How bad is air pollution from cars?

It’s serious—especially in cities. Cars are a leading source of nitrogen dioxide (NO2) and a significant contributor to fine particles (PM2.5) and ozone, driving respiratory and cardiovascular harm and climate change. Passenger cars alone are responsible for roughly 10% of global energy-related CO2 emissions, and traffic pollution is linked to millions of asthma cases in children each year. While tighter standards and electric vehicles are cutting tailpipe pollution in many places, non-exhaust particles from tires and brakes remain a growing concern.

What “car pollution” actually is

Car pollution isn’t just exhaust fumes. It includes gases and particles from combustion, plus particles from tires, brakes, and road wear that persist even with zero-emission drivetrains.

Main pollutants and why they matter

The pollutants released or formed because of road traffic have distinct sources and health effects. Understanding them clarifies why urban areas see the biggest impacts.

• NOx (nitrogen oxides): Emitted from engines, especially under high load. Drives formation of ozone and secondary particles; directly irritates airways.
• PM2.5 and PM10 (fine and coarse particles): From exhaust (diesel and gasoline, especially when poorly controlled) and non-exhaust sources (tires, brakes, road dust). PM2.5 penetrates deep into lungs and bloodstream.
• VOCs (volatile organic compounds): From fuel evaporation and incomplete combustion; react with NOx to form ozone.
• Ozone (O3): Not emitted directly; forms in sunlight from NOx and VOCs. Aggravates asthma, reduces lung function.
• Black carbon: Soot from diesel and other incomplete combustion; warms the climate and harms health.
• CO2: Principal greenhouse gas from fuel combustion; not toxic locally but drives climate change, which in turn worsens air quality via heat and wildfires.

Together, these pollutants create a mix often called traffic-related air pollution (TRAP), which is highest near busy roads and during peak traffic, and can extend across entire urban airsheds under certain weather conditions.

How bad is it for health?

Air pollution is responsible for millions of premature deaths each year worldwide, and traffic is a major contributor in urban settings. The burden falls disproportionately on people living near busy roads, children, older adults, and those with existing heart and lung disease.

Key health findings from recent research

Several large studies and assessments quantify how traffic pollution affects health across the life course.

• Childhood asthma: Global analyses attribute around 4 million new pediatric asthma cases annually to NO2 exposure, much of it from traffic, representing a substantial share of childhood asthma incidence in cities.
• Cardiorespiratory disease: Long-term exposure to PM2.5 and NO2 increases risks of heart attack, stroke, arrhythmias, and chronic obstructive pulmonary disease; short-term spikes trigger emergency visits.
• Pregnancy and development: Higher traffic pollution exposures are associated with low birth weight, preterm birth, and adverse neurodevelopmental outcomes in some studies.
• Near-road exposure: People living, working, or attending school within a few hundred meters of major roads experience significantly higher NO2 and ultrafine particle levels, with measurable health impacts.

Although emission controls have reduced per-vehicle exhaust pollutants in many high-income countries, urban health burdens remain substantial, and in rapidly motorizing regions the exposure is often increasing without strong controls.

How much do cars contribute compared with other sources?

Globally, transport is one of the largest sources of climate-warming emissions and a dominant source of some urban air pollutants. Passenger cars are a sizable share of that picture.

• Climate: Transport accounts for roughly a quarter of energy-related CO2 emissions globally; road vehicles produce the majority of that, and passenger cars alone contribute on the order of 10% of total energy-related CO2.
• Urban NOx: Road transport is the single largest source of NOx in many regions—for example, it accounts for around a third or more of NOx in the European Union, with similar patterns in many dense cities worldwide.
• Particles: Exhaust PM from modern gasoline cars is relatively low with filters, but diesel exhaust can still be significant without controls. Crucially, more than half of traffic-related PM today in many cities is non-exhaust (tires, brakes, road dust), which is not eliminated by tailpipe standards.
• Ozone formation: Cars are a major urban source of the NOx and VOCs that drive smog, especially during hot, sunny periods when ozone peaks.

The exact shares vary by city and country depending on fleet composition (diesel vs. gasoline), vehicle age, traffic volume, topography, and the effectiveness of emission standards and inspection programs.

Trends: getting cleaner, but not clean

Two things are true at once: per-vehicle exhaust emissions have fallen dramatically where strong standards are enforced, and yet road traffic remains one of the most consequential sources of harmful urban air pollution.

What’s improving

Several technology and policy shifts are reducing the most harmful emissions, particularly in countries with stringent standards and enforcement.

• Emission standards and diesel controls: Tight limits (e.g., Euro 6/VI, China 6, U.S. Tier 3 and heavy-duty rules) with aftertreatment systems have reduced NOx and PM from new vehicles by over 90% compared with pre-control fleets.
• Electrification: Electric vehicles (EVs) have zero tailpipe emissions of NOx, VOCs, and exhaust PM; global EV sales reached about 18% of new cars in 2023 and continued rising in 2024, lowering local pollution where adoption is high.
• Fuel quality: Low-sulfur fuels enable effective catalytic controls, cutting sulfur-related PM and improving NOx control performance.
• Urban policies: Low-emission zones, congestion charging, and better transit/walking/cycling infrastructure reduce traffic volumes and exposures.

