Or you can make a room spray with a few drops of essential oils, for a lighter fragrance. You can even use crystals as a room spray or a combo of EO and crystals. Just go light on the EO's. I find sometimes, the oil burner's can give off an overpoweringly strong scent, and strong fragrances can be a lung irritant to some people with COPD.
Actually I don't know why I didn't say this before but I actually make my own diffusers. It is super cheap to do. What I do is this: I get a small bottle( a plastic hair spray bottle with the top taken off will work) some essential oil, orange oil is fairly inexpensive pour in about 2 tablespoons(depending on the size of the bottle you may need more) Take 4 or 5 of those kabob skewers, you can buy a whole package for a few bucks cut off the pointy ends carefully and then dip both ends into the oil so both ends are coated and then set the skewers into the bottle and there you do a homemade diffuser! I have never used one on my altar but it is a great idea. This is really inexpensive and you can make it for under $10 maybe even under $5 depending on the oil and assuming you use a bottle you already have on hand. I have a 2oz glass bottle I use for a diffuser and some 4oz ones I have made for other people that were spray bottles. Or you could save a little more by cutting out the skewer cost and just make the spray like flammeous mentioned or you can do both and rotate in and out between the two and still spend very little money. When I made mine I used what I had on hand. I suppose in a pinch you could use a really small jar like a baby food jar and tooth picks instead of the skewers.
Some people with COPD not only cannot tolerate the smoke from incense, but will also react badly to the scents of oils from diffusers. So if he can't tolerate perfumes, air fresheners, etc. then I would also avoid using oils and diffusers.
If it is the scent of the incense or oil you want to help with your ritual or with meditation you can always place a small drop of diluted essential oil right under or on top of your nose. That way you can smell it but no one else will be bothered by it.
If you're looking for something other than incense to represent Air on your altar remember that the Quarter representations are simply that...something that speaks of that Element to you. One common substitution for incense/Air is a feather. Or get creative and find what speaks of Air to you.