Which gases are specifically measured for emissions during a state inspection?

The correct choice identifies the specific gases that are critical for measuring emissions during a state inspection. Carbon monoxide, hydrocarbons, nitrogen oxides, and particulate matter are significant pollutants that contribute to air quality issues and are closely monitored in vehicle emissions testing.

Carbon monoxide is a colorless, odorless gas that is a byproduct of incomplete combustion and poses serious health risks. Hydrocarbons result from unburned fuel and can lead to the formation of ground-level ozone, contributing to smog. Nitrogen oxides are pollutants formed at high combustion temperatures and are key contributors to both air pollution and the formation of acid rain. Lastly, particulate matter includes tiny particles that can penetrate deep into the lungs and are associated with various respiratory and cardiovascular problems.

These specific gases are selected for their relevance in assessing the environmental impact of vehicle emissions and their direct effects on public health and the environment.