USC’s Android air pollution app takes a crowd-sourced approach to cleaner skies


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Were you to be given a report on the way you use your smart phone every day, it might tell you that it was 75% e-mail, 15% web browsing, 7% text messaging and 3% Angry Birds.

If you agree with that rough picture, then you agree that smart phones are very much ‘me-oriented’ devices. Any idea that we’d use our phones for the betterment of society is like, not really an idea.


But a few mad computer scientists at the USC Viterbi School of Engineering want the phone-toting public to open its eyes to that possibility. They’ve released an Android app called Visibility that offers a cool way for smart phones to join the fight against air pollution.

The app gets you to use your phone’s camera to take a photo of the sky -- wherever you are, and however frequently you like. The phone sends the image to a database at USC, where computers analyze it to determine how much particulate matter is in the air you’ve photographed.

As with any crowd-sourced application, the more people that takes pictures on a given day and in a given city, the more detailed -- and potentially useful -- the results will be.

The USC team has devised an algorithm that uses the phone’s location and the direction it was pointing to determine how bright the sun should be in your image. It then looks at your photo to see how much that theoretical sunlight has been obscured, and from that calculates how much gunk is in the air (it doesn’t work yet on highly cloudy days).

‘The initial results look promising,’ Gaurav S. Sukhatme, a USC computer science and robotics professor, said in an e-mail. ‘On small sample sizes, the numbers we produce are pretty close to the numbers we can get from conventional methods.

‘What we don’t know is how things will work when the numbers get large and there is a lot of variance in weather conditions and non-expert users do the data gathering.’


That’s where the Android community -- and soon, it seems, iPhone users -- come in. You basically just take a snapshot of the sky, crop out any buildings or other non-sky elements, and press send. You can opt to share your precise GPS data, or have the computer erase it if you’re feeling private.

In a paper on the app, Sukhatme points out that in the western skies, the natural visual range should be close to 140 miles on a clear day. But over the decades, man-made pollution has reduced that to between 35 and 90 miles. And then there are the numerous, oft-cited health risks of airborne particulates, including lung and heart problems.

Air-quality measurement equipment is expensive and often sparsely deployed. That can result in an incomplete picture of air quality in many cities. But if everyone becomes a portable weather sensing station, the flood of new data could provide a much clearer picture of the wide blue skies

-- David Sarno