What chemical comes out of cars?

There isn’t just one chemical: the principal gas from a car’s tailpipe is carbon dioxide (CO₂), accompanied by water vapor and nitrogen; harmful pollutants can include carbon monoxide (CO), nitrogen oxides (NO and NO₂, collectively NOₓ), unburned hydrocarbons/volatile organic compounds (VOCs), particulate matter (PM), sulfur dioxide (SO₂), small amounts of nitrous oxide (N₂O) and methane (CH₄), and trace toxics like benzene and formaldehyde. Electric vehicles have no tailpipe emissions but still generate non-exhaust particles from tires and roads. What comes out depends on fuel type, engine technology, emissions controls, maintenance, and driving conditions.

What cars emit when they run

Combustion engines burn fuel in air, producing a mix dominated by nitrogen (from the air), carbon dioxide, and water vapor. Modern emissions controls cut many harmful pollutants dramatically, but cold starts, hard acceleration, and poor maintenance can increase emissions. The following are the main tailpipe constituents for gasoline and diesel vehicles.

• Carbon dioxide (CO₂): The primary greenhouse gas from burning fuel; scales closely with fuel consumed.
• Water vapor (H₂O) and nitrogen (N₂): Large fractions of exhaust; not primary air toxics, though water vapor can influence plume chemistry.
• Carbon monoxide (CO): A toxic gas formed when combustion is incomplete; controlled by catalytic converters but can spike during cold starts.
• Nitrogen oxides (NOₓ = NO + NO₂): Formed at high temperatures; key precursors to smog (ground-level ozone) and secondary particulate matter.
• Unburned hydrocarbons and VOCs: Fuel fragments that contribute to smog and include toxic species (e.g., benzene, toluene, formaldehyde).
• Particulate matter (PM₂.₅ and ultrafine particles): Soot and organic/metal particles; higher in diesel exhaust without filters, and in cold-start gasoline, especially direct-injection engines.
• Sulfur dioxide (SO₂): From sulfur in fuel; very low with today’s ultra-low-sulfur fuels but still present in small amounts.
• Nitrous oxide (N₂O) and methane (CH₄): Potent greenhouse gases emitted in small quantities; N₂O can be produced by catalytic converters.
• Ammonia (NH₃): Can slip from diesel SCR systems (urea-based) or form in rich operation of gasoline catalysts; contributes to secondary PM.

Together, these gases and particles shape both local air quality and global climate impacts, with CO₂ driving long-term warming and pollutants like NOₓ, VOCs, and PM affecting health and visibility in the near term.

Secondary pollutants formed in the air

Some of the most harmful effects arise not from what leaves the tailpipe directly, but from chemicals that form in the atmosphere when exhaust mixes with sunlight and other pollutants. Here are the key secondary products linked to vehicle emissions.

• Ozone (O₃): Not emitted directly; forms when NOₓ and VOCs react in sunlight, driving smog episodes.
• Secondary particulate matter: Nitrates and sulfates (from NOₓ and SO₂) and secondary organic aerosol (from VOCs) add to PM₂.₅ burdens.

These secondary pollutants can travel far from roadways, affecting regional air quality and public health even where traffic is light.

Non-tailpipe emissions

Even when tailpipes are clean or absent (as with electric vehicles), vehicles generate particles from tires, brakes, and road dust. These emissions increasingly dominate urban traffic-related PM in many regions.

• Tire wear particles: Microplastics and rubber fragments (e.g., styrene-butadiene), plus additives like zinc; resuspended by passing traffic.
• Brake wear: Metals and friction material particles; reduced in EVs and hybrids due to regenerative braking but not eliminated.
• Road dust: Abraded pavement and soil re-entrained into the air, influenced by vehicle mass and speed.

Non-exhaust particles contribute substantially to PM₂.₅ and ultrafine particle exposure near busy roads and are a growing focus of air-quality policy.

How modern technology changes emissions

Regulations and engineering have transformed vehicle emissions profiles. Technologies vary by fuel and model year, and they strongly influence what chemicals reach the air.

• Three-way catalytic converters (gasoline): Convert CO and hydrocarbons to CO₂ and water, and reduce NOₓ to nitrogen; most effective once warmed up.
• Gasoline particulate filters (GPF): Increasingly used on direct-injection engines to cut fine particles formed during cold starts and transients.
• Diesel particulate filters (DPF): Capture soot; when properly maintained, they slash PM emissions by over 90%.
• Selective catalytic reduction (SCR) with urea (diesel): Reduces NOₓ to nitrogen; may produce small ammonia slip if not well controlled.
• Alternative fuels: Compressed natural gas (CNG) cuts PM and some toxics but can increase methane slip; ethanol blends change VOC profiles.
• Hybrids and plug-in hybrids: Reduce fuel use and cold-start frequency, cutting CO₂ and pollutants per mile.
• Battery electric vehicles (EVs): Zero tailpipe emissions; total climate impact depends on electricity generation and charging patterns.

Overall, advanced aftertreatment and electrification markedly reduce harmful exhaust, though cold starts, real-world driving, and maintenance still matter—and non-exhaust particles remain an issue.

Health and climate impacts at a glance

Different exhaust constituents affect health and climate in distinct ways. The items below summarize the most consequential impacts linked to vehicle emissions.

