Does heavy air pollution improve takeoff performance?
Percentages of pollutants will not have a significant effect on earth as compared with temperature and pressure.  However, on a planet like Mars, with a CO2 atmosphere, the density difference may be significant enough to effect lift calculations.

Maybe NASA could go with a twisted Prandtl biplane using a high altitude electric motor and prop.  They have reached 95,000 feet on earth with Helios, but had issues with structural strength.