AerosoL heterogeneous Processing as a source of oxidants in Cold winter Atmospheres: application to Alaska and UK (ALPACA-UK)

空气污染是危害人类健康的首要环境风险。冬季污染事件导致世界许多地区违反空气质量(AQ)颗粒物污染标准，包括英国。尽管在这些事件中太阳光的可获得性有限，但大气中气溶胶颗粒的二次产生似乎对颗粒污染物浓度做出了重要贡献，这是现有的氧化机制无法解释的。在如此严重的冬季污染期间观察到的高水平硫酸盐无法用当前的空气质量模型来解释。亚硝酸(HONO)是污染大气中主要氧化剂--羟基的重要来源。越来越多的证据表明，通过颗粒物表面发生的非均相气溶胶化学作用产生的HONO在冬季条件下很重要，在受污染的冬季城市地区，HONO可能贡献了高达90%的初级OH产生。对这一来源的了解还不完全，空气污染预测模型中没有包括这一来源。在这里，我们将进行一项雄心勃勃的实验室、实地和模型研究的整合，通过利用最近开发的实验室能力、将通过计划中的国际实地活动获得的数据以及新的气溶胶化学模型方案，确定不同种类的HONO生产在高纬度城市(阿拉斯加费尔班克斯)和伦敦的作用。我们的方法将包括对现场采集的气溶胶样本进行实验室实验，在实验室中，我们将直接监测气溶胶过滤器产生的HONO随着光、湿度、温度和气溶胶成分的变化而变化。这些结果将被用来为气溶胶HONO的产生产生新的模式参数，并将使用化学盒模式框架与来自费尔班克斯的现场观测进行测试。最后，使用WRF-Chem模式的区域模式模拟将用于放大冬季费尔班克斯和英国伦敦地区气溶胶HONO源对空气质量的影响。我们的项目将提供新的参数和能力，将不同种类的HONO源包括在空气质量模式中，包括对气溶胶成分的依赖，我们将通过我们与全球和地区WRF-Chem模式社区的联系向社区提供这些信息。我们将与新的英国战略优先基金(SPF)清洁空气计划联系起来，利用新资助的英国排放模拟系统(UK-EMS)，并确定这些过程对最近伦敦冬季极端污染事件的影响，以及潜在空气污染缓解措施的效果。我们在实验室方法方面的最新进展以及计划在阿拉斯加费尔班克斯密集的冬季空气污染测量现场，为我们提供了一个及时的机会，让我们对冬季污染期间的异质HONO来源有新的理解。结果将有助于改善对世界许多地区冬季空气污染的理解和预测，这些地区在冬季出现寒冷、低阳光的条件。

Air pollution is the leading environmental risk to human health. Wintertime pollution events lead to violations of air quality (AQ) standards for particulate pollution in many regions of the world, including the UK. Despite limited sunlight availability in these events, secondary atmospheric production of aerosol particles appears to make an important contribution to particulate pollutant concentrations, which well-established oxidation mechanisms cannot explain. High levels of sulfate observed during such severe winter pollution episodes cannot be explained by current air quality models. Nitrous acid (HONO) is an important source of the chief atmospheric oxidant, OH, in polluted atmospheres. There is growing evidence that HONO produced via heterogeneous aerosol chemistry occurring on particle surfaces is important in wintertime conditions, where HONO may contribute up to 90% of primary OH production in polluted winter urban regions. There is incomplete understanding of this source and it is not included in air pollution forecasting models. Here we will undertake an ambitious integration of laboratory, field and modelling studies to establish the role of heterogeneous HONO production in a polluted high latitude city (Fairbanks, Alaska) and in London, through exploiting recently-developed laboratory capabilities, data that will become available through a planned international field campaign, and new model schemes for aerosol chemistry. Our approach will involve undertaking laboratory experiments on aerosol samples collected in the field, in which we will directly monitor the production of HONO from aerosol filters as a function of varying light, humidity, temperature and aerosol composition. These results will then be used to produce new model parameterisations for aerosol HONO production that will be tested against field observations from Fairbanks using a chemical box model framework. Finally, regional model simulations using the WRF-Chem model will be used to scale up the impacts of the aerosol HONO source on air quality in wintertime Fairbanks and London, UK. Our project will deliver new parameterisations and capabilities for including a heterogeneous HONO source in air quality models, including dependencies on aerosol composition, which we will make available to the community via our links with the global and regional WRF-Chem modelling communities. We will link with the new UK Strategic Priority Fund (SPF) Clean Air programme to exploit the newly funded UK Emissions Modelling System (UK-EMS), and to determine the impact of these processes on recent extreme wintertime pollution events in London, and on the efficacy of potential air pollution mitigation measures. Our recent advances in laboratory methods and a planned wintertime air pollution measurement field intensive in Fairbanks, Alaska, provide a timely opportunity to gain new understanding of a heterogeneous HONO source during winter pollution episodes. Outcomes will enable improved understanding and forecasting of wintertime air pollution across many regions of the world, where cold, low sunlight conditions occur in wintertime.