The potential impact of biogenic volatile organic compounds (BVOCs) from terrestrial vegetation on a Mediterranean area using two different emission models

Biogenic Volatile Organic Compounds (BVOCs) emitted from vegetation are precursors of ozone (O3), photochemical oxidants and secondary organic aerosols (SOA) in the lower troposphere. The interaction between urban polluted air plumes originated along the coasts of the Mediterranean basin with biogenic emission occurring inland contributes to the occurrence of exceedances of the air quality standards for O3 and fine suspended particles (PM10, PM2.5). This interaction is favoured by prevailing sea-land breeze circulation during persistent high-pressure conditions. The actual contribution of BVOC to photochemical pollution is still uncertain because the approaches used to assess the emissions from terrestrial vegetation are quite different. There is some evidence in literature that BVOC emissions from Mediterranean vegetation is not accurately estimated by models based on the plant functional types (PFT) approach. To investigate these issues, a Plant Specific Emission Model (PSEM) was developed and applied to the Campania region in Southern Italy, for which a detailed vegetation inventory has been built. BVOC emission maps estimated by PSEM were compared with those generated using a PFT methodology, evidencing significant differences. BVOC emissions from the two models were then used to predict the concentrations of precursors and products of photochemical smog pollution over the Gulf of Naples (Italy) using a chemical-transport model. Simulations were performed during a period characterised by high pressure conditions that favour an enhanced O3 production under a sea-breeze circulation regime. VOCs concentration profiles predicted by the two models were compared with field data collected over Mount Vesuvius using a tethered balloon coupled with a PTR-MS. The results proved the better capability of PSEM to predict the concentrations of many BVOCs, including isoprene and some of its primary oxidation products over the measuring site, and suggested the significant potential of BVOC emission to produce SOA over the gulf of Naples.