But measuring roadway air pollution and its sources is difficult. Not long after exiting the tailpipe, emissions blend together in a cloud above the street, making it difficult to pinpoint the worst offenders. Five percent of vehicles -- the old, the broken, or the poorly designed -- are responsible for 90 percent of toxic emissions.
Spanish researchers believe they have found a solution: an infrared camera system that can remotely measure vehicle emissions on a high-capacity road. Which cars are the culprits? This new camera system can find out.
The camera reads the unique infrared signatures of various emissions -- carbon dioxide, carbon monoxide, nitrogen oxides, hydrocarbons, etc. -- from a fixed point on the roadside, while plugging gas concentrations into a sophisticated software program. A quickly rotating wheel of lens filters enables one camera to measure the quantities of several gases from one car's tailpipe, even as the vehicle roars by at highway speed.The result is an emissions profile for every car on the road, a sort of chemical fingerprint.
In a test case this summer, the researchers analyzed the A6 leading into Madrid, one of Spain's biggest and busiest highways. The result, according to Victor Gil Gonzalez, who works in the Remote Sensing and Infrared Image Laboratory at the Universidad Carlos III in Madrid, was a series of cut-and-dry measurements indicating the worst polluters on the road.
"If you want to know which car is the highest emitter, you have to test it on the road," Gil explains. "We are able to quantify gas emissions, so we can see which cars are sending the most pollution into the air."
There's a certain degree of subtlety to this. As Gil points out, a car full of passengers and suitcases -- a sign of transportation efficiency -- will emit more exhaust than one with a lone driver. But the camera system also analyzes ratios, like the proportion of carbon monoxide to carbon dioxide, which in a properly functioning engine should remain low even during periods of heavy fuel consumption.
This team -- led by several Spanish companies and university researchers -- is not the first to use "remote sensing" to pinpoint the most environmentally damaging cars. A number of states, including Virginia, Texas and California, have performed on-road emissions tests aimed at identifying the worst offenders. If a car fails the test, a camera snaps a photo of its license plate and the driver may receive a notice or fine in the mail. Texas takes a million such measurements per year. But many on-road screenings require one lane of traffic, speed reductions or other altered road conditions.
The innovation in the Spanish monitor system is that it can provide real-time emissions data for a four-lane highway without the slightest disruption to traffic patterns. This not only means that it can pinpoint high-emissions vehicles; it can also provide crucial information to city planners focused on decreasing air pollution. Experiments in traffic planning -- higher speed limits, fewer lanes, synchronized traffic lights, a ban on trucks or buses -- finally have a measurement tool that can properly evaluate their effect.
As Gil sees it, such a camera is just one part of a comprehensive management policy for urban traffic. As cities continue to streamline their use of data -- the Spanish city of Santander monitors everything from parking spots to street lamps -- the causes and consequences of traffic remain inexplicably mysterious.
That's something that people should take issue with. Gil says, "The public is the final customer for this product."
Inset photo via UC3M.