Atmospheric Composition and Radiative forcing changes due to UN International Ship Emissions regulations (ACRUISE)

船舶通常燃烧低质量的燃料，并向海洋上方的大气中排放大量二氧化硫和微粒或气溶胶（高浓度有害）。在有云的情况下，二氧化硫迅速转化为更多的粒子质量，使它们的大小成为云滴形成的场所。鉴于约70%的航运活动发生在距离海岸400公里的范围内，船舶是沿海地区空气污染的一大来源，每年在全球造成40万人过早死亡。在英国，空气污染（包括船舶排放）每年导致4万人过早死亡。为了减少航运活动造成的空气污染，联合国国际海事组织（IMO）将从2020年1月起实施新规定，要求国际水域的船舶将其最大硫排放量从燃料质量的3.5%降低到0.5%。船舶排放的微粒可能会增加云滴的数量，并可能形成被称为船舶轨迹的明亮云层区域。主要由于这种影响，一些全球模式预测，船舶排放的微粒目前对全球气候具有显著的降温影响，掩盖了温室气体排放造成的一小部分变暖。因此，虽然船舶硫排放的减少预计将通过减少硫酸盐气溶胶使全球过早死亡人数减少近一半，但船舶温室气体（如二氧化碳）排放缺乏类似的减少可能导致整体气候变暖。然而，由颗粒物引起的降温幅度非常不确定，全球模式和基于卫星的估计之间存在很大差异。这可能是由于全球模式中气溶胶对云的影响的不精确表示或卫星探测船舶轨迹的偏差所致。此外，在监管具有挑战性的国际水域，航运公司如何应对2020年的法规（即合规程度和方法）在很大程度上是未知的，需要观察验证。我们将在2020年利用这一独特而激烈的“逆地球工程”事件。通过结合飞机观测、长期地面观测、卫星遥感和过程级模拟，研究2020年船舶硫排放法规对北大西洋大气成分、辐射强迫和气候的影响。该项目的结果将提高我们对船舶排放对空气质量和气候的影响的理解。

Ships generally burn low quality fuel and emit large quantities of sulfur dioxide and particulates, or aerosols (harmful at high concentrations), into the atmosphere above the ocean. In the presence of clouds the sulfur dioxide is rapidly converted into more particle mass growing them to sizes where they act as sites for cloud droplet formation. Given that about 70% of shipping activities occur within 400 km of the coast, ships are a large source of air pollution in coastal regions, causing 400k premature mortalities per year globally. In the UK, air pollution (including ship emissions) is responsible for 40,000 premature mortalities each year. In an effort to reduce air pollution from shipping activity, the United Nation's International Maritime Organization (IMO) is introducing new regulations from January 2020 that will require ships in international waters to reduce their maximum sulfur emissions from 3.5% by mass of fuel to 0.5%. Particulates emitted by ships may enhance the number of cloud droplets and potentially form regions of brighter clouds known as ship tracks. Largely because of this effect, some global models predict that ship emissions of particulates currently have a significant cooling influence on the global climate, masking a fraction of the warming caused by greenhouse gas emissions. So whilst a reduction in ship sulfur emission is predicted to almost halve the number of premature deaths globally via a reduction in sulfate aerosols, a lack of similar reductions in greenhouse gases from shipping (e.g. CO2) could lead to an overall climate warming. However, the magnitude of the cooling caused by particulates is very uncertain, with large discrepancies between global model and satellite-based estimates. This may be due to imprecise representations of the effects of aerosols on clouds in global models or biases in satellite detections of ship tracks. Furthermore, how shipping companies respond to the 2020 regulation (i.e. degree and method of compliance), in international waters where surveillance is challenging, is largely unknown and requires observational verification. We will take advantage of this unique and drastic "inverse geoengineering" event in 2020. By combining aircraft observations, long-term surface observations, satellite remote sensing, and process-level modelling, we will investigate the impact of the 2020 ship sulfur emission regulation on atmospheric composition, radiative forcing and climate in the North Atlantic. Results of this project will improve our understanding of the impact of ship emissions on air quality and climate.