Are vehicles a major cause of air pollution?

Yes—especially in cities. Emissions from road vehicles are a leading source of nitrogen dioxide (NO2) and a significant source of fine particles (PM2.5) in urban areas worldwide, though the overall contribution to air pollution varies by region and pollutant. Globally, transport is also a major driver of climate-warming emissions, and road traffic dominates transport-sector pollution.

What “vehicle pollution” includes

When people talk about pollution from vehicles, they usually mean both tailpipe emissions and the particles created by driving itself. The main pollutants affect air quality and climate in different ways.

• Nitrogen oxides (NOx, including NO2): Drive urban smog and ozone formation; traffic is a primary urban source.
• Fine particles (PM2.5) and coarse particles (PM10): Come from exhaust (especially diesel) and non-exhaust sources such as brake, tire wear, and road dust.
• Volatile organic compounds (VOCs) and carbon monoxide (CO): Contribute to ozone and can harm health directly.
• Ozone (O3): A secondary pollutant formed in sunlight from NOx and VOCs; elevated in and downwind of cities.
• Black carbon: Soot component of PM from diesel engines; strongly linked to health harm and climate warming.
• Carbon dioxide (CO2): The main greenhouse gas from burning fuel; not a local air toxic, but central to climate change.

Taken together, these pollutants explain why traffic-heavy corridors see the highest roadside exposures and why strategies must tackle both tailpipe and non-exhaust sources.

How big is the contribution? Global and regional snapshots

Global picture

Transport produces a large share of energy-related CO2 emissions worldwide, and road traffic accounts for the majority of transport-sector emissions. According to assessments used by the IPCC and IEA, transport is responsible for roughly a quarter of energy-related CO2, with road vehicles contributing around three quarters of that. For health-damaging air pollutants, vehicles are among several major sources globally—others include residential heating and cooking (especially solid fuels), industry, power generation, and agriculture—but vehicles are often the dominant source of urban NO2 and a meaningful contributor to urban PM2.5.

Cities and high-income regions

In many European and North American cities, road traffic is the leading source of NO2 and a significant share of PM2.5 at street level. Recent European Environment Agency data indicate road transport produces on the order of four in ten NOx emissions at the EU level, while its share of primary PM2.5 is smaller overall but can dominate at traffic hotspots. In the United States, EPA inventories show mobile sources are the largest category for NOx nationally, with on-road vehicles a major component; diesel trucks and buses, though a minority of vehicles, are disproportionate contributors.

Low- and middle-income countries

Rapid motorization, older vehicle fleets, and historically higher-sulfur fuels can make traffic a major local pollutant source, especially in corridors with heavy diesel bus and truck traffic and two- or three-wheelers. At the same time, residential biomass burning, industry, and open burning often contribute substantial PM2.5, so the balance of sources varies by city.

Evidence at a glance

The following selected datapoints summarize the role of vehicles in air pollution across contexts.

• Transport contributes roughly a quarter of global energy-related CO2; road vehicles produce the bulk of transport CO2 (IPCC/IEA assessments).
• Road transport is a leading source of NO2 in cities and a major NOx source in the EU and US; diesel heavy-duty vehicles are key contributors to urban NOx.
• Vehicles contribute a smaller share of primary PM2.5 at national scale in high-income regions, but traffic can dominate PM2.5 at roadside locations.
• Non-exhaust particles (brake, tire, road dust) now make up a growing share—and in many cases the majority—of traffic-related PM for modern light-duty fleets.
• WHO reports that nearly the entire global population breathes air exceeding health guidelines; transport is one of the major urban contributors.

Together, these figures show vehicles are central to urban air quality challenges while sharing responsibility with other sectors at regional and global scales.

Health impacts linked to vehicle emissions

Pollution from traffic harms health across the life course, with evidence strongest for NO2 and PM2.5 exposures common near busy roads.

• Respiratory: Higher risks of asthma onset in children, exacerbations in people with asthma, and chronic obstructive pulmonary disease flare-ups.
• Cardiovascular: Elevated risks of heart attacks, strokes, arrhythmias, and earlier mortality associated with PM2.5 and traffic-related pollutants.
• Pregnancy and infants: Links to low birth weight, preterm birth, and impaired lung development.
• Cognitive and metabolic: Associations with cognitive decline, dementia risk, and metabolic disorders are supported by growing evidence.
• Environmental justice: Communities near highways and freight hubs—often lower-income and minority—bear disproportionate exposures and health burdens.

Reducing traffic-related pollution yields rapid health benefits, particularly in neighborhoods closest to major roads and freight corridors.

Trends: getting better, but not enough

Tailpipe emissions per vehicle have fallen where modern standards and cleaner fuels are in place, and electrification is accelerating. Urban NO2 levels have generally declined over the past decade in Europe and North America. Yet growth in traffic, diesel freight, and non-exhaust particles means many cities still breach health guidelines—especially for PM2.5. Policy momentum is shifting to both zero-emission drivetrains and non-exhaust controls.

