What Is the Stuff That Comes Out of Cars Called?

It’s called car exhaust—also referred to as tailpipe emissions or vehicle emissions. In everyday driving, this exhaust consists mainly of gases like carbon dioxide (CO2), carbon monoxide (CO), nitrogen oxides (NOx), unburned hydrocarbons (HC), water vapor, and particulate matter (PM). Modern vehicles also generate “non-exhaust” emissions such as brake dust and tiny particles from tire wear.

What People Mean by “Stuff Coming Out of Cars”

When people notice fumes, haze, or smells around cars, they’re typically referring to exhaust flowing from the tailpipe as fuel is burned in the engine. The term “exhaust” captures the entire mix of gases and particles expelled after combustion. In addition, some “stuff” around cars isn’t from the tailpipe at all: microscopic particles from tires and brakes become airborne and contribute to urban air pollution.

What’s in Car Exhaust?

Car exhaust is a complex mixture whose makeup depends on the fuel (gasoline, diesel, ethanol blends, etc.), engine design, and whether the emissions controls are working and warmed up. Below are the major components and why they matter.

Common pollutants and byproducts

The following items represent the most commonly discussed substances found in vehicle exhaust and why they’re important to air quality and health.

• Carbon dioxide (CO2): The primary greenhouse gas from burning fuel; contributes to climate change.
• Carbon monoxide (CO): A toxic gas that reduces the blood’s ability to carry oxygen.
• Nitrogen oxides (NOx: NO and NO2): Irritate lungs and help form smog and ground-level ozone.
• Unburned hydrocarbons/volatile organic compounds (HC/VOCs): Some are toxic; they react with NOx to form ozone.
• Particulate matter (PM2.5, ultrafine particles): Tiny solids/liquids that penetrate deep into lungs; diesel exhaust is a major source, but direct-injection gasoline engines can produce it too.
• Sulfur compounds (SO2, sulfates): Lower in modern low-sulfur fuels but still present in small amounts.
• Ammonia (NH3): Can slip from catalytic systems and contribute to secondary PM formation.
• Nitrous oxide (N2O): A potent greenhouse gas emitted in small amounts as a catalyst byproduct.
• Water vapor (H2O): A benign byproduct of combustion, often visible as condensation on cold days.

Taken together, these substances determine both the visible plume you sometimes see—especially at cold start—and the invisible pollutants that affect health and climate over time.

Non-exhaust emissions: brakes and tires

Not all emissions come out of the tailpipe. As vehicles move and slow, components wear down and release particles into the air.

• Tire wear particles: Microscopic bits of rubber and road material; a growing share of urban particulate pollution.
• Brake wear dust: Metal-rich particles released during braking; regenerative braking in hybrids/EVs can reduce this.
• Road dust resuspension: Previously deposited particles kicked back into the air by passing traffic.

These non-exhaust sources matter even for vehicles with zero tailpipe emissions, and they’re a key focus for future air-quality improvements.

How Modern Cars Limit Emissions

Automakers use an array of technologies to cut harmful emissions before they leave the tailpipe. These systems are most effective once warmed up, which is why cold starts produce a disproportionate share of pollution.

1. Three-way catalytic converter: Converts CO to CO2, HC to CO2 and H2O, and NOx to nitrogen (N2) under balanced air–fuel conditions.
2. Oxygen sensors and precise fuel control: Keep the mixture near stoichiometric for optimal catalyst performance.
3. Exhaust gas recirculation (EGR): Lowers combustion temperatures to reduce NOx formation.
4. Gasoline particulate filters (GPF): Trap fine particles from direct-injection gasoline engines.
5. Diesel particulate filters (DPF): Capture soot from diesel exhaust, periodically regenerating to burn it off.
6. Selective catalytic reduction (SCR) with urea/AdBlue: Converts diesel NOx into nitrogen and water.
7. Evaporative emissions controls (charcoal canister, sealed systems): Limit fuel vapor (VOC) losses from the tank and lines.
8. Onboard diagnostics (OBD): Monitors systems and triggers a warning if emissions controls malfunction.

When maintained properly and fueled with low-sulfur fuel, these technologies dramatically reduce smog-forming and toxic emissions compared with earlier generations of vehicles.

Health and Environmental Impacts

Short-term exposure to tailpipe pollutants can irritate eyes, throat, and lungs, and aggravate asthma and cardiovascular conditions. Long-term exposure to fine and ultrafine particles, nitrogen dioxide, and certain hydrocarbons is associated with higher risks of heart disease, respiratory illness, and premature mortality. Environmentally, CO2 and N2O drive climate change, while NOx and VOCs form ground-level ozone that damages crops and ecosystems.

When There’s Little or No Tailpipe Exhaust

Battery electric vehicles (EVs) produce no tailpipe exhaust because there’s no combustion. Hydrogen fuel-cell electric vehicles emit water vapor at the tailpipe. However, all vehicles, regardless of powertrain, produce some non-exhaust emissions from tires, brakes, and road dust, though regenerative braking can mitigate brake dust substantially.

