Temporal considerations in the measurement of indoor mass transfer coefficients

Indoor pollutant mass transport, characterized by the “transport-limited deposition velocity”, vt, is dynamic and measurements of this mass-transfer coefficient can be influenced by changing conditions. We find that for large, but realistic, changes in indoor transport conditions during the sampling period, time-averaged measurements of vt can be in error by 40% or more. Measurements using a highly surface reactive species, such as nitric acid, incur the greatest error. The measurement error incurred for species that are moderately surface reactive, such as ozone, varies depending on the type of surfaces available for deposition. Further, the greater the magnitude and frequency in the fluctuations, the greater the error anticipated from time-averaged measurements of vt. An analysis of continuous flux measurements from field experiments in apartments, a lab and an office suggest that time-averaged measurements of vt will typically be in error by 5–15%.