Characterization of Volatile Organic Compound Emissions and CO₂ Uptake from Eco-roof Plants

Vegetation plays an important role in biosphere-atmosphere exchange, including emission of biogenic volatile organic compounds (BVOCs) that influence the formation of secondary pollutants. Gaps exist in our knowledge of BVOC emissions from succulent plants, which are often selected for urban greening on building roofs and walls. In this study, we characterize the CO₂ uptake and BVOC emission of eight succulents and one moss using proton transfer reaction - time of flight - mass spectrometry in controlled laboratory experiments. CO₂ uptake ranged 0 to 0.16 μmol [g DW (leaf dry weight)]^-1 s^-1 and net BVOC emission ranges -0.10 to 3.11 μg [g DW]^-1 h^-1. Specific BVOCs emitted or removed varied across plants studied; methanol was the dominant BVOC emitted, and acetaldehyde had the largest removal. Isoprene and monoterpene emissions of studied plants were generally low compared to other urban trees and shrubs, ranging 0 to 0.092 μg [g DW]^-1 h^-1 and 0 to 0.44 μg [g DW]^-1 h^-1, respectively. Calculated ozone formation potentials (OFP) of the succulents and moss range 4×10^-7 - 4×10^-4 g O₃ [g DW]^-1 d^-1. Results of this study can inform selection of plants used in urban greening. For example, on a per leaf mass basis, Phedimus takesimensis and Crassula ovata have OFP lower than many plants presently classified as low OFP and may be promising candidates for greening in urban areas with ozone exceedances.