Understanding the effect of outdoor pollution episodes and HVAC type on indoor air quality

• Compared PM 2.5 infiltration during inversions, dust, and wildfire smoke events. • HVAC system type affects indoor air quality during these pollution events. • Wildfire smoke had 4-5 times more PM 2.5 infiltration than inversions or dust events. • HVAC systems with air-side economizers had 3 times more infiltration than those without. This study evaluated the impact of poor outdoor air quality on indoor air quality over 18 months using 21 low-cost PM 2.5 sensors (at 17 indoor and two outdoor locations) with a focus on inversion, dust, and wildfire smoke events. In addition to the impact of outdoor air quality on indoor air quality, this study evaluated how different heating, ventilation, and air conditioning (HVAC) systems affect the infiltration of outdoor PM 2.5 in commercial buildings. Wildfire smoke events had the largest impact on indoor air quality. Infiltration factors averaged over all locations for inversion, dust, and wildfire smoke events were 0.07, 0.10, and 0.37, respectively. Additionally, HVAC systems equipped with an air-side economizer showed higher PM 2.5 infiltration factors compared to other systems regardless of pollution event.