Little Things Do Matter
Gas-phase sulfuric acid is important during
atmospheric particle
formation, but the mechanisms by which it forms
new particles
are unclear. Laboratory studies of the binary
nucleation of
sulfuric acid with water produce particles at rates
that are
many orders of magnitude too small to explain the
concentration
of sulfuric acid particles found in the atmosphere.
Sipilä et al. (p.
1243) now
show that gas-phase sulfuric acid does,
in fact, undergo nucleation
in the presence of water at a rate
fast enough to account for the
observed abundance of sulfuric
acid particles in the atmosphere.
These particles, which contain
1 to 2 sulfuric acid molecules each,
were not detectable previously,
owing to their small size, with
diameters as small as 1.5 nanometers.