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Odd-even phase II: This time, eye on ozone as well

In February, apart from particulate matter, gaseous pollutant ozone emerged dominant. Experts say ozone levels go up with the rise in temperature.

Written by Pritha Chatterjee |
Updated: April 9, 2016 8:41:15 am
new delhi, delhi odd even, delhi odd even phase 2, delhi odd even april, april odd even scheme, delhi transport, delhi news, latest news, ncr news According to the National Air Quality Index (AQI)’s monthly analysis report in February, on seven days when PM 2.5 was the dominant pollutant, ozone levels spiked simultaneously.

As Delhi prepares for Phase II of the odd-even scheme this month, along with particulates, the government plans to monitor ozone levels to assess the impact of the programme. According to Central Pollution Control Board (CPCB) analysis, in the last fortnight — on March 15, 17, 18, 20, 23, 24, 27 and 29 — ozone emerged as the dominant pollutant along with particulates. In February, apart from particulate matter, gaseous pollutant ozone emerged dominant for the entire month. The CPCB is yet to release the complete monthly analysis reports of air quality index for March.

According to the National Air Quality Index (AQI)’s monthly analysis report in February, on seven days when PM 2.5 was the dominant pollutant, ozone levels spiked simultaneously. Ozone was the dominant pollutant along with PM 2.5 on February 15, 16, 22, 23, 26, 27 and 28. Particulates including PM 10 and PM 2.5 remained the dominant pollutants through winter last year, and January this year, when the first phase of the odd-even scheme was implemented.

Watch video Odd-Even Phase II Scheme: Ex-Servicemen March In Unison For Odd-Even Role

Experts say ozone levels go up with the rise in temperature, 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,” says Anumita Roychowdhury executive director, Centre for Science and Environment. Since hydrocarbons, a critical component in the formation of ozone, are associated with vehicle exhaust fumes, reducing cars on the streets during the odd-even scheme should impact ozone levels, she adds.


Dr T K Joshi from the Centre for Occupational and Environmental Health at Maulana Azad Medical College says ozone should serve as a good indicator of impact of air quality since particulate levels may not be as high in April, compared to the first leg of the odd-even scheme. “The pollutant profile during April is different. While particulate levels are a problem through the year, ozone is the bigger crisis during the month,” he says. Doctors say ozone 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 also the only pollutant which has a one hour notified average safe limit of 180 micrograms per cubic metre. Along with carbon monoxide, it also has an eight-hour average safe limit of 100 micrograms per cubic metre. All other pollutants have 24 hour averages. ���So, inhaling ozone for even one hour can be harmful for people with existing respiratory disorders,” explains Dr Joshi.

Meanwhile, comparisons of average AQI for February show Delhi’s air quality fared better than January, 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, according to CPCB.

Experts say the spike in temperatures in February helped control particulate matter. Sporadic rains over March further helped improve particulate matter levels. Experts say from March-April, as temperatures increase, levels of particulates generally scale down, compared to the winter months. “This year, thanks to two spells of rain seen in this month, we have seen a further drop in particulate matter levels. Due to Westerly Disturbances seen in Afghanistan, showers have carried on for 48-72 hours in two spells. Humidity levels have also been high, going up to 90 per cent,” says a senior scientist from Delhi Pollution Control Committee. This relief was restricted to particulates, as ozone levels have remained high, he adds.

CPCB scientists, however, caution particulate levels should also be monitored. “PM 2.5 levels can be most directly associated with vehicles. Therefore, to assess the impact of the scheme, the levels of PM 2.5 are the most direct evidence. Ozone is formed with different pollutants… so it should be studied as well, but other factors necessary for its formation… and other gaseous pollutants need to be monitored and factored in,” says a scientist. According to scientists, in the first few days of April, particulates emerged as the dominant pollutants. According to CPCB’s daily analysis of AQI , on April 1 and 2, PM 10 and PM 2.5 again emerged as the dominant pollutants in Delhi.

DTC gears for Phase II

Focus on
Maintenance of buses to address issue of breakdowns.

400 buses: Daily average breakdown figure last year in the 4,000-strong fleet.

In summers: Due to overheating of engines, breakdown rates go up.

Experience: Over the past years, bus engines, especially those of AC buses and the old standard floor buses, have burst into flames as day temperatures have soared, taking the daily breakdown rate to over 600 a day.

30 to 45 mins: Targeted reaction time to breakdowns in the first phase, but glitches resulted in the usual one-and-half-hour to two-hour grind to get a bus repaired. The breakdown rate in January was the same as the December average of about 300 buses a day.

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