Assessing the impact of clean air policies in cities like Beijing, Delhi, and London using secondary air quality data.

Abstract

This study evaluates the effectiveness of clean air policies in London, Delhi, and Beijing using WHO air quality data (2011-2019) for PM2.5, PM10, and NO₂, alongside a structured review of major national and city-level interventions. Using a comparative case study design, the analysis combines descriptive trend assessment with a semi-quantitative policy index that scores ambition, enforcement strength, and sectoral coverage.

London’s Ultra Low Emission Zone produced substantial reductions in NO₂ but delivered only modest declines in PM2.5 and PM10, reflecting its transport-focused design. Delhi achieved sharp decreases in PM10 after CAP, GRAP, and NCAP, yet PM2.5 and NO2 remained persistently high due to weak enforcement, fragmented governance, and seasonal stubble burning. Beijing recorded the fastest and most sustained improvements, with PM2.5 falling by more than 30% following the Clean Air Action Plan and large-scale coal-to-gas transitions, though at significant social and economic cost.

Across all three cities, the results show that policy ambition and enforcement capacity matter more than policy breadth alone. Effective clean air strategies are those that align closely with dominant emission sources, ensure consistent implementation, and remain socially sustainable.