What Cars Emit the Most

Most cars emit carbon dioxide (CO2) more than anything else when “emissions” are discussed as climate pollution; however, if you count all exhaust components by sheer volume or mass, vehicles mostly expel nitrogen (from the air they inhale) and water vapor, with CO2 the dominant greenhouse gas and the largest tailpipe output related to climate change.

What “the most” means—and why it matters

“Emissions” can mean different things: the total gases coming out of a tailpipe, the pollutants that harm health, or the greenhouse gases that warm the planet. By mass of climate-relevant emissions, CO2 dominates. By composition of exhaust, nitrogen and water vapor are largest because engines mostly pass through the air they intake and create water during combustion. For urban air quality, smaller quantities of nitrogen oxides (NOx), volatile organic compounds (VOCs), carbon monoxide (CO), ammonia (NH3), and fine particles (PM2.5) matter most, while non-exhaust sources like tire and brake wear increasingly dominate particle pollution.

By sheer mass from the tailpipe

Considering the whole exhaust stream from internal-combustion cars, most of what comes out is not “pollution” but the byproducts and leftover components of air and combustion. Here’s how that typically breaks down in normal operation.

• Nitrogen (N2): The largest fraction of exhaust by volume and mass; it enters with intake air and exits largely unchanged.
• Water vapor (H2O): Formed when hydrogen in fuel burns; substantial in warm exhaust and condenses as visible water in cold conditions.
• Carbon dioxide (CO2): The main carbon-containing product of combustion and the largest climate pollutant from vehicles.
• Oxygen (O2): A small leftover fraction if combustion isn’t perfectly stoichiometric.
• Pollutants (NOx, CO, unburned hydrocarbons/VOCs, particulate matter): Tiny fractions by mass compared with the above but disproportionately harmful to health and air quality.

The dominance of nitrogen and water reflects engine chemistry; the central climate concern is CO2, while even trace amounts of regulated pollutants can drive smog and health impacts.

By climate impact: greenhouse gases

For climate change, the primary concern is greenhouse gases. Gasoline and diesel cars overwhelmingly emit CO2, with trace nitrous oxide (N2O) and methane (CH4) contributing a smaller but non-zero share of warming.

• Carbon dioxide (CO2): The dominant greenhouse gas from cars. Typical real-world tailpipe CO2 for modern gasoline cars spans roughly 250–450 g/mile (about 155–280 g/km), varying by vehicle size and driving. New U.S. light-duty vehicles average roughly the mid-300s g/mile.
• Nitrous oxide (N2O): Emitted in small amounts from high-temperature combustion and aftertreatment chemistry; minor by mass but potent per molecule.
• Methane (CH4): Very small for gasoline and diesel; higher for vehicles fueled by natural gas. Still much smaller than CO2 for conventional cars.

Bottom line: CO2 is by far the largest greenhouse gas emitted by cars, and thus the chief driver of transport-related warming.

By local air pollution: what harms health

For smog and health, the focus shifts to pollutants that create ozone or fine particles, or directly irritate lungs and hearts. Modern emission controls have cut exhaust pollutants dramatically, but some remain—and non-exhaust sources now loom larger.

• Non-exhaust particles (tire, brake, and road wear): In many urban areas, these now account for more than half of road-traffic PM2.5, as exhaust PM has fallen with filters and cleaner engines.
• Nitrogen oxides (NOx): Promote ozone and secondary PM; still a key urban pollutant, especially from older diesel vehicles and during cold starts or hard acceleration.
• Volatile organic compounds (VOCs): From unburned fuel and evaporation (plus exhaust); combine with NOx to form ozone.
• Carbon monoxide (CO): Greatly reduced by catalytic converters but remains a concern in enclosed or poorly ventilated spaces.
• Ammonia (NH3): Can slip from modern catalysts and form secondary PM2.5 downwind.

These pollutants are small by mass compared with CO2 but drive most of the near-term health burden from traffic, especially along busy corridors.

How much CO2 does a car emit?

CO2 can be estimated directly from fuel use, because nearly all the carbon in fuel becomes CO2 at the tailpipe. The factors below are widely used in policy and reporting.

• Gasoline: About 8.89 kg CO2 per U.S. gallon burned (≈2.35 kg per liter).
• Diesel: About 10.16 kg CO2 per U.S. gallon (≈2.68 kg per liter).
• Per distance: Real-world averages for conventional light-duty vehicles typically land around 250–450 g CO2 per mile (≈155–280 g/km), depending on vehicle size, speed, and driving style.

Because CO2 scales almost linearly with fuel burned, improving fuel economy or driving fewer miles cuts CO2 directly.

Electric and hybrid vehicles: different emission profiles

Battery-electric vehicles have zero tailpipe emissions, eliminating exhaust CO2, NOx, and PM. Their climate impact depends on the electricity mix: on today’s average grids, EVs typically reduce lifecycle greenhouse-gas emissions by roughly 50–70% versus comparable gasoline cars, with larger benefits on cleaner grids. EVs and hybrids also cut brake dust via regenerative braking, though tire wear particles still occur and can be similar or slightly higher if the vehicle is heavier.

