Up to the present time, the nucleation or new formation of particles in the atmosphere has been a great enigma. Until recently, research was based on the assumption that sulphuric acid played the central role in particle formation. However, laboratory experiments and field tests have consistently provided conflicting results. In the lab, considerably higher concentrations of sulphuric acid are required for nucleation to take place than in the atmosphere itself. Now scientists from the Paul Scherrer Institute (PSI) have found out the cause for these conflicting results from their smog chamber. These findings will advance climate research to a significant degree.