4. (20 points) The pH of pure water in equilibrium with atmospheric CO2 was found by applying a charge balance on the ions in solution. After applying appropriate assumptions, the resulting charge balance was [H+]=[HCO3]. How high would atmospheric CO2 concentrations (ppm) need to be to decrease the pH of water in equilibrium with 1 atm total pressure to pH=5.45 ? (Note: KHCO2=0.033363mol/(L atm),Ka1=106.35, and Ka2=1010.33 )