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Hydrofluorocarbons (HFCs) are widely used as cooling agents in refrigeration and air conditioning, as solvents in industrial processes, and as fire-extinguishing agents, foam blowing, and aerosol propellants. They have been used in large quantities as the primary substitutes for ozone-depleting substances regulated under the Montreal Protocol. HFC refrigerant gases are the fastest-growing atmospheric greenhouse gases and amongst the most potent. The Kigali Amendment (KA) to the Montreal Protocol is an international agreement to gradually reduce the consumption and production of HFCs. It is well established that full global compliance with the current KA phasedown schedule will not mitigate future emissions at levels consistent with the Paris Agreement target to limit global warming in this century to 1.5°C, compared to pre-industrial levels. Even though full compliance with the KA phasedown schedule is projected to achieve substantial avoided warming (0.2 to 0.4°C) by the end of this century but is insufficient to achieve a 1.5°C-consistent target. Therefore, in this study, we present HFC emissions in the pre-Kigali baseline scenario analyze HFC phase-down under the Kigali Amendment (KA), Maximum Technically Feasible Reduction (MTFR), and develop alternative pathways due to the enhanced ambition of parties to the Montreal Protocol to phase-down HFCs. However, in keeping with the Montreal Protocol’s history of strengthening through regular amendments, this study indicates that fast-tracking HFC phasedown under the KA will be consistent with the Paris Agreement targets following the example of accelerated phase-out of hydrochlorofluorocarbons (HCFCs) under the Montreal Protocol.

This study focuses on implications of differences between recent global emissions inventories for simulated trends in anthropogenic aerosol abundances and radiative forcing (RF) over the 1990–2019 period. We use the ECLIPSE version 6 (ECLv6) and CEDS year 2021 release (CEDS21) as input to the chemical transport model OsloCTM3 and compare the resulting aerosol evolution to corresponding results derived with the first CEDS release, as well as to observed trends in regional and global aerosol optical depth (AOD). Using CEDS21 and ECLv6 results in a 3 % and 6 % lower global mean AOD compared to CEDS in 2014, primarily driven by differences over China and India, where the area average AOD is up to 30 % lower. These differences are considerably larger than the satellite-derived interannual variability in AOD. A negative linear trend over 2005–2017 in global AOD following changes in anthropogenic emissions is found with all three inventories but is markedly stronger with CEDS21 and ECLv6. Furthermore, we confirm that the model better captures the sign and strength of the observed AOD trend over China with CEDS21 and ECLv6 compared to using CEDS, while the opposite is the case for South Asia. We estimate a net global mean aerosol-induced RF in 2014 relative to 1990 of 0.08 W m−2 for CEDS21 and 0.12 W m−2 for ECLv6, compared to 0.03 W m−2 with CEDS. Using CEDS21, we also estimate the RF in 2019 relative to 1990 to be 0.10 W m−2, reflecting the continuing decreasing trend in aerosol loads post-2014. Our results facilitate more rigorous comparison between existing and upcoming studies of climate and health effects of aerosols using different emission inventories.

Despite policies that have improved air quality, the populations of the Association of Southeast Asian Nations (ASEAN) continue to experience a large health burden due to air pollution exposure. Solutions for further improving air quality exist and could result in large health benefits, as well as co-benefits, among others, for climate change and sustainable development. However, significant financing, coordination, and capacity barriers continue to limit the effective implementation of such solutions.

A shift from fossil fuel to renewable energy is crucial in achieving climate goals of 2 degrees Celsius. However, the renewable energy technologies, solar photovoltaics, wind turbines, and electric vehicles are metal-intensive, while the mining and smelting processes to obtain the relevant metals are emissions-intensive. We estimate future PM2.5 emissions from mining and smelting to meet the metal demand of renewable energy technologies in two climate pathways to be around 0.3-0.6 Tg/yr in the 2030-2040 period, which could be around 10-30% of total anthropogenic PM2.5 emissions in many countries in those years. The concentration of mineral reserves in a few regions means the impacts are also regionally concentrated. The regional distributions of global emissions relative to metal demand depend on the metal production regionality and emission abatement measures. Stronger emissions abatement could reduce metal-related emissions by over 90% and avoid emission hotspot creation.

