Measurement guidelines

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Thank you for participating in iSPEX-EU, the first Europe-wide citizen campaign of the iSPEX project! With your help and that of thousands of other people, this will be the largest-ever citizen campaign for air pollution.

Please follow the measurement guidelines outlined below:

All iSPEX measurements are done on cloud-free days and in daylight. Before you start, make sure you have the iSPEX add-on and your iPhone –with the iSPEX app installed– at hand. To perform an iSPEX measurement, go outdoors and proceed as follows:

  1. Find an open space such as a square, park, or similar location where there are no objects –e.g. buildings, trees or otherwise –obstructing your view on the sky.
  2. Place the add-on onto your phone, in front of the main camera. Start the app.
  3. Make sure the sun is behind you. Hold your iPhone with iSPEX in front of you, with your arm fully extended and in-line with your shadow. The iPhone should be held vertically, such that you can see the screen and iSPEX points at the horizon. Click ‘Proceed’ to start.
  4. Slowly move your arm upwards to scan the sky, until your arm is in a vertical position.
  5. Repeat this last step to take a second measurement. This second measurement is needed.
  6. Your preliminary result, a color-coded representation of your sky condition based upon your measurements, is now shown.
  7. Press ‘Share’ to upload your measurements to the iSPEX database. Note: this may take few minutes depending upon your Internet connection (Wifi or 3/4G). No connection available? Keep the app activated and get to a location with connection within 10 minutes to submit your measurements.
  8. Once your measurement is submitted, a map with all preliminary iSPEX measurement results is shown. You can also view this map on

Note: The polarizer that comes with the iSPEX add-on is not needed to take an iSPEX measurement.

Although iSPEX measurements can be made at all times during the day provided there is daylight, most useful times for measurements with iSPEX are the first part of the morning and late afternoon, at  7-11 am and 4-8 pm local summer time.

You can download these measurement guidelines also in .pdf.

iSPEX manual

iSPEX manual

More questions? Please visit our Questions & Answers page where we provide answers to frequently asked questions.