Indoor air quality impacts of ventilation ducts: Ozone removal and emissions of volatile organic compounds

The concentrations of contaminants in the supply air of mechanically ventil ated buildings may be altered by pollutant emissions from and interactions with duct materials. We measured the emission rate of volatile organic comp ounds (VOCs) and aldehydes from materials typically found in ventilation du cts. The emission rate of VOCs per exposed surface area of materials was fo und to be low for some duct liners, but high for duct sealing caulk and a n eoprene gasket. For a typical duct, the contribution to VOC concentrations is predicted to be only a few percent of common indoor levels. We exposed s elected materials to similar to 100-ppb ozone and measured VOC emissions. E xposure to ozone increased the emission rates of aldehydes from a duct line r, duct sealing caulk, and neoprene gasket. The emission of aldehydes from these materials could increase indoor air concentrations by amounts that ar e as much as 20% of odor thresholds. We also measured the rate of ozone upt ake on duct liners and galvanized sheet metal to predict how much ozone mig ht be removed by a typical duct in ventilation systems. For exposure to a c onstant ozone mol fraction of 37 ppb, a lined duct would initially remove s imilar to 9% of the ozone, but over a period of 10 days the ozone removal e fficiency would diminish to less than 4%. In an unlined duct, in which only galvanized sheet metal is exposed to the airstream, the removal efficiency would be much lower, similar to 0.02%. Therefore, ducts in ventilation sys tems are unlikely to be a major sink for ozone.