From winter to summer, Delhi's air has shown a slow but steady rise in carbon monoxide levels this year till May, with monthly data pointing to a consistent pattern of elevated concentrations.
According to data by Envirocatalysts, a research and advisory think tank, the monthly average carbon monoxide concentration (CO)stood at 2.5 milligrams per cubic metre (mg/NM3) in January, matching the level recorded in January 2021 and marking the highest reading for the month in the past five years.
This year, Delhi recorded an average carbon monoxide concentration of 1.89 mg/NM3 during the January-May period, the highest level since 2022, when the average stood at 1.90 mg/NM3, according to the data.
Indian standards set the permissible limit at 2 mg/NM3 (8-hour average), while WHO guidelines place it at 4 mg/NM3 (24-hour average).
In February, the average was 2.20 mg/NM3, the highest for the month since February 2021, when it stood at 2.50 mg/NM3.
Carbon monoxide is a toxic, colourless and odourless gas that reduces the blood's ability to carry oxygen by binding with haemoglobin. Exposure to elevated levels can lower oxygen supply to vital organs such as the heart and brain, leading to headaches, dizziness and fatigue.
Carbon monoxide levels were recorded at 2 mg/NM3 on 22 days, indicating concentrations largely remained at the lower end of the range. On 16 days, levels were recorded at 3 mg/NM3, while data for the remaining days were not specified in the available breakdown.
In March, the average carbon monoxide concentration was 1.90 mg/NM3, the highest for the month since March 2017, when it reached 2.70 mg/NM3, the data showed.
Levels were recorded at 2 mg/NM3 on 22 days, indicating stability at this level. The pollutant dropped to 1 mg/NM3 on six days, while it rose to 3 mg/NM3 on three days.
April recorded an average concentration of 1.60 mg/NM3, the highest since April 2023, when it stood at 1.80 mg/NM3, the numbers showed.
Carbon monoxide levels were recorded at 1 mg/NM3 on 13 days, while 2 mg/NM3 was recorded on 15 days. The level rose to 3 mg/NM3 on two days.
May recorded 1.30 mg/NM3, matching the level recorded in May 2024 and marking the highest May concentration since then.
In May, 30 days recorded carbon monoxide levels below 2 mg/NM3, indicating generally subdued pollution levels. On one day, the pollutant was recorded at exactly 1 mg/NM3.
Long-term or high-level exposure may increase the risk of chest pain, irregular heartbeat and other cardiovascular complications.
"High vehicle numbers and local emissions from them along with local combustion of other materials is the leading case of high CO buildup, higher CO levels indicate that the combustion activities are on the rise in the city which needs to be curtailed particularly the increasing private vehicle ownership making a shift towards cleaner electric run public transportation modes," Sunil Dahiya, founder and lead analyst at Envirocatalysts, said.
He further added that this will not just reduce the pollution but will also make the city more walkable, liveable and less congested.
Speaking on the health problems associated with exposure to carbon monoxide, Dr Manisha Mendiratta of Sarvodaya Hospital Faridabad said, "As a silent and invisible killer, carbon monoxide poisons the body through oxygen depletion in the bloodstream, which poses dire consequences for the health of humans."
He said carbon monoxide is especially harmful to pregnant women as this oxygen depletion can cut off the supply of necessary oxygen to an unborn child, and it is even more harmful to children who require much more oxygen due to higher metabolism rates, making them vulnerable to the negative impact that comes with oxygen deprivation, he said.
Dr Rajesh Upadhyay of Yashoda Medicity said, "People exposed to high levels of carbon monoxide may develop headaches, tiredness, dizziness, trouble concentrating or a general feeling of weakness. Because these symptoms are common, many people may not realise that polluted air is part of the problem."
For the elderly, the risks can be even greater as many older adults already live with heart or lung conditions, he said, adding that lower oxygen levels can worsen breathlessness, fatigue and heart-related problems, making everyday activities harder.
