Mumbai registered the sharpest decrease (-42.1%) in carcinogenic PM2.5 levels in air in Jan this year compared to the same period in 2023 and -17.3% compared to Jan 2019, according to an analysis of air quality in major national cities. Kolkata showed the most significant improvement of 50.6% in PM 2.5 levels. Jaipur experienced the highest increase in toxicity in its air.