Any type of humidity will lower the effectiveness of a carbon filter, unless you keep the carbon filter heated with embedded heat strips like most industrial carbon filter have included in their design. But for a grow area, if you keep the airflow at 1/2 of the rated volume flowing through the carbon filter, even at 75% humidity without heating strips, the carbon filter will get most of the smells! But if you are in a place that you are worried about the smells, I would still have a ONA bucket at the end of the exhaust tube if I wasn't venting outside, and or high up!