Bicyclists and public-bus commuters in San Diego are exposing themselves to a whole lot of crap in the air, according to new research.

Well, how's this for a kick in the Pearl Izumi thermal tights: Bicycling to work might help reduce your carbon footprint, but may also be terrible for your heath.

That's the frustrating word from a team of scientists at the University of California, San Diego, who are testing out the crowdsourcing of air-pollution monitoring. The researchers gave smartphones that sense pollution to 30 study participants, and then tracked their environmental data feeds for a month. The upshot was that the participants doing the most to reduce carbon emissions by cycling or riding the bus "were the people who experienced the highest levels of exposure to pollutants," according to lead investigator William Griswold.

How is this even possible? It has to do with the fluid, inconsistent nature of air pollution. Over the course of a day, smog levels can rise or fall greatly along well-trafficked routes like highways and intersections. So if somebody decides to bike home during the evening near a pollution "hot spot," they could be sucking in a lot of foul stuff like ozone and carbon monoxide, say the scientists:

The sensors made this clear for users. Wendy Chapman, an associate professor at the UC San Diego School of Medicine, was one of them. She often bikes to work and discovered that pollution on her route varies widely. She was exposed to the most pollution when she used the bike path along State Route 56. But when she drove home on that same road, she had virtually no exposure.

What's so bad about taking the bus, then? In no big surprise, it turns out that bus stops and shelters are major hot spots for nasty air. Commuters get exposed to waves of exhaust while waiting for the coach to arrive or while queuing in line to board.

But it's not time to throw your Cannondale into the metal shredder, yet. The researchers found that by making minor adjustments in route, commuters can cut down on the pollution that seeps into their lungs. This might involve biking just one block removed from a busy street, for instance. Bus riders can minimize their doses of noxious gases by standing away from the back of the vehicle, where the air-quality stinks.

These conclusions are just one interesting thing to flow out of what Griswold's team is calling the CitiSense project. In the future, they hope to have a legion of tricked-out smartphone users moving through the city, establishing a real-time geographic map of air quality. People who don't have the phones can install an app that displays the data anyway. In this way, folks with breathing conditions like asthma will be able to chart their way around the toxic clouds that pop up over the course of the day. In a city like San Diego, which only has about 10 air-quality monitoring stations, this army of flesh-and-machine sensing units will provide a clearer picture of what's really in the air, block by block.

Top photo courtesy of smog over Westchester, Los Angeles, courtesy of Scazon on Flickr.

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