How the Use of CNG in Automobiles Has Reduced Pollution in Our Cities

You step out of your house in the morning and the air has that familiar sting. A sharp, invisible weight that makes you blink. Delhi residents have lived with this feeling for decades. Mumbai auto-rickshaw drivers breathe it all day. Bengaluru office-goers commute through it. Vehicular pollution has been one of the most stubborn, most visible failures of urban India and for a long time, nobody seemed to have a practical answer.

CNG (Compressed Natural Gas) became that answer. Not perfectly. Not permanently. But in a country where public buses once belched black diesel smoke and three-wheelers ran on leaded petrol, the shift to CNG was a genuine turning point. Road transport is a major contributor to urban air pollution in Delhi, particularly for nitrogen oxides (NOx) and transport-related PM2.5 emissions, though the contribution varies by season and pollutant. The numbers are sobering. But they would have been far worse without CNG.

This article explains exactly what CNG does to vehicle emissions, the real data behind the clean-air gains cities have seen, where the limits of CNG lie and what you should know as a vehicle owner right now.
 

What Is CNG and Why Does It Burn Differently From Petrol or Diesel?

CNG is primarily methane (CH4) stored in reinforced cylinders at very high pressure, around 200 bar. That sounds technical, but the practical difference is simple. Methane has the cleanest molecular structure of any hydrocarbon fuel. When it burns, it produces far less carbon residue, virtually no soot and no sulphur compounds.

Petrol and diesel, by comparison, are complex mixtures of hydrocarbons. They burn less completely. Diesel combustion specifically generates particulate matter, the fine black particles that enter your lungs and stay there. CNG combustion leaves almost no particulate residue. This single difference is what drove India's Supreme Court to mandate CNG for public transport in Delhi two decades ago.

There is another chemical advantage that matters. Methane is lighter than air. If it leaks from a cylinder, it disperses upward and dissipates rather than pooling on the ground. Petrol and diesel vapours are heavier than air and accumulate near the ground, creating both explosion and inhalation risks that CNG simply does not have.
 

The Supreme Court Mandate That Changed Delhi's Air

The most significant turning point in India's CNG journey was not a government scheme. It was a lawsuit.

M.C. Mehta, an environmental lawyer, filed a public interest petition in the Supreme Court in the 1980s, drawing attention to the catastrophic deterioration of Delhi's air quality. After years of hearings, the Court issued a landmark directive requiring Delhi's entire public transport fleet (buses, auto-rickshaws and taxis) to convert to CNG by 2002.

The outcome was dramatic. By late 2002, diesel buses had made an almost complete exit from Delhi's roads. By the early 2000s, tens of thousands of Delhi’s buses, taxis and auto-rickshaws had shifted to CNG under the Supreme Court mandate. The Court also ordered the phasing out of pre-1990 commercial vehicles, eliminating the oldest and most polluting segment of the fleet in one move.

The particulate matter reduction that followed was measurable. When heavy commercial diesel vehicles switch to CNG, particulate matter emissions can drop by one to two orders of magnitude, that is not a typo. Studies and court submissions at the time showed dramatically lower particulate emissions from CNG vehicles compared to older diesel fleets. Delhi's transformation from the early 2000s set the template that other Indian cities have since followed, including Mumbai for its auto-rickshaws and taxis.
 

The Actual Emission Numbers: What CNG Cuts and What It Does Not

Here is where honest reporting matters. CNG is not a zero-emission fuel. But compared to diesel-era vehicles, the reductions in specific pollutants are substantial.

Note: Reductions are approximate and vary based on vehicle type, engine technology and maintenance. Source: ICCT, CPCB and peer-reviewed studies. The NOx figure is covered separately below.

The BS VI (Bharat Stage VI) emission standard, India's cleanest engine norm, has added another layer of improvement. A 2024 remote sensing study by the Real Urban Emissions (TRUE) Initiative and ICCT found that real-world NOx emissions from private cars fell by 81% between BS IV and BS VI and from buses by nearly 95%.
 

