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

Ozone is not considered an indoor air pollutant primarily because it is a naturally occurring molecule found in the atmosphere, mainly in the stratosphere, where it forms a protective layer that absorbs the majority of the sun's harmful ultraviolet radiation. While ozone does play a role as a pollutant outdoors, especially in urban areas where it is a significant component of smog, when it comes to indoor environments, ozone levels are generally low. Most indoor air quality issues stem from pollutants that come from human activities or materials indoors, such as mold, carbon monoxide, and pet dander.

Mold thrives in damp environments and can release spores and volatile organic compounds (VOCs) that significantly contribute to indoor air quality problems. Carbon monoxide is a colorless, odorless gas produced by burning fossil fuels, and it can accumulate indoors, leading to serious health risks. Similarly, pet dander, which consists of small particles shed from skin, fur, and feathers of pets, can trigger allergic reactions and asthma in sensitive individuals. Thus, while ozone is an important environmental consideration, it is not a typical indoor air pollutant in the same way the other options are.