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

船只通常燃烧低质量的燃料，向海洋上空的大气排放大量二氧化硫和颗粒物，或称气溶胶(高浓度时是有害的)。在云层存在的情况下，二氧化硫迅速转化为更多的粒子质量，使它们长大到作为云滴形成地点的大小。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，每年导致全球40万人过早死亡。在英国，空气污染(包括船舶排放)每年造成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月起出台新规定，要求国际水域的船舶将最大硫排放量从燃油质量的3.5%降至0.5%。船舶排放的颗粒可能会增加云滴的数量，并可能形成更明亮的云区，称为船迹。在很大程度上由于这种效应，一些全球模型预测，船舶排放的颗粒物目前对全球气候产生了重大的降温影响，掩盖了温室气体排放造成的变暖的一小部分。因此，尽管船舶硫排放的减少预计将通过硫酸盐气溶胶的减少将全球过早死亡的数量减少近一半，但航运产生的温室气体(例如二氧化碳)缺乏类似的减少可能会导致整体气候变暖。然而，颗粒物造成的降温幅度非常不确定，全球模型和基于卫星的估计之间存在很大差异。这可能是由于在全球模型中对气溶胶对云的影响的表述不准确，或者是由于卫星对船舶航迹的探测存在偏差。此外，航运公司如何在监督具有挑战性的国际水域对2020年的条例(即遵守程度和方法)作出反应，在很大程度上是未知的，需要观察性核查。2020年，我们将充分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，我们将调查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。该项目的成果将提高我们对船舶排放对空气质量和气候影响的了解。

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.