Shipping is the largest means of moving freight globally. Ships consume dirty fuels, making them one of the most important sources of anthropogenic aerosol in the marine atmosphere. Aerosols from shipping can affect the climate directly through absorption and scattering of radiation, with an overall cooling effect to the atmosphere.
They can also indirectly influence the climate by changing cloud properties, e.g., albedo and lifetime, which further cools the atmosphere. Two key challenges for assessing future climate impact of shipping emission are (i) knowing the status of the present-day aerosol system – as a baseline from which any climate predictions are made and (ii) quantifying the amount of pollutants emitted. Currently little consensus exists on the impact of shipping emissions in the Arctic and North Atlantic Atmosphere (ANAA) primarily due to a lack of observations and insufficient model skills. Recent modelling work suggests that the Arctic aerosol baseline should account for a disparate range of natural sources. Few models are sufficiently comprehensive, and while some models can reproduce aerosol in some Arctic regions, there is evidence that models can produce similar results via different sources and processes. An inability to reflect the aerosol baseline processes can have significant impact on the reliability of future climate projections. Shipping is also undergoing significant changes. In January 2020, a new International Maritime Organisation (IMO) regulation comes into force, which reduces, by more than 80%, the sulphur content in maritime fuel oils. Superimposed on that, recent climate induced changes in Arctic sea ice are opening up new seaways enabling shorter sea passages between key markets. Significant growth in shipping via the North West Passage (NWP) is anticipated in the coming years. Thus, there is a short window of opportunity to define current atmospheric conditions, against which the impact of these changes must be determined. SEANA will take advantage of the above-mentioned opportunity to make multiple atmospheric measurements over multiple platforms to understand the present-day baselines – sources of aerosol particles including the contribution from shipping – and to determine the response of ANAA aerosol to new fuel standards after 2020. Extended measurements will be conducted at two stations adjacent to the NWP enabling the source of particles to be apportioned using receptor modelling approaches. In addition, SEANA will participate in a Korean cruise to the west side of the NWP, and a NERC cruise to the east, to measure both natural and anthropogenic particles and aerosol processes in two contrasting Arctic environments. These new observations will be integrated with recent / ongoing measurements at partner ANAA stations to generate a benchmark dataset on aerosol baseline in ANAA to constrain processes in the UK’s leading global aerosol model, ensuring that the model is reproducing the baseline aerosol in the ANAA faithfully. We will then test the models’ response to significant reductions in shipping sulphur emissions using observations taken during the transition to low-sulphur fuels in 2020. The revised model, which can reproduce current "baselines" and accurately predict the response of emission changes in the ANAA, will then be used to predict the future impact of shipping on air quality, clouds and radiative forcing under multiple sea-ice and shipping scenarios. SEANA will deliver a major enhancement of UK’s national capacity in capturing baseline ANAA aerosol and responses to emission regulations, results of which will inform shipping policy at high-latitudes.