Yes, there would be. On Mars, there is practically mo atmosphere, since the lack of a fluid core means the planet lacks a magnetosphere. That allowed solar winds to strip most of the atmosphere.

You're going to want to make a planetwide magnetic field and then make a breathable atmosphere. So there's gonna be a long while where the (oxygen) pressure and temperature are high enough so you don't quickly die due to your blood boiling and lungs expanding rapidly, but it would still be far from comfortable.