Parameterizing the formation rate of new particles: The effect of nuclei self-coagulation

The study is based on the work of Lehtinen et al. (2007) [Lehtinen, K. E. J., Dal Maso, M., Kulmala, M., & Kerminen, V.-M. (2007). Estimating nucleation rates from apparent particle formation rates and vice versa: Revised formulation of the Kerminen–Kulmala equation. Journal of Aerosol Science, 38, 988–994] who derived formulae connecting “real” and “apparent” nucleation rates. The parameterization neglected self-coagulation of newly formed particles and clusters, however, and here we have extended the previous work to include the effects of the self-coagulation. Our main focus was on calculating the “apparent” nucleation rate, i.e. the rate at which particles appear at sizes larger than the critical cluster size, as a function of the “real” nucleation rate. The revised parameterization was comprehensively tested against an explicit aerosol dynamic model at diverse atmospheric conditions. It was found out that nuclei self-coagulation has importance to new particle formation when Jnuc/Q>10−2 where Jnuc is the nucleation rate and Q is the production rate of condensable vapours. This corresponds to the nucleation rates ranging from >10 cm−3 s−1 (free troposphere) to >104 cm−3 s−1 (polluted boundary layer) depending on the atmospheric conditions. In terms of the particle number concentration, the calculations performed with the explicit model and the predictions of revised parameterization were generally within an order of magnitude. Several issues related to applications in large-scale models were also discussed.