What’s changing in policy and technology

Recent moves show how governments and industry are tackling vehicle pollution across multiple fronts.

• Electrification: Nearly one in five new cars sold globally in 2024 were electric, with faster uptake for city buses and delivery fleets.
• Stronger standards: The EU’s Euro 7 regulation introduces the first limits on brake and tire particle emissions and modernizes testing; the U.S. has finalized tougher standards for heavy-duty NOx and greenhouse gases for late-decade models.
• Cleaner fuels: Ultra-low-sulfur fuels are now the norm in most markets, enabling advanced exhaust controls.
• Urban measures: Low- and zero-emission zones, congestion charging, and freight consolidation are expanding to cut traffic emissions where people live.
• Non-exhaust focus: Emerging requirements for low-wear brake systems and durable tires aim to curb particles from braking and abrasion.

These steps are bending the curve, but meeting health-based air quality guidelines will require faster fleet turnover, broader adoption, and attention to heavy-duty and non-exhaust sources.

What reduces vehicle-driven air pollution fastest?

To clean city air quickly and durably, evidence points to a mix of technology, fuel, and demand-side measures, with a focus on the most polluting segments and places.

1. Electrify buses, delivery vans, and urban trucks first—high mileage and urban duty cycles maximize air-quality gains.
2. Tighten and enforce NOx and PM standards for new and in-use vehicles, including periodic inspection and remote sensing to catch high emitters.
3. Ensure ultra-low-sulfur fuels everywhere to enable effective exhaust aftertreatment where combustion engines remain.
4. Shift trips to public transport, walking, and cycling; redesign streets to make alternatives safe and convenient.
5. Manage traffic and freight: congestion pricing, low-emission zones, and off-peak logistics reduce emissions where exposure is highest.
6. Target non-exhaust particles with low-wear brakes, tire standards, road cleaning, and speed management.
7. Protect hotspots: ventilation and filtration in schools/housing near busy roads; green buffers where appropriate.
8. Improve data: high-resolution monitoring and source apportionment to direct actions where they deliver the most health benefit.

Prioritizing dense urban corridors and heavy-duty fleets delivers the quickest and largest health improvements, while broader fleet electrification secures long-term gains.

Bottom line

Vehicles are a major cause of urban air pollution—especially for NO2 and traffic-related particles—and a significant contributor to climate pollution. Their importance varies by region and pollutant, but cutting traffic emissions is essential for cities to meet health-based air quality standards. Strong standards, rapid electrification, smart urban design, and attention to non-exhaust sources can deliver cleaner air quickly and equitably.

Summary

Emissions from vehicles are a major driver of urban air pollution worldwide and a significant source of climate-warming CO2. While other sectors also contribute—often more to regional PM2.5—traffic typically dominates city NO2 and contributes substantially to roadside PM. Progress is underway through electrification, cleaner fuels, and tighter standards, including new rules targeting brake and tire particles. The most effective path combines rapid electrification of high-mileage urban fleets, robust in-use controls, demand shifts to cleaner modes, and measures that reduce non-exhaust particles and protect communities near busy roads.

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. 

Are cars the main cause of air pollution?

Across the U.S., vehicle emissions are the largest source of carbon monoxides (56% nationwide and up to 95% in cities) and nitrogen oxides (45% is attributed to the transportation sector). California’s transportation sector accounts for nearly 80% of nitrogen oxide pollution and 80% of the pollutants that cause smog.

What is the biggest contributor to air pollution?

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.

What percentage of pollution is made by cars?

Vehicles cause a significant portion of U.S. greenhouse gas emissions, accounting for approximately 28% of total U.S. emissions in 2023. Specifically, light-duty vehicles (cars, SUVs, light trucks) are the largest contributors to this, making up 57% of the transportation sector’s emissions. Air pollution from vehicles includes harmful pollutants like nitrogen oxides and fine particulate matter, with transportation being responsible for roughly a quarter of premature deaths linked to PM2.5 from all sources.
 
Breakdown of Vehicle-Related Air Pollution

• Carbon Dioxide (CO2): Opens in new tabThe U.S. EPA reports that transportation is the largest source of U.S. greenhouse gas emissions, with about 28% coming from the transportation sector. 
• Nitrogen Oxides (NOx): Opens in new tabOn-road vehicles are a major source of NOx emissions, contributing significantly to the overall total of this pollutant. 
• Fine Particulate Matter (PM2.5): Opens in new tabVehicle emissions are a substantial source of PM2.5, with studies linking transportation to a significant number of premature deaths. 

Breakdown by Vehicle Type

• Light-Duty Vehicles: Opens in new tabPassenger cars, SUVs, and light trucks are the largest sources of greenhouse gas emissions within the transportation sector. 
• Medium and Heavy-Duty Trucks: Opens in new tabWhile making up a smaller number of vehicles, these trucks contribute disproportionately to NOx and PM2.5 emissions. 

Impact on Health 

• Transportation-related emissions are a major cause of both particulate matter and ozone-related deaths, with studies suggesting they are responsible for up to one-quarter of premature deaths from PM2.5.