Delhi’s air quality remains “very poor”

Delhi”s air quality remained “very poor” on Tuesday and is predicted to turn “severe” this week due to unfavourable meteorological conditions.

The city”s air quality index (AQI) was 346 at 9 am. The 24-hour average AQI was 318 on Monday and 268 on Sunday.

An AQI between zero and 50 is considered “good”, 51 and 100 “satisfactory”, 101 and 200 “moderate”, 201 and 300 “poor”, 301 and 400 “very poor”, and 401 and 500 “severe”.

The maximum wind speed is expected to be 8 kmph on  Tuesday, according to the India Meteorological Department.

The minimum temperature was 8.1 degrees Celsius on Tuesday and the maximum is expected to settle around 26 degrees Celsius, the weather department said.

Calm winds and low temperatures trap pollutants close to the ground, while favourable wind speed helps in their dispersion.

The central government”s Air Quality Early Warning System for Delhi said air quality is likely to remain in the upper end of the “very poor” category due to unfavourable meteorological conditions.

There is a possibility of the air quality reaching the “severe” category between December 4 and December 7, it said.

The city”s ventilation index — a product of mixing depth and average wind speed – will be around 2,000 m2/s on Tuesday.

Mixing depth is the vertical height in which pollutants are suspended in the air. It reduces on cold days with calm wind speed.

A ventilation index lower than 6,000 sqm/second, with the average wind speed less than 10 kmph, is unfavourable for dispersal of pollutants.

The share of stubble burning in Delhi”s pollution has reduced as the harvesting season has ended.

The contribution of stubble burning in neighbouring states to Delhi”s PM2.5 levels was 7 percent on Monday and 6 percent on Sunday, according to the Ministry of Earth Sciences” air quality monitor, SAFAR.