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Background Modeling Report Disclaimer The findings, interpretations, and conclusions expressed in this work do not necessarily reflect theviews of The World Bank, its Board of Executive Directors, or the governments they represent.The World Bank does not guarantee the accuracy, completeness, or currency of the data includedin this work and does not assume responsibility for any errors, omissions, or discrepancies in theinformation or liability with respect to the use of or failure to use the information, methods, processes,or conclusions set forth. The boundaries, colors, denominations, and other information shown onany map in this work do not imply any judgment on the part of The World Bank concerning the legalstatus of any territory or the endorsement or acceptance of such boundaries. The contents of thiswork are intended for general informational purposes only and are not intended to constitute legal,securities, or investment advice, an opinion regarding the appropriateness of any investment, or asolicitation of any type. Some of the organizations of The World Bank Group or their affiliates mayhave an investment in, provide other advice or services to, or otherwise have a financial interest in,certain of the companies and parties named herein. Nothing herein shall constitute or be construedor considered to be a limitation upon or waiver of the privileges and immunities of any of theorganizations of The World Bank Group, all of which are specifically reserved. Rights and permissionsThe material in this work is subject to copyright. Because The World Bank Group encourages dissemination of its knowledge, this work may be reproduced, in whole or in part, for non-commercialpurposes as long as full attribution to this work is given and all further permissions that may berequired for such use (as noted herein) are acquired. The World Bank Group does not warrant thatthe content contained in this work will not infringe on the rights of third parties and accepts noresponsibility or liability in this regard. All queries on rights and licenses should be addressed toWorld Bank Publications, The World Bank Group, 1818 H Street NW, Washington, DC 20433, USA;e-mail:pubrights@worldbank.org.Cover photo: ©ngairamandara Acknowledgements This modeling report contributes to the World Bank “Accelerating Access to Clean Air for a LivablePlanet” report, which identifies the main sources of current global air pollution and details howintegrated climate change and air quality management policies could yield significant reductionsin future air pollution exposure. In addition to providing details about the methodology used for the modeling exercise, it exploreskey directions for policies and measures that would deliver improved air quality—especially in theregions currently experiencing the most air pollution—while paying special attention to the economiccapacities of low- and middle-income countries. The report also includes a quantitative assessment of the cost-effectiveness of proven emissioncontrol options to help identify measures that meet the objective of improved global air qualitywithout placing undue economic pressure on countries in order to achieve the World HealthOrganization’s interim targets. This methodology report was prepared by Markus Amann (World Bank) based on inputs prepared byWolfgang Schöpp and the team at the International Institute for Applied Systems Analysis (IIASA),which included Gregor Kiesewetter, Fabian Wagner, Zbigniew Klimont, Florian Lindl, Pallav Purohit,Adriana Gomez-Sanabria, Shaohui Zhang, Robert Sander, Jessica Slater. The Global Program on Sustainability Trust Fund provided funding to support this report. It wasedited by Jennifer Stastny and designed by Mariaan van Zyl. Contents Main Messages Contents1.Introduction 1.Introduction2. Methodology 2.Methodology122.1Approach122.2Pollutant focus132.3Modelingcurrent and futureexposure to air pollution152.3.1Modeling tools152.3.2Spatial resolution172.3.3Future air quality scenarios2.1 Approach2.2 Pollutant focus2.3 Modeling current and future exposure to air pollution2.3.1 Modeling tools2.3.2 Spatial resolution2.3.3 Future air quality scenarios2.3.4 Cost-effectiveness analysis12131515162022 213. Global air quality in 2020 24 244. Perspectives to 2040 3.Global air quality in 2020254.Perspectives to 20404.1A baseline projection for 2040:the Stated Policies scenario294.1.1Emissiontrendsbyregion294.1.2Population exposure4.2Policies and measures that havesuccessfully decoupled air pollution and economic growth344.3Thescope for further policyinterventions in 2040354.4A clean air scenario for 2040with a focus on the worst polluted areas394.4.1An illustrative target for 2040:Halve the number of people exposed to PM2.5concentrations of more than 25 μg/mμin 2020.4.1 A baseline projection for 2040: the Stated Policies scenario4.1.1 Emission trends by world region4.1.2 Population exposure4.2 Policies and measures that have successfully decoupl