Questions about the CO2 concentration of water at atmospheric equilibrium
It's been my understanding that when injecting co2, a 1.0 drop in pH should equal roughly 30 ppm of CO2, and this is because the concentration at equilibrium with the surrounding air should be around 3 ppm. Looking at a pH/KH/CO2 chart, using 3 ppm as the starting point and following to the left at any KH, a pH difference of 1.0 point always equals 30 ppm.
Well... I've heard 3 ppm, I've also heard it's likely closer to 2 ppm, I've also heard it's anywhere from 2-4 ppm. Where did these values come from? Knowing the atmospheric co2 concentration, I assume we can calculate co2 concentration in aqueous solution at atmospheric equilibrium using Henry's law. Is this correct? Has anyone done this?
Another question I have is how much does temperature affect the co2 concentration at atmospheric equilibrium?