Influence of aerosol lifetime on the interpretation of nucleation experiments with respect to the first nucleation theorem

S Ehrhart,J Curtius

doi:10.5194/acp-13-11465-2013

Abstract

Abstract. The SAWNUC (Sulphuric Acid Water NUCleation) microphysical aerosol nucleation model is used to study the effect of reactor walls on the interpretation of nucleation experiments with respect to nucleation theory. This work shows that loss processes, such as wall losses, influence the interpretation of nucleation experiments, especially at low growth rates and short lifetimes of freshly nucleated particles. In these cases the power dependency of the formation rates, determined at a certain particle size, with respect to H2SO4 does not correspond to the approximate number of H2SO4 molecules in the critical cluster as expected by the first nucleation theorem. Observed ∂log(J)/∂log([H2SO4]) therefore can vary widely for identical nucleation conditions but different sink terms.

Highlights

Nucleation of aerosol particles is a frequent phenomenon in the atmosphere (Kulmala et al, 2004)
The black line connects the integer numbers of H2SO4 molecules in the neutral critical cluster derived from Eq (4); the blue line labelled Jcrit shows n∗ derived from the slope of the logarithm of the “true” nucleation rate
In the case of a particle counter that measures subcritical clusters, here shown for a case of 1 nm, the derived n∗1.0 is independent of the H2SO4 concentration but is below the “true” n∗ over a wide range of [H2SO4]

Summary

Introduction

Nucleation of aerosol particles is a frequent phenomenon in the atmosphere (Kulmala et al, 2004). In laboratory experiments losses to the wall of the reaction vessel and the dwell time in flow tubes limit the lifetime of the newly formed particles. Kerminen and Kulmala (2002) published an approach to take losses to preexisting particles into account when correcting from measured formation rates to particle formation rates at a certain smaller diameter, usually a presumed critical diameter. This approach does not include losses of clusters below the critical size, nor does it include losses to vessel walls or the limited dwell time in flow tubes. Losses to walls of large chambers are usually assumed to be comparable to losses to pre-existing particles in ambient measurements (e.g. Kirkby et al, 2011), meaning the walls fulfil the same role as a population of large aerosol particles

Methods

Results

Conclusion