What is the most likely contributor to my asthma--smog, pneumonia, or genetics?

Factual Questions
1

I was diagnosed with exercise-induced asthma over a year ago. This either developed or presented itself after I began a regular exercise routine, including cardio 4x times/week. I’m not a fan of having any “chronic” illness, minor as this is on the scale of things, and I’m curious why at 29 I developed it.

I know that obviously a personal case study would be needed to get any real idea of causes (and even then, I know it would still be a maybe/if/could be), but I’m curious what the most likely contributing cause wuold be to this annoying adult-onset asthma. (It’s the chronic kind, not acute–I get feelings of pressure and shortness of breath, and on rare occasions wheezing. Usually I don’t notice unless I’m doing something strenuous.)

The main factors I consider:

  1. Air quality. I do live in the San Gabriel Valley in Southern California, where smog isn’t the worst, but it’s far from clean-air living. I do notice the asthma is worst in hot weather.

  2. Pneumonia. I had it in 1994, and it took me over a year to recover (meaning, breathe without crackling/wheezing/hacking/etc). The doc at the time said the left lung might not ever be the same…but I never noticed a problem until 7-8 years later.

  3. Genetics. Could be I was just designed to get asthma. Whee. (My sister had mild asthma as a kid, but that’s it. No one else in my family has any sort of respiratory condition.)

Just curious about what studies typically point to as the greatest contributing factor. (And wondering if a move out of the SGV would be of any benefit.)

2

I suspect all these factors are involved, it’s not a case where you can pin it on one. In my case, there are several triggers I have to keep a suspicious eye on if I want to avoid attacks.

Have you tried a HEPA filter? I have one in my bedroom (it runs very quietly) and stopped wheezing the next morning. I still have chronic asthma but it's much less troublesome.
3

I have no asthma in my family. I developed it when I was 27. Sometimes things just happen

4

My asthma was so mild and intermittant it wasn’t diagnosed for years (looking back, though, it was apparent it had been aroudn for awhile).

It is possible that you had some asthma for awhile but it was missed before you started your regular exercise program.

5

If can figure out exactly why you developed asthma, fame and fortune await you (well, fame anyway. In the medical world, anyway. Or at least in the pulmonary medical world).
It’s known that many things trigger asthma attacks in people who are already asthmatics – triggers include ozone (smog), animal &insect dander, particular allergens and other things.
But what causes someone to become susceptible is not known very well. I think there are some indications that chronic exposure to ozone pollution is linked to a higher incidence of asthma, but nationwide asthma rates have been rising even as air quality has been steadily increasing since 1970.