An improved parameterization for sulfuric acid–water nucleation rates for tropospheric and stratospheric conditions

Abstract

[1] In this paper we present parameterized equations for calculation of sulfuric acidwater critical nucleus compositions, critical cluster radii and homogeneous nucleation rates for tropospheric and stratospheric conditions. The parameterizations are based on a classical nucleation model. We used an improved model for the hydrate formation relying on ab initio calculations of small sulfuric acid clusters and on experimental data for vapor pressures and equilibrium constants for hydrate formation. The most rigorous nucleation kinetics and the thermodynamically consistent version of the classical binary homogeneous nucleation theory were used. The parameterized nucleation rates are compared with experimental ones, and at room temperature and relative humidities above 30% they are within experimental error. At lower temperatures and lower humidities the agreement is somewhat poorer. Overall, the values of nucleation rates are increased compared to a previous parameterization and are within an order of magnitude compared with theoretical values for all conditions studied. The parameterized equations will reduce the computing time by a factor 1/500 compared to nonparameterized nucleation rate calculations and therefore are in particular useful for large-scale models. The parameterized formulas are valid at temperatures between 230.15 K and 305.15 K, relative humidities between 0.01% and 100%, and sulfuric acid concentrations from 10 4 to 10 11 cm À3 . They can be used to extrapolate the classical results down to 190 K. The parametrization is limited to cases where nucleation rates are between 10 À7 and 10 10 cm À3 s À1, and the critical cluster contains at least four molecules.INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 1610 Global Change: Atmosphere (0315, 0325); 0365 Atmospheric Composition and Structure: Troposphere-composition and chemistry; KEYWORDS: nucleation, sulfuric acid, water, aerosol formation Citation: Vehkamäki, H., M. Kulmala, I. Napari, K. E. J. Lehtinen, C. Timmreck, M. Noppel, and A. Laaksonen, An improved parameterization for sulfuric acid -water nucleation rates for tropospheric and stratospheric conditions,

Aerosol microphysics modules in the framework of the ECHAM5 climate model – intercomparison under stratospheric conditions

“…Previously, M7 has integrated the differential equation for the aerosol compounds using a computationally efficient operator splitting scheme (Vignati et al, 2004). However, this approach may result in numerical errors when time steps typical for global scale models are used.…”

“…M7 (Vignati et al, 2004) is the microphysical core of aerosol module HAM (Stier et al, 2005) of ECHAM5. The aerosol microphysics module M7 describes the aerosol sizedistribution by 7 log-normal modes, predicting the mode size, mixing state, and composition.…”

“…Since these microphysics modules have been designed for large scale models, they parameterize aerosol microphysical processes and use assumptions to resolve the aerosol size distribution. Binary homogeneous nucleation of sulphate aerosols is treated identically in all the three modules using nucleation scheme by Vehkamäki et al (2002) extending it for high concentrations of sulphate using collision rate as nucleation rate (H. Vehkamäki, personal communication, 2008). For other microphysical processes the treatment varies between the modules.…”

“…When insoluble size sections are used the number of size sections in SALSA is 20. For nucleation, SALSA applies the parameterization by Kerminen and Kulmala (2002), which determines the formation rate of 3 nm particles from the nucleation rate given by the Vehkamäki et al (2002) scheme. Condensation of gas phase compounds onto the particles is calculated concurrently with nucleation using the analytical predictor of nucleation and condensation method (Jacobson, 2005).…”

“…be simplified. The aerosol distribution in aerosol modules is described in most cases using the bulk approach (Liao and Seinfeld, 2005;Liu et al, 2005;Reddy et al, 2005;, modal approach (Ghan et al, 2001;Wilson et al, 2001;Herzog et al, 2004;Vignati et al, 2004;Lauer et al, 2005;Stier et al, 2005), and sectional approach (Weisenstein et al, 1997;Jacobson, 2001;Timmreck, 2001;Rodriguez and Dabdub, 2004;Spracklen et al, 2005;Hommel, 2008;Kokkola et al, 2008). In the bulk approach, only the aerosol mass is prognostic.…”