This year’s Diwali was the most polluted in three years. Between 2014 and 2016, PM 2.5 concentration went from 484 micrograms per cubic metres in 2014 and 606 micrograms per cubic metres in 2015 to 883 micrograms per cubic metres this year, according to data gathered from the Centre for Science and Environment.
Data from Delhi Pollution Control Committee (DPCC) has shown that pollution has been rising on Diwali since 2010 and this year was no different. What sets this year apart, however, is what followed Diwali. Each year, pollution levels fall after Diwali. But this year, pollution levels peaked after the festival.
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Senior DPCC officials said this was caused by lack of winds. “Each year, during this time, we see slow wind speed of up to 0.5 metres per second at night but the speed picks up during the day. That’s why, over the last few years, pollution levels were higher during the night as compared to the day. This year, however, the wind speed is not picking up pace and we are seeing speeds of 0.3 metres per second even during the day,” said M P George, a scientist associated with the DPCC.
A Central Pollution Control Board report said the average wind speed around Diwali last year was 3.4 metres per second, while it was 1.3 per second this year. “High wind speed blows pollution away from the city, clearing the air. That happened last year. This year, however, the case is different,” George said. According to George, this year’s weather conditions are similar to those in 2012. Diwali in 2012 was the most polluted in the last five years.
Another factor that has aided the build-up of pollutants is the low mixing height this year as compared to the last. Mixing height is the homogenous layer of air about the surface of the ground. Lower mixing height in the atmosphere aids accumulation of pollutants.
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