Assessment of the sensitivity of model responses to urban emission changes in support of emission reduction strategies

© 2023 The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/The sensitivity of air quality model responses to modifications in input data (e.g. emissions, meteorology and boundary conditions) or model configurations is recognized as an important issue for air quality modelling applications in support of air quality plans. In the framework of FAIRMODE (Forum of Air Quality Modelling in Europe, https://fairmode.jrc.ec.europa.eu/) a dedicated air quality modelling exercise has been designed to address this issue. The main goal was to evaluate the magnitude and variability of air quality model responses when studying emission scenarios/projections by assessing the changes of model output in response to emission changes. This work is based on several air quality models that are used to support model users and developers, and, consequently, policy makers. We present the FAIRMODE exercise and the participating models, and provide an analysis of the variability of O3 and PM concentrations due to emission reduction scenarios. The key novel feature, in comparison with other exercises, is that emission reduction strategies in the present work are applied and evaluated at urban scale over a large number of cities using new indicators such as the absolute potential, the relative potential and the absolute potency. The results show that there is a larger variability of concentration changes between models, when the emission reduction scenarios are applied, than for their respective baseline absolute concentrations. For ozone, the variability between models of absolute baseline concentrations is below 10%, while the variability of concentration changes (when emissions are similarly perturbed) exceeds, in some instances 100% or higher during episodes. Combined emission reductions are usually more efficient than the sum of single precursor emission reductions both for O3 and PM. In particular for ozone, model responses, in terms of linearity and additivity, show a clear impact of non-linear chemistry processes. This analysis gives an insight into the impact of model’ sensitivity to emission reductions that may be considered when designing air quality plans and paves the way of more in-depth analysis to disentangle the role of emissions from model formulation for present and future air quality assessments.Peer reviewe

Environmental impacts of exhaust gas cleaning systems in the Baltic Sea, North Sea, and the Mediterranean Sea area

