The principle of fine dust measurements using a smartphone corresponds to that of simple optical sensors.
"Instead of the conventional infrared LED in the sensor, the flashlight of the smartphone emits light into the measurement area. This light is scattered by the possibly existing dust or smoke," said computer scientist Matthias Budde.
"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," said Budde, who developed the system as a member of the research group TECO of Karlsruhe Institute of Technology (KIT)'s Chair for Pervasive Computing.
The smartphone sensors are not yet as precise as specialised instruments. However, their costs are much lower and Budde plans to enhance accuracy by a high measurement density.
Measurements of many, closely adjacent sensors may be combined to results of reduced inaccuracy.
Due to their close vicinity, the sensors might also be calibrated against each other.
Budde thinks that a potential application scenario is joint measurement or participatory sensing: Interested citizens measure data at various places in their city and share them.
These data may then be used to draw up a fine dust pollution map for the respective city in real time.
The sensor is planned to be attached to the smartphone by means of a magnet, for instance. Adaptation of electronics will 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 for measurement.
The images can be evaluated locally or transmitted to a computer system that combines these data with other measurements and sends them back. Then, the fine dust concentration is displayed by the phone.
Presently, the smartphone sensor can measure concentrations of about one microgramme per cubic metre. This is sufficient for detecting coarse dust and smoke, but not for typical fine dust concentrations in the microgramme range.