Long-term measurements of OH reactivity

恶劣的空气质量被DEFRA列为英国公共健康的最大环境风险，最近，在伦敦一名9岁女孩死亡的里程碑式验尸官裁决中，暴露在空气污染中首次被列为死亡原因。据报道，空气污染会影响人体的每个器官，并与心血管和呼吸系统疾病、血管性痴呆症和阿尔茨海默病等疾病有关。每年，空气污染导致全球超过420万人过早死亡，给英国经济造成约150亿英镑的损失。空气的性质是由大气成分决定的，对大气成分的了解对制订改善空气质素的政策至为重要。大气成分受工业、车辆废气和工厂等多种来源排放到大气中的痕量物种的排放速度和化学组成所控制。氮氧化物和挥发性有机化合物(VOCs)排放到大气中会导致复杂的化学反应，这些化学反应主要是由自然产生的OH自由基引发的。这种化学作用会产生臭氧(O3)和二次有机气溶胶(SOA)等二次污染物，影响气候，危害人类健康。然而，在10,000多种不同的大气VOCs中，只能识别和测量一小部分的浓度，这限制了我们对空气质量提供准确评估和预测的能力。尽管存在这些挑战，但有可能量化大气中未测量物种的存在和影响。由于排放到大气中的大多数物种都与OH自由基发生反应，测量环境空气中OH自由基的总损失率提供了一种方法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。OH总损失率的这种测量被用来定义OH反应性(KOH)，它可以被认为代表氧化成二次污染物的气团中的活性污染物的总负荷。对OH反应性的长期测量能力具有开发新的空气质量指标的潜力，该指标定义了生产臭氧和SOA等二次污染物的运行中的化学状态，并能够监测污染物排放的变化趋势，评估大气模型中考虑污染物的反应性和影响的准确性和程度，并提供更准确的空气质量预测。然而，由于缺乏合适的技术，常规和长期的羟基反应性测量受到阻碍。在这项工作中，我们将开发一种新的仪器来进行长期的羟基反应性测量。我们将在伯明翰最近开发的NERC城市空气质量测量超级站点上对OH反应性进行长期测量，并使用这些测量来评估用于预测大气成分和空气质量的模型。与目前用于短期密集测量活动的仪器相比，这项工作开发的仪器将更轻、更便宜、更灵活，由于更坚固和自动化的设计，更低的功耗和更低的人力需求。该仪器将有可能用于地面、飞机和船载平台的大气测量，以及大气模拟室的实验室测量和对车辆排放的直接测量。最终，这项工作将提供一个强大的仪器，为广泛测量大气化学中的一个关键参数提供机会。增加大气模型中反应性测量的可用性和更广泛地使用，将大大改善我们对大气成分和空气质量的理解。

Poor air quality has been cited by DEFRA as the greatest environmental risk to public health in the UK, and exposure to air pollution has recently been listed for the first time as a cause of death in a landmark coroner's ruling on the death of a nine year old girl in London. Air pollution has been reported to affect every organ in the body and has been linked to illnesses including cardiovascular and respiratory diseases, vascular dementia, and Alzheimer's disease. Each year, air pollution causes over 4.2 million premature deaths worldwide and costs the UK economy ~£15 billion. The properties of our air are governed by atmospheric composition, the understanding of which is vital to the development of policies aimed at improving air quality.The composition of the atmosphere is controlled by the emission rates and chemistry of trace species emitted into the atmosphere from a wide range of sources including industry, vehicle exhausts and plants. Emissions of nitrogen oxides and volatile organic compounds (VOCs) into the atmosphere lead to complex cascades of chemical reactions which are predominantly initiated by naturally occurring OH radicals. This chemistry results in the generation of secondary pollutants such as ozone (O3) and secondary organic aerosol (SOA), which impact the climate and are harmful to human health. However, it is only possible to identify and measure the concentrations of a small fraction of the vast array of over 10,000 different atmospheric VOCs, which limits our ability to provide accurate assessments and predictions of air quality.Despite such challenges, it is possible to quantify the presence and impacts of unmeasured species in the atmosphere. Since most species emitted into the atmosphere react with OH radicals, measurements of the total loss rate of OH radicals in ambient air provides a means to quantify the presence of unmeasured species, and the extent to which they contribute to the production of ozone and SOA. Such measurements of the total OH loss rate are used to define the OH reactivity (kOH), which can be considered to represent the total loading of reactive pollutants in an air mass that oxidise to secondary pollutants.The capability for long-term measurements of OH reactivity has the potential for development of a new air quality metric that defines the chemical regime in operation for production of secondary pollutants such as ozone and SOA, and enables monitoring of changing trends in pollutant emissions, evaluation of the accuracy and extent to which the reactivity and impacts of pollutants are considered in atmospheric models, and the provision of more accurate air quality forecasts. However, routine and long-term measurements of OH reactivity are hindered by a lack of suitable techniques.In this work we will develop a novel instrument to make long-term measurements OH reactivity. We will make long-term measurements of OH reactivity at the recently developed NERC urban air quality measurement supersite in Birmingham and use these to evaluate models used to predict atmospheric composition and air quality. Compared to instruments currently in use for short-term intensive measurement campaigns, the instrument developed in this work will be lighter, cheaper and more mobile, with lower power consumption and lower staffing demands owing to a more rugged and automated design. The instrument will have potential for atmospheric measurements from ground-based, aircraft and shipborne platforms, as well as laboratory measurements in atmospheric simulation chambers and direct measurements of vehicle emissions.Ultimately, this work will deliver a robust instrument, providing opportunities for widespread measurements of a key parameter in atmospheric chemistry. Increased availability and more widespread use of reactivity measurements in atmospheric models will lead to significant improvements to our understanding of atmospheric composition and air quality.