Impact of green and white roofs on air handler filters and indoor ventilation air

Rooftop surfaces near building outdoor air intakes may contribute to the mass loading on filters and compounds emitted to ventilation air downstream of the filter. In laboratory analyses, we characterized microbial composition, primary volatile organic compound (VOC) emissions, ozone removal rates, and VOC emissions in the presence of ozone on filters collected from air handlers located on the green and white roof sections of a big-box retail store. Total DNA masses per area of filter were 26.3 ± 11.9 ng cm⁻² and 6.3 ± 6.5 ng cm⁻² for green and white roof filters respectively, with higher mass observed in winter compared to the fall season. Of eight VOCs quantified at constant 23 °C and 50% RH across both seasons, fluxes of m/z 33.02 (putatively attributed to methanol) dominated VOC emissions for green, 10.96 ± 3.09 μmol m⁻² hr⁻¹, white, 12.02 ± 3.41 μmol m⁻² hr⁻¹, and unused filters, 5.64 ± 1.08 μmol m⁻² hr⁻¹. Ozone removal across all filters varied from 3.5% ± 2.8%–14% ± 2.8%, depending on temperature and RH condition. Fluxes of eight quantified VOCs were lower in the presence of ozone, apart from m/z 69.07 (putatively attributed to isoprene), where the presence of ~180 ppb inlet ozone resulted in increased fluxes by a factor of ~2.4. A steady-state mass balance predicted increases in ventilation air methanol levels by green roof filters ranging 0.10 μg m⁻³ to 19.44 μg m⁻³, depending on filter face velocity and filter geometry.