What Air Pollution Do Cars Cause?

Cars pollute the air by emitting nitrogen oxides (NOx), fine particles (PM2.5 and PM10), carbon monoxide (CO), volatile organic compounds (VOCs), and greenhouse gases like carbon dioxide (CO2); they also shed non-exhaust particles from brakes and tires. These pollutants create smog and soot, worsen respiratory and heart disease, and warm the climate. Below is a clear breakdown of what cars emit, how those emissions form, and why they matter for health and the environment.

What pollutants do cars emit?

Road vehicles produce a mix of direct tailpipe emissions and non-exhaust particles. The following list outlines the main pollutants linked to health and climate impacts.

• Nitrogen oxides (NO and NO2, collectively NOx): key ingredients in smog and ozone; irritate lungs and inflame airways.
• Particulate matter (PM2.5 and PM10) and ultrafine particles: microscopic solids and droplets that penetrate deep into the lungs and bloodstream.
• Carbon monoxide (CO): a colorless gas from incomplete combustion that reduces oxygen delivery in the body.
• Volatile organic compounds (VOCs): hydrocarbons (e.g., benzene, toluene) and aldehydes (e.g., formaldehyde, acetaldehyde) that contribute to ozone and some of which are carcinogenic.
• Greenhouse gases: primarily carbon dioxide (CO2); also nitrous oxide (N2O) from catalytic converters and small amounts of methane (CH4).
• Ammonia (NH3): produced by three‑way catalysts, contributing to secondary PM (ammonium nitrate) in urban air.
• Sulfur oxides (SOx): now very low in regions with ultra‑low sulfur fuels, but still relevant where sulfur content is higher.
• Non-exhaust particles: brake wear (iron, copper, antimony), tire wear (synthetic rubber, zinc, microplastics such as 6PPD-quinone), and resuspended road dust.

Together, these emissions drive both near-road health risks and regional air-quality problems like ozone episodes and haze, while also contributing to climate change.

How do these pollutants form?

Different technologies and driving conditions influence which pollutants are produced. The following points explain the main formation pathways.

• High-temperature combustion forms NOx; peak temperatures and lean mixtures in engines favor NOx production.
• Incomplete combustion yields CO and VOCs, especially during cold starts before catalysts reach operating temperature.
• Diesel engines and gasoline direct-injection (GDI) engines can produce higher particle numbers; diesel particulate filters (DPFs) and gasoline particulate filters (GPFs) capture most but not all PM.
• VOCs from fuel evaporation occur from hot-soak conditions, refueling, and permeation; modern evaporative controls reduce but do not eliminate these.
• Ozone is not emitted directly; it forms downwind as NOx and VOCs react in sunlight.
• Ammonia slip occurs when three‑way catalysts over-reduce NOx, releasing NH3 that later forms secondary PM.
• Braking and tire abrasion generate particles regardless of fuel type; regenerative braking in hybrids and EVs reduces brake wear but tire wear persists.

These mechanisms explain why urban peaks often occur during rush hours, cold weather starts, and sunny conditions that speed ozone formation.

Health and environmental impacts

Vehicle-related pollutants affect both immediate human health and broader environmental systems. The items below summarize the key impacts supported by public health and atmospheric research.

• PM2.5 and ultrafine particles: linked to heart attacks, stroke, lung cancer, pregnancy complications, and premature death; no safe threshold per WHO guidelines.
• NO2: associated with asthma development and exacerbation, reduced lung function, and increased emergency visits, especially among children.
• Ozone: causes chest tightness, coughing, and reduced lung function; harms crops and ecosystems.
• Benzene and other VOCs: some are carcinogenic; aldehydes irritate eyes and airways.
• CO: impairs oxygen transport; dangerous for people with cardiovascular disease and for fetuses.
• Greenhouse gases: CO2 dominates transport’s climate impact; N2O has high warming potential and persists for decades.
• Non-exhaust PM: carries metals and organic compounds; tire-derived chemicals like 6PPD-quinone are toxic to aquatic life.

The combined burden is highest near busy roads, logistics hubs, and in densely populated corridors, but secondary pollutants like ozone and secondary PM can travel far downwind.

Tailpipe versus non-exhaust emissions

Understanding the split between tailpipe and non-exhaust sources helps target mitigation effectively. The following points contrast their characteristics and trends.

• Tailpipe emissions have fallen sharply in many regions due to catalytic converters, DPFs/GPFs, and stringent fuel standards, yet real-world spikes still occur during cold starts, high loads, and malfunctions.
• Non-exhaust emissions now account for a growing share of urban PM from traffic, as brakes, tires, and road dust are not eliminated by engine controls.
• Electric vehicles have zero tailpipe emissions, which eliminates NOx, CO, and tailpipe PM locally; regenerative braking reduces brake dust, while tire wear remains and may depend on vehicle weight, tire design, and driving style.

As tailpipe controls improve and electrification expands, non-exhaust sources become relatively more important, making tire and brake standards and street cleaning more impactful.

How big is the contribution?

