28 May 2025: Megan Brown

Speaker: Megan Brown (Cambridge)

Date: Wednesday 28 May 2025

Time: 15:00

Location: 3.34

Ozone Secrets: Exploring Chemistry in the Martian Atmosphere

Mars is a cold and arid planet, with an atmosphere less than 1% the surface pressure of Earth's. Yet it undergoes excessive seasonal changes, from thick water ice clouds at high latitudes (aphelion – furthest from the Sun) to global dust storms engulfing the entire planet (perihelion – closest to the Sun). The chemical components in the atmosphere are similar to those known on Earth - CO₂, O₂, H₂O – but in different quantities and under extreme conditions on Mars. Hydroxyl radicals (OH and HO₂) catalyse the reformation of CO₂ and are responsible for carbon dioxide being the primary constituent of the atmosphere (95%). Ozone is a key trace gas for understanding these chemical reactions: it can be detected via UV spectrometers aboard satellites and is sensitive to short-lived hydroxyl radicals. The discrepancy between observed ozone and ozone modelled through global climate models implies missing or inaccurate chemistry in our knowledge of the martian atmosphere.

One possible explanation for this ozone deficit could be the heterogeneous uptake of hydroxyl radicals on water ice particles. This causes a depletion in HOx and an increase in ozone. Using atmospheric models, we show evidence that heterogeneous reactions occur, but have a greater impact on ozone under conditions when water vapour abundance is minimal.

Another possibility could be due to nitrogen species (N₂, NO, NO₂) in the atmosphere, which, on Earth, are known to have a complex relationship with ozone formation and destruction. The presence of nitrogen species could, if under the right circumstances, lead to the formation of hydrogen cyanide (HCN). HCN is a pre-cursor to the formation of amino acids and acts as a biomarker. Such circumstances would include lightning generated from the dust storms which occur during Mars' dusty season. Using ozone as a proxy for the chemistry, we aim to develop an atmospheric chemical scheme with the addition of nitrogen reactions and lightning emissions to simulate the formation of HCN in Mars' atmosphere.