From the Desk to the Sky: Emissions of Indoor-Generated VOCs from a Mechanically Ventilated Office Building to the Urban Atmosphere

Abstract:

Volatile organic compounds (VOCs) are an important class of air pollutants that play a significant role in the formation of atmospheric secondary organic aerosol (SOA) and ozone, both of which exhibit adverse effects on human health. Humans and their activities in the built environment, such as cooking, cleaning, and application of volatile chemical products, result in elevated concentrations of indoor VOCs relative to the outdoors. Following their release to indoor air, VOCs will undergo chemical transformation or be removed from indoor air via surface deposition or ventilation. The transport of indoor-generated VOCs to the atmosphere via mechanical ventilation systems may be an important source of urban VOCs, especially in the densely populated areas. This study investigates the emissions of indoor-generated VOCs from a mechanically ventilated office to the proximate urban atmosphere.

A one-month measurement campaign was conducted in a modern, open-plan office (maximum occupancy of 20 people) in a LEED (Leadership in Energy and Environmental Design) certified office building at Purdue University. The office is equipped with a precisely controlled and monitored heating, ventilation, and air conditioning (HVAC) system. A proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) with a multi-location valve system was employed to monitor spatially-resolved VOC concentrations at multiple locations throughout the HVAC system, including the rooftop outdoor air intake and exhaust duct to the outdoors. Together with precisely monitored airflow data, the net emission rate (exhaust minus intake) of the indoor-generated VOCs from the office to the urban atmosphere can be estimated. Net VOC emission rates were determined for different office ventilation conditions and occupancy levels. Preliminary results indicate that the net emission rate of indoor-generated VOCs from the office to the atmosphere was approximately 2000 mg per day, with major contributions from acetone, methanol, cyclic volatile methylsiloxanes, acetic acid, and monoterpenes.