Ozone (O₃) in the atmosphere of Mars is produced following the photolysis of CO₂ and is readily destroyed by the hydrogen radicals (HO_x) released by the photolysis and oxidation of water vapor. As a result, an anti‐correlation between ozone and water vapor is expected. We describe here the O₃‐H₂O relationship derived from 4 Martian years of simultaneous observations by the SPICAM spectrometer onboard the Mars Express spacecraft. A distinct anti‐correlation is found at high latitudes, where the O₃ column varies roughly with the −0.6 power of the H₂O column. The O₃ and H₂O columns are uncorrelated at low latitudes. To evaluate our quantitative understanding of the Martian photochemistry, the observed O₃‐H₂O relationship is then compared to that predicted by a global climate model with photochemistry. For identical model and observed abundances of H₂O, the model underpredicts observed ozone by about a factor of 2 relative to SPICAM when using the currently recommended gas‐phase chemistry. Sensitivity studies employing low‐temperature CO₂ absorption cross sections, or adjusted kinetics rates, do not solve this bias. Taking into account potential heterogeneous processes of HO_x loss on clouds leads to a significant improvement, but only at high northern latitudes. More broadly, the modeled ozone deficits suggest that the HO_x‐catalyzed photochemistry is too efficient in our simulations. This problem is consistent with the long‐standing underestimation of CO in Mars photochemical models, and may be related to similar difficulties in modeling O₃ and HO_x in the Earth's upper stratosphere and mesosphere.

中文翻译：

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SPICAM观测并通过全球气候模型计算的火星上臭氧与水蒸气柱之间的关系

火星大气中的臭氧（O ₃）是在CO ₂光解之后产生的，很容易被光解和水蒸气氧化释放的氢自由基（HO _x）破坏。结果，预计臭氧与水蒸气之间会产生反相关。我们在这里描述了由火星快车上的SPICAM光谱仪同时观测火星4年而得出的O _3- H ₂ O关系。在高纬度地区，O ₃色谱柱随H ₂ O色谱柱的-0.6幂而变化，存在明显的反相关。O ₃和H ₂O列在低纬度时不相关。为了评估我们对火星光化学的定量理解，然后将观测到的O ₃ -H ₂ O关系与全球气候模型与光化学预测的关系进行比较。对于相同的模型和观测到的H ₂ O丰度，当使用当前推荐的气相化学方法时，该模型将观测到的臭氧相对于SPICAM低估了约2倍。使用低温CO ₂吸收截面或调整动力学速率进行的敏感性研究不能解决该偏差。考虑到HO _x的潜在异质过程云层的损失导致显着改善，但仅限于北部高纬度地区。更广泛地讲，模拟的臭氧不足表明，在我们的模拟中，HO _x催化的光化学效率太高。这个问题与火星光化学模型中对CO的长期低估是一致的，并且可能与对地球上层平流层和中层中的O ₃和HO _x进行建模时遇到的类似困难有关。