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众健康面临的最大环境风险（DEFRA, 2017），最近与痴呆症有关（Carey等人，2018），据估计，英国每年有4万多人过早死亡（皇家内科医学院，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，需要了解大气中痕量挥发性有机化合物的排放率、浓度和化学性质。然而，我们只能识别和测量大气中存在的大量挥发性有机化合物中的一小部分的浓度（Goldstein和Galbally， 2007），这阻碍了我们提供准确预测空气质量和气候的能力。尽管存在这一挑战，但由于几乎所有排放到大气中的物种都与OH发生反应，因此可以通过测量大气中OH自由基消耗的速率，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）（Heard和Pilling, 2003； Stone等人，2012）。大气中总OH损失率的测量可以用来定义OH反应性，它是描述OH损失率（kOH）的伪一级速率系数，是OH化学寿命的倒数（TOH = 1/kOH）。将OH反应性测量值与基于OH汇（包括CO、NO、NO2和VOCs）观测值的计算值与OH自由基动力学的实验室测量值进行比较，提供了一种确定观测到的OH汇的全全性的方法（Yang等人，2016；Fuchs等人，2017），从而可以评估未测量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测量OH反应性的仪器，包括利兹小组的工作，该小组已经证明了伦敦大量挥发性有机化合物（>=C9）和生物源排放的重大影响（Ingham等人，2009；Stone等人，2016；Whalley等人，2016），但这些仪器往往仅限于短期密集测量。长期测量OH反应性的能力，可提高我们监察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素和气候预测的能力。长期测量OH反应性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.