Despite significant reductions in nitrogen emissions achieved in Europe during the last three decades, eutrophication remains an environmental concern in the Baltic Sea basin. Recently, a number of comprehensive modelling studies have been conducted for the HELCOM Commission to inform the 2021 update of the Baltic Sea Action Plan. The calculations have focused on trends in airborne nitrogen deposition to the Baltic Sea and its nine sub-basins during the 2000-2017 period, the identification and ranking of the main contributors to deposition, as well as future projections for 2030, assuming compliance with the Gothenburg Protocol and the EU NEC Directive. This paper synthesizes the main results from these studies and puts them into the context of maximum allowable nutrient inputs to the Baltic Sea. According to our results, the airborne annual deposition to the Baltic Sea in 2017 amounted to 122.6 Gg(N) of oxidized nitrogen and 105.3 Gg(N) of reduced nitrogen, corresponding to a decrease since 2000 by, respectively, 39% and 11%. In order to filter out the large inter-annual variability due to meteorology and to better reflect trends in emissions, weather-normalized depositions of nitrogen have been calculated as well, according to which the decreases since 2000 amount to 35%, 7% and 25% for oxidized, reduced and total nitrogen, respectively. In 2017, Germany, Poland and Denmark were the most important contributors to airborne deposition of total (oxidized + reduced) nitrogen to the Baltic Sea. Agriculture contributed most to reduced nitrogen deposition, while the transport sector contributed most to oxidized nitrogen deposition. Agriculture in Germany was the single-most important contributor to nitrogen deposition to the Baltic Sea basin in 2017 (accounting for about 15% of the total), but there are numerous other important sectoral contributions. Emissions of nitrogen from the nine HELCOM Contracting Parties contributed 49%, 76% and 61% to oxidized, reduced and total nitrogen deposition, respectively. Assuming full compliance with the EU NEC Directive and the Gothenburg Protocol, significant further reductions in nitrogen deposition can be achieved by 2030, down to an annual deposition of 72.7 Gg(N) and 84.7 Gg(N) of oxidized and reduced nitrogen, respectively.

This brief outlines how the 'Triple R framework’—Response, Recovery and Redesign—can help align different government agency and other stakeholder interests behind the kind of integrated clean air, climate, and health policies that can deliver co-benefits.

Over the last decades the European Union has established strict air quality objectives, together with a comprehensive legal framework that should facilitate the achievements of these objectives. As a consequence, air quality has drastically improved in Europe, although the long-term objectives are still not met. The EU clean air legislation played an important role in these air quality improvements. Most importantly, the legal framework provided an effective response mechanism strategy to manage the complex interlinkages between the multitude of pollution sources and the regionally dispersed impacts on air quality which span across different legislation. These connections, which are a direct consequence of the physical nature of the key air pollutants (i.e., their long residence time in the atmosphere), make response strategies that extend beyond individual cities and countries indispensable. In order to implement effective policy responses, the area of the European Union is now considered as one airshed containing 27 Member States, and action needs to be coordinated between countries, regions, and city administrations. The clean air legislation of the EU acknowledges that the European Union as a supra-national institution has to play an important coordinating role in the policy response. It has been found practical to combine three legal pillars into a comprehensive EU clean air legislation framework: • The Ambient Air Quality Directives, • The National Emission Ceilings Directive, and • Source-specific performance standards. One important feature of EU policy that contributed to the success is that, in addition to the key obligations for reaching air quality standards and reducing emissions, all directives contain specific requirements and mechanisms for monitoring, reporting, validation and enforcement. Although the recent nature of some of the directives does not always allow for practical experience, systematic stock-taking on the strengths and weaknesses of older legislation has been recently conducted. This report summarizes the findings emerging from these assessments and indicates options for improvements that could be of interest for the design of effective clean air policies in other parts of the world. While the EU legal framework has obviously been developed for the EU situation, there might be important lessons, particularly on monitoring, review and verification, that could provide relevant insights for other countries which face similar complexities in air quality management, e.g., the need to involve multiple governance levels across State borders.

The fast economic and population growth in India’s urban areas and the limited control of pollution are causing public health problems and significant environmental degradation, including air, water, land and greenhouse gases, which undermines the potential for sustainable socioeconomic development of the country, particularly with impacts on the poor. To improve air quality and enhance economic and social development, the Government of India has issued a National Ambient Air Quality Standard (NAAQS) for annual average PM2.5 concentrations of 40 �g/m3. However, this standard is widely exceeded, and according to the World Health Organisation (WHO), India was home to 13 out of the 15 most polluted cities worldwide in terms of PM2.5 concentrations in 2016. This study explores pathways towards achieving the NAAQS in India in the context of the dynamics of social and economic development up to 2050. For this purpose, we employ two well-established scientific modelling tools that explore the socio-economic drivers of pollution (the GCAM model), in particular, energy consumption, and the GAINS model that explores effective policy interventions to reduce population exposure and health impacts. We estimate that in 2015 more than half of the Indian population, i.e. about 670 million people, was exposed to ambient PM2.5 concentrations that do not comply with India’s NAAQS, and less than 1% enjoyed air quality conforming with the global WHO guideline value of 10 �g/m3. Without further political action, this figure is not expected to improve. While the existing emission control measures are effectively decoupling the trends of air pollutant emissions from economic growth, their impacts on ambient air quality are not directly visible since they are compensated by the rapid expansion of economic activities. The analysis reveals that advanced technical emission controls can deliver air quality improvements in India, but will not be sufficient to achieve the NAAQS everywhere. However, a package of development and decarbonization measures that are usually taken for other policy priorities can deliver significant co-benefits on air quality and achieve compliance with NAAQS for the vast majority of the population.

