This seems like nonsense on a conservation of energy basis. Putting vents on trains would cost a similar amount of energy as using fans to blow large volumes o

This seems like nonsense on a conservation of energy basis. Putting vents on trains would cost a similar amount of energy as using fans to blow large volumes of air (at ~400 ppm CO2) into carbon-capture systems, and the result would be to slow down the trains and cause them to use more fuel or electricity. Secondly, who is going to pay for this? If CO2 is going to be a valuable commodity itself, then that's because it's going to be used in an industrial process as a feedstock for fuel or material production. In that case, train operators might find this to be an interesting proposition, if the value of the captured CO2 is a good deal higher than the resulting increase in fuel/electricity costs needed to operate these trains. As far as industrial production, this doesn't look good either. It's far easier to just put large atmospheric CO2 capture systems right next to the chemical production system without having to haul trainloads of CO2 all over the place.