What proportion of anthropogenic CO2 emissions react with atmospheric water vapor?

Question

Carbolic acid....lol. Never heard that before. :)

Answer 1

CO2 doesn't react with H2O.  CO2 and H2O form a hydrate, carbonic acid (and if anyone says they form carbolic acid I'll scream, people, for the love of christ, carbolic acid is PHENOL, not carbonic acid (sorry, for some reason everyone on Y!A thinks carbonic acid = carbolic acid)).  However, the equilibrium coefficient for the hydration reaction

CO2 + H2O <->  H2CO3

is very small, something on the order of 10^-3.5, so even in water there isn't much H2CO3 running around compared to dissolved unhydrated CO2 (at least for pH values less than 5.6 (at higher pH values you get a lot of bicarbonate (HCO3-) and carbonate (CO3=)).

So I don't see how your question makes sense, or what you are really trying to ask.  Not very much CO2 gets taken out of the atmosphere by water vapor.  Wet deposition of CO2 is not very large because rainwater is acidic and you can't get very much CO2 into acidic solutions with only 380 ppm partial pressure of CO2 in the gas phase.  Air-sea gas exchange and air-leaf gas transfer are the dominant mechanisms.  

Edit:  You can figure that the concentration of CO2 in cloudwater will be on the order of 10^-5 moles/liter.  That number comes from multiplying the Henry's Law constant (10^-1.5 moles/(L-atm)) times the partial pressure of CO2 in the atmosphere (approx. 10^-3.5 atm).  Of course, most cloud droplets just evaporate and the dissolved CO2 in the droplets just go right back into the gas phase as CO2.  Rainwater is very ineffective at removing CO2 from the atmosphere, since each liter of rainwater only removes 10^-5 moles of CO2 from the atmosphere.  To put that in perspective, there are roughly 100 moles of CO2 in a column of air 1 m^2 and 6000 m high.  Therefore, it would take 100 moles / 10^-5 m/L = 10^7 L of rain to strip all that CO2 out of the 6 km column of air given that the partial pressure of CO2 in air is only around 380 ppm.  That much rain would be equivalent to a column of water 10 km high.  Not very realistic unless you are a biblical flood kind of guy.  

Wet deposition is only important for really soluble gases like SO3, NH3, and one other major one I know exists but am totally blanking on right now.  c'est live.

Answer 2

It's tiny.  The reaction is:

H20 + CO2 = H2CO3

But the 'equilibrium constant" is tiny, AND the amount of CO2 in the air is tiny.  Together those two things mean this reaction will stay far to the lefthand side.

Yeah, that was said above.  This is short and sweet.

Answer 3

Does it even matter?  It's really irrelevant to the fact that emission levels are exceeding any and all natural processes of CO2 absorption.  That's why the atmospheric levels are rising.

If we didn't have 50 years of direct atmospheric CO2 measurements, then the hypothesis you seem to be promoting might give hope to a natural process of keeping the atmospheric CO2 levels low. But that hasn't happened.