Megacity and local contributions to regional air pollution: an aircraft case study over London-猫眼课题宝

DOI：

10.5194/acp-2019-955

发表时间：

2019-11

期刊：

Atmospheric Chemistry and Physics

影响因子：

6.3

通讯作者：

中科院分区：

地球科学1区

文献类型：

作者：

K. Ashworth;S. Bucci;P. Gallimore;Junghwa Lee;Beth S. Nelson;A. Sanchez-Marroquín;M. Schimpf;Paul Smith;Will S. Drysdale;J. Hopkins;James D. Lee;J. Pitt;P. Di Carlo;R. Krejci;J. McQuaid

抽象。2017年7月，三次环绕伦敦大城市的研究飞行作为EUFAR（欧洲空中研究设施）组织的学生和早期职业研究人员STANCO培训学校的一部分进行。测量是由英国的机载大气测量设施（FAAM）BAe-146-301大气研究飞机进行的，目的是采样，测量和量化特大城市流出污染对周围地区空气质量的影响。条件是非常有利的空中测量，和所有三个航班都能够观察到明确的污染事件沿着飞行path.A风向的一个小的变化提供了足够不同的空气质量起源超过2天，这样一个独特的污染羽流从伦敦，归因于海洋排放量和双峰分散的污染面积的组合造成的本地和运输排放量进行了测量。我们能够分析伦敦排放对更广泛地区空气质量的影响，以及当地污染源对污染事件的贡献程度。伦敦的逆风背景空气在这两天相对清洁; CO浓度为88-95 ppbv，总（测量）挥发性有机化合物（VOC）为1.6-1.8 ppbv，NOx为0.7-0.8 ppbv。在伦敦的下风处，我们遇到了所有物种的海拔，CO>100 ppbv，VOC 2.8-3.8 ppbv，CH 4>2080 ppbv和NOx>4 ppbv，个别污染事件的峰值浓度更高。在第一次飞行中，O3的水平与NOx呈负相关，在定义明确的伦敦羽流中，逆风处的O3浓度从37 ppbv下降到126 ppbv。通过城市顺风的垂直平面估计了来自伦敦的总污染物通量。我们计算出的CO2通量在先前估计的不确定性范围内，但我们对CH 4和CO的估计存在更大的差异。第二天，风较轻，顺风O3浓度升高至39-43 ppbv（从32 ppbv上升到35 ppbv），反映了更古老的污染对区域背景的贡献。污染物浓度的升高比第一天分散在更广泛的区域，尽管我们也遇到了一些来自当地来源的明显的瞬时增强。这一系列飞行表明，即使在大城市外流的地区，如英国东南部，当地的新排放和更远的英国污染源也会对污染事件产生重大影响。在特大城市周围高度复杂的大气层中，高本底污染水平与各种时空尺度的当地污染源混合，城市热岛使大气动态进一步复杂化，因此使用污染物比率来跟踪和确定空气质量老化可能是无效的。因此，必须对各个来源进行充分表征和限制，以了解伦敦等大城市周围的空气质量。研究飞机通过对特定来源进行有针对性的采样和纵向研究，监测排放强度和排放曲线随时间的变化趋势，提供了这种能力。

Abstract. In July 2017 three research flights circumnavigating the megacity of London were conducted as a part of the STANCO training school for students and early career researchers organised by EUFAR (European Facility for Airborne Research). Measurements were made from the UK's Facility for Airborne Atmospheric Measurements (FAAM) BAe-146-301 atmospheric research aircraft with the aim to sample, characterise and quantify the impact of megacity outflow pollution on air quality in the surrounding region. Conditions were extremely favourable for airborne measurements, and all three flights were able to observe clear pollution events along the flight path. A small change in wind direction provided sufficiently different air mass origins over the 2 d such that a distinct pollution plume from London, attributable marine emissions and a double-peaked dispersed area of pollution resulting from a combination of local and transported emissions were measured. We were able to analyse the effect of London emissions on air quality in the wider region and the extent to which local sources contribute to pollution events. The background air upwind of London was relatively clean during both days; concentrations of CO were 88–95 ppbv, total (measured) volatile organic compounds (VOCs) were 1.6–1.8 ppbv and NOx was 0.7–0.8 ppbv. Downwind of London, we encountered elevations in all species with CO>100 ppbv, VOCs 2.8–3.8 ppbv, CH4>2080 ppbv and NOx>4 ppbv, and peak concentrations in individual pollution events were higher still. Levels of O3 were inversely correlated with NOx during the first flight, with O3 concentrations of 37 ppbv upwind falling to ∼26 ppbv in the well-defined London plume. Total pollutant fluxes from London were estimated through a vertical plane downwind of the city. Our calculated CO2 fluxes are within the combined uncertainty of those estimated previously, but there was a greater disparity in our estimates of CH4 and CO. On the second day, winds were lighter and downwind O3 concentrations were elevated to ∼39–43 ppbv (from ∼32 to 35 ppbv upwind), reflecting the contribution of more aged pollution to the regional background. Elevations in pollutant concentrations were dispersed over a wider area than the first day, although we also encountered a number of clear transient enhancements from local sources. This series of flights demonstrated that even in a region of megacity outflow, such as the south-east of the UK, local fresh emissions and more distant UK sources of pollution can all contribute substantially to pollution events. In the highly complex atmosphere around a megacity where a high background level of pollution mixes with a variety of local sources at a range of spatial and temporal scales and atmospheric dynamics are further complicated by the urban heat island, the use of pollutant ratios to track and determine the ageing of air masses may not be valid. The individual sources must therefore all be well-characterised and constrained to understand air quality around megacities such as London. Research aircraft offer that capability through targeted sampling of specific sources and longitudinal studies monitoring trends in emission strength and profiles over time.

Megacity and local contributions to regional air pollution: an aircraft case study over London

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