Shipping is responsible for a range of different pressures affecting air quality, climate, and the marine environment. Most social and economic analyses of shipping have focused on air pollution assessment and how shipping may impact climate change and human health. This risks that policies may be biased towards air pollution and climate change, whilst impacts on the marine environment are not as well known. One example is the sulfur regulation introduced in January 2020, which requires shipowners to use a compliant fuel with a sulfur content of 0.5% (0.1% in SECA regions) or use alternative compliance options (Exhaust Gas Cleaning Systems, EGCS) that are effective in reducing sulfur oxide (SOx) emissions to the atmosphere. The EGCS cleaning process results in large volumes of discharged water that includes a wide range of contaminants. Although regulations target SOx removal, other pollutants such as polycyclic aromatic hydrocarbons (PAHs), metals and combustion particles are removed from the exhaust to the wash water and subsequently discharged to the marine environment. Based on dilution series of the Whole Effluent Testing (WET), the impact of the EGCS effluent on marine invertebrate species and on phytoplankton was found to vary between taxonomic groups, and between different stages of the invertebrate life cycle. Invertebrates were more affected than phytoplankton, and the most sensitive endpoint detected in the present project was the fertilisation of sea urchin eggs, which were negatively affected at a sample dilution of 1 : 1,000,000. Dilutions of 1: 100,000 were harmful to early development of several of the tested species, including mussels, polychaetes, and crustaceans. The observed effects at these low concentrations of EGCS effluent were reduced egg production, and deformations and abnormal development of the larvae of the species. The ecotoxicological data produced in the EMERGE project were used to derive Predicted No Effect Concentration values. Corresponding modelling studies revealed that the EGCS effluent can be considered as a single entity for 2-10 days from the time of discharge, depending on the environmental conditions like sea currents, winds, and temperature. Area 10-30 km outside the shipping lanes will be prone to contaminant concentrations corresponding to 1 : 1,000,000 dilution which was deemed harmful for most sensitive endpoints of WET experiments. Studies for the Saronikos Gulf (Aegean Sea) revealed that the EGCS effluent dilution rate exceeded the 1 : 1,000,000 ratio 70% of the time at a distance of about 10 km from the port. This was also observed for 15% of the time within a band of 10 km wide along the shipping lane extending 500 km away from the port of Piraeus. When mortality of adult specimens of one of the species (copepod Acartia tonsa) was used as an endpoint it was found to be 3-4 orders of magnitude less sensitive to EGCS effluent than early life stage endpoints like fertilisation of eggs and larval development. Mortality of Acartia tonsa is commonly used in standard protocols for ecotoxicological studies, but our data hence shows that it seriously underestimates the ecologically relevant toxicity of the effluent. The same is true for two other commonly used and recommended endpoints, phytoplankton growth and inhibition of bioluminescence in marine bacteria. Significant toxic effects were reached only after addition of 20-40% effluent. A marine environmental risk assessment was performed for the Öresund region for baseline year 2018, where Predicted Environmental Concentrations (PECs) of open loop effluent discharge water were compared to the PNEC value. The results showed modelled concentrations of open loop effluent in large areas to be two to three orders of magnitude higher than the derived PNEC value, yielding a Risk Characterisation Ratio of 500-5000, which indicates significant environmental risk. Further, it should be noted that between 2018-2022 the number of EGCS vessels more than quadrupled in the area from 178 to 781. In this work, the EGCS discharges of the fleet in the Baltic Sea, North Sea, the English Channel, and the Mediterranean Sea area were studied in detail. The assessments of impacts described in this document were performed using a baseline year 2018 and future scenarios. These were made for the year 2050, based on different projections of transport volumes, also considering the fuel efficiency requirements and ship size developments. From the eight scenarios developed, two extremes were chosen for impact studies which illustrate the differences between a very high EGCS usage and a future without the need for EGCS while still compliant to IMO initial GHG strategy. The scenario without EGCS leads to 50% reduction of GHG emissions using low sulfur fuels, LNG, and methanol. For the high EGCS adoption scenario in 2050, about a third of the fleet sailing the studied sea areas would use EGCS and effluent discharge volumes would be increased tenfold for the Baltic Sea and hundredfold for the Mediterranean Sea when compared to 2018 baseline discharges. Some of the tested species, mainly the copepods, have a central position in pelagic food webs as they feed on phytoplankton and are themselves the main staple food for most fish larvae and for some species of adult fish, e.g., herring. The direct effect of the EGSE on invertebrates will therefore have an important indirect effect on the fish feeding on them. Effects are greatest in and near shipping lanes. Many important shipping lanes run close to shore and archipelago areas, and this also puts the sensitive shallow water coastal ecosystems at risk. It should be noted that no studies on sub-lethal effects of early 19 life stages in fish were included in the EMERGE project, nor are there any available data on this in the scientific literature. The direct toxic effects on fish at the expected concentrations of EGCS effluent are therefore largely unknown. According to the regional modelling studies, some of the contaminants will end up in sediments along the coastlines and archipelagos. The documentation of the complex chemical composition of EGCS effluent is in sharp contrast to the present legislation on threshold levels for content in EGCS effluent discharged from ships, which includes but a few PAHs, pH, and turbidity. Traditional assessments of PAHs in environmental and marine samples focus only on the U.S. Environmental Protection Agency (EPA) list of 16 priority PAHs, which includes only parent PAHs. Considering the complex PAHs assemblages and the importance of other related compounds, it is important to extend the EPA list to include alkyl-PAHs to obtain a representative monitoring of EGCS effluent and to assess the impact of its discharges into the marine environment. An economic evaluation of the installation and operational costs of EGCS was conducted noting the historical fuel price differences of high and low sulfur fuels. Equipment types, installation dates and annual fuel consumption from global simulations indicated that 51% of the global EGCS fleet had already reached break-even by the end of 2022, resulting in a summarised profit of 4.7 billion €2019. Within five years after the initial installation, more than 95% of the ships with open loop EGCS reach break-even. The pollutant loads from shipping come both through atmospheric deposition and direct discharges. This underlines the need of minimising the release of contaminants by using fuels which reduce the air emissions of harmful components without creating new pollution loads through discharges. Continued use of EGCS and high sulfur fossil fuels will delay the transition to more sustainable options. The investments made on EGCS enable ships to continue using fossil fuels instead of transitioning away from them as soon as possible as agreed in the 2023 Dubai Climate Change conference. Continued carriage of residual fuels also increases the risk of dire environmental consequences whenever accidental releases of oil to the sea occur.nonPeerReviewe