This is something I know a little bit about having travelled through many South American cities especially. One was so bad ai felt sick with a metallic taste after 20 minutes walking from home.
Here's a few tips I've learnt.
1) There is a kickstarter project for a blueooth device that logs air quality in various metrics
2) I don't know where I read this but I heard the pollution drops off quickly at less than 30m from the road
3) Cars soak up more pollution than bicycles - so change your air filter. In fact, where can we buy carbon activated filter material for a custom upgrade to squeeze into our cars?
4) I wore a full gas mask on a few car journeys. It can make the difference between getting out of your car feeling like yoiu've run a marathon and getting out feeling just a bit cramped. It looks silly but why not try it to confirm to yourself if there's a problem worth working on that "pollen" filter?
5) You can get slimmer masks designed for cyclists. I mention this on my blog. Filtering is a compilcated business. I've found the main thing is to filter those particulates including the rubber off the tyres. I'm not too sure about the gasses. These have an effect but it seems less immediate to me.
6) You can get plants to filter air in your home. I'd like to see a air con system intregrating such a system on a rooftop. There was a Slashdot article on this.
7) You can get a 12v airfilter to go on your passenger seat but it isn't cheap and it works by recycling the air rather than catching it on the way in
8) Looking at truckers forums I've noticed this is definately a big problem that is killing people. This is totally unneccessary. I hope we can help them with cabin filters?