Despite concerns about stubble burning and pollution, the air quality in Delhi and Mumbai remained in the 'moderate' category. Delhi's Air Quality Index (AQI) improved slightly to 83 from Tuesday's reading of 89. In Mumbai, the overall air quality was also 'moderate', but certain areas like Chhatrapati Shivaji Terminus (CST) and Mazagaon recorded 'very poor' air quality. The AQI scale categorizes air quality into six categories, and authorities and citizens need to monitor and take measures to improve the air quality in these cities.