As the Delhi government prepares for the next phase of the odd-even scheme in April, analysis by the Central Pollution Control Board (CPCB) has shown that with 15 ‘very poor’ days and 13 poor days, air pollution levels continued to be high in February. The nodal agency has also found that apart from particulate matter which was the dominant pollutant through the winter season last year, and January this year, the gaseous pollutant Ozone has emerged as the dominant pollutant last month.
According to the National Air Quality Index (AQI)’s monthly analysis report, on seven days when PM 2.5 was the dominant pollutant, Ozone levels spiked. Ozone was the dominant pollutant along with PM 2.5 on February 15, 16, 22, 23, 26, 27 and 28. Experts say Ozone levels go up with the rise in temperatures, as the gas is formed from a photochemical reaction which needs high sunlight. “Ozone does not have any source of its own. It is formed due to a photochemical reaction between other gaseous pollutants like nitrogen dioxide with hydrocarbons. So heat and sunlight is a huge factor which triggers this reaction,” AnumitaRoychowdhury executive director, Centre for Science and Environment explained.
Ozone is associated with severe health effects. Doctors say it reduces lung function by inflammation and scarring the lining of the lungs. It can also cause chest pain, coughing and exacerbate existing respiratory diseases like asthma and bronchitis. “Ozone is the only pollutant which has a one hour notified average safe limit of 180 micrograms per cubic metre. Along with Carbon Mono Oxide, it also has an eight-hour average safe limit of 100 micrograms per cubic metre. All other pollutants have 24 hour averages. So even inhaling ozone for one hour can be harmful for people with existing respiratory disorders,” Dr T K Joshi, director of the centre for occupational and environmental health at Maulana Azad Medical College explained.
With the next round of the odd even scheme coming up from April 15-30, experts say monitoring the Ozone levels will be an important indicator of its success. “Ozone levels start rising around February, and remain high through March, April and May. Since Ozone is formed due to a chemical reaction between hydrocarbons and other gases, reducing these emissions by bringing down the number of cars in the road, should in effect, result in the additional benefit of also reducing Ozone,” Roychowdhury from CSE explained.
Meanwhile, comparisons of average AQI for February show Delhi’s air quality fared better than the previous month, despite the 15 days of odd even scheme it enjoyed. In February, average AQI was recorded at 293 in the poor range, with a maximum of 372 and a minimum AQI of 186. In January, Delhi had recorded an average AQI of 362 in the very poor range, with maximum and minimum values at 434 and 269 respectively according to CPCB. In January, there were 23 very poor days, and eight severe days, where particulate matter was identified as the dominant pollutant. Experts say the spike in temperatures seen in February, helped control particulate matter. “In February due to weather factors including intermittent rains, and a definite rise in temperatures, particulate matter levels have been better, and there has not been any severe day in February. But ozone levels have started rising very early in the year, probably due to the high temperatures this year,” a senior scientist from CPCB explained.
