You do not have to cater to every random request from a guest. Tell him you will not open all the windows for hours to air out the house. Then list all the ways you use airfresheners in your home that you do not plan to stop doing for his reservation - scented lotion, scented candles, scented laundry detergent, scented hand soap, scented deodorant, scented shampoo, perfume, toilet bowl cleaner, floor cleaner, whatever you have that you use that "re-odorizes" the house.
Reiteratie, if this will be a problem, he should book elsewhere where he will be more comfortable. People with allergies and sensitivity to environmental/industrial smells know they have a tough time so being upfront about his needs should have been key and a respectful way of allowing you decline should you not want to be a part of cleansing your home of smells.
Do not cancel on his behalf. He has a duty to be upfront about his needs and failed to do so. He should do the cancelling.