Turbulent aerosols (particles suspended in a turbulent fluid) are
fundamental to understanding chemical and kinetic processes in
many areas in the natural sciences, and in technology.

An example is the  problem of rain initiation. It has been argued that 
small-scale turbulent motion may facilitate the coalescence of
microscopic water droplets ('visible moisture') into
raindrops. This idea has a long history, but a satisfying theory 
has been elusive, and the topic remains a subject of intensive research.
Other examples are the dynamics of soot particles in the turbulent gas
flow in diesel-engine exhausts, and buoyant particles on the surface
of a turbulent liquid, and settling of particles under gravity in
turbulent flows. Turbulent aerosols are also of
great importance to more fundamental questions, such as the problem of planet formation.
It is not yet understood how the planets in our solar system
formed out of the dust around the growing sun; too little is known
about the collisions, interactions, and aggregation processes of the dust grains.

In this talk I summarise recent analytical progress
in understanding clustering and collision processes in turbulent
aerosols. By way of example I to describe three new results
from the references below.

Mehlig & Wilkinson, Phys. Rev. Lett. 92 (2004) 250602
Duncan, Mehlig, Ostlund & Wilkinson, Phys. Rev. Lett. 95 (2005) 165503
Wilkinson, Mehlig & Bezuglyy, Phys. Rev.  Lett. 97 (2006) 048501
Gustavsson, Mehlig, Wilkinson & Uski, Phys. Rev. Lett. 101 (2008) 174503
Gustavsson & Mehlig, unpublished (2010)