Silent killers SO2, NO2 made Delhi a gas chamber in Nov

Posted on Dec 5 2017 - 6:42pm by admin

Particulates remained the primary concern of agencies but levels of noxious gases also rose steeply

NEW DELHI : The concentration of poisonous gases such as nitrogen dioxide and carbon monoxide rose up to seven times their safe limit in November, when Delhi was covered by a choking haze for several days.

Since the pollution control agencies were busy with the exceptionally high levels of particulate matter — PM2.5 and PM10, the most dominant pollutants in Delhi’s air, these gases escaped scrutiny.

The Supreme Court-appointed Environment Pollution (Prevention and Control) Authority considers the part matter levels to enforce the Graded Response Action Plan, which was for the first time this year. The EPCA is planning to take into account other pollutants from next year.

Levels of ozone and ammonia also fluctuated drastically.


High level of NO2 in the air has become a concern for experts and scientists. Air quality data shows that NO2 levels shot up by more than seven times above the safe standards in areas such as Punjabi Bagh over the last four November days. It had shot up to 588ug/m3 on November 28.

“NO2 is primarily the result of burning diesel. It can’t be said for certain why it increased to such levels in Punjabi Bagh without a detailed analysis, but it could be because of the high density of vehicular population,” said Anumita Roychowdhury executive director at Centre for Science and Environment.


The gas, a key smog element, has dropped below the safe standards in Delhi primarily because of use of cleaner fuels. Though it did not breach the safe standards for a single day in Delhi, in other NCR cities such as Ghaziabad and Bhiwadi, it was at dangerous levels.

“Monitoring SO2 is important because it triggers the formation of secondary pollutants. SO2 often condense and convert into other pollutants, reflecting a reduction in its own level,” said SN Tripthi head of the Centre for Environmental Science and Engineering at IIT Kanpur.


Ozone is a threat to asthma patients and can cause premature death, if it is high even for a short duration during the day. It forms primarily when nitrogen oxides, carbon monoxide (CO) and volatile organic compounds (VOCs), react in the atmosphere in the presence of sunlight.

The level of O3 shot up above the safe standards on some days at places such as Anand Vihar, Delhi University North campus and Lodhi Road. The maximum level was recorded at DU where it had shot up to 143 above the permissible limit of 100.


On Lodhi Road, it had shot up at least three times above the safe standards on certain days. Once in the air, this gas can linger for more than a month and its presence affects concentrations of other greenhouse gases, including methane, ozone and carbon dioxide.

“Carbon monoxide is usually emitted during burning of garbage or incomplete combustion,” said Dilip Ganguly assistant professor at Centre for Atmospheric Sciences at IIT Delhi.

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