Uptake and reactivity of formaldehyde on lime-cement-plaster under typical indoor air conditions

Inorganic construction materials are chiefly envisaged as structural materials. However, they provide unexplored interfaces with characteristic surface chemistry to interact with indoor gases. This work proposes for the first time an insight on uptake abilities of lime-cement-plaster toward indoor pollutant. Because of toxicity and regulation policies, formaldehyde is selected as representative indoor pollutant. This work explores gas-material interaction to elucidate fate of formaldehyde onto lime-cement-plaster and addresses air quality impact. Uptake and fate of formaldehyde onto plaster is addressed using Field and Laboratory Emission Cell coupled with SIFT Mass Spectrometer. The experimental sequence is continuously deployed on 90 days to address realistic and long-term behaviour of formaldehyde uptake. Experimental approach evidences that from 65 to 77% of formaldehyde inlet concentration is continuously taken up on plaster samples throughout experimental sequence. Concomi-tantly, methanol is observed showing the reactivity of formaldehyde uptake on this material-class. Diffuse Reflectance Infrared Spectroscopy evidences that formaldehyde undergoes heterogeneous Cannizzaro reaction on the plaster surface. This surface reaction proceeds with adsorbed formaldehyde, even in the absence of gaseous pollutant supply. The quantitative balance of the disproportionation process is proposed along the experimental sequence to clarify the fate of formaldehyde encompassing gaseous and adsorbed-phase. The evidenced surface process can impact formaldehyde budget in indoor air, thus relevant parameters are deter-mined to allow further implementation of this reactive contribution to indoor air quality models. This work settles perspectives for passive mitigation of indoor formaldehyde, and points at the need to address reaction products for their indoor air quality impact.

Automated summary

This study provides new insights into the uptake abilities of lime-cement-plaster towards indoor pollutants, focusing on formaldehyde. The results show that plaster samples continuously take up 65-77% of the formaldehyde inlet concentration and reveal the heterogeneous Cannizzaro reaction of formaldehyde on the plaster surface. This surface process has the potential to impact indoor air formaldehyde budget and should be considered in indoor air quality models.