The basic idea is to couple an air quality monitor with a smart phone and them map the data on a web site. Imagine the quantity and density of observations that could be collected in the Salt Lake Valley (outdoor and indoor) in this fashion. It is a little unclear from the video and the article precisely what can currently be measured, but the Aircasting web site suggests carbon monoxide and nitrogen dioxide. The video suggests they can measure particulate matter too (perhaps this is inferred based on the correlation between carbon monoxide and particulate matter). In any event, any of these measurements are useful.
Addendum, 7:15 AM 7 June: I realized after hastily writing this last night that I probably should dig a little deeper. Information on the air monitor and how to build one is here. Additionally, there are accuracy, sampling, and calibration issues that need to be addressed, so "shovel-ready" might have been overly optimistic. Nevertheless, I do see this as an example of what could be done along the Wasatch Front.