The high frequency of severe air quality days witnessed in winter was one of the reasons the Delhi government decided to enforce the odd-even numbered vehicle rule formula to make an attempt at reducing the high particulate matter and nitrogen oxide levels.
Air pollution during November and December this winter worsened compared to last year with air quality deteriorating into the 'severe' category on most days, an analysis of pollution data by Centre for Science and Environment (CSE) shows. As per the National Air Quality Index (NAQI), when pollution touches the severe levels it is more likely to have a direct impact on even healthy people, who do not suffer from respiratory ailments and can seriously impact those with diseases such as bronchitis and asthma. The NAQI, launched this year, is a pollution monitoring system wherein the pollution levels are indicated in a colour coded system, divided into six categories from good to severe.
The high frequency of severe air quality days witnessed in winter was one of the reasons the Delhi government decided to enforce the odd-even numbered vehicle rule formula to make an attempt at reducing the high particulate matter and nitrogen oxide levels.
CSE's analysis of NAQI data shows that November 2015 had 73 per cent of days in severe category against 53 per cent in November 2014. December 2015 had 67 per cent of days in severe category as against 65 per cent in 2014. In fact, there was not a single day in December 2015 when the air quality was 'good' or 'satisfactory'.
Globally, three continuous days with severe levels of pollution is considered as a smog episode and this winter the capital has already witnessed 11 such smog episodes. According to CSE, such levels have lasted for ten consecutive days as well.
In its analysis, CSE has said that if half the cars stay off the road in support of the odd-even system, the total load of particulate matter and nitrogen oxide can be halved from the car segment, cutting down on nitrogen oxide, benzene and carbon monoxide emissions. Reiterating the impact of vehicles on air quality, a recent study of the Indian Institute of Technology-Kanpur showed that in winters, vehicles are second largest emitters of PM 2.5 pollutant after road dust. These pollutants are particles less than 2.5 micrometers in diameter and get deposited in our respiratory organs and are also known to be carcinogenic, leading to lung cancer.
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