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Delhi's air quality improved a shade and remained in the 'poor' category throughout the day today on the back of strong surface winds, but dipped towards the evening. The day's average air quality index (AQI), based on the readings till 4 pm, was 292, classified as 'poor' by the Central Pollution Control Board (CPCB). A poor AQI was last recorded on November 19. However, around 7 pm, the AQI had slipped to the 'very poor' category, which CPCB's air lab chief Dipankar Saha attributed to local emissions, largely from vehicles. The dominant pollutants captured by 17 CPCB monitors across the city were PM2.5 and NO2, largely products of vehicular emissions. "Pollution levels were high during the morning hours due to cloudy conditions which increases moisture in the air and traps pollutants. "But as the day progressed, wind speed picked up and temperature also rose, which helped in dispersion of particulate matter," Saha said. The AQI scale ranges from 0-500.
The advisory that comes with 'poor' category air says it may trigger breathing discomfort to most people on prolonged exposure. According to the System of Air Quality Forecasting and Research (SAFAR), the 24-hour average (rolling) levels of ultrafine particulates PM2.5 and PM10 were 137 and 229 micrograms per cubic metre at 7 pm, as against the prescribed limits 60 and 100.