Evidence of indoor sinks for formaldehyde through the field measurements using passive flux sampler and mass balance

A measurement campaign was conducted in 24 student rooms where formaldehyde emissions from all the indoor surfaces were measured using a passive flux sampler (PFS) parallel to monitoring of indoor and outdoor concentrations as well as the assessment of air exchange rate. Two mass balance models were used to predict indoor concentrations basing on input data recorded during this measurement campaign. The first model only takes into account the total emission from the indoor sources and the incoming and outgoing flows of compound brought by the air exchange rate. The second model added to these terms a further component related to the overall rate of removal processes (or "indoor sinks") which was assessed in these same rooms during a previous field test campaign. A good agreement was found between the concentrations calculated by the model with the component relative to indoor removal processes and the measured concentrations. On the other hand, the predicted concentrations with a first model tend to highly overestimate the measured concentrations by a factor 1.9 on average. Apportionment of formaldehyde inputs and losses in the rooms was estimated and discussed. The results highlighted that indoor removal processes are a component to consider for formaldehyde budget indoors.