Why BS VI Standards Matter More Than Fuel Alone

A vehicle’s real-world emissions depend not only on fuel type, but also on emission-control technology. BS VI norms introduced diesel particulate filters (DPFs), selective catalytic reduction (SCR) systems and tighter NOx limits across vehicle categories. This means a modern BS VI diesel vehicle can emit dramatically less pollution than older diesel fleets that originally triggered the push toward CNG in the early 2000s. Fuel quality still matters, but maintenance, aftertreatment systems and compliance enforcement increasingly determine whether a vehicle remains clean on the road.
 

The NOx Problem: Where CNG Gets Complicated

CNG's record on particulate matter is excellent. Its record on nitrogen oxides is more complicated and you deserve to know this. The same ICCT-TRUE 2024 study that sampled over 110,000 vehicles in Delhi and Gurugram found something that challenged the prevailing narrative. CNG commercial fleets (particularly taxis and light goods vehicles) were showing real-world NOx emissions far above lab limits. Class II CNG light goods vehicles were emitting up to 14.2 times their NOx lab limit. Taxis running on CNG were emitting 4 times above their permissible limit.

Why does this happen? Several reasons. Poor maintenance, degraded aftertreatment systems, high-load continuous operation and in some cases, older retrofitted kits that were never designed for modern engine configurations. The vehicles pass a laboratory test and then fail on the road.

NOx is not harmless. It contributes to the formation of ground-level ozone, a secondary pollutant that affects respiratory health year-round. Several Delhi monitoring stations have periodically recorded NO2 concentrations above national ambient air quality standards.

The takeaway is this: CNG genuinely cleaned up PM and CO emissions, which were the defining crises of the early 2000s. It bought Indian cities a critical window of cleaner air. But the next challenge of NOx and ozone requires better maintenance enforcement, not just fuel switching.
 

CNG's Impact Across India's Major Cities

Delhi led the way, but the ripple effect reached cities across the country.

• Delhi
  Delhi’s public transport system continues to rely heavily on CNG buses, alongside a growing electric bus fleet. The capital's bus count grew from under 10,000 in 1990 to nearly 20,000 by 2005, largely because the Supreme Court mandate also required an increase in the bus fleet. More buses on cleaner fuel meant fewer private vehicle trips and lower per-capita emissions.
• Mumbai
  The widespread adoption of CNG for auto-rickshaws and taxis transformed one of India's most congested urban centres. Mahanagar Gas Limited (MGL) supplies CNG to the city's commercial fleet and CNG vehicle registrations in MGL's area rose 47% year-on-year in October 2024 alone.
• Pune, Ahmedabad and Lucknow
  The PMPML bus fleet in Pune has progressively moved to CNG and Gujarat has been one of the largest CNG vehicle markets in the country given its early infrastructure investments.
• Pan-India growth
  CNG vehicle sales across India grew 33% year-on-year in the first half of 2024, reaching over 5.5 lakh units in just six months. Buses and vans saw the sharpest jump i.e., a 71% increase, reflecting sustained public transport investment. The total CNG vehicle count in India is expected to reach 75 lakh by end of FY2025, up from 26 lakh in FY2016, a nearly 3x increase in nine years.

CNG Stations: The Infrastructure That Made It Possible

A cleaner fuel is useless if nobody can access it. India's CNG refuelling infrastructure has grown dramatically over the past decade.

Note: Data sourced from MoPNG reports and industry analyses by Crisil. Rural coverage remains thin. CNG stations are concentrated in metro cities and along National Highways under the City Gas Distribution (CGD) network expansion.

The government has significantly expanded City Gas Distribution (CGD) coverage through PNGRB licensing rounds, extending CNG infrastructure into many additional districts beyond major metros. This is the structural change that is enabling CNG's spread from metros to Tier 2 and Tier 3 cities.

Still, a comparison worth noting: against 7,000 CNG stations, India has over 70,000 petrol and diesel outlets. The infrastructure gap is real, particularly for inter-city travel.
 

