I had severe asthma up until I got pregnant with my first child and that seemed to change a lot of things in my body, so now I only have mild symptoms from time to time.
The biggest helps for me have been:
An air filter on our furnace/ac.
Caution with foods I eat. I'm allergic to nuts and some fruits, plus the usual assortment of pollens.
Avoidance of any exposure to molds. I'm now convinced that my parents house that I grew up in had some kind of mold problem. The day I moved out I started feeling a lot better (of course it may have something to do with stressful environment too.) But also there was a piece of plywood under our deck that had gotten moldy. Just picking it up and taking it to the trash gave me problems.
A shot of espresso now and then. For some reason a huge jolt of caffeine works almost as well as the albuterol inhaler.
Avoiding (when possible) sudden temperature changes. I keep the house pretty cool in the winter, that way it's less of a shock when I go outside. Same goes for the ac in the summer.
Unfortunately even though I rarely have a severe episode anymore, my lungs are still damaged from when I was a kid.
Sorry your husband has to go through all of this. It is very difficult. Hopefully he'll find some medications that help.