Collision

Contact freezing is among the freezing modes in clouds which is most difficult to study and quantify. One reason for this is the difficulty to assess how many collisions between particles and supercooled droplets are needed to cause the droplet to freeze. Most experiments that have been performed so far only report a bulk frozen fraction of droplets in presence of many particles. In our Collision experiment we try to get a better control on this by studying the collision rate and the freezing rate independently under similar conditions.

Droplets of controlled sized are injected into a temperature controlled chamber. Simultaneously, a flow of aerosol particles is drawn through the chamber. The frozen fraction of the droplets can be measured at different positions in the chamber with our IODE detector. For collision efficiency measurements the droplets can be collected at the bottom of the chamber. The collected aerosol mass is measured with ICP-MS mass spectrometry and allows to calculate a collision efficiency.