Rain and wind bring pollution levels down in Delhi; relief could be short-lived

PM10 levels at Mandir Marg. (Source: Delhi Pollution Control Committee)

With pollutants being washed away by rain, particulate matter levels fell to concentrations within the 24-hour prescribed limit early on Friday. At Mandir Marg, for instance, the PM 10 level was 40 µg/m3 at 6 am, down from a peak of 617 µg/m3 at 12 pm on Thursday, data from the Delhi Pollution Control Committee (DPCC) shows. This, however, had risen once again to 213 µg/m3, at 7 pm on Friday. The 24-hour standard for PM 10 is 100 µg/m3.

Similarly, the PM 2.5 level at Mandir Marg fell to 20 µg/m3 at 6 am on Friday, a sharp fall from 490 µg/m3 at 12 pm on Thursday. PM 2.5 levels also rose Friday evening to 171 µg/m3 at 7 pm. The 24-hour standard for PM2.5 is 60 µg/m3.

Thursday had been the seventh day this month that the AQI in Delhi was in the ‘severe’ category, with low wind speeds preventing the dispersion of accumulated pollutants in the city. Wind speed of less than 10 kmph can be unfavourable for the dispersion of pollutants.

PM 2.5 levels at Mandir Marg. (Source: Delhi Pollution Control Committee)

Under the influence of the western disturbance, wind speed picked up to be around 18 kmph on Friday afternoon, with gusty winds hitting a maximum speed of around 35 kmph, according to India Meteorological Department (IMD) officials.

Kuldeep Srivastava, scientist at IMD, said the impact of the western disturbance is likely to continue till Saturday afternoon. “Clouds are expected on Saturday, but no rainfall. Wind speed will be around 15 kmph on Saturday, and this is likely to begin decreasing, to be around 10 kmph on Sunday, and 8 to 10 kmph on Monday,” he said. A forecast issued by the Air Quality Early Warning System on Friday said the air quality is likely to be in the ‘poor’ category on Saturday. It could, however, deteriorate and be in the ‘very poor’ category on Sunday, and in the ‘severe’ category on Monday, the day after Diwali, going by the forecast.

The maximum temperature recorded on Friday was 22.7 degrees Celsius, seven degrees below the normal, and only 6.5 degrees more than the minimum temperature of 16.2 degrees recorded early on Friday. From 2011 onwards, the city recorded a lower maximum temperature in November only once before – 22 degrees Celsius on November 29, 2019, data from the IMD shows.

The IMD forecast also points to the likelihood of a drop in temperature. A bulletin issued on Friday said minimum temperatures are likely to fall by two to four degrees over many parts of northwest India from Saturday onwards.

Delhi’s minimum temperature is likely to fall to around 13 degrees by November 13.

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