Investigation of Volatile Organic Compounds Emissions in Different Stages of HVAC System
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Efficient heating, ventilating, and air-conditioning (HVAC) systems are essential for improving indoor air quality and human health. However, HVAC systems those days typically rely on mechanical ventilation and filters to reduce air pollution. Volatile organic compound (VOC), a common type of gas phase air pollution, is usually neglected but is considerably higher indoors than outdoors and can cause severe health problems. This research explored how the VOC concentrations changed in different steps of the HVAC system and investigated the relation between VOCs and the HVAC system, building, and occupants. This research aimed to 1) identify and quantify health-related VOC concentrations within the building and compare them with current guidelines; 2) compare VOC concentrations in separate steps of the HVAC system; 3) explore temporal tendencies and source apportionment of VOCs. VOCs were monitored and quantified using a proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) with additional measurements of CO, CO2, CH4, NH3, and CH2O using cavity ringdown spectroscopy instrumentation from Picarro through a four-valve switching chamber. This process allowed us to sample multipoint pollutants in mixed air, post-filter air, supply air, and return air in a frequent switching sequence. Our observations show that long-term exposure to some health-related VOCs in the sampled building, such as benzene, formaldehyde, and trimethylbenzene, can potentially cause health problems. The average VOC concentrations were highest in the return air and lowest in the mixed air for most indoor source VOCs. The unexpected VOC concentration increase in supply air suggested a leak in the HVAC system. This study will fill fundamental knowledge gaps in the HVAC system and offer quantitative evidence of how HVAC systems influence chemistry in indoor environments by heating, cooling, and filtering the air. With an improved understanding of the association among indoor VOCs, HVAC systems, buildings, and occupants, engineers can design more effective ventilation systems for buildings that minimize indoor VOCs and reduce the risk of health concerns for occupants.