Modern Buildings Act as a Dynamic Source and Sink for Urban Air Pollutants
TIANREN WU, Antonios Tasoglou, Danielle Wagner, Jinglin Jiang, Heinz Huber, Philip Stevens, Nusrat Jung, Brandon E. Boor,
University of Cincinnati Abstract Number: 323
Working Group: Indoor Aerosols
AbstractTo meet indoor air quality and thermal comfort requirements for occupants, there is substantial air exchange between buildings and the urban atmosphere. In modern, mechanically ventilated buildings, HVAC systems drive air exchange between indoor and outdoor environments. The dynamic exchange of air between the two may influence urban air quality as buildings account for a large fraction of land use in cities. A field measurement campaign was conducted in an office to investigate how buildings affect the source and sink behavior of air pollutants. Direct measurements of volatile organic compounds (VOCs), ozone (O
3), and fine particulate matter (PM
2.5) were made throughout the HVAC system to determine net emission rates between the office and proximate urban air. The composition of urban air changed dramatically as it entered and circulated throughout the building due to interactions with various elements of the indoor environment. The office and its HVAC system were found to act as a net sink for O
3 and PM
2.5 for urban air, with mean net emission rates of -47.6±31.3 and -2.3±2.4 mg h
-1, respectively. This is primarily attributed to the enhanced ozone reactivity of indoor and occupant surfaces and in-duct aerosol filtration. Real-time VOC measurements via proton transfer reaction time-of-flight mass spectrometry revealed that the office serves as a net source of VOCs to urban air due to emissions from occupant activities and indoor surface reservoirs, with a mean net emission rate of 78.0±73.5 mg h
-1. The per unit office area emission rates of isoprene and monoterpenes are comparable to those for forests and other vegetation areas. Changes in exhaust airflow rates, occupancy, and outdoor air concentrations caused significant temporal variations in the net emission rates. The HVAC system acts as an interface between indoor and outdoor atmospheres and strongly modulates the net mass transfer of pollutants between the two.