Suppression of air pollution via aerosol mediated removal of peroxy radicals

空气质量是一个紧迫的社会问题，每年约有700万人死于室外和室内空气污染的综合影响。其中两种主要污染物是气态臭氧（也会影响作物产量和破坏生态系统）和特殊物质（PM），这两种物质也会通过吸收和散射太阳辐射来影响气候系统。降低这些化合物浓度的政策往往是相互独立地实施的，重点是减少不同来源的不同化合物的排放。臭氧是一种二次污染物，因此不会直接排放到大气中，而是通过化学链反应产生的，即挥发性有机化合物（VOCs）在氮氧化物（NOx）的存在下被氧化。就臭氧而言，减排政策的科学依据取决于特定区域的光化学状况。两种完善的臭氧产生机制是所谓的“VOC限制”机制和“NOx限制”机制，在所述“VOC限制”机制中，需要减少VOC排放以减少臭氧，在所述“NOx限制”机制中，需要减少NOx排放。哪一种制度的运作取决于哪些化学反应限制臭氧的产生。在过去的三十年里，NOx或VOC限制政策之间的这种分离支撑了臭氧控制战略，决策者通过减少NOx或VOC排放来减少臭氧。另一方面，PM污染的控制集中在减少一组不同的化合物（硫，炭黑，灰尘等）。因此，几十年来，臭氧和PM污染一直被认为是有效的独立的问题与无关的政策，用于控制PM和Ozone.This建议建立在一个新的第三个“气溶胶抑制”制度的研究人员的发现，其中的主要过程限制臭氧的产生是反应性的去除到气溶胶表面的过氧自由基。在这些地区，减少颗粒物和臭氧的政策之间存在着强烈的相互作用。减少气溶胶污染的努力会导致臭氧浓度增加的意外后果。考虑到气溶胶吸收HO2的速率的不确定性，如果要更新政策，就必须更好地了解这一机制。这一建议将解决这些计算中仍然存在的一些不确定性。我们将开发一种新的仪器，用于直接现场测量过氧自由基在气溶胶上的去除率，并将首次在实验室中测量有机过氧自由基在气溶胶表面上的反应速度。新的现场能力将部署在英国和测量（连同那些从日本合作者），从实验室的结果将被用来制定新的参数化，这将使异质去除更准确地表示在大气模型。我们将使用简单的零维箱模型和更复杂的三维化学传输模型来量化对地面和全球臭氧浓度的影响，以及过去，现在和未来的大气氧化率。通过这种方式，我们将探讨新的臭氧制度对空气质量和气候的重要性。这一建议汇集了来自利兹、约克和曼彻斯特的各小组的领先互补专门知识，这些小组在现场测量、气相和非均匀气溶胶过程的实验室测量以及一系列空间尺度的数值模拟方面具有相当丰富的经验。

Air quality is a pressing societal concern with around 7 million people dying per year from the combined effect of outdoor and indoor air pollution. Two of the key pollutants are gaseous ozone (which can also influence crop yields and damage ecosystems) and particular matter (PM), both of which also influence the climate system through the absorption and scattering of solar radiation. Policies to reduce the concentrations of these compounds are often implemented independently of each other and focus on reducing the emissions of different compounds with different sources. Ozone is a secondary pollutant, and so is not directly emitted into the atmosphere but produced by chemical chain reactions where volatile organic compounds (VOCs) are oxidized in the presence of oxides of nitrogen (NOx).For ozone, the scientific basis for emission reduction policy depends on the photochemical regime of a given region. Two well established regimes for ozone production are the so-called "VOC limited" regime where reductions in the VOC emissions are required in order to reduce ozone, and the "NOx limited" regime where reduction in NOx emissions is required. Which regime operates depends on which chemical reactions limit ozone production. This separation between NOx or VOC limited policies has underpinned ozone control strategies over the last three decades where policymakers have either reduced NOx or VOC emissions to reduce ozone. Controls of PM pollution, on the other hand, have focussed on the reduction of a different set of compounds (sulfur, black carbon, dust etc.). Thus, for decades ozone and PM pollution have been considered as effectively separate problems with unrelated policies for controlling PM and ozone.This proposal builds on the discovery by one of the investigators of a new third "aerosol inhibited" regime where the dominant process limiting ozone production is the reactive removal of peroxy radicals onto aerosol surfaces. In these locations there is a strong interaction between policies to reduce particulate matter and ozone. Efforts to reduce aerosol pollution would lead to the unintended consequence of increasing ozone concentration.Given the uncertainties on the rate of uptake of HO2 onto aerosols, a better understanding of this regime is necessary if policy is to be updated. This proposal will address a number of uncertainties that remain in these calculations. We will develop a new instrument for the direct field measurement of the rate of removal of peroxy radicals onto aerosols, and will measure for the first time in the laboratory how quickly organic peroxy radicals react on the surface of aerosols. The new field capability will be deployed in the UK and the measurements (together with those from a Japanese collaborator) and the results from the laboratory will be used to formulate new parameterizations which will allow heterogeneous removal to be more accurately represented in atmospheric models. We will use simple zero-dimensional box models and more complex three dimensional chemical transport models to quantify the impact on surface and global ozone concentrations, and atmospheric oxidation rates in the past, present and future. In this way we will explore the importance of the new ozone regime for air quality and climate.This proposal brings together leading complementary expertise from groups in Leeds, York and Manchester who have considerable experience in field measurements, laboratory measurements of gas-phase and heterogeneous aerosol processes, and numerical modelling on a range of spatial scales.