Questions & answers

Posted by .

How do I join the campaign and where can I obtain the iSPEX add-on?

The iSPEX add-on is available for free in all participating cities. Please contact the local organiser in your city to join iSPEX-EU and obtain an add-on.

Where can I obtain the iSPEX app?

The iSPEX app is available for download in the App Store.

What are these so-called aerosols and where do they come from?

Aerosols are tiny, solid particles and liquid droplets drifting in our atmosphere. Examples of aerosols are soot, sea salt, tiny sand particles, and volcanic ash.

Where do these aerosols come from?

Most of these aerosols –about 90 percent– are of natural origin. Typical sources are sea-spray, volcanic eruptions, forest fires, and sand storms. The remaining 10 percent of aerosols are anthropogenic, or human-made, and have a wide variety of origins. Anthropogenic aerosol sources include traffic, industry, biomass burning.

How tiny are these aerosols that we measure with iSPEX?

Aerosols typically range in size from a few nanometers –less than the size of the smallest viruses– to several tens of micrometers –the diameter of a thin human hair–.

Why do scientists need to know about aerosols? What does iSPEX want to achieve?

Aerosols are an important part of air pollution. To assess the impacts of aerosols on health, climate, and air traffic, the properties of aerosols –their type, size, and origin, dynamics and behaviour in the atmosphere– must be measured in fine detail. With iSPEX you can turn your smartphone into an optical sensor to measure these aerosol properties, at technically any location and any daytime hour. iSPEX-EU aims to form a network of thousands of people that perform iSPEX measurements, a network that can provide aerosol information at locations and times that are not covered by current professional monitoring efforts. So, by joining iSPEX-EU you can contribute to aerosol science!

How does iSPEX work?

Aerosols interact with sunlight —they scatter and absorb sunlight, and they change its polarization (a property of light). With iSPEX you measure both the sunlight intensity and polarization. This means that an iSPEX measurement contains information on the amount and on the type and size of aerosol(s) in the atmosphere. On a very sunny day with a perfect blue sky without any clouds or aerosols the sunlight that you can observe at the Earth’s surface is at its most intense and it is polarized. In contrast, on a very hazy day with a large amount of aerosols the sunlight is far less intense and polarized.

What do I do with the polarizer that comes with the iSPEX add-on?

The polarizer can make any light into completely polarized light. Hold it in front of iSPEX and turn it around and see how this changes the live spectrum in the app. The polarizer is not needed to perform an iSPEX measurement.

My iSPEX app doesn’t work. How can I solve this?

When you encounter technical issues with the iSPEX app, please make sure first that you have:

  • OS7 or higher running on your iPhone (4/4S/5/5S)
  • Installed the latest version of the app
  • Switched on location services (to be found under settings > privacy). This is needed for the app to add your location to your measurement —such that it can be placed on the iSPEX live map and taken along in the post-processing to obtain the iSPEX map of aerosol information over your city— and to work with the compass—to capture the measurement angles at which the app takes the pictures during the scan that you make
  • Appropriate internet connection (3/4G, with data roaming switched on, or Wifi) to share and upload your iSPEX measurement (this is a data package of ~200-600 kB, containing the pictures, location and angular information). iSPEX measurements are not stored in the app or elsewhere on your iPhone.

Check the latest app version its known issues. A general description of the app can be found here.

None of the above solves your problem? Please then contact us through

When starting the measurement the app reports the ‘iSPEX add-on is not found’. What is the problem?

Sometimes the app does not recognise the add-on. This could mean the add-on is either not placed correctly -check the measurement guidelines to see how it should be attached appropriately. It could also mean that when starting up the measurement, the iSPEX add-on is pointed at something which is too dark. For example, when pointed at the dark road, it might not see enough of a spectrum and thinks that it is not attached. To solve this, it is best to point iSPEX at something bright such as the sky when starting up. 

After taking a measurement with iSPEX I am asked to fill out my name. Is this needed?

No, providing your name is optional. If you do provide your name, it will be shown on the live map accompanying your measurement.

What does my color-code representation of the sky condition mean?

Dark blue means your measurements indicate a very clear sky with a minimal amount of aerosols. Light blue represents a clear sky (a small amount of aerosols), light brown a slightly hazy sky (a moderate amount of aerosols), and dark brown a very hazy sky (a large amount of aerosols).

What happens with my iSPEX measurement after I have shared it?

The preliminary result – the color-coded representation of your sky condition based upon your iSPEX measurements – will appear on the live map in the app and on this website. After the campaign, all iSPEX measurements will be analysed and processed carefully to obtain maps of iSPEX-based aerosol information over Europe. This step is required to filter out measurements that contain buildings and obtain the most accurate result. The final maps of iSPEX-based aerosol information will be published on this website.

A preview of how such a map would look like can be viewed here. The scientific results, including the final maps of iSPEX based aerosol information, of our initial citizen campaign in the Netherlands in 2013 are described here.

iSPEX app latest release

Latest release: v2.0.7
Release date: 5 October 2015.
Known issues:

  • The color-code may sometimes vary randomly. This is due to incontrollable behaviour of the iPhone camera and is corrected for in our post-processing —after you have shared your measurement.