Usage, Conditions, and What You See

Cold starts and short trips often create the most noticeable plumes because catalysts and filters haven’t warmed up. White “smoke” on a cold day is typically water vapor condensing; bluish smoke can signal oil burning, and black smoke often indicates rich fueling or diesel soot when a filter isn’t functioning.

Summary

The “stuff that comes out of cars” is called exhaust, or tailpipe emissions: a mix dominated by CO2, plus pollutants like CO, NOx, hydrocarbons, and particulate matter. Thanks to catalytic converters, particulate filters, and other controls, today’s vehicles emit far less pollution than in the past, though non-exhaust particles from brakes and tires remain an ongoing challenge. EVs eliminate tailpipe exhaust entirely, but continued attention to all sources is essential for cleaner air.

What is the exhaust from cars called?

Tailpipe. The tailpipe is the final link in the exhaust system—it routes the exhaust gases, which have been cleaned up by the catalytic converter, away from the vehicle and into the atmosphere. The tailpipe routes the exhaust gases away from the vehicle and into the atmosphere.

What is the end of the exhaust called?

The end of the exhaust is called the tailpipe or exhaust tip. The tailpipe is the final pipe that vents the exhaust gases to the atmosphere, while the exhaust tip is the decorative outer part that is often visible on the vehicle.
 
Key Terms

• Tailpipe: The entire final pipe that carries gases from the muffler or resonator to the outside of the vehicle. 
• Exhaust Tip: The visible, often decorative, outer end of the tailpipe. It can be straight, angled, or feature a polished finish. 
• Muffler/Silencer: A component located near the rear of the exhaust system that reduces noise before the gases exit through the tailpipe. 
• Cat-back: This term refers to the section of the exhaust system from the catalytic converter to the final vent. 

Can a car run without a catalytic converter?

Yes, a car can technically run without a catalytic converter, but it will produce significantly more harmful emissions, potentially trigger a check engine light, and may experience reduced engine performance. Furthermore, operating a vehicle without a catalytic converter is illegal in most places and will result in failure during emissions tests.
 
What happens when you drive without a catalytic converter?

• Increased Emissions: Opens in new tabThe primary function of a catalytic converter is to reduce toxic pollutants like carbon monoxide and nitrogen oxides, converting them into less harmful substances. Without it, these harmful gases are released directly into the atmosphere. 
• Engine and Performance Issues: Opens in new tabThe engine’s computer is designed to work with a catalytic converter, and removing it can lead to decreased fuel economy, poor acceleration, and a potential decrease in overall engine performance. 
• Louder Exhaust: Opens in new tabThe catalytic converter also acts as a muffler, so its absence will result in a significantly louder exhaust sound. 
• Check Engine Light: Opens in new tabThe car’s system will detect the missing or malfunctioning catalytic converter, which will typically trigger the check engine light. 
• Unpleasant Odors: Opens in new tabA strong, unpleasant smell will likely emanate from the exhaust. 

Why you shouldn’t drive without one

• Environmental Harm: The increased release of harmful pollutants contributes to air pollution. 
• Legal Consequences: It is illegal in many locations to operate a vehicle without a functioning catalytic converter, which can lead to fines. 
• Failing Inspections: Your car will not pass an emissions test, and potentially other safety or vehicle inspections, without a catalytic converter. 

Can I drive my car if the exhaust is blowing?

No, you generally cannot and should not drive with a broken exhaust, as it creates significant risks including exposure to dangerous carbon monoxide fumes inside the vehicle, potential fire hazards, increased pollution, reduced engine performance, loud and distracting noises, and the possibility of the exhaust falling off completely, leading to further damage and safety issues. You should have the vehicle towed to a repair shop as soon as possible.
 
Health & Safety Risks

• Carbon Monoxide Poisoning: Opens in new tabA broken exhaust allows poisonous and odorless carbon monoxide gas from the engine to enter the passenger cabin through the ventilation system, which can lead to unconsciousness or death. 
• Fire Hazard: Opens in new tabA leak can allow oxygen to enter the exhaust system, increasing the temperature and potentially causing a fire under the car’s engine. 
• Exhaust Falling Off: Opens in new tabA damaged or loose exhaust pipe could detach and drag on the ground, posing a hazard to your vehicle and others, and potentially tearing the entire system off. 

Vehicle & Engine Issues

• Reduced Engine Performance: A broken exhaust system disrupts the engine’s pressure regulation and air-fuel balance, leading to poor acceleration, rough idling, and reduced power. 
• Increased Fuel Consumption: The disruption can cause the engine to work harder, resulting in decreased fuel efficiency. 
• Damage to Other Components: Excessive heat and vibrations from a severe leak can damage nearby wiring, hoses, or other underbody components. 

Legal & Environmental Concerns

• Illegal Emissions: Excessive emissions from a damaged exhaust can be illegal in some areas, potentially leading to fines. 
• Legal Penalties: Driving a vehicle with a loud, unroadworthy exhaust can also attract unwanted attention from law enforcement and result in summons and fines. 

What to Do 

• Get it Towed: Do not risk driving the vehicle. Have it towed to a professional auto repair shop immediately.
• Contact a Professional: A mechanic can properly diagnose and repair the broken exhaust system to prevent further problems.