Climatology and Diurnal Variation of Ozone Column Abundances for 2.5 Mars Years as Measured by the NOMAD‐UVIS Spectrometer

The distribution of Mars ozone (O3) is well established; however, our knowledge on the dayside diurnal variation of O3 is limited. We present measurements of Mars O3 column abundances, spanning Mars Year (MY) 34 to the end of MY 36, by the Ultraviolet and VIsible Spectrometer (UVIS), part of the Nadir and Occultation for MArs Discovery (NOMAD) instrument, aboard the ExoMars Trace Gas Orbiter. UVIS provides the capability to measure dayside diurnal variations of O3 and for the first time, a characterization of the dayside diurnal variations of O3 is attempted. The observed O3 climatology for Mars Years (MY) 34–36 follows the established seasonal trends observed through previous O3 measurements. At aphelion, the equatorial O3 distribution is observed to be strongly correlated with the water ice distribution. We show that the early dust storm in MY 35 resulted in a near‐global reduction in O3 during northern spring and the O3 abundances remained 14% lower in northern summer compared to MY36. Strong latitudinal and longitudinal variation was observed in the diurnal behavior of O3 around the northern summer solstice. In areas with a weak O3 upper layer, O3 column abundance peaks in the mid‐morning, driven by changes in the near‐surface O3 layer. In regions with greater O3 column abundances, O3 is observed to gradually increase throughout the day. This is consistent with the expected diurnal trend of O3 above the hygropause and suggests that in these areas an upper O3 layer persists throughout the Martian day. Plain Language Summary Ozone, a highly reactive gas, plays an important role in the chemical cycles of both carbon and hydrogen on Mars. As ozone is tightly correlated to the presence of the difficult to detect odd hydrogen species, measurement of the ozone distribution can provide vital insight into the Martian photochemistry. We present the ozone abundances measured by the UVIS spectrometer aboard the ExoMars Trace Gas Orbiter, spanning Mars years (MYs) 34–36 and attempt to characterize the daily variations in ozone. The ozone follows the expected seasonal trends, with the highest ozone abundances observed at polar regions in the spring, autumn and winter seasons of both hemispheres and very little ozone during southern summer, outside the northern polar latitudes. An enhancement in equatorial ozone during northern summer is observed, with MY 35 showing lower ozone abundances compared to MY 36, likely the effect of an early dust storm in MY 35 or the lon