The vertical height, in which pollutants are suspended, comes down, due to low wind speed and cold temperatures. Once the verticle height of pollutants comes down, their concentration gets increased closer to the surface.
Delhi’s AQI is improving! In a ray of hope, the infamous air quality of the national capital has shown slight improvement in December 2019 compared to the corresponding time period in 2018. Delhi’s air quality index (AQI) shows the average air quality was better in December 2019 in comparison to December 2018. The average AQI in December 2019 was 337 which is lower than December 2018’s average AQI of 360. However, Both the months of December in 2018 as well as 2019 witnessed eight ‘severe’ air quality days. This is despite that fact that temperature dropped considerably in December 2019 compared to December 2018, according to IE report.
The Central Pollution Control Board (CPCB) data shows that the peak AQI in December 2019 was recorded 446. In December 2018, peak AQI was recorded 450. In December 2019, there are 8 ‘severe’ days, 7 ‘poor’ days and 3 ‘moderate days’. In December 2018, 8 ‘severe’ days, 4 ‘poor’ days, and 1 ‘moderate day’. December 30, 2019 was the coldest day in 119 years in Delhi. December 2019 was also the second coldest December in 119 years. December 2019 in Delhi recorded an average maximum temperature of 18.76 degrees Celsius. In December 2018, the average maximum temperature was 28.5 degrees Celsius, the IE report says.
There are reasons why air quality starts to deteriorate in winter. The vertical height, in which pollutants are suspended, comes down, due to low wind speed and cold temperatures. Once the verticle height of pollutants comes down, their concentration gets increased closer to the surface. India Meteorological Department scientist Kuldeep Srivastava said while maximum temperatures dipped to a record low in December 2019, the minimum temperatures were more or less normal. He said the wind speed was also high for the most part in December 2019, compared to that of 2018. Due to this factor, dense fog episodes were few.
In Delhi, there was extreme weather in December 2019. If the air quality in the national capital has shown improvement since 2018 then it’s the result of action by agencies to control pollution, a senior CPCB official was quoted as saying by IE.
If we analyse take three year’s data, December 2017 emerges as the cleanest one. The average AQI of December 2017 recorded 316 and the month had witnessed a single ‘severe’ day. The peak AQI in December 2017 was 469. In December 2017, there 1 ‘severe’ day, 9 ‘poor’ days and 2 ‘moderate’ days. In December 2017, the average maximum temperature was recorded at 27.9 degrees Celsius.