Why CNG Makes Economic Sense for City Drivers?

Environmental benefits are compelling. But what drives daily behaviour in India is the cost per kilometre. Fuel prices vary by city and are revised periodically by retailers and city gas distributors. As of May 2026, CNG continued to offer a materially lower per-kilometre running cost than petrol in most Indian metros.

Note: Mileage figures are approximate and vary by vehicle model, load and driving conditions. CNG mileage refers to km per kg of gas consumed.

The savings for a daily commuter covering 50 km a day add up quickly. On a petrol vehicle doing 15 km/litre, that is roughly 3.3 litres per day, or about Rs. 325. The same commute on CNG at 22 km/kg uses roughly 2.3 kg, costing about Rs. 196. That is a saving of around Rs. 129 per day, or nearly Rs. 47,000 annually. For auto-rickshaw drivers and cab operators with far higher daily mileage, the difference is life-changing.

Running a CNG vehicle? Make sure your motor insurance policy reflects the correct fuel type and that your CNG kit is declared to your insurer. Failure to disclose a retrofitted CNG kit may affect claim assessment or lead to disputes during settlement. Compare the right car insurance options at SMC Insurance.

 

CNG and Vehicle Insurance: What Owners Often Get Wrong

Switching to CNG affects more than your fuel bill. It has direct implications for your motor insurance policy and many owners miss this.

When a vehicle is retrofitted with an aftermarket CNG kit, the insurer must be informed. Installing a CNG kit without declaring it to your insurance company is a policy modification that, if undisclosed, can lead to claim denial, especially if the damage involves the fuel system. IRDAI guidelines require insurers to cover the CNG kit, but only if it has been declared and endorsed on the policy.

Original Equipment Manufacturer (OEM) CNG vehicles (cars sold with factory-fitted CNG systems, like Maruti Suzuki's CNG variants or Tata's iCNG models) carry fewer complications since the factory variant is already declared in the registration certificate. For retrofitted vehicles, the kit must be BIS-certified and declared at your nearest RTO before informing your insurer.

Your car insurance premium will increase slightly when the CNG kit is added to the policy. But this is a necessary cost, not an optional one. The alternative is a claim that gets rejected at exactly the moment you need it most. You can also explore comprehensive car insurance add-ons that offer broader protection for CNG vehicles, including engine protection covers.

 

CNG vs. Petrol vs. EV: Where Does CNG Stand in 2025-26?

CNG occupies a clear, honest position in India's fuel transition. Electric vehicles are gaining ground. EV adoption has accelerated in Delhi over the past few years. The Delhi government's Draft EV Policy 2.0 even proposes eventually phasing out CNG two-wheelers and autos. Nationally, the government targets 30% electrification of vehicles by 2030.

But EVs face their own constraints: charging infrastructure, range anxiety and higher upfront cost. In the current real-world environment, particularly for commercial operators running high daily mileage, CNG remains the most economically viable clean-fuel option. The honest answer: for city commuters and commercial operators in 2025-26, CNG is still the most practical step toward cleaner, cheaper urban mobility.
 

Wrapping Up

CNG did not solve India's pollution crisis. But it interrupted it at a critical moment. In the early 2000s, when diesel smoke was a daily reality for lakhs of commuters in Delhi, the Supreme Court mandate pushed the country toward a cleaner alternative. The particulate matter reductions that followed were real and documented. Cities breathed a little easier.

Two decades later, India has over 75 lakh CNG vehicles on its roads, 7,000-plus refuelling stations and a market that is growing at nearly 7% annually. The fuel costs Rs. 3-4 per kilometre versus Rs. 5.50-7 for petrol which is a gap that matters to every household running a daily commuter vehicle.

For the average vehicle owner, the path forward is simple: if you use CNG, declare your kit, maintain your vehicle and ensure your insurance is correctly endorsed. For cities still debating, the data supports CNG as a transitional fuel, not the final answer, but a necessary step between diesel-era pollution and a zero-emission future.

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