19 Dec 2012

Sensors in smartphones monitor pollution

Researchers from the Department of Computer Science, University of California, San Diego, have built a small fleet of portable pollution sensors that allow users to monitor air quality in real-time on their smart phones.

Dubbed CitiSense, the system is reported to be the only air-quality monitoring system capable of delivering real-time data to users’ mobile phones and home computers.

Data from the sensors can also be used to estimate air quality throughout the area where the devices are deployed, providing information to everyone, not just those carrying sensors.

“We want to get more data and better data, which we can provide to the public,” said William Griswold, a computer science professor at the Jacobs School of Engineering at UC San Diego and the lead investigator on the project. “We are making the invisible, visible.”

According to Griswold, just 100 of the sensors deployed in a fairly large area could generate a wealth of data—well beyond what a small number of EPA-mandated air-quality monitoring stations can provide. For example, San Diego County has 3.1 million residents, 4,000 square miles—and only about 10 stations.

The CitiSense sensors detect ozone, nitrogen dioxide and carbon monoxide, the most common pollutants emitted by cars and trucks.

The user interface then displays the sensor’s readings on a smart phone by using a colour-coded scale for air quality based on the EPA’s air quality ratings, from green (good) to purple (hazardous).

Researchers provided the sensors for four weeks to a total of 30 users, including commuters at UC San Diego and faculty, students and staff members in the computer science department at the Jacobs School of Engineering.

Users discovered that pollution varied not only based on location, but also on the time of the day.

For example, when Charles Elkan, a professor in the Department of Computer Science and Engineering, drove into work in mid-morning, the readings on his sensor were low.

But when he drove back home in rush hour in the afternoon, readings were sometimes very high.

"Being part of the study allowed [me] to gauge how worried about pollution I should actually be," he said. "However, air quality in San Diego is fairly good."

Elkan envisions a day in the near future when the sensors used by CitiSense will be built into smart phones, allowing virtually everyone to keep tabs on the levels of pollution they encounter every day.

"The ultimate goal of CitiSense is to build and deploy a wireless network in which hundreds of small environmental sensors carried by the public rely on cell phones to shuttle information to central computers where it will be analyzed, anonymized and delivered to individuals, public health agencies and the community at large," he says. "The sensors currently cost $1,000 per unit, but could easily be mass-produced at an affordable price."

Technical challenges remain; the data exchanges between smart phones and sensors use up a great deal of the phones’ batteries.

During field tests, researchers provided users with two chargers—one for home and one for work—to ensure that their phones were not going to run out of power.

To extend battery life, researchers are experimenting with uploading data from the sensors to the phones every 15 minutes or only when the user wants to retrieve the information.

Methods to turn off a phone’s GPS—a huge drain of the devices’ batteries—when the device is immobile have also been developed.

Photo credit: Jacobs School of Engineering

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