Co2 concentrations in the atmosphere are stable around 408 ppm (parts per million), which translates to approximately 1016 molecules cm-3 . what is the mass concentration of co2 in units of μg m-3 ? given the annual rate of increase of co2 of 1.6 ppm yr-1 , what is the projected co2 concentration in 2100 in units of ‘ppm’ and ‘μg m-3 ’? hint: assume an air density of 2.4×1019 molecules cm-3 .