I have had a similar experience to Dahon.Steve and have quit my meds. I have a long history of asthma and spent a good deal of time in an oxygen tent when I was a young lad. It pretty much went away when I reached puberty, but came back when I was an adult. When I was in my last year of university and under a lot of stress, my asthma was getting worse by the month and I was on a salbutamol inhaler and on steroids. After I finished university I moved to Toronto and the day I arrived my asthma stopped. Haven’t had any major problems with it for about 12 years or so and my inhailer will expire before I use it up. If I do have an asthma attack, it is when I am exercising in the cold and I will take one puff from my inhaler and it prevents that attack.

i recall about ten years ago, there was a brief fad (?) in which bikers in urban areas would wear these things called "greenscreens", which were activated charcoal filters you put over your nose and mouth. I never noticed too much of a difference from 'em, but the filters would indeed start looking pretty icky after a while.

I tried them when they first came out about 10 or so years ago hated em only wore mine once couldn't breathe properly in them and created a lot of vapor fogged up the old goggles. I see a lady every day wear one of those full face 3M vapor mask they really do not work that well on pollution there are to many particles in the smog clogs up the filters they are designed for fumes. ANd I think that is all the greenscreens were good for also. Same kind of filtering system.

Iv'e noticed when I ride early in the morning , when the traffic is sparse , when a car passes the exhaust seems realy strong & choking Also when the weathers cold I seem to get a lot of nasal mucus ( good time to practice my snot rocket skills when theres not much traffic about )

A couple of tips for riding in urban/polluted areas:

1. Try to breathe through your nose rather than taking large breaths through your mouth. There are certain "filters" in your nose that will keep some of the particles out of your lungs.

2. If you're commuting and it's a ride you'll be doing regularly, look for a route that uses less trafficked streets.

3. If there is a particular vehicle (a bus, garbage truck etc) in front of you that is spewing out an unusually high amount of smog, slow down and let it get ahead of you. There's no shame in riding like a "granny" for a few hundred metres in order to protect your lungs.

4. Don't let it prevent you from riding. I've seen quite a few studies on this, and they tend to indicate that the level of pollution is much higher inside a car than outside a car. Basically if you commute by bike, you'll be getting a considerably higher quality of air, and that can't be a bad thing.

Re: the mucus issue. I think it probably has more to do with colder weather than with pollution. I tend to have more of it in "winter" than in summer, and our winters aren't even real winters. It should also be noted that our summers generally have heavier traffic as our population triples during the tourist season.