Litter VOC emissions inventory from deciduous urban trees in the mediterranean region

Over the last decade, litter from vegetation in natural ecosystems has been progressively recognized as a non-negligible source of biogenic volatile organic compound (BVOC). It thus accounts for a significant source contributing to ozone and secondary organic aerosol (SOA) formation, as well as volatile allelochemicals driving plant growth and development. However, no study has focused on urban litter so far. To fill this gap, litter of fifteen deciduous urban tree species were collected in autumn 2023 in several locations of Marseilles city to screen their VOC emissions by PTR-ToF-MS analysis and obtain their respective emission factors (emission rates at 30 °C) using PTR-ToF-MS. The selected species were common in mediterranean cities: Ailanthus altissima (Mill.), Ginkgo biloba L., Acer monspessulanum L., Aesculus hippocastanum L., Cercis siliquastrum L., Morus australis Poir., Robinia pseudoacacia L., Quercus pubescens Willd., Sophora japonica L., Ficus carica L., Vitis vinifera L., Liquidambar styraciflua L., Celtis australis L., Platanus x acerifolia Willd., and Tilia platyphyllos Scop. In addition to the traditional terpenoids (isoprene, monoterpenes, sesquiterpenes), and the highly volatile oxygenated compounds (methanol, acetone, acetaldehyde), a very large number of additional VOCs were detected with a high chemical diversity, including sulfur- and nitrogen-containing compounds (e.g. dimethylsulfide or DMS, acetonitrile) as well as highly oxygenated species (e.g methyl salicylate or C₄H₈O₆). Emission factors ranged from low (1.23 μg_VOC g_DM^-1 h^-1) for G. biloba to extremely high (258.94 μg g_DM^-1 h^-1) for L. styraciflua, and were not related to the number of VOCs emitted. Instead, high emitters exhibited high emissions of only a few compounds, as observed for L. styraciflua, whose emissions were dominated by just monoterpenes and hexenal.