Build a low-tech air quality sensor
During recent years, collective awareness regarding air quality issues has risen among Europeans. Citizens across Europe feel misinformed regarding air quality issues in their country.
The hackAIR cardboard sensor aims to provide an answer to those worries. Built with low cost, commercially available off-the-shelf products, is an easy to use module, designed to provide reliable measurements about the concentration of air pollutants.
How it works
The sensor consists of an empty milk box covered with petroleum jelly exposed for 24 hours on the PMs. After collecting the milk box and using a smartphone macro-lens a picture is taken as close as possible.
The smartphone runs the computer vision algorithms on the captured photo and send the results to the central hackAIR system.
1. Get an empty carton of milk, clean it and let it dry.
2. Cut square pieces with dimensions 5cm x 5cm.
3. Along the diagonal axis of your choice draw two small dots with the tip of a pencil, near the centre of the test surface.
4. Bend the surface slightly outward, along the same diagonal axis you chose earlier. This, will result to a constant capture of air particles, on the surface.
5. Pierce the upper right corner and put a thread through the whole.
6. At the lower left corner, adjust a counter weight (batteries, paper clippers, coins, etc).
7. Apply a small amount of petroleum jelly on the test surface using the butter knife. Before applying the petroleum jelly, make sure the test surface is clean and completely dry.
Where should I place my sensor?
Place the sensor at your balcony or outside your window. Make sure the test surface (the one with the petroleum jelly), is facing towards the general wind direction.
For better results, it is recommended to keep the hackAIR COTS sensor dry, and the test surface clean before the application of petroleum jelly.
How to capture your image
After 24 hours of constant exposure, retrieve the sensor. When you exceed the 24 hour exposure the COTS sensor is useless and you need to replace it simple because it is not predicted by the algorithm or the pilot measurements which are currently contacted by the writer. Also, exposing the test surface for less than 24h, will result in a lower amount of accumulated air particle in the Vaseline layer.
Place the aforementioned macro lens on top of the two small dots, you previously drew. Let your mobile adjust the focus of its camera and capture your image. Use flash if necessary (if the picture is dark, due to poor lighting inside the room using flash is recommended).
Upload the photo on the hackAIR app (there are instructions there).
Depending on your lens model the necessary distance between the lens and the test surface may differ. Make sure you read the manual of your lens model first.
When you buy lens, make sure they are super macro and not just macro. Macro lenses do not offer the necessary zoom for capturing the desired picture. A simply comparison between the macro and super macro lens could be read here.
You should aim for the two dots you made with your pencil during the preparation of the sensor. As mention above, the necessary distance between the lens and the test surface may differ depending on the lens you use.