Smartphone optical system reveals airborne dust concentration

28 May 2014

Scientists at KIT, Karlsruhe develop system for mobile devices to create crowd-sourced pollution map.

Health conditions caused by fine dust pollution have been highlighted in recent reports from big cities such as Beijing and, more recently, Paris. But if you wish to know about the scale of this problem in your local environment, what can you do? For example, what is the pollution concentration around your favorite jogging route? A relatively cheap and simple solution may soon be at hand.

Scientists at Germany’s Karlsruhe Institute of Technology (KIT) are developing a sensor that can easily be connected to a smartphone. The aim is that users will work together to produce a pollution map via participatory sensing.

KIT computer scientist Matthias Budde, who developed the system as a member of TECO, KIT’s research group, explained the principle of fine dust measurement by smartphone: “Instead of a conventional infrared LED in the sensor, the phone’s flash emits light into the measurement space. The light is scattered by any dust or smoke particles and the camera serves as a receptor and takes a picture representing the measurement result. The brightness of the pixels can then be converted into the dust concentration.”

Accuracy

The computer scientists have carried out comparative measurements to prove that the principle works. The smartphone sensors are not yet as precise as specialized instruments. However, their costs are much lower. Budde added, “Detectors at the official measurement stations operated by the Baden-Württemberg State Agency for the Environment, Measurement & Nature Conservation are precise, but also large, expensive and static. In Karlsruhe, for instance, only two such measurement stations have been established.”

Budde is planning to enhance accuracy by using a high measurement density by combining results from many sensors closely arranged in a given area. Sensors so arranged might also be calibrated against each other. He is hoping that such “crowd-sourced” data could be created by interested citizens who measure data at various places in their city and share them, together creating a fine dust pollution map for a whole city in real time.

He described the simple technical arrangement of the dust sensor thus: “It is attached to the smartphone by means of a magnet. Adaptation of electronics is not be required. Users who want to join participatory sensing will have to download the corresponding app. At the measurement point desired, the sensor is attached to the cell phone and the users take a photo or a video of the atmosphere. Images can be evaluated locally or transmitted to a central computer that combines and proesses them. Then, the fine dust concentration is displayed by the user’s phone.”

Presently, the smartphone sensor can measure concentrations of about one microgram per cubic meter. This is sufficient for detecting coarse dust and smoke, but not for typical fine dust concentrations in the microgram range. The KIT scientists now plan to further increase the sensitivity of the sensors by bundling the flash in the sensor with hemispherical lenses. This principle has been achieved in a smaller second prototype.

It is also planned that the devices will no longer compress the photos automatically, but supply raw data, which should further increase the accuracy of the measurement. Budde believes that a smartphone sensor able to detect typical fine dust will be developed next year.

Powerful and versatile phones

Scientists working in a variety of disciplines have in recent years been taking advantage of the quality optics and microelectronics available in smartphones to develop a range of economical and versatile mini-labs and sensors, such as the Finnish-Swedish development of a mini microscope, in which samples are placed directly on the phone’s image sensor, as reported by optics.org in December 2013.

Below is a video showing KIT’s smartphone approach to measuring fine dust concentration (in German) :

About the Author

Matthew Peach is a contributing editor to optics.org.