The composition and properties of black carbon aerosol particles change continuously after emission during transport in the atmosphere. Coagulation, condensation, and photochemistry are contributing processes, collectively termed “aging”. Understanding these processes is important for assessing the climate impacts of black carbon aerosol. The use of single particle mass spectrometers has allowed unprecedented insight into black carbon mixing state and associated aging processes, however it is difficult to fully exploit these measurements using traditional modal or sectional models. The particle resolved aerosol model PartMC-MOSAIC, on the other hand, is a suitable interface to connect to these observations from the modeling side. In this work, we present the first PartMC - MOSAIC case study that uses data from an aerosol time-of-flight mass spectrometer (ATOFMS) to constrain the model. The instrument was deployed during the 2010 MEGAPOLI winter campaign in Paris, France.
PartMC-MOSAIC is a Lagrangian box model that resolves the per-particle composition and hence provides a detailed representation of black carbon mixing state and aging processes. The model simulates a representative group of particles distributed in composition space, treating coagulation, condensation and other important processes on individual particle levels. For the initial conditions of the aerosol population and for the particle emissions the quantitative chemical composition estimates from the ATOFMS measurements collected during MEGAPOLI was used. The particle population was tracked for several hours as it evolves, undergoing coagulation, dilution with the background air, and chemical transformations in the aerosol and gas phase. The model output is compared with the ATOFMS mixing state observation. The work also tries to quantify contribution of coagulation and condensation to black carbon aging and discuss the implications of black carbon aging for cloud condensation nucleation activity