Composition and Measurement of Charged Atmospheric Clusters

Abstract

Atmospheric charged clusters are formed in a series of rapid chemical reactions after ionisation, leaving a central ion X + or X − clustered with n ligands (Y) n . In solar system tropospheres and stratospheres there are two distinct cluster regimes: the terrestrial planets contain largely hydrated clusters (i.e. Y = H 2 O), whereas the gas planets and their moons have organic or nitrogenated cluster species. These classifications are largely based on model predictions, since hardly any measurements are available. The few existing composition measurements are reviewed, including the recent detection of massive charged particles in Titan's upper atmosphere. Technologies for both remote sensing and in situ measurements of atmospheric charged clusters are discussed. Preliminary measurements in the terrestrial atmosphere are presented indicating that ambient charged cluster species interact with downwelling infra-red radiation at 9.15 µm, even in the presence of cloud. This supports the possibility of future infrared detection of charged clusters.

Solar Influences on Climate

“…For these processes to affect climate they must exert an appreciable influence on the atmosphere's radiative properties. There is a small direct infrared absorption by cluster ions in the atmosphere [e.g., Aplin , 2008], but as aerosol and cloud droplets are known to have large radiative influences, effects of cosmogenic ions on clouds and aerosols have so far received the most attention. In particular, the growth of UCN to sufficient sizes to permit cloud droplet formation (as CCN) has been suggested as a mechanism for a possible cosmic ray–cloud dependence (see also section 3.2.4), though this effect has been shown in a climate model study to be much smaller than observed changes in clouds would suggest [ Pierce and Adams , 2009].…”

Recent advances in global electric circuit coupling between the space environment and the troposphere

“…Infra-red absorption in atmospheric air was measured using a bespoke filter radiometer tuned to the ion absorption band centred on 9.15 m (Aplin and McPheat, 2008) at Reading University Atmospheric Observatory, U.K., a well-instrumented meteorological and atmospheric electrical station. In the experiment, described in more detail by Aplin (2008), bipolar ion concentrations n were calculated from 5 minute averages of 1s samples of the atmospheric Potential Gradient F and conduction current J z using…”

Charge Generation and Separation Processes

“…Such knowledge is essential if one wishes to evaluate the importance of processes whose efficiency is critically dependent on the strength and orientation of an external field. The pre-existence of a global background electric field (usually referred to as "fair weather" field, see the chapter by Aplin et al 2008 in this issue) ensures that the water particles suspended in the atmosphere will become polarized. In a vertical, downward directed field (conventionally defined to be negative), such polarization will cause an excess of positive charge to accumulate in the lower part of the particle, while negative charge will be preferably located in the upper part.…”