Are cities ready to synergise climate neutrality and air quality efforts?

• The linkage between climate mitigation and air quality is examined for 362 cities. • Sectoral contributions to PM2.5 levels and GHG emissions are strongly aligned. • Cities value air quality as a co-benefit of climate action and can act on it. • Two approaches are identified in ambient air quality action: proactive vs reactive. • Disciplinary and departmental silos need to be overcome. This study investigates the alignment of climate change mitigation with air quality initiatives in 362 (mostly European) cities eligible under the Climate-Neutral and Smart Cities Mission, hence targeting net-zero greenhouse gas (GHG) emissions by 2030. It examines ambient air quality, particularly PM 2.5 levels, and GHG emissions, considering physical attributes, policy frameworks, and local authority actions. The research finds a north-to-south gradient in air quality, with northern cities exhibiting better air conditions, and a strong correlation between sectors contributing to GHG emissions and air pollution. Cities' strategies are dominated by cross-sectoral plans and assessing air quality as a co-benefit of climate mitigation is common practice, suggesting potential for synergistic approaches to climate and air quality goals, supported by the political authority that cities typically exert over relevant policy areas. Machine learning analysis (XGBoost) highlights national context, population density, and climate class as significant predictors of PM 2.5 levels, with policy variables indicating that proactive health and justice measures in city governance may correlate with improved air quality. The study advocates for a co-benefits approach in urban policy-making to effectively address climate change and air quality challenges, and it emphasises the need for transdisciplinary research and governance to optimise outcomes and reduce trade-offs.