Policies and trends to watch

Regulators have tightened standards for exhaust pollutants and are beginning to address non-exhaust emissions. Europe’s next rules bring the first dedicated limits and test methods for brake and tire emissions, and cities worldwide are expanding low-emission and zero-emission zones. Automakers are rapidly increasing electrified model offerings, and efficiency standards continue to push down CO2 per mile.

What drivers and cities can do now

Practical steps can reduce both climate and health impacts from cars, even before broader policy shifts take full effect.

• Drive less when possible: Combine trips, use public transit, walk, or cycle for short distances.
• Choose cleaner vehicles: Opt for EVs or high-efficiency hybrids; right-size the vehicle to your needs.
• Cut fuel use: Maintain tire pressure, remove excess weight, and drive smoothly to avoid hard acceleration.
• Reduce non-exhaust PM: Favor regenerative braking (in hybrids/EVs), avoid oversized wheels/tires, and choose lower-abrasion tires when available.
• Support clean-air policy: Back strong emission standards, brake/tire rules, and urban designs that reduce traffic and speed spikes.

Taken together, these actions lower CO2 substantially and reduce the local pollutants that harm health in neighborhoods.

Summary

If you mean greenhouse gases, cars emit carbon dioxide (CO2) the most—and that’s the primary climate concern. If you mean the physical contents of tailpipe exhaust, nitrogen and water vapor dominate by mass, with CO2 next and regulated pollutants in much smaller amounts. For city air quality, however, even tiny quantities of NOx, VOCs, CO, NH3, and particles matter—and non-exhaust sources like tire and brake wear now account for a large share of traffic-related PM. Transitioning to cleaner vehicles, driving less, and tightening standards for both exhaust and non-exhaust emissions are the most effective ways to cut the harms.

What gas do cars emit the most?

carbon dioxide
A typical passenger vehicle emits about 4.6 metric tons of carbon dioxide per year.

What is the #1 polluter on planet Earth?

China is the world’s biggest annual greenhouse gas polluter, responsible for nearly a third of global emissions, followed by the United States and India. While China leads in absolute annual emissions, the per capita emissions ranking changes, with countries like Qatar and the United States having higher per person pollution levels due to large individual energy consumption.
 
Absolute vs. Per Capita Emissions

• Absolute Emissions: Opens in new tabThis measures the total amount of pollution from a country. China emits the most carbon dioxide (CO2) annually. 
• Per Capita Emissions: Opens in new tabThis measures the pollution per person in a country. When looking at this metric, countries like the United States, Qatar, and Montenegro have higher emissions per person than China, which has a large population. 

Top Polluters by Annual Emissions

1. China: The largest annual emitter of greenhouse gases, accounting for roughly one-third of the world’s total. 
2. United States: The second-largest annual polluter. 
3. India: The third-largest annual polluter. 

Other Factors

• Historic vs. Current Emissions: Opens in new tabThe total historical contribution to climate change is another important factor to consider. 
• Efforts to Reduce Emissions: Opens in new tabDespite being the top polluter, China is making significant efforts to reduce its emissions by rapidly expanding renewable energy sources like wind and solar. 

What toxins do cars emit?

Vehicle pollutants harm our health and contain greenhouse gases that cause climate change. Burning gasoline and diesel fuel creates harmful byproducts like nitrogen dioxide, carbon monoxide, hydrocarbons, benzene, and formaldehyde.

Do cars give off CO2 or CO?

Cars produce both carbon dioxide (CO2) and carbon monoxide (CO). Carbon dioxide is a result of complete fuel combustion and is a greenhouse gas, while carbon monoxide is a product of incomplete combustion and is a toxic, invisible gas. Modern catalytic converters significantly reduce CO emissions, but poorly tuned or older cars, or situations like a car running in an enclosed garage, can lead to dangerously high levels of carbon monoxide.
 
Carbon Dioxide (CO2) 

• What it is: A greenhouse gas that results from the complete burning of gasoline and diesel fuel in an engine.
• Effects: Contributes to climate change.

Carbon Monoxide (CO)

• What it is: A toxic, invisible gas produced when fuel doesn’t burn completely. 
• Effects: Harmful to human health and can be fatal in enclosed spaces. 

Why Cars Produce Both

• Complete Combustion: Opens in new tabWhen fuel burns perfectly with enough oxygen, the primary products are water vapor and carbon dioxide. 
• Incomplete Combustion: Opens in new tabIn reality, fuel combustion in a car engine is not always complete, especially at certain engine conditions or if the engine is poorly maintained, leading to the production of carbon monoxide. 

How CO emissions are reduced 

• Catalytic Converters: Modern cars are equipped with catalytic converters, which are designed to convert carbon monoxide into less harmful carbon dioxide before the exhaust leaves the vehicle.

When CO levels are dangerous

• Faulty Exhaust Systems: Opens in new tabLeaks in the exhaust system can allow carbon monoxide to escape before it’s converted by the catalytic converter. 
• Enclosed Spaces: Opens in new tabOperating a car in a closed area like a garage can lead to CO buildup, as there might not be enough oxygen for the catalytic converter to work effectively or for the gas to dissipate.