Infra-red effects of atmospheric cluster-ions

Cluster-ions, tiny electrically charged particles, are continuously generated in the atmosphere by natural radioactivity (from rocks beneath porous surface materials), and cosmic rays (from space). The nanometre-sized cluster-ions consist of a few molecules hydrogen-bonded to a charged central atom. Bending and stretching of the hydrogen bonds means that these cluster-ions absorb infra-red radiation. Infra-red effects of atmospheric cluster-ions have already been observed both in the laboratory and in an atmospheric experiment. The infra-red absorption of cluster ions could potentially have both global and continuous effects on weather and climate, motivating the need to better quantify the effects for inclusion in meteorological and radiative transfer models. This project will involve investigation of the atmospheric effects of the cluster ions.

This will be an experimental project, with the techniques developed first in a laboratory, before atmospheric measurements take place. The methodology will involve artificially enhancing the natural background cluster-ion concentration with, for example, a corona ion source, and measuring both the ionisation and the infra-red absorption. Electric fields can be applied to remove the cluster-ions, to evaluate the change in infra-red absorption between their presence and absence. Natural fluctuations in atmospheric ionisation due to space weather events and radioactivity will also be exploited. The aim of the project is to determine how the infra-red absorption varies with cluster-ion concentration across a range of atmospheric conditions, a currently neglected effect in atmospheric and climate models.