This report identifies 25 clean air measures that can positively impact human health, crop yields, climate change and socio-economic development, as well as contribute to achieving the Sustainable Development Goals. Implementing these measures could help 1 billion people breathe cleaner air by 2030 and reduce global warming by a third of a degree Celsius by 2050.

This document describes the methodology developed for the GAINS PMEH project. This methodology provides a framework for translating detailed data on emission control technologies and measures, atmospheric transport, costs, socio-economic development and health indicators from the GAINS databases into such a format and level of aggregation that they can be displayed and turned into an interactive decision support tool at various spatial scales, in particular the megacity scale. As an example we discuss the prototype for Hanoi and its environs.

India is currently experiencing degraded air quality, and future economic development will lead to challenges for air quality management. Scenarios of sectoral emissions of fine particulate matter and its precursors were developed and evaluated for 2015-2050, under specific pathways of diffusion of cleaner and more energy-efficient technologies. The impacts of individual source sectors on PM2:5 concentrations were assessed through systematic simulations of spatially and temporally resolved particulate matter concentrations, using the GEOS-Chem model, followed by population weighted aggregation to national and state levels. We find that PM2:5 pollution is a pan-India problem, with a regional character, and is not limited to urban areas or megacities. Under present-day emissions, levels in most states exceeded the national PM2:5 annual standard (40 mu g m(-3)). Sources related to human activities were responsible for the largest proportion of the present-day population exposure to PM2:5 in India. About 60% of India's mean population-weighted PM2:5 concentrations come from anthropogenic source sec-tors, while the remainder are from "other" sources, windblown dust and extra-regional sources. Leading contributors are residential biomass combustion, power plant and industrial coal combustion and anthropogenic dust (including coal fly ash, fugitive road dust and waste burning). Transportation, brick production and distributed diesel were other contributors to PM2:5. Future evolution of emissions under regulations set at current levels and promulgated levels caused further deterioration of air quality in 2030 and 2050. Under an ambitious prospective policy scenario, promoting very large shifts away from traditional biomass technologies and coal-based electricity generation, significant reductions in PM2:5 levels are achievable in 2030 and 2050. Effective mitigation of future air pollution in India requires adoption of aggressive prospective regulation, currently not formulated, for a three-pronged switch away from (i) biomass-fuelled traditional technologies, (ii) industrial coal-burning and (iii) open burning of agricultural residue. Future air pollution is dominated by industrial process emissions, reflecting larger expansion in industrial, rather than residential energy demand. However, even under the most active reductions envisioned, the 2050 mean exposure, excluding any impact from windblown mineral dust, is estimated to be nearly 3 times higher than the WHO Air Quality Guideline.

Bottom-up emission inventories provide primary understanding of sources of air pollution and essential input of chemical transport models. Focusing on SO2 and NOx, we conducted a comprehensive evaluation of two widely-used anthropogenic emission inventories over China, ECLIPSE and MIX, to explore the potential sources of uncertainties and find the clues in improving emission inventories. We first compared the activity rates and emission factors used in two inventories, and investigated the reasons of differences and the impacts on emission estimates. We found that SO2 emission estimates are consistent between two inventories (with 1 % differences), while NOx emissions in ECLIPSE's estimates are 16 % lower than those of MIX. Discrepancies at sectorial and provincial level are much higher. We then examined the impacts of different inventories on model performance, by using the nested GEOS-Chem model. We finally derived top-down NOx emissions by using the NO2 columns from the Ozone Monitoring Instrument (OMI) and compared with the bottom-up estimates. To our knowledge, this is the first work where source-sector comparisons are made along with the remote sensing retrievals and chemical transport modeling. Through the comparison between bottom-up emission inventories and evaluation with top-down information, we summarized the potential directions for further improvement in inventory development.

