Which gases are the deterrent for the mechanical ventilation in enclosed parking garages?

The correct choice is based on understanding the specific gases that are typically present in vehicle emissions and the potential hazards they pose in enclosed spaces such as parking garages.

Carbon monoxide and nitrogen dioxide are both byproducts of combustion processes in vehicles. Carbon monoxide (CO) is particularly harmful because it is colorless and odorless, making it difficult for individuals to detect. It can accumulate in enclosed spaces and pose serious health risks, including headaches, dizziness, and even fatalities at high levels.

Nitrogen dioxide (NO2) is another toxic gas that can contribute to respiratory problems and is also formed during the combustion of fossil fuels. In enclosed parking garages, the accumulation of these gases can create unsafe air quality conditions, necessitating the use of mechanical ventilation systems to ensure that fresh air is circulated and that concentrations of these harmful pollutants are kept within safe limits.

In contrast, the other choices contain gases that either do not pose the same level of risk concerning mechanical ventilation in parking garages or are not primarily associated with vehicle emissions. Therefore, choosing carbon monoxide and nitrogen dioxide reflects an understanding of the specific air quality concerns relevant to mechanical ventilation in such environments.