<P> Sulfur dioxide in the atmosphere is thought to be a tracer of current volcanic activity . It has become especially interesting due to the long - standing controversy of methane on Mars . If methane on Mars were being produced by volcanoes (as it is in part on Earth) we would expect to find sulfur dioxide in large quantities . Several teams have searched for sulfur dioxide on Mars using the NASA Infrared Telescope Facility . No sulfur dioxide was detected in these studies, but they were able to place stringent upper limits on the atmospheric concentration of 0.2 ppb . In March 2013, a team led by scientists at NASA Goddard Space Flight Center reported a detection of SO in Rocknest soil samples analyzed by the Curiosity rover . </P> <P> As reported by the European Space Agency (ESA) on September 29, 2013, a new comparison of spacecraft data with computer models explains how global atmospheric circulation creates a layer of ozone (O 3) above Mars's southern pole in winter . Ozone was most likely difficult to detect on Mars because its concentration is typically 300 times lower than on Earth, although it varies greatly with location and time . The SPICAM--an UV / IR spectrometer--on board Mars Express has shown the presence of two distinct ozone layers at low - to - mid latitudes . These comprise a persistent, near - surface layer below an altitude of 30 km, a separate layer that is only present in northern spring and summer with an altitude varying from 30 to 60 km, and another separate layer that exists 40--60 km above the southern pole in winter, with no counterpart above the Mars's north pole . This third ozone layer shows an abrupt decrease in elevation between 75 and 50 degrees south . SPICAM detected a gradual increase in ozone concentration at 50 km until midwinter, after which it slowly decreased to very low concentrations, with no layer detectable above 35 km . The reporting scientists think that the observed polar ozone layers are the result of the same atmospheric circulation pattern that creates a distinct oxygen emission identified in the polar night and also present in Earth's atmosphere . This circulation takes the form of a huge Hadley cell in which warmer air rises and travels toward the south pole before cooling and sinking at higher latitudes . Mars is on a quite elliptical orbit and has a large axial tilt, which causes extreme seasonal variations in temperature amongst the northern and southern hemispheres . Mars's temperature difference greatly influences the amount of water vapor in the atmosphere, because warmer air can contain more moisture . This, in turn, affects the production of ozone - destroying hydrogen radicals . </P> <P> In early 2016, Stratospheric Observatory for Infrared Astronomy (SOFIA) detected atomic oxygen in the atmosphere of Mars . This was the first time in forty years it was detected, the last time being the Viking and Mariner missions in the 1970s . </P> <P> The atmosphere of Mars is a resource of known composition available at any landing site on Mars . It has been proposed that human exploration of Mars could use carbon dioxide (CO) from the Martian atmosphere to make rocket fuel for the return mission . Mission studies that propose using the atmosphere in this way include the Mars Direct proposal of Robert Zubrin and the NASA Design reference mission study . Two major chemical pathways for use of the carbon dioxide are the Sabatier reaction, converting atmospheric carbon dioxide along with additional hydrogen (H), to produce methane (CH) and oxygen (O), and electrolysis, using a zirconia solid oxide electrolyte to split the carbon dioxide into oxygen (O) and carbon monoxide (CO). </P>

How does the atmosphere of mars compared to the atmosphere of earth