Simulation of fine organic aerosols in the western Mediterranean area during the ChArMEx 2013 summer campaign

摘要

The simulation of fine organic aerosols with CTMs (Chemistry Transport Models) in the westernMediterranean basin has not been studied until recently. The ChArMEx (the Chemistry-Aerosol MediterraneanExperiment) SOP 2 (Special Observation Period 2) intensive field campaign in summer of 2013 gathered a largeand comprehensive dataset of observations allowing the study of different aspects of the Mediterranean atmosphereincluding the formation of organic aerosols (OA) in 3D models. In this study, we used the CHIMERE CTM toperform simulations for the duration of the SAFMED (Secondary Aerosol Formation in the MEDiterranean) period(July to August 2013) of this campaign. In particular, we evaluated four schemes for the simulation of OA,including the CHIMERE standard scheme, the VBS (Volatility Basis Set) standard scheme with twoparameterizations including aging of biogenic secondary OA, and a modified version of the VBS scheme whichincludes fragmentation and formation of non-volatile OA. The results for these four schemes are compared toobservations at two stations in the western Mediterranean basin, located in Cap Corse (Corsica) and Cap Es Pinar(Mallorca). These observations include OA mass concentration, PMF (positive matrix factorization) results ofdifferent OA fractions, and C observations showing the fossil or non-fossil origins of carbonaceous particles. Itis concluded that the modified VBS scheme is close to observations in all three aspects mentioned above; thestandard VBS scheme without BSOA (Biogenic Secondary Organic Aerosol) aging also has a satisfactoryperformance in simulating the mass concentration of OA, but not for the source origin analysis comparisons. Inaddition, the OA sources over the western Mediterranean basin are explored. OA shows a major biogenic origin,especially at several hundred meters height from the surface; however over the Gulf of Genoa near the surface, theanthropogenic origin is of similar importance. A general assessment of other species was performed to evaluatethe robustness of the simulations for this particular domain before evaluating OA simulation schemes. It is alsoshown that the Cap Corse site presents important orographic complexity which makes comparison between modelsimulations and observations difficult. A method was designed to estimate an orographic representativeness errorfor a list of species and yields an uncertainty of between 50–85 % for primary pollutants, and around 2–10 % forsecondary species, for these species model to observations comparisons are only little impacted by orography.