Hullo Gromit,
Yes! I keep an albuterol inhaler in my saddlebag at all times. I usually take one hit before I head out, and that usually tides me over for 20 miles or so. In colder weather I may have a little tougher time.

I live in L.A., and while the weather is great, the air quality can be an issue. One thing that has really helped me is yoga, believe it or not. I had a really wonderful instructor teach me some "asthma specific" poses and breathing routines about 3 years ago, and I think they've really helped. Of course, the results are not immediate, they occur over time, with regular practice, but yoga can play a part in managing your asthma.

Google "yoga for asthma" for more specific info. And good luck!