Simulation of fine organic aerosols in the western Mediterranean area during the ChArMEx 2013 summer campaign
Authors: Cholakian Arineh , Beekmann Matthias , Colette Augustin , Coll Isabelle , Siour Guillaume , Sciare Jean , Marchand Nicolas , Couvidat Florian , Pey Jorge , Gros Valerie , Sauvage Stéphane , Michoud Vincent , Sellegri Karine , Colomb Aurélie , Sartelet Karine , Langley DeWitt Helen , Elser Miriam , Prévot André S. H. , Szidat Sonke , Dulac François 
Published: May 2018

Abstract. The simulation of fine organic aerosols with
CTMs (chemistry–transport models) in the western Mediterranean basin has not
been studied until recently. The ChArMEx (the Chemistry-Aerosol Mediterranean
Experiment) SOP 1b (Special Observation Period 1b) intensive field campaign
in summer of 2013 gathered a large and comprehensive data set of observations,
allowing the study of different aspects of the Mediterranean atmosphere
including the formation of organic aerosols (OAs) in 3-D models. In this study,
we used the CHIMERE CTM to perform 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 two parameterizations including aging of
biogenic secondary OA, and a modified version of the VBS scheme which
includes fragmentation and formation of nonvolatile OA. The results from
these four schemes are compared to observations at two stations in the
western Mediterranean basin, located on Ersa, Cap Corse (Corsica, France),
and at Cap Es Pinar (Mallorca, Spain). These observations include OA mass
concentration, PMF (positive matrix factorization) results of different OA
fractions, and 14C observations showing the fossil or nonfossil origins
of carbonaceous particles. Because of the complex orography of the Ersa site,
an original method for calculating an orographic representativeness error
(ORE) has been developed. It is concluded that the modified VBS scheme is
close to observations in all three aspects mentioned above; the standard VBS
scheme without BSOA (biogenic secondary organic aerosol) aging also has a
satisfactory performance in simulating the mass concentration of OA, but not
for the source origin analysis comparisons. In addition, 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, the anthropogenic origin is of
similar importance. A general assessment of other species was performed to
evaluate the robustness of the simulations for this particular domain before
evaluating OA simulation schemes. It is also shown that the Cap Corse site
presents important orographic complexity, which makes comparison between model
simulations and observations difficult. A method was designed to estimate an
orographic representativeness error for species measured at Ersa and yields
an uncertainty of between 50 and 85 % for primary pollutants, and around
2–10 % for secondary species.