Secondary Organic Aerosol Prediction in Realistic Atmospheres (SOAPRA)

气溶胶颗粒是空气质量下降的主要驱动因素，并显著抵消了温室气体造成的变暖。有机组分经常被观察到占主导地位的质量的细颗粒物（PM）和二次有机气溶胶（SOA）是主要的贡献者。由于空气污染每年造成全球11%的死亡，空气温度上升幅度在巴黎协定缔约方所追求的目标的0.5摄氏度以内，因此需要对有机气溶胶颗粒质量负荷进行准确预测，以便为政策决策提供信息。我们将询问最近具有里程碑意义的研究中提出的实验结果，以调查大气混合物中SOA形成的机制。我们将包括新的机械化学的理解，从这项工作发展到一个耦合模型的气体光化学和气溶胶的形成。将模型与测量的气体和气溶胶成分进行详细比较，将使我们对真实的大气中可能发生的相互作用的理解具有前所未有的信心。我们将使用该模型来演示在含有天然和人造污染物的气团中预期的相互作用的大小，这有望首次对真实的大气中SOA的形成进行合理的机械解释。我们将开发一个氧化化学导致SOA形成在现实的大气混合物，包括生物和人为前体之间的相互作用的机械定量表示。我们将通过与现有的和新出现的实验数据进行比较来证明其预测能力，并使用它来评估SOA形成的潜力和VOC混合物中VOC的不确定性范围：适用于真实的大气的NOx制度。我们最近的研究（McFigans等人，2019年）是变革性的，因为它表明，在气态前体的混合物中形成的颗粒物质不能被假定为独立于混合物组分形成的颗粒物质的总和。我们证明了这是由两种效应引起的：i）氧化剂清除;前体分子对可用氧化剂的竞争;以及ii）产物清除;否则将反应形成冷凝颗粒物质的氧化产物之间的气相相互作用。这两种效应导致需要一个现实的处理SOA的形成在混合物中，以预测大气PM负荷及其对人类健康和气候的影响。我们有大量已发表和（尚未）未发表的实验室和室内实验的数据，调查SOA的形成从氧化的个别VOC及其混合物。在每一个，我们量化的形成高含氧有机分子（HOM）被发现是主要贡献者的浓缩SOA质量。挥发性有机化合物包括主要的生物和人为类的SOA前体的关键物种。我们将扩展大气VOC氧化的基准机制，将HOM的最新机制理解纳入我们的耦合光化学和气溶胶微物理的腔室模型。我们将优化模拟使用该模型与实验数据进行比较，并进行进一步的模拟，以建立SOA形成在大气中的关键依赖关系。大规模的空气质量和气候模型需要捕捉这些关系，以使人们对它们的预测充满信心。我们将包括一个简化的机制，基于相同的框架，作为我们更详细的计划到EMEP区域污染模型，以证明挥发性有机化合物的大气混合物的相互作用对区域PM的影响。

Aerosol particles are key drivers of reduced air quality and provide significant offsetting of warming by greenhouse gases. The organic fraction is frequently observed to dominate mass of fine particulate matter (PM) and secondary organic aerosol (SOA) is the major contributor. With air pollution responsible for 11 % of global deaths annually and air temperature rise within 0.5 degree C of the target pursued by Paris Agreement signatories, accurate forecasts of organic aerosol particle mass loadings are required to inform policy decisions.We will interrogate experimental results presented in our recent landmark study to investigate the mechanisms determining SOA formation in atmospheric mixtures. We will include new mechanistic chemical understanding developed from this work into a coupled model of gaseous photochemistry and aerosol formation. Detailed comparison of the model with measured gaseous and aerosol composition will enable unprecedented confidence in our understanding of the interactions that can occur in the real atmosphere. We will use the model to demonstrate the magnitude of interactions to be expected in airmasses containing natural and manmade pollutants that promises to enable reasonable mechanistic interpretation of SOA formation in the real atmosphere for the first time.What... We will develop a mechanistic quantitative representation of oxidative chemistry leading to SOA formation in realistic atmospheric mixtures including interactions between biogenic and anthropogenic precursors. We will demonstrate its predictive capability by comparison with existing and emerging experimental data and use it to evaluate the potential for SOA formation and uncertainty ranges across VOC mixtures at VOC:NOx regimes applicable to the real atmosphere.Why... Our recent study (McFiggans et al., 2019) was transformative in that it showed that the formation of particulate mass in mixtures of gaseous precursors cannot be assumed to be the sum of that formed independently from the components of the mixture. We demonstrated that this resulted from two effects: i) oxidant scavenging; competition of the precursor molecules for the available oxidant and ii) product scavenging; vapour phase interactions between oxidation products that would have otherwise reacted to form condensed particulate mass. These two effects lead to the requirement for a realistic treatment of SOA formation in mixtures in order to predict atmospheric PM loading and its effect on human health and climate.How... We have data from a large number of published and (as yet) unpublished laboratory and chamber experiments, investigating SOA formation from the oxidation of individual VOC and their mixtures. In each, we quantify the formation of highly-oxygenated organic molecules (HOM) found to be major contributors to the condensed SOA mass. The VOC include key species from the major biogenic and anthropogenic classes of SOA precursors. We will extend the benchmark mechanism for atmospheric VOC oxidation to incorporate the most recent mechanistic understanding of HOM into our chamber model of coupled photochemistry and aerosol microphysics. We will optimise simulations using this model by comparison with the experimental data and conduct further simulations to establish the critical dependencies of SOA formation in the atmosphere. Large scale air quality and climate models will need to capture these relationships to enable confidence to be placed in their predictions. We will include a simplified mechanism based on the same framework as our more detailed scheme into the EMEP regional pollution model to demonstrate the impact of interactions in atmospheric mixtures of VOC on regional PM.