Mass accretion and ozone reactivity of idealized indoor surfaces in mechanically or naturally ventilated indoor environments

In indoor environments, accretion of mass to materials may provide sites for surface chemistry that differ from those of the original material. Since indoor surfaces are a major sink of oxidant gases, surface mass accretion may impact indoor O₃ chemistry. In this study, the effect of surface mass accretion on O₃ surface deposition was tested by deploying cleaned borosilicate glass plates in two types of indoor environments: a mechanically ventilated (MV) office and a naturally ventilated (NV) residence located in Singapore. In each environment, seven replicate glass plates and one field blank were deployed for between 7 and 56 days and examined in a laboratory chamber for O₃ deposition rate and surface reaction probability. Average mass accretion to plates, deployed in a horizontal position and including deposited particles, was 10.6 mg/(m² d) in the MV office vs. 18.5 mg/(m² d) in the NV residence and the comparison is at the threshold of statistical significance (p = 0.054). Ozone reactivity to the plates increased in magnitude and persistence with longer plate deployment. Ozone reaction probabilities to cleaned plates prior to deployment ranged [0.06–0.74] × 10⁻⁶ for two hours of observable removal whereas plates deployed for 56 days ranged [0.15–1.2] × 10⁻⁶ for four hours of observable removal. Regressions of cumulative O₃ removed during chamber tests vs. mass accreted show removal of 4.3 nmol O₃/mg for the NV residence and 2.4 nmol O₃/mg for the MV office. These results imply that accretion of mass to surfaces may alter indoor O₃ transformation pathways.