Vehicle emissions contribute to fine particulate matter (PM 2.5) and tropospheric ozone air pollution, affecting human health, crop yields and climate worldwide. On-road diesel vehicles produce approximately 20 per cent of global anthropogenic emissions of nitrogen oxides (NO x), which are key PM 2.5 and ozone precursors. Regulated NO x emission limits in leading markets have been progressively tightened, but current diesel vehicles emit far more NO x under real-world operating conditions than during laboratory certification testing. Here we show that across 11 markets, representing approximately 80 per cent of global diesel vehicle sales, nearly one-third of on-road heavy-duty diesel vehicle emissions and over half of on-road light-duty diesel vehicle emissions are in excess of certification limits. These excess emissions (totalling 4.6 million tons) are associated with about 38,000 PM 2.5 - and ozone-related premature deaths globally in 2015, including about 10 per cent of all ozone-related premature deaths in the 28 European Union member states. Heavy-duty vehicles are the dominant contributor to excess diesel NO x emissions and associated health impacts in almost all regions. Adopting and enforcing next-generation standards (more stringent than Euro 6/VI) could nearly eliminate real-world diesel-related NO x emissions in these markets, avoiding approximately 174,000 global PM 2.5 - and ozone-related premature deaths in 2040. Most of these benefits can be achieved by implementing Euro VI standards where they have not yet been adopted for heavy-duty vehicles.

Eric Zusman presented at the International Symposium: IIASA and Japan - Future prospects for closer collaboration centering around “The World in 2050 (TWI2050)” project - on 31 Jan. 2017 as a panelist.

To quantify changes in air pollution over Europe at the 2050 horizon, we designed a comprehensive modelling system that captures the external factors considered to be most relevant, and that relies on up-to-date and consistent sets of air pollution and climate policy scenarios. Global and regional climate as well as global chemistry simulations are based on the recent representative concentration pathways (RCP) produced for the Fifth Assessment Report (AR5) of the IPCC (Intergovernmental Panel on Climate Change) whereas regional air quality modelling is based on the updated emissions scenarios produced in the framework of the Global Energy Assessment. We explored two diverse scenarios: a reference scenario where climate policies are absent and a mitigation scenario which limits global temperature rise to within 2 °C by the end of this century. This first assessment of projected air quality and climate at the regional scale based on CMIP5 (5th Coupled Model Intercomparison Project) climate simulations is in line with the existing literature using CMIP3. The discrepancy between air quality simulations obtained with a climate model or with meteorological reanalyses is pointed out. Sensitivity simulations show that the main factor driving future air quality projections is air pollutant emissions, rather than climate change or intercontinental transport of pollution. Whereas the well documented "climate penalty" that weights upon ozone (increase of ozone pollution with global warming) over Europe is confirmed, other features appear less robust compared to the literature, such as the impact of climate on PM2.5. The quantitative disentangling of external factors shows that, while several published studies focused on the climate penalty bearing upon ozone, the contribution of the global ozone burden is somewhat overlooked in the literature.

This Final Report summarizes the IIASA contributions to the SLCP Assessment for LAC project. IIASA has delivered all agreed outputs with respect to modelling work required to develop baseline and mitigation scenarios where key SLCP mitigation measures were identified. The results in form of gridded emission fields were provided to the impact and climate modelling groups involved in the project. The developed protocol for data collection allowed to acquire a harmonized data set on emissions within the region for which a number of issues were identified and it was compared with the GAINS database, leading to its improvement. This exchange between the national experts and IIASA modelling team opens up a possibility for further collaboration where also ROLAC will play a role as the information has been stored there. The final historical inventories have been harmonized with the global GAINS database and served development of scenarios. While the GAINS model has been further developed to consider specific LAC circumstances and availability of new data, the baseline and mitigation scenarios were developed in a consistent way with the global UNEP/WMO Assessment allowing a comparison of the results. The finally selected SLCP measures include additional options which were not part of the global assessment, for example, reduction of gas flaring, introduction of Marques brick kilns, shale gas options, and options to mitigate HFCs.

Wildfires are not only a threat to human property and a vital element of many ecosystems, but also an important source of air pollution. In this study, we first review the available evidence for a past or possible future climate-driven increase in wildfire emissions in Europe. We then introduce an ensemble of model simulations with a coupled wildfire– dynamic-ecosystem model, which we combine with published spatial maps of both wildfire and anthropogenic emissions of several major air pollutants to arrive at air pollutant emission projections for several time slices during the 21st century. The results indicate moderate wildfire-driven emission increases until 2050, but there is a possibility of large increases until the last decades of this century at high levels of climate change. We identify southern and north-eastern Europe as potential areas where wildfires may surpass anthropogenic pollution sources during the summer months. Under a scenario of high levels of climate change (Representative Concentration Pathway, RCP, 8.5), emissions from wildfires in central and northern Portugal and possibly southern Italy and along the west coast of the Balkan peninsula are projected to reach levels that could affect annual mean particulate matter concentrations enough to be relevant for meeting WHO air quality targets.