AbstractThis study evaluates the influence of aerosol processes on the particle number (PN) concentrations in three
major European cities on the temporal scale of 1 h, i.e., on the
neighborhood and city scales. We have used selected measured data of particle size distributions from previous campaigns in the cities of Helsinki, Oslo and Rotterdam. The
aerosol transformation processes were evaluated using the aerosol dynamics model MAFOR, combined with a simplified treatment of roadside and urban atmospheric dispersion. We have compared the model predictions of particle number
size distributions with the measured data, and conducted sensitivity analyses regarding the influence of various model input variables. We also present a simplified parameterization for aerosol processes, which is based on the more complex aerosol process computations; this simple model can easily be implemented to both Gaussian and Eulerian urban dis-
persion models. Aerosol processes considered in this study were (i) the coagulation of particles, (ii) the condensation and evaporation of two organic vapors, and (iii) dry deposi-
tion. The chemical transformation of gas-phase compounds was not taken into account. By choosing concentrations and particle size distributions at roadside as starting point of the computations, nucleation of gas-phase vapors from the exhaust has been regarded as post tail-pipe emission, avoid-
ing the need to include nucleation in the process analysis.