Which of the following is NOT one of the primary methods used to improve indoor air quality?

• A. Filtration
• B. Source control
• C. Ventilation
• D. Humidification

Answer: (D)

The main idea tested is how we actively improve indoor air quality. The standard trio used to manage IAQ focuses on controlling the pollution sources, bringing in outdoor air to dilute contaminants (ventilation), and using filtration to capture particulates. These three address how pollutants enter, persist, and are removed from the indoor environment.

Humidification isn’t considered one of these primary methods. It’s about maintaining appropriate moisture levels for comfort and building health, not directly removing pollutants. If humidity gets too high, it can encourage mold growth, dust mites, and other issues that worsen IAQ. So while humidity control is important for overall indoor environment quality, it doesn’t function as a primary pollutant-removal strategy like source control, ventilation, or filtration.