Hugh co2 numbers will not supreme smell, well at least in my experience. It can suppress maturation of the buds but this is based on information from the fruit industry. Co2 will supress ethelyn amd ethelyn is what makes fruit mature.
The bananas in the store? They were picked green, very green, then gased with ethelyn when the needed to be shipped to the store.
Smell and taste are the results of the terpine profile of the bud. What destroys terpines is intense light and heat. Some are destroyed at as low of temps as 75 degrees.
High co2 near the end is just a waste as the plants are not chugging like they do during veg and the first half of flower. After the flowers bulk up, things really slow down and theor metabolic rate is low enough that the can't take advantage of elevated co2 levels.
If you want to increase smell then raise the lights in the last week or two before harvest and crank the AC.
If your in hydro, also turn down water temps to pretty much as low as you can. Cutting water depths in 1/2 is also good if your in dwc.
We can't raise our lights because we are vertical but we do set the thermostat on the AC to 67, which results in leaf temperatures closest to the bulb to be around 75.
Harvest before the lights come on, we don't do the whole kill the lights until your done trimming because we harvest the tops and then harvest the lowers about a week to 10 days later.. also.a good idea when you have monster sized plants..
Finally, keep.your drying room cool. We used to run a huge dehu in our drying room. A big Santa fe, but it just cranked out to much god damn heat. Probably because our drying room is encased (walls and ceiling) in 7/8 plywood on the inside and 1/16 steel sheeting on the outside... a little overkill but, if you had 30-40 lbs of buds in your drying room...
Anywho, we installed a small home depot wall banger in the wall (with a steel cage around it
) and it works perfectly to keep it a nice 70 degrees in there.
40 percent humidity the first 1-2 days. After chop, then 50 for a 2-3 days then set it and forget it at 60. Takes about 10 days total.