The way my bus leaks air, lack of outside air in the vehicle is not a problem ;o))All kidding aside, I am aware of that increased CO2.  It is something that one has to be careful of, especially in a modern, well sealed car.
Dave B.

-----Original Message-----
From: Dan N <dn92610@gmail.com>
To: ddbjorkman@verizon.net <ddbjorkman@verizon.net>
Sent: Fri, Feb 1, 2019 1:18 pm
Subject: Re: Air recirculator

hi Dave, 
I remember having seen a van that have it at Syncro Fest some year ago... it looks like a flap that close and open the fresh opening and at that time I am not interested and I didn't investigate further.
fyi... I have read somewhere that all the cars from Europe have some sort of continuos fresh air flowing into the cabin.. supposedly to keep the driver alert and not drowsy on long distance trip.... the reason is (as they say) the carbon dioxide (CO2) form our breathing could make us drowsy and less alert on a long drive... of course we can remediate this by opening a window a crack... and that Air Recirculator from Chris is mean to control that fresh air flow.
I hope this help.dan