ppm and %
1% = 10,000 ppm
2% = 20,000 ppm (see other threads for this being the current estimate of water concentreation)
Equator = 50 ppm H (by weight?)
Mass of H in 2% H2O? amu=1+1 out of 1+1+16 i.e. 1/9 of total H2O
So 2% H2O equates to (2/9)% H i.e. 2,222 ppm H - 41 times as rich as the equator.
Seems to me a natural 41 x enrichment is a good starting point, rather than working from 50 ppm...