Cars cause air pollution primarily through their exhaust systems, which emit a mix of harmful gases and particles. The key pollutants are carbon monoxide (CO), nitrogen oxides (NOx), hydrocarbons (HC), and particulate matter (PM). These are released from the combustion of gasoline or diesel fuel. Additionally, non-exhaust sources like tire and brake wear release microplastics and heavy metals into the air. While modern emissions control systems like catalytic converters have significantly reduced the per-car pollution, the sheer volume of vehicles on the road makes the transportation sector a major contributor to urban smog, health problems, and greenhouse gas emissions.
The internal combustion engine is an imperfect chemical reactor. Burning fuel produces carbon dioxide (CO₂), a primary greenhouse gas, but it also generates harmful byproducts due to incomplete combustion and high-temperature reactions. Nitrogen and oxygen from the air react in the engine's cylinders to form NOx, a primary component of smog. Unburned fuel evaporates or is expelled as hydrocarbons.
Beyond the tailpipe, vehicles contribute to pollution in less obvious ways. Every time you apply the brakes, the friction grinds small particles from the brake pads, releasing dust containing copper and other metals. Similarly, tire wear is a significant and growing source of microplastic pollution in air and water. Furthermore, the evaporation of fuel from the fuel tank and carburetor, even when the car is off, releases hydrocarbons directly into the atmosphere.
The impact of these emissions is substantial. The Environmental Protection Agency (EPA) states that transportation is the leading source of several key air pollutants in the United States. The following table outlines the primary pollutants and their main effects.
| Pollutant | Primary Source in Cars | Main Environmental/Health Impact |
|---|
| Carbon Monoxide (CO) | Incomplete fuel combustion | Reduces oxygen delivery in the bloodstream; can be fatal in enclosed spaces. |
| Nitrogen Oxides (NOx) | High-temperature combustion | Contributes to smog, acid rain, and respiratory illnesses. |
| Hydrocarbons (HC) | Unburned fuel, evaporation | Contributes to ground-level ozone (smog), which can cause lung damage. |
| Particulate Matter (PM) | Diesel exhaust, brake/tire wear | Linked to asthma, lung cancer, and cardiovascular problems. |
| Carbon Dioxide (CO₂) | Complete fuel combustion | The principal greenhouse gas contributing to climate change. |
