Show that the ammonium ion NH4+, 1ppb(mole fraction) is equivalent to 0.56 ppb (mass fraction) or .74 ugm-3 at T=298 and 1 atm.
Start by solving for mass concentration
Note that mass fraction is related to mole fraction as
mass fraction= (Mi/Mtotal) * mole fraction
Mtotal = 28.96e-3 kgmol-