These steps have produced measurable drops in roadside NO2 and exhaust PM in many high-income cities, with associated health benefits, even as traffic volumes have grown.

What’s not improving enough

Some pollution sources are persistent or even growing as fleets get heavier and traffic remains intense.

• Non-exhaust particles: Tire and brake wear now dominate traffic PM in many cities; heavier vehicles—including some larger EVs—can increase tire wear unless mitigated by regenerative braking and tire advances.
• Legacy fleets and enforcement gaps: Older vehicles without effective controls, and poor maintenance or tampering, keep emissions high in many regions.
• Ozone in hot climates: As heatwaves intensify with climate change, ozone episodes are becoming more frequent and severe in susceptible regions.
• Exposure inequities: Lower-income and minority communities often live closer to high-traffic corridors, bearing disproportionate health burdens.

Because non-exhaust PM is not addressed by tailpipe rules, it requires complementary strategies on vehicle weight, braking systems, road dust management, and traffic reduction.

What would make the biggest difference

Reducing health and climate damage from cars requires a layered approach that combines cleaner vehicles with fewer, shorter, and safer trips.

• Accelerate fleet turnover: Retire the oldest, highest-emitting vehicles; enforce inspection and maintenance; prevent emissions-control tampering.
• Electrify rapidly and smartly: Support EV adoption for cars, vans, buses, and two/three-wheelers; pair with cleaner power grids; prioritize high-mileage fleets (taxis, ride-hail, delivery).
• Cut non-exhaust PM: Promote regenerative braking, lower vehicle mass, advanced brake systems, improved tire formulations, and regular street cleaning/dust suppression.
• Shift and avoid trips: Invest in reliable public transport, safe walking and cycling networks, and transit-oriented development; use pricing and parking policy to reduce congestion.
• Protect people where they live and learn: Route planning for heavy traffic, roadside vegetation barriers where appropriate, school air filtration, and building ventilation upgrades.
• Tighten standards and enforcement: Align with best-practice emission standards for light- and heavy-duty vehicles and ensure real-world compliance.

These measures work best together: cleaner vehicles reduce emissions per kilometer, while traffic reduction and smarter city design lower total kilometers driven and exposures.

Bottom line

Air pollution from cars remains a major public-health and climate problem, especially in cities and along busy corridors. Strong standards, electrification, and better urban mobility have already made a dent, but meaningful risk persists—particularly from NO2, ozone, and non-exhaust particles. The faster cities and countries pair zero-emission vehicles with fewer high-pollution trips and targeted protections for exposed communities, the faster the health gains will arrive.

How bad do cars pollute the air?

Cars are a major source of air pollution, but the exact amount varies by location and the specific pollutants. Globally, cars contribute significantly to greenhouse gas (GHG) emissions and are responsible for large portions of pollutants like carbon monoxide (CO) and nitrogen oxides (NOx). A typical passenger vehicle in the U.S. can emit around 4.6 metric tons of CO2 annually, but this can change based on the vehicle’s fuel type, fuel economy, and miles driven.
 
What types of pollution do cars produce?

• Greenhouse Gases (GHGs): Primarily carbon dioxide (CO2), which contributes to climate change. 
• Carbon Monoxide (CO): A harmful gas that cars are a significant source of. 
• Nitrogen Oxides (NOx): Formed when high-temperature engines burn nitrogen in the air. 
• Methane (CH4), Nitrous Oxide (N2O), and Volatile Organic Compounds (VOCs): Other pollutants emitted by gasoline vehicles. 

What is the overall impact of car pollution?

• Climate Change: GHGs from vehicles are a major factor in global climate change. 
• Health Issues: Car pollutants can lead to respiratory illnesses like asthma, heart disease, eye irritation, and even birth defects. 
• Smog Formation: NOx and other pollutants from vehicles contribute to the formation of ground-level ozone, or smog. 
• Environmental Damage: NOx contributes to acid rain and affects water quality and soil. 

Factors influencing car pollution:

• Fuel Consumption: More fuel burned means more CO2 emissions. 
• Vehicle Type: Different types of vehicles (e.g., passenger cars, trucks) have different emission profiles. 
• Miles Driven: The more miles a vehicle is driven, the more pollution it produces. 
• Fuel Economy: Higher fuel economy (miles per gallon) generally results in lower emissions. 

How can pollution be reduced?

• Electric Vehicles (EVs): EVs charged with renewable energy produce no CO2 or NOx emissions. 
• Fuel Efficiency: Improving fuel economy reduces emissions. 
• Driving Habits: Reducing the number of miles driven can lower emissions. 

Which type of car causes the most pollution?

Diesel vehicles contribute 60% of NOx emissions in U.S. transportation. NOx causes environmental issues such as acid rain and deteriorated water quality and contributes to acidification of soils and surface waters. It also forms ground-level ozone (smog) and PM2. 5, both harmful to health and the environment.

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. 

What is the #1 source of air pollution on Earth?

Vehicle emissions, fuel oils and natural gas to heat homes, by-products of manufacturing and power generation, particularly coal-fueled power plants, and fumes from chemical production are the primary sources of human-made air pollution.