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Portable sensors enable monitoring of pollution on smart phones; inferring pollution maps with greater granularity

Aqi3
Left. EPA AQI map of the San Diego County region,with a box added to indicate UCSD campus. Right. AQI map generated using data collected by CitiSense for the UCSD campus area during a five-minute window on same date and time. Boxes represent pollution reading locations during that window. Nikzad et al. Click to enlarge.

Computer scientists at the University of California, San Diego have built a portable pollution sensors that transmit transmit their air quality readings to smart phones, allowing users to monitor air quality in real time.

In a study of 16 commuters using CitiSense, reported in a paper at the Wireless Health 2012 conference, the CitiSense measurements were found to vary significantly from those provided by official regional pollution monitoring stations, enabling the identification of pollution hot spots and microenvironments that would otherwise be difficult using typical monitoring.

Moreover, applying geostatistical kriging techniques to our data allows CitiSense to infer a regional map that contains considerably greater detail than official regional summaries. These results suggest that the cumulative impact of many individuals using personal sensing devices may have an important role to play in the future of environmental measurement for public health.

—Nikzad et al.

Citisense
A view of the inside of the CitiSense sensor: the three cylindrical components detect ozone, nitrogen dioxide and carbon monoxide. Click to enlarge.

The CitiSense sensors detect ozone, nitrogen dioxide and carbon monoxide, the most common pollutants emitted by cars and trucks. The user interface displays the sensor’s readings on a smart phone by using a color-coded scale for air quality based on the EPA’s air quality ratings, from green (good) to purple (hazardous).

CitiSense is the only air-quality monitoring system capable of delivering real-time data to users’ cell phones and home computers at any time, the team says. 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.

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, according to the researchers. For example, San Diego County has 3.1 million residents, 4,000 square miles, and only about 10 stations.

We want to get more data and better data, which we can provide to the public. We are making the invisible visible.

—William Griswold, a computer science professor at the Jacobs School of Engineering at UC San Diego and the lead investigator on the project

Citisense2
User interface. Click to enlarge.

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. Computer scientists presented findings from these field tests at the Wireless Health 2012 conference in San Diego earlier this year.

Some of the sensors now are currently on loan to researchers at San Diego State University who are gauging air quality in San Ysidro, a community right on the border between the United States and Mexico, and one of the most polluted areas in San Diego County. Researchers hope to secure a grant from the National Institutes of Health to monitor air quality for school-age asthmatic children in that area and to determine what can be done to limit their exposure to pollutants.

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. The sensors currently cost $1,000 per unit, but could be mass-produced at a more affordable price.

In addition to principal investigator Griswold, the CitiSense team included School of Medicine and Calit2 professor Kevin Patrick; computer science professors Ingolf Krueger, Tajana Simunic Rosing, Hovav Shacham and Sanjoy Dasgupta; as well as graduate students and postdoctoral researchers Piero Zappi, Nima Nikzad, Elizabeth Bales, Celal Ziftci, Nichole Quick and Nakul Verma.

A key factor in the project’s success was a breakthrough made by a group led by Dasgupta. The group used a method called Latent Variable Gaussian Regression to capture high-quality data from the sensors in an uncontrolled environment. The method allowed researchers to remove noise from the data.

Sensors will differ. Sensors will fail. People will breathe on them. We wanted to make sure we got good data in these conditions.

—William Griswold

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.

CitiSense is funded by a $1.5 million grant from the National Science Foundation. Qualcomm, Inc. donated funds for the cell phones used for the project.

Resources

Comments

Stanley Garland

Can someone enlighten me as to the practical application of such a technology? It seems pretty novel in that it makes the cell phones into air sensors but how could that be used?

ToppaTom

I think they want to spread many sensors around to get a more detailed map of pollution and monitor them more often to get a better time plot.

I don't know why they would want to use cell phones as relays, maybe short range sensors are cheaper and cell phone users would cough up some cash (and get up-to-date data in return).

ai_vin

@Teach
They're not turning cell phones into sensors, they've just made portable pollution sensors that transmit their air quality readings to smart phones. Based on the picture, the actual sensor is very small so TT is likely correct about the short range and the need to use relays.

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