BVOC emissions in a changing climate: comparison of plant-specific and plat functional type emission models

Biogenic Volatile Organic Compounds (BVOCs) are organic trace gases mainly composed by isoprenoids, alcohols, carbonyls and acids, released in the atmosphere by terrestrial plants. Since some isoprenoids react with OH radical and O3 much faster than many anthropogenic VOC, their emission can affect the tropospheric levels of O3, photochemical oxidants and secondary organic aerosols (SOA). Various tree species are characterized by quite different emission factors for BVOCs, ranging from neglectable to significant values. A plant-specific emission model (PSEM) based on a detailed mapping of the tree species of forest covered areas can produce a quite different BVOC emission flux, with respect to models based on a Plant Functional Type (PFT) approach. The impact of a species-specific estimate of BVOC emissions over Europe has been estimated through the comparison with PFT approach results to evaluate the impact of a detailed vegetation mapping to improve BVOC emissions estimate. The comparison showed that PSEM estimates lower isoprene than both MEGAN V2.1 and V3.2, potentially driving a smaller impact on ozone production, and terpenes emissions higher than MEGAN V2.1 but lower than V3.2, with possible larger/smaller impact on SOA production. The expected increase of BVOC emissions due to the climate change forcing has been estimated computing the percent variation of isoprene and monoterpenes emission over a decade period. Different geographic areas of significant extention show increases exceeding 25% of the mean values estimated during the 2000-2019 period, with larger increases over eastern continental Europe and parts of the Mediterranean basin. PSEM estimates larger increases than CAMS-GLOB-BIO v3.0. The expectable BVOC emission change under future climatic conditions has been estimated considering the meteorological conditions predicted by EC-Earth3 CMIP6 simulation of the SSP 3.7.0 scenario. The mean emissions predicted for 2045-2055 have been compared with those computed by PSEM over a coherent subset for the historical period covering the last 11 years (2009-2019). The space distribution of the emissions does not change in the future scenario and a general increase of emissions is predicted for all the considered chemical species, mainly due to the predicted increase of both temperature and radiation flux. The most significant increase of emissions is concentrated over central and eastern Mediterranean and over the Balkan peninsula for isoprene, while it appears more extended over eastern continental Europe and southern Scandinavia for monoterpenes and sesquiterpenes.