Atmospheric OH reactivity in central London: observations, model predictions and estimates of in situ ozone production
Atmospheric OH reactivity in central London: observations, model predictions and estimates of in situ ozone production
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DOI：
10.5194/acp-16-2109-2016
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发表时间：
2015-11
影响因子：
6.3
通讯作者：
L. Whalley;D. Stone;B. Bandy;R. Dunmore;J. Hamilton;J. Hopkins;James D. Lee;A. Lewis;D. Heard
中科院分区：
文献类型：
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作者：
L. Whalley;D. Stone;B. Bandy;R. Dunmore;J. Hamilton;J. Hopkins;James D. Lee;A. Lewis;D. Heard
摘要。本文介绍了2012年夏季伦敦市中心城市背景大气中羟基自由基（OH）反应性的近连续测量。OH的反应性行为被认为广泛地依赖于气团的来源，在测量之前，当空气从伦敦中部向东经过时，观察到最高的反应性和最明显的日剖面。在整个26天的观测期内，平均下来，OH反应性在上午达到峰值~ 27 s−1，在下午达到最小值~ 15 s−1。在早高峰时段，有一天OH反应活性最高达116 s−1。使用主化学机制的详细盒模型来计算OH反应性，并受到来自气相色谱火焰离子化检测器（GC- fid）和二维GC仪器的挥发性有机化合物（VOCs）的扩展测量数据集的约束，这些挥发性有机化合物包括重分子量（高达C12）的脂肪性VOCs，氧化性VOCs以及生物源性VOCs α-蒎烯和柠檬烯。比较观察到的OH反应性和模拟的OH反应性，使用(i)一套标准的VOC测量（C2-C8碳氢化合物和少量氧化的VOCs）和（ii）更全面的清单，包括高达C12的物种。当只考虑标准VOC套件的反应性时，模拟的反应性比测量的反应性低（33%）。如果还考虑较高VOCs（大于或等于C9）的反应性，则测量的和模拟的反应性之间的差异得到改善，达到15%以内，α-蒎烯和柠檬烯的生物源化合物的反应性及其氧化产物几乎完全负责这种改善。如果对未分配的二维GC峰的反应性和降解机制进行估计，可以进一步提高模型重现OH反应性的能力（达到6%以内）。忽略较高的VOCs（小于或等于C9）（特别是α-蒎烯和柠檬烯）和模型生成的中间体的贡献将模拟OH浓度增加41%，并且从RO2的产生计算的原位臭氧产生的幅度显着降低（60%）。这项工作强调，任何未来的臭氧减排战略都应考虑生物排放和人为排放在影响伦敦空气质量方面所起的作用。
Abstract. Near-continuous measurements of hydroxyl radical (OH) reactivity in the urban background atmosphere of central London during the summer of 2012 are presented. OH reactivity behaviour is seen to be broadly dependent on air mass origin, with the highest reactivity and the most pronounced diurnal profile observed when air had passed over central London to the east, prior to measurement. Averaged over the entire observation period of 26 days, OH reactivity peaked at ∼ 27 s−1 in the morning, with a minimum of ∼ 15 s−1 during the afternoon. A maximum OH reactivity of 116 s−1 was recorded on one day during morning rush hour. A detailed box model using the Master Chemical Mechanism was used to calculate OH reactivity, and was constrained with an extended measurement data set of volatile organic compounds (VOCs) derived from a gas chromatography flame ionisation detector (GC-FID) and a two-dimensional GC instrument which included heavier molecular weight (up to C12) aliphatic VOCs, oxygenated VOCs and the biogenic VOCs α-pinene and limonene. Comparison was made between observed OH reactivity and modelled OH reactivity using (i) a standard suite of VOC measurements (C2–C8 hydrocarbons and a small selection of oxygenated VOCs) and (ii) a more comprehensive inventory including species up to C12. Modelled reactivities were lower than those measured (by 33 %) when only the reactivity of the standard VOC suite was considered. The difference between measured and modelled reactivity was improved, to within 15 %, if the reactivity of the higher VOCs (⩾ C9) was also considered, with the reactivity of the biogenic compounds of α-pinene and limonene and their oxidation products almost entirely responsible for this improvement. Further improvements in the model's ability to reproduce OH reactivity (to within 6 %) could be achieved if the reactivity and degradation mechanism of unassigned two-dimensional GC peaks were estimated. Neglecting the contribution of the higher VOCs (⩾ C9) (particularly α-pinene and limonene) and model-generated intermediates increases the modelled OH concentrations by 41 %, and the magnitude of in situ ozone production calculated from the production of RO2 was significantly lower (60 %). This work highlights that any future ozone abatement strategies should consider the role that biogenic emissions play alongside anthropogenic emissions in influencing London's air quality.