Answer:
Mars does have an atmosphere, although it is extremely thin. 95.32% (by mole fraction or volume) of the atmosphere is carbon dioxide. The rest of the atmosphere is made up of nitrogen (2.7%), argon (1.6%), oxygen (0.13%), carbon monoxide (0.07%), water vapor (0.03%) and nitric oxide (0.013%). There are also traces of a few other gases such as neon (2.5 μmol/mol), krypton (300 nmol/mol), formaldehyde (130 nmol/mol), xenon (80 nmol/mol), ozone (30 nmol/mol) and methane (10.5 nmol/mol).
As noted, the atmosphere is very thin. The atmospheric pressure on the surface of Mars varies from around 30 pascals (0.0044 psi) on Olympus Mons's peak to over 1,155 pascals (0.1675 psi) in the depths of Hellas Planitia, with a mean surface level pressure of 600 pascals (0.087 psi), compared to Earth's sea level average of 101.3 kilopascals, i.e. 101,300 pascals.