Special issue  

We conducted the Fifth International Workshop on Ice Nucleation (FIN) to (1) understand the microphysics of how particles nucleate ice, (2) determine the number of ice forming particles as a function of atmospheric properties such as temperature and relative humidity, (3) measure the atmospheric distribution of ice forming particles and (4) ascertain the role of anthropogenic activities in producing or changing the behaviour of ice forming particles. To accomplish these goals we held three distinct workshops on the topic of atmospheric ice nucleation. The first was an intercomparison of instruments to determine the composition of ice forming particles in a controlled laboratory setting. This took place in autumn 2014 at the location of the last ice nucleation instrument intercomparison: the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) chamber located at the Karlsruhe Institute of Technology. The second was an intercomparison of instruments used to determine cloud formation conditions. This activity also took place at AIDA and was conducted in spring 2015. Because ice nucleation predominantly takes place at the low temperatures found at high altitude, a critical requirement for the third workshop was a facility that offers access to free-tropospheric air masses with minimal local particle sources. We used the Desert Research Institute’s recently renovated Storm Peak Laboratory for this workshop in autumn 2015.