Transport’s share varies by city and country, but the pattern is consistent: road traffic is a leading source of urban NOx and a significant source of PM, while it is also a major source of CO2. The following points provide context using widely cited assessments.

• Globally, road transport accounts for roughly the mid‑teens percent of energy‑related CO2 emissions; passenger cars are a major portion of that total.
• In many cities, road traffic is the dominant contributor to NO2 near roads and a key driver of ozone formation regionally.
• Non-exhaust PM from traffic can rival or exceed tailpipe PM in cities with modern emission controls.

Local inventories and monitoring data are essential for precise shares, but the overall picture consistently shows road vehicles as central to urban air-quality management and climate goals.

What about electric vehicles and hybrids?

Powertrain choice changes the pollution profile. The points below summarize how hybrids and EVs compare with conventional cars.

• Hybrids reduce fuel consumption and tailpipe pollution by recovering braking energy and optimizing engine operation, especially in stop‑and‑go traffic.
• Battery electric vehicles (EVs) have no tailpipe emissions; life‑cycle greenhouse gas benefits depend on the electricity mix, but analyses through 2024 show lower life‑cycle CO2 in most regions and rapidly improving as grids decarbonize.
• EVs still produce non-exhaust PM from tires and road dust; regenerative braking typically cuts brake wear substantially.

Electrification is therefore most effective for cutting urban NOx, CO, and tailpipe PM immediately, while continued grid decarbonization deepens climate benefits over time.

Regulations and trends (up to 2024–2025)

Policy remains a primary driver of cleaner air from transport. The list below highlights notable regulatory developments.

• United States: The EPA finalized multi‑pollutant standards for model years 2027–2032 light‑ and medium‑duty vehicles in 2024, tightening fleetwide limits and enabling large NOx, PM, and CO2 reductions. Heavy‑duty NOx standards for MY 2027+ were also finalized earlier. California’s Advanced Clean Cars II targets 100% zero‑emission light‑duty sales by 2035.
• European Union: Euro 7 legislation approved in 2024 keeps passenger‑car tailpipe limits similar to Euro 6 but adds first‑ever limits for brake particle emissions and tire abrasion, strengthens heavy‑duty limits, and sets durability requirements (including for EV batteries).
• Fuel quality: Ultra‑low sulfur fuels in North America, Europe, and parts of Asia enable advanced aftertreatment and minimize SOx and sulfate PM; regions with higher‑sulfur fuels still face additional pollution.
• Inspection and maintenance: Programs to detect malfunctioning emission controls remain important because a small share of “high emitters” can contribute disproportionately to urban pollution.

These policies, combined with rapid adoption of cleaner technologies, are steadily reducing tailpipe pollution, while new standards begin to address non-exhaust sources.

How can individuals and cities reduce car-related air pollution?

Reducing emissions requires action from drivers, fleet operators, and policymakers. The following list outlines practical steps at multiple levels.

• Choose cleaner vehicles: prioritize EVs or efficient hybrids; ensure vehicles meet the latest emission standards.
• Drive and maintain smartly: smooth acceleration, correct tire pressure, timely maintenance, and functioning emission controls; avoid idling and short cold-start trips when possible.
• Cut non-exhaust PM: favor regenerative braking (hybrids/EVs), use low-dust brake pads, and high-durability, low-abrasion tires; support street cleaning to reduce resuspension.
• Shift modes: walk, cycle, and use public transit when feasible; consolidate trips and adopt telepresence to cut VMT (vehicle miles traveled).
• Urban policy: invest in transit, safe cycling networks, low‑emission or zero‑emission zones, congestion pricing, and curbside management to reduce traffic and exposure.
• Electricity and logistics: decarbonize power grids, deploy charging infrastructure, and electrify delivery fleets and buses in high‑exposure corridors.

Together, these actions can quickly reduce harmful pollution where people live and breathe, while also lowering greenhouse gas emissions.

How do we know what cars emit?

Measuring and modeling emissions has become more sophisticated and realistic. The points below explain common approaches used by regulators and researchers.

• On-road testing: portable emission measurement systems (PEMS) capture real‑world emissions under varied driving, complementing lab tests.
• Remote sensing: roadside instruments detect high emitters and quantify fleet distributions without stopping vehicles.
• Air monitoring and source apportionment: fixed and mobile monitors, chemical tracers (e.g., NOx/CO ratios, metals from brakes), and receptor models attribute pollution to traffic.
• Emission inventories and dispersion models: integrate technology data, driving patterns, and meteorology to estimate contributions and evaluate policy scenarios.

These tools help identify hotspots, enforce standards, and prioritize interventions with the greatest health benefits.

Summary

Cars cause air pollution by emitting NOx, PM, CO, VOCs, and greenhouse gases from their tailpipes, and by shedding particles from brakes and tires. These pollutants drive smog, increase the risk of heart and lung disease, and warm the climate. Emissions are highest during cold starts and hard acceleration, and while modern controls have cut tailpipe pollution dramatically, non-exhaust PM remains a growing share. Electrification, stringent standards (including new limits for brake and tire emissions in the EU), cleaner fuels, better maintenance, and smarter urban design can together deliver cleaner air and a safer climate.