Abstract. Aerosol particles have an important role in Earth's
radiation balance and climate, both directly and indirectly through
aerosol–cloud interactions. Most aerosol particles in the atmosphere are
weakly charged, affecting both their collision rates with ions and neutral
molecules, as well as the rates by which they are scavenged by other aerosol
particles and cloud droplets. The rate coefficients between ions and aerosol
particles are important since they determine the growth rates and lifetimes
of ions and charged aerosol particles, and so they may influence cloud
microphysics, dynamics, and aerosol processing. However, despite their
importance, very few experimental measurements exist of charged aerosol
collision rates under atmospheric conditions, where galactic cosmic rays in
the lower troposphere give rise to ion pair concentrations of around 1000 cm−3. Here we present measurements in the CERN CLOUD chamber of the
rate coefficients between ions and small (<10 nm) aerosol particles
containing up to 9 elementary charges, e. We find the rate coefficient of a
singly charged ion with an oppositely charged particle increases from 2.0
(0.4–4.4) × 10−6 cm3 s−1 to 30.6 (24.9–45.1) × 10−6 cm3 s−1 for particles with charges of 1 to
9 e, respectively, where the parentheses indicate the ±1σ
uncertainty interval. Our measurements are compatible with theoretical
predictions and show excellent agreement with the model of
Gatti and Kortshagen (2008).