Aerosols are small solid or liquid particles suspended in a gas. They enter our atmosphere from both natural and anthropogenic sources and are pretty ubiquitous.
Aerosols can make the air look hazy when you look over a mountain range or a polluted city by scattering light. They’re the reason you can see your breath on a cold morning and they can form the seeds we need to make clouds. This is because the aerosol particles provide a surface for water vapour to condense onto and form droplets.
Aerosols can be lofted ready-formed into our atmosphere, for example as sea spray, dust from the desert, small particles from incomplete combustion in engines and many other sources.They can also form from the gas phase in the atmosphere. This process of gas-to-particle conversion is called nucleation. It occurs when low volatility vapours (i.e. ones that have slow evaporation rates) in the atmosphere reach high enough concentrations to condense into small particles. These newly formed particles are around 1nm in size (1nm = 1 x 10 -9 ) but need to grow to around 50 – 100nm before they can influence clouds. Aerosols grow when vapours condense onto them, or by coagulation with other small particles.