Eco-efficient coatings for healthy indoors: Ozone deposition velocities, primary and secondary emissions

Volatile organic compounds (VOCs) and ozone (O3) are harmful pollutants present in indoor air. Indoor concentrations of VOCs are typically higher than outdoors, due to the presence of indoor sources like building materials and ozone-surface reactions. The study aims to identify and quantify the ozone reactivity and primary and secondary emissions of different indoor coatings. The coatings selected for the study were three gypsum-based plastering mortar, with and without the addition of a bio-waste from Acacia dealbata (raw bark, BA, and bark heated at 250 °C, BA250), two clay plasters (one with sand and the other with seashells as additional aggregate), applied both as basecoat and topcoat (on drywall), and one un-coated drywall. All the products tested had ozone deposition velocities that would reduce the indoor ozone concentration meaningfully if implemented in a real indoors, contributing to the improvement of indoor air quality. The gypsum-based plaster shows the lowest ozone deposition velocity, but also the lowest primary and secondary emissions. The addition of bark, either BA or BA250, increased by 50% the ozone deposition velocity of the coating but also increased primary and secondary emissions by 80% (BA) and 200% (BA250), with methanol (m/z 33.030) accounting for about 60% of the increase. The addition of crushed seashells to the formulation of the clay-based plasters lowered the secondary emission yields (102% and 120% respectively, when applied as base and topcoat).