The old-school Toyota RAV4 EV you see above is the California Air Resources Board's version of a non-participant observer. The all-electric vehicle cruises around the state measuring airborne pollution. Since it's powered by batteries, there are no tailpipe emissions created as CARB tries to get a handle on how dirty the roadway air is.
The problem, CARB says, is that it is difficult to measure air pollution levels, "during calm conditions at night and in the early morning." There are over 250 stationary air monitoring sites in California today, but the Board wanted a way to expand where and when it can test for things like ultrafine particles, carbon dioxide and nox. The original plan for the Mobile Monitoring Platform – as the RAV4 EV is officially called – was to "Investigate Spatial, Diurnal and Seasonal Pollution Gradients" on California's highways and ports. The RAV4 EV was originally expected to cost $280,000 (see pages 11-12 in this PDF from 2009), but a new report in the Modesto Bee says it had a total of $300,000 just in monitoring equipment.
Michael Benjamin, CARB's chief of air monitoring, told the Bee that the MMP, "paints a thorough picture about what air quality is in any given community." More importantly, the stationary and mobile testing equipment can tell CARB when and where the air is getting cleaner. Which is the whole point, after all.