Which of the following is NOT considered an indoor air pollutant?

Ozone is primarily considered an outdoor air pollutant. It is formed through a chemical reaction between volatile organic compounds (VOCs) and sunlight in the atmosphere, particularly in urban areas with heavy traffic and industrial emissions. While ozone can have harmful effects on health and the environment, its presence is more characteristic of outdoor air pollution than that of indoor air pollution.

In contrast, carbon monoxide, nitrogen dioxide, and radon are commonly found in indoor environments. Carbon monoxide is a colorless, odorless gas produced by combustion processes, making it a risk in poorly ventilated spaces with gas appliances or vehicles. Nitrogen dioxide can be emitted from gas stoves and heaters, contributing to respiratory problems indoors. Radon is a naturally occurring radioactive gas that can seep into buildings from the ground, presenting a significant health risk when accumulated indoors.