Experimental Evidence of the Feeding of the Free Troposphere with Aerosol Particles from the Mixing Layer

Aerosol particles emitted by both natural and anthropogenic sources have direct and indirect radiative impacts. Within the planetary mixing layer (ML), these particles are subjected to a large number of removal processes, e.g., rain, sedimentation, coagulation, and thus have a relatively short lifetime. Once aerosols are transported into the free troposphere (FT), their atmospheric lifetime increases significantly and they tend to be representative of large spatial areas. The work presented here shows evidence of anthropogenic emissions being transported from the ML to the FT during a cold period in February 2012. Using a wide range of in-situ measurements of aerosol chemical and physical properties at the Puy de Dome (PUY) station, as well as LIDAR measurements (at the Cezeaux site) of atmospheric back scattering we studied the exchange between the ML and the FT. Criteria used to identify when the PUY station was sampling in the ML or in the FT included mixing layer height estimates from LIDAR measurements, trace gas measurements, and air mass trajectories. Within the FT, we observed a gradual change in aerosol physical properties with increases in aerosol mass concentrations of up to 2 times the starting concentration, as well as increases in the number of larger particles (particle diameter >150 nm). Aerosol chemical properties showed increases in organic and nitrate particles. A series of linear fits were made through the data providing information on how different parameters change as a function of time. The impact of these changing aerosol properties are discussed in relation to the potential influence on aerosol direct and indirect effects. This work presents a unique combination of observations, and provide valuable data for future model validation.