Click to test air quality

Computer scientists from Viterbi School of Engineering, University of Southern California, USA, launched software that uses the sky’s pictures to test air quality. Sameera Poduri, who worked on the project, explained the technology to Shruti Chowdhari

By Shruti Chowdhari
Published: Sunday 31 October 2010

What inspired you to monitor air pollution through a cellphone?

imageIn Los Angeles, we always worry about air quality. In the past few years, there has been a revolution in the cellphone technology. They are equipped with programmable sensors like cameras, GPS systems and compasses.

If each phone can act as a crude mobile weather station, we can easily monitor air quality.

Explain the concept of this application.

We invented free software. The sky’s visibility is directly related to concentration of harmful haze aerosols, tiny particles, dust or water droplets and engine exhaust in the air. Such aerosols turn the blue of a sunlit clear sky gray.

The user must take a picture of the sky in a direction that excludes buildings, trees and clouds. The phone’s accelerometers and compass capture its position in 3D, while the GPS data and time compute the sun’s position. It calculates the camera and solar orientation.

It uploads this data with the image—a small (100 KB) black and white file—to a central computer, which analyses the image to estimate pollutant content and returns a message to the user. The computer registers the data. We have an Android application which can be used in India and an iPhone application is enroute.

imageWhat are the drawbacks of this technology?

The software Visibility is not precise and estimates only an aggregate visibility value measuring transparency of air or visual range. So, it cannot investigate the chemical nature of the pollutant. The image must focus all or mostly on the sky, which makes user judgment critical.

Since the application is only a prototype, we are trying to improve the models and algorithms. A lot of these changes will be based on data and feedback received from users whose judgement is critical for accuracy.

In what way is the data received from this application helpful?

One of the biggest challenges with air pollution monitoring is that the sensors are expensive and sparsely deployed. Crowd-sourcing by employing many users with smartphones, will help fill gaps in the existing maps of air quality.

Therefore, contribution of photographs by users is extremely critical. We hope that maximum users download and try the application to help us improve our software.

Subscribe to Weekly Newsletter :

Comments are moderated and will be published only after the site moderator’s approval. Please use a genuine email ID and provide your name. Selected comments may also be used in the ‘Letters’ section of the Down To Earth print edition.