Air Systems Cleaning Specialist (ASCS) Practice Exam

The correct choice identifies the entry of outdoor pollutants into the indoor environment as a significant factor contributing to indoor air quality issues. When outdoor air carries various pollutants, such as particulate matter, chemicals, pollen, and dust, these can infiltrate indoor spaces through openings like windows, doors, and ventilation systems. This influx of contaminants can elevate the concentration of harmful substances indoors, thereby deteriorating air quality and posing health risks to occupants.

In contrast, regular maintenance of HVAC systems generally promotes better air quality by ensuring that the system operates efficiently and filters are clean, helping to reduce indoor pollutants rather than increase them. High outdoor air quality would typically not contribute negatively to indoor air conditions; rather, it would enhance overall indoor air quality when allowed inside. Meanwhile, while air purifiers are designed to improve air quality by removing contaminants, they do not in themselves introduce pollutants into indoor spaces, rather they can mitigate their effects if properly used. Thus, the entry of outdoor pollutants remains a key contributor to indoor air quality problems.