Nothing beats air exchange for ventilation. Ionizing air purifiers use ozone to reduce odors and does nothing for air exchange. It might reduce odors, but I don't think it does anything to purify air other than reduce particulates. This is just my opinion of course. I have a bathroom fan and a light proof vent in my darkroom and it works well. The better solution is to have a hood type of ventilator close to the source of fumes.