While the debate continues over the impact of the odd-even policy on particulate matter (PM) levels, air quality monitoring by the Delhi Pollution Control Committee (DPCC) — at close to 170 locations since January 1 — shows that levels of gaseous pollutants such as carbon monoxide (CO) and nitrogen dioxide (NO2) remain high.
Both gaseous pollutants are associated with combustion, particularly from vehicles. As per national standards, the safe limit for CO is 4 mg per cubic metre for one hour and 2 mg/m3 for eight hours. The safe limit for NO2 is 80 micrograms per metre cube (µg/m3).
Sources said according to the data collected, both CO and NO2 levels remain below the permissible limit at most locations during the day, but begin to rise at about 6 pm and after 8.30 am – both times when vehicular traffic increases.
“The pattern shows that values see an increasing trend when more vehicles are on the road, and peak later when other sources such as trucks are on the road,” said a scientist. CO levels usually remain between 1.2-2 mg/m3 at other times. Like particulate matter, sources say gaseous pollutants such as CO also remain high in the border areas of south, northeast, east and northwest Delhi.
So far, the DPCC has only released data on PM 2.5 during the odd-even dates, which the agency’s scientists maintain is the pollutant most closely associated with vehicular pollution.
Scientists said gaseous pollutants can be harmful and have a faster impact on the body than particulates, which take a while to permeate into the body.
“CO reduces the oxygen-carrying capacity of blood and has an immediate effect on health. So even exposure to it in small quantities can cause headaches and make one feel nauseous. If the concentration of exposure increases, it reduces the passage of oxygen to vital organs which can be life-threatening,” said Dr T K Joshi, director of the centre for occupational and environmental medicine at MAMC.
Dr Joshi added that since gaseous pollutants are strongly associated with combustion from different sources, including vehicles, measuring their levels along with particulate matter is vital to understanding the policy’s impact on air quality.