Rain respite: After month of pollution, Delhi air slightly better

According to officials at the India Meteorological Department (IMD), the Safdarjung observatory saw 1 mm of rain between 2 am and 4 am on Saturday (File)

Light rain early on Saturday morning brought Delhi’s air quality to ‘poor’ — an improvement from the ‘very poor’ and ‘severe’ levels that the city witnessed last week. This is the first time since October 16 that ‘poor’ air quality was recorded in the city. According to officials at the India Meteorological Department (IMD), the Safdarjung observatory saw 1 mm of rain between 2 am and 4 am on Saturday. Data from the Delhi Pollution Control Committee station at Mandir Marg, which is closest to the observatory, shows that PM (particulate matter) 2.5 levels shot up to 249 µg/m3 at 3 am and came down to 172 µg/m3 at 4 am. Around 4 pm, the concentration was down to 105 µg/m3.

Air quality is usually better in the afternoon as compared to the night as temperature and wind speed during the day are higher. The acceptable limit of PM 2.5 is 60 µg/m3. Over the past week, the Delhi Fire Services and the municipal corporations have tried to reduce the concentration of pollutants in the air by spraying water from a height to mimic rain. At ITO, the move did not have too much of an impact.

According to data by the Central Pollution Control Board, while PM 2.5 was around 110 µg/m3 before sprinkling 70,000 litres of water, it came down to 106 at 4 pm. It was recorded at 129 µg/m3 at 5 pm, and shot up above 200 µg/m3 at 11 pm, showing almost negligible gains. According to IMD officials, natural rain is spread over a much larger area and has a longer-lasting effect. But Saturday’s rain was so light that the impact started to wane by night.

“There was a clear dip in PM 2.5 till evening after the rain, but as it got colder, the concentration started increasing. At 8.30 pm, the concentration was around 155 µg/m3,” a senior official said. According to the SAFAR forecast, Delhi is expected to see ‘very poor’ air quality on Sunday and Monday. IMD officials have forecast a foggy morning on Sunday, followed by clear sky. The temperature is expected to be between 14 degrees and 24 degrees Celsius.