Comparison of aerosol chemistry transport model simulations with lidar and Sun photometer observations at a site near Paris

The ability of the aerosol chemistry transport model CHIMERE to simulate the vertical aerosol concentration profiles at a site near the city of Paris is evaluated using routine elastic backscatter lidar and Sun photometer measurements. The comparisons of model aerosols with measurements are carried out over a full year time period between October 2002 and September 2003. The methodology we propose here is new: From the model concentration outputs (optical properties varying with chemical composition and mass vertical distribution) we simulate the lidar backscattering profiles and compare them with the observed ones. The comparisons demonstrate the ability of the model to reproduce correctly the aerosol vertical distributions and their temporal variability. However, the aerosol load within the boundary layer is generally underestimated by the model, in particular during the afternoon hours and the summertime period. Several sensitivity tests indicate that this underestimation may have two origins: the lack of secondary organic and, to a lesser extent, mineral aerosols inside the model. The second deficiency is due to the absence of erosion/ resuspension of soil material in the primary aerosol sources considered here; the first deficiency is probably due to incomplete knowledge about the formation of organic species in a photochemically active atmosphere. The results also show that the particles ranging from 0.08 to 1.25 μm in radius represent more than 89% of the volume backscattering at 532 nm, while the coarse particles are not efficient in terms of optical properties. The missing aerosol mass must therefore be found within the accumulation mode.