Long-term measurements of OH reactivity: A new metric for air quality

据报道，糟糕的空气质量是英国公共健康面临的最大环境风险(DEFRA，2017)，最近被认为与痴呆症有关(Carey等人，2018)，据估计，英国每年有超过40,000人过早死亡(皇家医师学院，2016)。旨在解决空气质量和气候等问题的政策依赖于对大气成分的准确了解，这要求了解大气中痕量VOCs的排放速率、浓度和化学组成。然而，只能识别和测量大气中存在的大量VOCs中的一小部分的浓度(Goldstein和Galbally，2007年)，这阻碍了我们提供准确的空气质量和气候预测的能力。尽管存在这一挑战，但仍有可能通过测量大气中OH自由基的消耗速率来量化未测量物种的存在以及它们对臭氧和SOA产生的贡献程度(Yang等人，2016)，因为排放到大气中的几乎所有物种都与OH发生反应(Hed和Pilling，2003；Stone等人，2012)。对大气中总的OH损失速率的测量可以用来定义OH的反应性，它是描述损失(KOH)的伪一级速率系数和OH的化学寿命(TOH=1/KOH)的倒数。对OH反应性的测量与基于对OH汇(包括CO、NO、NO2和VOCs)的观测以及对OH自由基动力学的实验室测量的计算之间的比较，提供了一种确定观察到的汇的全面性的手段(Yang等人，2016；Fuchs等人，2017)，这使得能够评估未测量的物种对空气质量和气候的潜在贡献(Kirchner等人，2001；Yang等人，2016)。虽然已经开发了几种仪器来测量OH反应性，包括利兹小组的工作，它已经证明了大VOCs(&GT；=C9)和伦敦的生物来源排放(Ingham等人，2009；Stone等人，2016；Whalley等人，2016)，这些工具往往仅限于短期密集测量。进行长期的OH反应性测量的能力将增强我们监测污染物排放变化趋势、评估排放清单以及提供更准确的空气质量和气候预测的能力。对氢氧化氢反应性的长期测量将为决策者提供一个令人兴奋的空气质量新指标。

Poor air quality has been reported as the greatest environmental risk to public health in the UK (DEFRA, 2017), has recently been linked to dementia (Carey et al., 2018), and is estimated to cause over 40,000 premature deaths in the UK each year (Royal College of Physicians, 2016). Policies designed to address issues such as air quality and climate rely on accurate knowledge of atmospheric composition, requiring understanding of the emission rates, concentrations, and chemistry of trace VOCs in the atmosphere. However, it is only possible to identify and measure the concentrations of a small fraction of the vast array of VOCs present in the atmosphere (Goldstein and Galbally, 2007), which hinders our ability to provide accurate predictions of air quality and climate. Despite this challenge, it is possible to quantify the presence of unmeasured species, and the extent to which they contribute to the production of ozone and SOA (Yang et al., 2016), through measurements of the rate at which OH radicals are consumed in the atmosphere, since almost all species emitted into the atmosphere react with OH (Heard and Pilling, 2003; Stone et al., 2012). Measurements of the total OH loss rate in the atmosphere can be used to define the OH reactivity, which is the pseudo-first-order rate coefficient describing the loss (kOH) and the inverse of the chemical lifetime of OH (TOH = 1/kOH). Comparison between measurements of OH reactivity and calculations based on observations of OH sinks, which include CO, NO, NO2 and VOCs, and laboratory measurements of OH radical kinetics, provides a means to determine the comprehensiveness of the observed sinks (Yang et al., 2016; Fuchs et al., 2017), which enables assessment of the potential contribution of unmeasured species to air quality and climate (Kirchner et al., 2001; Yang et al., 2016).While several instruments have been developed to measure OH reactivity, including work in the Leeds group which has demonstrated significant impacts of large VOCs (>=C9) and biogenic emissions in London (Ingham et al., 2009; Stone et al., 2016; Whalley et al., 2016), these instruments tend to be limited to short-term intensive measurements. The capability to make long-term OH reactivity measurements would enhance our abilities to monitor changing trends in pollutant emissions, to assess emissions inventories, and to provide more accurate air quality and climate forecasts. Long term measurements of OH reactivity would provide an exciting new metric for air quality for use by policy makers.