Effectiveness of air pollution reduction policies and financial accessibility in ASEAN countries

Abstract Objective . This study aims to assess the effectiveness of air pollution reduction policies across ASEAN member states, with a particular focus on identifying implementation gaps. It further seeks to examine how development finance contributes to enabling or constraining these policy efforts, especially in the context of rapid urbanization, industrialization, and recurrent transboundary haze in the region. Methods . We employed a mixed-methods design. Quantitatively, we analyzed population-weighted annual PM 2.5 concentrations from 2010 to 2021 using data from the State of Global Air 2020. Qualitatively, we conducted a systematic review of peer-reviewed and grey literature using AI-assisted screening and analyzed official development assistance (ODA) data from major multilateral and bilateral donors. Findings . PM 2.5 levels have generally declined in ASEAN since 2010, although concentrations remain high in Myanmar, Cambodia, and Thailand. Countries with strong regulatory frameworks and financial support showed greater reductions. Periods of increased ODA investment (e.g., 2011, 2013, 2017) coincided with notable PM 2.5 declines, although these patterns reflect temporal associations rather than causal effects. However, national air quality standards remain poorly aligned with WHO guidelines, and air monitoring systems vary significantly. Transboundary haze and limited political commitment continue to hinder regional enforcement and cooperation. Conclusion . Policy effectiveness in ASEAN appears to be associated with national commitment and financial accessibility, rather than determined by any single policy or funding mechanism. Strengthened regional governance, alignment of air quality and climate agendas, and targeted development finance are essential to achieving WHO air quality standards. ASEAN-specific policy mechanisms and sustained international cooperation will be critical to closing the implementation gap and improving health outcomes.