Why is it important to consider both indoor and outdoor air quality in BE engineering decisions?

• A. Indoor air quality is independent of outdoor
• B. Outdoor sources can infiltrate indoors, and indoor activities can influence outdoor air quality
• C. Only outdoor air quality matters
• D. Outdoor air quality is irrelevant to indoor

Answer: (B)

Air quality indoors and outdoors are connected through a two-way flow of air and pollutants. Outdoor pollutants can infiltrate buildings via infiltration, ventilation, and HVAC operations, so the outdoor environment directly shapes what occupants breathe inside. At the same time, activities inside—cooking, cleaning, use of solvents, combustion—emit pollutants that can be exhausted outdoors and can also influence outdoor air quality through vents and stacks. Because of this bidirectional exchange, decisions about ventilation rates, filtration, sealing, and source control affect both indoor and outdoor environments.

This is why the best choice emphasizes that outdoor sources can infiltrate indoors and indoor activities can influence outdoor air quality. It ensures a holistic approach to protecting occupant health, meeting regulations, and minimizing environmental impact. Other views—saying indoor is independent of outdoor, or that only outdoor air matters, or that outdoor air is irrelevant to indoor—ignore the real coupling between the two environments.