• CO₂: Main driver of climate change from vehicles; directly tied to fuel consumption.
• CO: Reduces blood oxygen delivery; dangerous at high concentrations in enclosed or poorly ventilated areas.
• NO₂ and NOₓ: Irritate airways, exacerbate asthma, and contribute to ozone and secondary PM formation.
• PM₂.₅ and ultrafine particles: Penetrate deep into lungs and bloodstream; linked to cardiovascular and respiratory disease.
• VOCs (e.g., benzene, formaldehyde): Some are carcinogenic or irritating and drive smog chemistry.
• Ozone (secondary): Triggers respiratory symptoms and reduces lung function, especially during heat and sunlight.
• SO₂: Respiratory irritant and precursor to sulfate PM; generally low with modern low-sulfur fuels.
• N₂O and CH₄: Potent greenhouse gases with smaller but non-negligible vehicle contributions.

Mitigating both climate and health burdens requires cutting CO₂ and controlling smog- and PM-forming pollutants through cleaner tech and fuels.

What determines what comes out of a car

Tailpipe chemistry varies widely trip to trip. The following factors most strongly influence emissions.

• Engine and fuel type: Gasoline vs. diesel vs. CNG vs. electric; direct vs. port injection; turbocharging.
• Aftertreatment condition: Catalyst, DPF, SCR effectiveness and maintenance status.
• Operating state: Cold starts, short trips, hard accelerations, and high loads elevate emissions.
• Fuel quality: Sulfur and aromatics affect emissions and catalyst performance.
• Vehicle mass and tires: Heavier vehicles increase non-exhaust PM from tires and road wear.
• Driving and environment: Speed, congestion, altitude, and temperature shape real-world outcomes.

Good maintenance, smoother driving, and cleaner fuels and power can materially reduce both exhaust and non-exhaust emissions.

Summary

There is no single “chemical” coming out of cars. The dominant gas is carbon dioxide, alongside water vapor and nitrogen, while harmful pollutants include carbon monoxide, nitrogen oxides, unburned hydrocarbons, particulate matter, and trace toxics. Modern emissions controls and electrification have greatly reduced many tailpipe pollutants, though cold starts and non-exhaust particles from tires, brakes, and roads remain substantial contributors to urban air pollution and climate impacts.

What is the stuff that comes out of cars called?

Exhaust emissions are a mixture of different gases and particles emitted by vehicles when the engine is running. These emissions can reduce the quality of the air around us, particularly in big cities that are congested with cars.

What chemicals come from cars?

Cars emit various harmful chemicals, including the greenhouse gas carbon dioxide (CO2), and air pollutants like carbon monoxide (CO), nitrogen oxides (NOx), particulate matter (PM), and volatile organic compounds (VOCs). These emissions, from both exhaust and fuel vapors, contribute to smog, lung diseases, and climate change, with different emissions causing specific health problems such as breathing issues and heart problems.
 
Key Chemicals and Their Effects

• Carbon Dioxide (CO2): Opens in new tabA major greenhouse gas that contributes to climate change. 
• Carbon Monoxide (CO): Opens in new tabA colorless, odorless, and poisonous gas that can cause dizziness, fatigue, and confusion by affecting the brain and heart. 
• Nitrogen Oxides (NOx): Opens in new tabThese react with other chemicals in the presence of sunlight to form ground-level ozone, a key component of smog, which irritates the lungs. 
• Particulate Matter (PM): Opens in new tabTiny solid particles and liquid droplets that can lodge deep in the lungs, causing respiratory problems and potentially contributing to cardiovascular issues. 
• Volatile Organic Compounds (VOCs): Opens in new tabA group of chemicals that include substances like benzene, which are linked to respiratory problems and cancer. 
• Sulfur Dioxide (SO2): Opens in new tabAnother pollutant from burning fuel, it can cause shortness of breath and chest pain, and contributes to acid rain. 

Sources of These Emissions

• Exhaust: The primary source of these pollutants, including unburned fuel and products of fuel combustion. 
• Fuel Evaporation: Gasoline vapors can escape into the atmosphere during refueling or when evaporating from the engine and fuel system, especially in warm weather. 
• Interior Materials: Some pollutants can off-gas from materials inside the vehicle. 

Environmental and Health Impacts

• Air Pollution and Smog: Emissions contribute to smog, a brownish haze that can make breathing difficult and exacerbate respiratory illnesses. 
• Respiratory Problems: Many emissions, such as particulate matter, ozone, and nitrogen oxides, can cause or worsen conditions like asthma, bronchitis, and emphysema. 
• Climate Change: Carbon dioxide and other greenhouse gases emitted by cars trap heat, leading to climate change. 
• Cardiovascular Issues: Exposure to fine particulate matter has been linked to heart problems. 
• Cancer Risk: Some VOCs, like benzene, are toxic air pollutants linked to cancer. 

How harmful are exhaust fumes?

To put it simply, Carbon monoxide Kills! Working near exhaust fumes exposes you to poisonous carbon monoxide (CO) gas, which is present in large amounts in vehicle exhaust fumes. Overexposure to this odorless and colorless gas can cause death. Even mild exposure to CO can cause headaches, dizziness, nausea and fatigue.

What chemicals come out of a car exhaust?

These chemicals include benzene, formaldehyde, carbon monoxide, ethylbenzene, and 1,3-butadiene. The sooty residue of gasoline engine exhaust is also a mixture of many chemicals. These include benzo(a)pyrene and other members of a group of Proposition 65-listed chemicals called polycyclic aromatic hydrocarbons.