The Gas Phase Chemistry of Aluminum in Planetary Atmospheres

Aluminum (Al) atoms can be injected by frictional heating of meteorites as they enter the comparatively dense upper atmospheres of planets. Permanent layers of a range of metals are present due to this process and can provide a useful probe of larger scale atmospheric dynamics. The gas phase chemistry of the metals influences the shape and seasonality of the layers, long term trends and determines the formation of larger molecules which can condense to form nanometer scale meteoric smoke particles (MSPs). MSPs are thought to act as a nucleation source for high altitude ice clouds on Earth and Mars, while Al chemistry at higher temperatures (>1000 K) is also important for the early stages of particle formation around dying stars.

The atmospheric lifetime of Al atoms is relatively short in the presence of O₂ which reacts rapidly to form the more dominant species AlO. In this study we have experimentally measured AlO reacting with a range of atmospherically relevant species: O₂, O­₃, CO₂ and H₂O. This was achieved using the Pulsed Laser Photolysis Laser Induced Fluorescence (PLP-LIF) technique in a temperature controlled reactor (190 - 810 K). Temperature and pressure dependent rate coefficients were determined for the AlO reactions and the relative atmospheric importance of these rates are compared, using Earth as an example. This neutral Al chemistry reaction scheme will then be combined with measurements of Al ion reactions and included in a version of the Whole Atmosphere Community Climate Model (WACCM) for both Earth and Mars.