No, even with root foods, the problem is not CO2, the problem is metals.
You will get 11 times more metals in your fruits and vegetables (comparing to the supermarkets products) if you try to grow foods on your balcony.
Cadmium, chromium, lead, zinc, nickel, copper, ... why ? because the car parts are deterioring themselves with the time, and finally the metals of the motor, exhaust, etc... will go in the air with carbon monoxide and finally the plants will absorb them.
The worst is cadmium, it is very toxic. Imagine what you are breathing everyday if you live in a big city, in addition to CO2. We can envy future generations with more electric cars.
So, I suggest not to cultivate in cities.
These data have been provided on streets where there are between 5,000 and 50,000 vehicles per day. If you are isolated and there are less than a hundred of vehicles, then the risk drastically reduces and you can plant what you want.
Source : http://www.ncbi.nlm.nih.gov/pubmed/22445920