Delhi AQI dips to 290, but relief may be brief

Following days of toxic, post-Diwali smog blanketing the national capital, Delhi's air quality improved slightly to the 'poor' category on Sunday, with the Air Quality Index (AQI) reaching 290 by 4 pm.Across the city's 58 monitoring stations, 34 registered 'poor' air quality and 23 logged 'very poor', leaving only Delhi Cantonment in the 'moderate' zone. NSIT Dwarka recorded the capital's worst air, with an AQI of 364. Earlier that morning, the Sameer app had placed the city's air in the 'very poor' bracket at 350.Per the Central Pollution Control Board (CPCB) scale, an AQI of 0–50 is 'good', 51–100 is 'satisfactory', 101–200 is 'moderate', 201–300 is 'poor', 301–400 is 'very poor', and 401–500 is 'severe'. Delhi had been stuck in the 'very poor' tier continuously since November 11, with hourly readings repeatedly nearing, and once breaching, the 'severe' threshold. Prior to Sunday, the last 'poor' AQI reading was 299 on November 10, preceded by 261 on November 1.Real-time PM2.5 source apportionment data from the Air Quality Early Warning System and the Integrated Decision Support System identified biomass burning, encompassing stubble burning, domestic solid biofuels, wood, and dung cakes—as Sunday's primary pollutant source at 37.1 per cent. Secondary organic aerosols, which are fine particulates generated by atmospheric gas reactions, ranked second at 22 per cent, trailed by vehicular emissions (17.2 per cent) and secondary inorganic aerosols (9.6 per cent). Smaller shares came from waste burning, such as municipal, plastic, and rubber waste (5.5 per cent), mixed combustion (4.3 per cent), mineral dust and ash (2 per cent), firecrackers (1.6 per cent), and industrial emissions (0.6 per cent).This relief is expected to be brief. According to the Air Quality Early Warning System, Delhi's air will likely stay 'poor' on November 16 before deteriorating back to 'very poor' on November 17 and 18, remaining in that bracket for the following six days.Meteorologists credited Sunday's temporary dip in pollution to light rain and stronger winds helping disperse trapped pollutants. The India Meteorological Department (IMD) noted that parts of Delhi experienced drizzle or very light rain over the preceding 24 hours, accompanied by southwesterly surface winds peaking at 15 kmph. Skies were mostly cloudy before turning partly cloudy by afternoon, with southwesterly winds blowing up to 10 kmph.However, the IMD's forecast bulletin projects the city's ventilation index to drop steadily, from 16,000 square metres per second on November 15 to 15,000 on November 16, 7,500 on November 17, and 6,000 on November 18. The bulletin noted that a ventilation index below 6,000 square metres per second, combined with average wind speeds under 10 kmph, creates poor conditions for dispersing pollutants.