Enhanced growth rate of atmospheric particles from sulfuric acid

Abstract

Abstract. In the present-day atmosphere, sulfuric acid is the most important vapour for aerosol particle formation and initial growth. However, the growth rates of nanoparticles (<10 nm) from sulfuric acid remain poorly measured. Therefore, the effect of stabilizing bases, the contribution of ions and the impact of attractive forces on molecular collisions are under debate. Here, we present precise growth rate measurements of uncharged sulfuric acid particles from 1.8 to 10 nm, performed under atmospheric conditions in the CERN (European Organization for Nuclear Research) CLOUD chamber. Our results show that the evaporation of sulfuric acid particles above 2 nm is negligible, and growth proceeds kinetically even at low ammonia concentrations. The experimental growth rates exceed the hard-sphere kinetic limit for the condensation of sulfuric acid. We demonstrate that this results from van der Waals forces between the vapour molecules and particles and disentangle it from charge–dipole interactions. The magnitude of the enhancement depends on the assumed particle hydration and collision kinetics but is increasingly important at smaller sizes, resulting in a steep rise in the observed growth rates with decreasing size. Including the experimental results in a global model, we find that the enhanced growth rate of sulfuric acid particles increases the predicted particle number concentrations in the upper free troposphere by more than 50 %.

Frequent new particle formation over the high Arctic pack ice by enhanced iodine emissions

“…3c). Sub-10 nm aerosol growth can be enhanced by dipolar interactions 45,46 but the enhancement factor (EF) for HIO 3 is not known. By applying the sulfuric acid EF 45 most of the growth could be explained within uncertainty by HIO 3 alone (Fig.…”

“…The black lines are the error bars due to the uncertainty of sulfuric and iodic acid concentration. The red dashed bars show the predicted growth rate when considering also the charge enhancement factor (EF) derived from Stolzenburg et al 45 Since for the last three events iodic and sulfuric acid measurements are not available, we report only the measured growth rates.…”

“…This is in analogy with the sulfuric acid case and reasonable given the high RH values experienced during MOCCHA. Finally, the mass diameter was converted into a mobility diameter adding 0.3 nm as suggested by Larriba et al 88 The sulfuric acid growth rate EF was derived from Stolzenburg et al 45 and applied also to the HIO 3 growth. This EF is based on a mechanism driven by vander-Waals forces between UFP and neutral molecules and depends on the condensing species.…”

Review of Hanson et al. Measurement Report: Sulfuric Acid Nucleation and Experimental Conditions in a Photolytic Flow Reactor

“…As you mention, some recent studies suggest an enhanced collision rate of sulfuric acid molecules (Stolzenburg et al 2020but also Halonen et al 2019 leading to faster growth rates. How much would it affect your results if you include such collision enhancement in your calculations?…”

Impacts of coagulation on the appearance time method for sub-3 nm particle growth rate evaluation and their corrections

“…This is because only the condensation of sulfuric acid is considered whereas other vapors may also contribute to new particle growth. The enhancement due to Van der Waals force is considered when calculating the coagulation coefficient (Alam, 1987;Chan and Mozurkewich, 2001;Stolzenburg et al, 2019). The appearance time retrieved from the measured aerosol size distributions was smoothed before estimating the particle growth rate.…”