Delhi's air quality improved to the 'poor' category on Sunday, with the Air Quality Index (AQI) settling at 290 at 4 pm, offering some respite after several day. NSIT Dwarka recorded the highest pollution level, with an AQI of 364.Earlier in the morning, Delhi's air quality remained in the 'very poor' category, with an AQI of 350, according to the Sameer app, reported PTI.