Delhi recorded the season’s lowest minimum temperature for a second straight day on Monday, and its air quality worsened, though it stayed in the “moderate” category.The 24-hour average air quality index (AQI) was 174 in the Central Pollution Control Board’s (CPCB) 4pm bulletin on Monday, up from 153 on Sunday. (Vipin Kumar/Hindustan Times)The minimum was 16.2°C, 0.8 degrees lower than Sunday’s 17°C, the previous low for the season. The maximum was 31.4°C.The India Meteorological Department (IMD) expects temperatures to fall further, with light rain likely on Thursday and Friday from a cyclonic system over the Bay of Bengal.The 24-hour average air quality index (AQI) was 174 in the Central Pollution Control Board’s (CPCB) 4pm bulletin on Monday, up from 153 on Sunday.Also Read | The pollutants in Delhi's air, and why they are hard to traceAs the Capital headed into the new week, the weather held the night’s pollution close to the ground, according to an HT analysis of IMD’s weather-balloon readings from Safdarjung.

At 4.30am, a layer of warm air (an inversion) sat about 200 metres above the city, lower than Sunday’s 300 metres, and the air near the ground at Safdarjung was calm overnight.Monday afternoon, the weather’s impact on air pollution was mixed. By 4.30pm the sun had mixed the pollution about 1,150 metres up, below the usual 1,750 metres for late October.

The wind through that layer averaged 17km/h, close to the usual 15km/h. Those figures come from the HT analysis, which pairs the balloon readings with wind estimates from the European Centre for Medium-Range Weather Forecasts.

But the balloon itself measured a stronger wind, 20km/h, which would explain why pollution did not spike to higher levels that are typical during this season.Also Read | Delhi set to witness more rain, cooler days this week, says IMD forecastThe evening brought no relief. Safdarjung airfield reported calm air in all five of its reports between 4pm and 9.30pm, and no rain.

Readings varied across the city. At 9pm, 13 of the 57 stations reporting an AQI were in the “poor” category, 42 were “moderate” and two were “satisfactory”, according to CPCB data.To be sure, the air quality has been better than in previous years.

The AQI averaged 199, the second-lowest for that week in the 12 years since 2015, according to HT’s analysis. The week includes Dussehra, on October 20.