Despite a record dip in mercury in the past month, the city’s air quality index (AQI) was comparatively better than the previous December. While there were eight ‘severe’ air quality days last month, same as 2018, the average AQI was 337 in 2019. This was lower than the average AQI of 360 recorded in December 2018, but higher than the 316 recorded in December 2017, which had only one ‘severe’ day.
Data from the Central Pollution Control Board (CPCB), analysed by The Indian Express, shows there were also higher number of ‘moderate’ and ‘poor’ air quality days in December 2019 compared to the December before that.
A senior CPCB official said, “We have had extreme weather in December 2019. If the air quality has improved since the previous year, it’s the result of action by agencies to control pollution.”
On December 30, the city recorded its second coldest December and the coldest day in 119 years. Usually, with cold temperatures and low wind speed, the vertical height in which pollutants are suspended comes down, as a result of which their concentration increases closer to the surface. Due to this, air quality starts to deteriorate in winter.
Kuldeep Srivastava, a scientist at IMD, said even though maximum temperatures dipped to a record low this December, the minimum temperatures were more or less normal. “Wind speed too was high for the most part in December, compared to last year. Because of this, dense fog episodes were few,” he said.
The average maximum temperature recorded in December 2019 was 18.76 degrees Celsius, significantly lower than 28.5 degrees Celsius recorded the previous December, and 27.9 degrees Celsius the year before that.
In December 2017, Srivastava said the impact of strong easterly winds was reflected in the air quality as it kept pushing out pollutants. The CPCB official said the main contributors in December were confined to regional emissions from waste and biomass burning, vehicular industrial emissions, and construction activities.
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