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主要环境风险。在包括英国在内的世界许多地区，冬季污染事件导致颗粒物污染违反空气质量（AQ）标准。尽管在这些事件中可利用的阳光有限，大气中产生的二次气溶胶颗粒似乎对颗粒污染物浓度有重要贡献，这是成熟的氧化机制无法解释的。目前的空气质量模式无法解释在这种严重的冬季污染事件中观测到的高浓度硫酸盐。亚硝酸（HONO）是污染大气中主要大气氧化剂OH的重要来源。越来越多的证据表明，在冬季条件下，通过颗粒表面发生的非均质气溶胶化学产生的HONO很重要，在冬季污染的城市地区，HONO可能贡献高达90%的初级OH产量。对这一来源的了解不完全，而且它没有包括在空气污染预测模型中。在这里，我们将进行一项雄心勃勃的实验室、实地和建模研究的整合，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和气溶胶化学的新模型方案，来确定在一个受污染的高纬度城市（阿拉斯加费尔班克斯）和伦敦的异质HONO生产的作用。我们的方法包括对实地收集的气溶胶样本进行实验室实验，直接监测气溶胶过滤器产生的HONO随光照、湿度、温度和气溶胶成分的变化而变化。然后，这些结果将用于产生气溶胶HONO生产的新模型参数化，该模型将使用化学盒模型框架对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气溶胶HONO源对英国费尔班克斯和伦敦冬季空气质量的影响。我们的项目将提供新的参数化和能力，包括在空气质量模型中包含异质HONO源，包括对气溶胶成分的依赖，我们将通过与全球和区域WRF-Chem建模社区的联系向社区提供。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），并确定这些过程对伦敦最近冬季极端污染事件的影响，以及对潜在空气污染缓解措施的有效性的影响。我们在实验室方法和计划在阿拉斯加费尔班克斯进行的冬季空气污染密集测量方面的最新进展，为在冬季污染事件中获得非均匀HONO源的新认识提供了及时的机会。研究成果将有助于提高对冬季寒冷、日照不足的世界许多地区冬季空气污染的了解和预测。

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.