What can help improve Delhi’s air quality? Wind, warm weather & some rain

Wind: One of the most crucial factors, higher wind speed can help disperse particulate matter, which is the primary pollutant in winter, quickly. This was also demonstrated on Friday, when a slight increase in wind speed led to an improvement in AQI. At Anand Vihar, for example, the concentration at 1 pm was 371 µg/m3 (against an acceptable limit of 60 µg/m3) and the wind speed was a little over 1 kilometre per hour. By 3 pm, PM 2.5 was at 144 µg/m3, as the wind speed rose to 2.8 kilometres per hour.

According to the Air Quality Early Warning System for Delhi, an average wind speed of less than 10 km per hour is unfavourable for dispersion of pollutants. However, even a small increase brings relative improvement.

Forecast: According to the IMD, wind speed is expected to be between 4 and 6 km per hour till Monday. Some relief is expected after that as the wind speed during the day is expected to be between 10 and 12 km per hour.

Temperature: A dip in temperature, especially when the sky is clear at night, leads to a phenomenon called temperature inversion. In winter, when the atmospheric pressure is higher, a clear sky means that the ground loses heat quickly and the air around it cools down. Above it is a layer of warmer air, which acts like a lid, trapping the cold air. Along with the cold air, pollutants from vehicles and dust also get trapped. This inversion determines mixing height, which is the area available for pollutants to disperse. The higher the mixing height, the better it is.

Forecast: The temperature is expected to be between 29 and 14 degrees Celsius over the next seven days. According to the Air Quality Early Warning System for Delhi, the mixing height is expected to be around 2,450 m on Saturday, and will improve further to 2,700 m on Sunday but will dip to 1,850 on Monday.

Rain: One of the reasons this October was the most polluted since 2020 was the dry weather. Rain helps the particulate matter and dust in the air settle, improving AQI. Delhi saw only one rainy day this October as opposed to 7 and 6 days in previous years.

Forecast: Over the next seven days, no rain is expected in Delhi.