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Cars release hydrocarbons, nitrogen oxides, carbon monoxide, and carbon dioxide into the air when they burn fuel. Each of these substances has an effect on the cleanliness and overall quality of the air.

• Hydrocarbons react in the presence of nitrogen oxides and sunlight to form ground-level ozone, which is a major component of smog. Ozone (O3) can irrate the eyes, damage the lungs, and cause respiratory problems.
• Nitrogen oxides (NOx) are involved in the formation of ground-level ozone and contributes to acid rain.
• Carbon monoxide (CO) is a product of incomplete combustion of fuel which contains carbon. When humans are expossed to high levels of carbon monoxide it reduces the flow of oxygen in the bloodstream.
• Carbon dioxide (CO2) is a product of complete combustion of fuel. It does not directly affect human health but is a "greenhouse gas" that traps the Earth's heat and contributes to global warming.

Vehicle emission standards are set to reduce the amount of harmful pollutants entering the air and they are enforced by law in each state.

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Environmental Issue Scenarios