First detection of ozone in the mid-infrared at Mars: implications for methane detection

TL;DR

This paper reports the first detection of ozone in the mid-infrared on Mars using the ExoMars TGO, revealing ozone's spectral features and potential interference with methane detection during a specific seasonal phase.

Contribution

It presents the first mid-infrared spectral detection of Martian ozone and discusses its implications for methane measurement interference.

Findings

Ozone detected at high northern latitudes (>65N) with 100-200 ppbv near 20 km altitude.

Ozone spectral features overlap with methane detection bands, affecting measurement accuracy.

Ozone levels observed are consistent with previous ultraviolet observations.

Abstract

The ExoMars Trace Gas Orbiter (TGO) was sent to Mars in March 2016 to search for trace gases diagnostic of active geological or biogenic processes. We report the first observation of the spectral features of Martian ozone (O3) in the mid-infrared range using the Atmospheric Chemistry Suite (ACS) Mid-InfaRed (MIR) channel, a cross-dispersion spectrometer operating in solar occultation mode with the finest spectral resolution of any remote sensing mission to Mars. Observations of ozone were made at high northern latitudes (>65N) prior to the onset of the 2018 global dust storm (Ls = 163-193). During this fast transition phase between summer and winter ozone distribution, the O3 volume mixing ratio observed is 100-200 ppbv near 20 km. These amounts are consistent with past observations made at the edge of the southern polar vortex in the ultraviolet range. The observed spectral signature of ozone at 3000-3060 cm-1 directly overlaps with the spectral range of the methane (CH4) nu3 vibration-rotation band, and it, along with a newly discovered CO2 band in the same region, may interfere with measurements of methane abundance.