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Enhanced growth rate of atmospheric particles from sulfuric acid
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2020
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Source: Atmospheric Chemistry and Physics, 20(12), 7359-7372
[PDF-1.12 MB]
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Journal Title:Atmospheric Chemistry and Physics
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NOAA Program & Office:
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Description: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 %.
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Source:Atmospheric Chemistry and Physics, 20(12), 7359-7372
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Rights Information:CC BY
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