Simulation of atmospheric nucleation mode: A comparison of nucleation models and size distribution representations


Atmospheric particle formation and growth were investigated using different nucleation models and size distribution representations. Nucleation was modeled using recently developed parameterizations for binary nucleation of water and sulphuric acid and ternary nucleation of water, sulphuric acid, and ammonia. A comparison with older nucleation parameterizations, combined with full aerosol dynamics, demonstrated that the difference in nucleation rate (1-2 orders of magnitude) is clearly reflected in the resulting total particle concentration. A comparison of binary and ternary nucleation schemes showed that above 240 K the ternary nucleation rate exceeds the binary by over 10 orders of magnitude, indicating that in most cases, at lower tropospheric conditions, only ternary nucleation can be relevant. In addition, the performance of aerosol dynamics models applying either a multimodal monodisperse or a fixed sectional size distribution representation was evaluated against a molecular resolution model, which follows the changes in the nucleation mode particle size distribution molecule by molecule. Regarding total number concentration, the sectional method converged to the molecular resolution approach when increasing the number of size sections. With strong condensational growth, however, numerical diffusion problems were evident. Overall, the performance of the sectional method with low number of sections was not satisfactory. The monodisperse method gave very good results, at least in terms of total number, when the background modes were set to match the condensation sinks of respective lognormal modes. On the basis of our study the multimodal monodisperse method seems to be a possible candidate when selecting the size distribution approach for large-scale atmospheric models.