Influence of Outdoor Oxidant on the Indoor Air Concentrations of Formic Acid

Secondary emission products generated through chemical reactions become a recent concern in relation to indoor air quality. We have focused on formic acid (HCOOH) whose generation mechanism in indoor air has been unknown. In this study, we examined influence of oxidant on the indoor air concentrations of HCOOH and emission process of HCOOH by both laboratory experiments and field measurements. Firstly, emission fluxes of HCHO and HCOOH from plywood were determined using a small bowl-type stainless chamber. The emission flux of HCOOH increased with those of HCHO under ambient air containing oxidant. While the oxidant was removed in the chamber, HCOOH significantly emitted with NO2 at the chamber outlet. We then concluded HCOOH is a product of the gas phase reaction between HCHO, NO2 and O3. Field measurements conducted at a newly-build detached house supported the conclusion as that indoor concentrations of HCOOH increased with an increase in concentrations of the oxidant introduced from outdoor by air ventilation.