According to New Scientist, a revolution is taking place in air pollution monitoring. As sensor packages become smaller, cheaper and less power hungry, it's becoming feasible to move from networks of a few large, fixed sensors to networks of hundreds of mobile sensors. "Mobile" implying both "people" and (as you've probably already guessed) "pigeons." Yes, a U.S. technology artist has on several occasions launched flocks of pigeons wearing sensors, GPS units, and cell phones from various California roofs. The pigeons, of course, immediately and fatally plummet to the ground.
Just kidding about the plummet part. The pigeons actually take flight and report their positions and pollution readings to a server that plots the data on an interactive Web page. But this is not the important part. The important part is that stronger, smarter, more reliable sensor platforms are available in the form of people. Volunteers (well, they might be volunteers...they might also be undergraduates desperate for a passing grade) are increasingly carrying sensor packages around cities in an effort to map and measure levels of toxic chemicals and particulates. Which is fine as far as it goes.
The real opportunity comes when GPS-enabled cell phones have pollution sensors built into them by default and we all become mobile sensor platforms. The important word at this point is: lawsuit. The magic happens when our cell phones become dosimeters--devices that record our lifetime exposure to each air pollutant. Since it's apparently fairly easy to determine the source (which factory, mine, power plant, incinerator, etc.) of a pollutant, it may be possible to argue that your late-in-life medical condition is the result of prolonged exposure to dangerously high levels of something emitted by (say) the municipal bus fleet. I have no idea how the case would turn out, but there's one thing for certain: unlike the cigarette companies, the city couldn't argue that you had a choice about inhaling.