Indoor mass transfer coefficient measurements of ozone using nitrite-coated filters

Indoor ozone concentrations are partly controlled by the rate of ozone transfer to indoor surfaces. The goal of this research is to improve our understanding of indoor ozone transport processes, thus allowing us to better estimate ozone exposure and evaluate indoor pollution models. Experiments were conducted in a laboratory chamber and at field sites (office, lab, lab/office and apartment) to directly measure the transport-limited deposition velocity for ozone, vt,ozone. To do this, we quantified the total flux of ozone to a nitrite- coated filter (attached to an appropriate surface) by measuring the amount of nitrate formed after a sufficient exposure interval in a chamber or room. We call this system the DeVO (deposition velocity measurement of ozone) method. Under a variety of chamber mass transfer conditions, vt,ozone ranged from 0.10 to 1.0 cm sec-1. In the lab and lab/office field locations, spatially averaged values of vt,ozone ranged from 0.2 to 0.3 cm sec-1. The spatially average values of vt,ozone in an apartment also ranged from 0.1 to 0.3 cm sec-1. By measuring the spatial distribution of vt,ozone, we also show that mass transfer rate can vary from 0.1 to 1.4 cm sec-1 within an apartment with a recirculation fan operating. Field measurements using this method are predicted to be somewhat higher than the predicted range of values (0.02 to 0.2 cm sec-1) because the filter is much smaller than the characteristic room dimensions. Overall, the measurements are consistent with the measurements using an independent continuous method called “the deposition velocity sensor” or “DeVS” --Abstract, page iii