Mumbai records highest road traffic CO₂ emissions per km among metros

Mumbai recorded the highest road traffic carbon dioxide (CO₂) emissions per kilometre of road length among major Indian cities, driven by high vehicle density, according to a new high-resolution emissions dataset published in Scientific Data. Other large metros such as Delhi, Bengaluru, Chennai, Hyderabad and Pune also showed high levels of nitrogen oxides (NOx) and carbon monoxide (CO) emissions from road transport, a TOI report said.

High vehicle density drives emissions across major cities

The study mapped daily road traffic CO₂ and air pollutant emissions at a 500-metre resolution across 15 Indian cities for 2021. It was led by researchers from France’s Laboratoire des Sciences du Climat et de l’Environnement and Université Paris-Saclay, with contributions from IIT Bombay and Paris-based urban mobility data firm NEXQT SAS. The work forms part of the CHETNA project, which aims to track city-wise high-resolution carbon emissions across more than 100 Indian cities.

A city-wise comparison showed a clear link between vehicle density and emissions per kilometre of road. Mumbai stood out with both the highest traffic density and the highest CO₂ emissions per km. Chandigarh, Chennai, Pune and Bengaluru were grouped in a high-density, high-emissions cluster, though at lower levels than Mumbai. Delhi ranked in the mid-high range, while Guwahati, Indore and Jaipur recorded lower traffic density and emissions.


Comparison of vehicle density per km in select cities

• Mumbai: 9.5–10 vehicles per km
• Chandigarh, Chennai, Pune, Bengaluru: 9–9.5 vehicles per km
• Hyderabad, Kolkata, Vadodara: 8–8.9 vehicles per km
• Delhi: 8.3–8.5 vehicles per km

Road transport CO₂ emissions per km in major cities

• Mumbai: 5–6 tonnes of CO₂ per km of road
• Chandigarh: slightly above 5 tonnes per km
• Chennai, Pune: close to 5 tonnes per km
• Bengaluru: under 5 tonnes per km
• Hyderabad, Kolkata, Vadodara: 4–4.5 tonnes per km
• Delhi: over 4 tonnes per km

While Delhi falls in the mid-range for CO₂ emissions per km, it joins Mumbai and Bengaluru as the top three cities for total road traffic CO₂ emissions. However, per capita emissions were similar across almost all 15 cities, at under 0.2 tonnes of CO₂ per person annually, indicating comparable vehicle usage per resident, the report said.

Pollutant-wise estimates showed that NOx and CO dominated road transport emissions across all cities. Larger metros such as Mumbai, Delhi, Bengaluru, Chennai, Hyderabad and Pune recorded higher NOx and CO emissions than smaller cities including Guwahati, Mangaluru and Tiruppur. Traffic-related particulate pollutants such as PM₁₀, PM₂.₅ and black carbon were present at moderate levels in major cities but were lower in magnitude than NOx and CO.

Dr Sundeep Salvi, director of Pulmocare Research and Education Foundation and president of the India Chest Society, told TOI that carbon monoxide is particularly harmful as it interferes with oxygen delivery in the body, reducing oxygen circulation in the blood and damaging the lungs. He said carbon dioxide primarily contributes to global warming and does not cause direct health effects at normal ambient levels.

“All vehicular pollutants are harmful, but particulate matter is of greatest concern as it can enter the bloodstream and affect multiple organs. Nitrogen oxides are also harmful to the lungs and form ozone in sunlight, further damaging lung tissue,” Salvi told TOI.

Harish C Phuleria, associate professor at IIT Bombay’s Centre for Environmental Science and Engineering and a contributor to the study, told TOI that the CHETNA project aims to develop high spatial and temporal resolution data for carbon and air pollutant emissions for around 100 Indian cities. He said the methodology would be scaled up to other cities and extended to sectors such as residential, power, heavy industries, MSMEs and aviation, with the data to be made available through web portals and city-specific dashboards.

Phuleria added that a major workshop is planned in Mumbai in February 2026 to engage stakeholders from participating cities and gather feedback on the data and dashboards. The study has been accepted for publication in Scientific Data, a Nature portfolio journal.

(With inputs from TOI)