PMCAMx-UF, a three-dimensional chemical transport model focusing on the simulation of the ultrafine particle size distribution and composition has been extended with the addition of reactions of chemical aging of semivolatile anthropogenic organic vapors, the emissions and chemical aging of intermediate-volatility organic compounds (IVOCs), and the production of extremely low-volatility organic compounds (ELVOCs) by monoterpenes. The model is applied in Europe to quantify the effect of these processes on particle number concentrations. The model predictions are evaluated against both ground measurements collected during the PEGASOS 2012 summer campaign across many stations in Europe and airborne observations by a zeppelin measuring above Po Valley, Italy. PMCAMx-UF reproduces the ground level daily average concentrations of particles with a diameter larger than 100 nm (N.sub.100) with normalized mean error (NME) of 45 % and normalized mean bias (NMB) close to 10 %. For the same simulation, PMCAMx-UF tends to overestimate the concentration of particles with a diameter larger than 10 nm (N.sub.10) with a daily NMB of 23 % and a daily NME of 63 %. The model was able to reproduce more than 75 % of the N.sub.10 and N.sub.100 airborne observations (zeppelin) within a factor of 2.