Which pollutants are primarily measured during an emissions test?

The primary pollutants measured during an emissions test are hydrocarbons, carbon monoxide, and nitrogen oxides. These specific pollutants are chosen due to their significant impact on air quality and public health.

Hydrocarbons are organic compounds that can contribute to the formation of ground-level ozone and smog, particularly in urban areas. They can come from fuel combustion in vehicles and are a key focus of emissions testing to mitigate smog and improve air quality.

Carbon monoxide is a colorless, odorless gas that is harmful when inhaled. It results from incomplete combustion of fossil fuels and is critical to monitor, as it can pose serious health risks, especially in enclosed spaces.

Nitrogen oxides, which include nitrogen monoxide and nitrogen dioxide, are produced from high-temperature combustion processes, such as those found in vehicle engines. These gases not only contribute to air pollution but also play a role in acid rain and the formation of ground-level ozone, making their measurement essential in keeping emissions within regulatory limits.

The other pollutants listed in the incorrect options are important in their own right but are not the primary focus of standard vehicle emissions tests.