What are two common pollutants measured during the emissions test?

The correct answer identifies two significant pollutants, carbon monoxide (CO) and nitrogen oxides (NOx), that are typically measured during emissions tests. These pollutants are crucial for assessing vehicle emissions because they are directly linked to the combustion process in internal combustion engines.

Carbon monoxide is a colorless, odorless gas produced when there is incomplete combustion of carbon-containing fuels. High levels of CO can have serious health effects on humans and contribute to air pollution. Monitoring CO levels helps ensure that vehicles meet safety and environmental standards.

Nitrogen oxides, particularly a mix of nitric oxide (NO) and nitrogen dioxide (NO2), are generated during high-temperature combustion processes, such as those found in car engines. NOx emissions are significant contributors to the formation of ground-level ozone and smog, which can harm respiratory health and degrade air quality. By measuring NOx emissions, regulatory agencies can evaluate how well a vehicle is controlling pollution.

In contrast, while the other options mention pollutants relevant to environmental health, they are not as commonly focused on in the context of vehicle emissions testing. For example, while carbon dioxide is a significant greenhouse gas, it is not typically a direct concern in emissions tests aimed at immediate air quality problems. Likewise, while hydrocarbons and ozone are