要。通过研究不同的气象和化学机制的作用，本研究希望增加对空气污染事件演变的当前理解。(C) 2011 Elsevier Ltd.版权所有。
The Community Multiscale Air Quality (CMAQ) model is used in order to quantify reasons for the buildup of ozone over South East England during the August 2003 heatwave. Unlike previous studies, the effects of individual meteorological and chemical processes on the temporal evolution of the episode are assessed quantitatively in the present work. The performance of the modelling system was briefly evaluated. The modelling system was able to capture the evolution of the episode, with increasing ozone levels during the period 1-4 August 2003, and maximum values afterwards. Analysis of the results of the CMAQ model indicates that three mechanisms were mainly responsible for the episode: (i) horizontal transport from mainland Europe in the presence of a long-lived high-pressure system, (ii) convergence of westerly and easterly near-surface winds, and (iii) downward entrainment of ozone-rich air from residual layers in the free troposphere. The downward entrainment of ozone from residual layers in the morning is found to be key to enhancing ozone levels during the day. The relevance of this mechanism is supported by the good agreement of the model vertical ozone distribution with that derived from Light detection and ranging (Lidar) measurements. The process analysis of the rate of change of ozone concentration shows that both horizontal transport and vertical transport were equally important in explaining the variability of ozone. The contribution of chemical processes to the increase of ozone concentration as simulated by the modelling system is relatively small close to the surface. However, its contribution to the decrease of ozone concentration there becomes as important as that of meteorological processes. By investigating the role of separate meteorological and chemical mechanisms, this study hopes to add to the current understanding of the evolution of air pollution episode. (C) 2011 Elsevier Ltd. All rights reserved.