Measurements by thousands of citizen scientists in the Netherlands using their smartphones and the iSPEX add-on are delivering accurate data on fine air particles in the atmosphere that add valuable information to professional measurements. The scientific article that presents these first results of the iSPEX project is being published today in Geophysical Research Letters.

iSPEX is a new atmospheric measurement method in the form of a low-cost add-on for smartphone cameras. The iSPEX-app instructs participants to scan the blue sky while the phone’s built-in camera takes pictures through the iSPEX add-on. The photos record both the spectrum and the linear polarization [2,3] of the sunlight that is scattered by suspended fine air particles, and thus contain information about the properties of these particles. While such properties are difficult to measure, much better knowledge on atmospheric particles is needed to understand their effects on health, climate and air traffic. Thousands of participants performed iSPEX measurements throughout the Netherlands on three cloud-free days in 2013. This large-scale citizen science experiment allowed the iSPEX team to verify the reliability of this new measurement method.

Maps of fine air particles

After a rigorous quality assessment of each submitted data point, measurements recorded in specific areas within a limited amount of time are averaged to obtain sufficient accuracy. Subsequently the data are converted to Aerosol Optical Thickness (AOT), which is a standardized quantity related to the total amount of atmospheric particles. The iSPEX AOT data match comparable data from satellites and the AERONET ground station at Cabauw, the Netherlands. In areas with sufficiently high measurement densities, the iSPEX maps can even discern smaller details than satellite data.

Citizen science network

The great strength of iSPEX is the measurement philosophy: the establishment of a citizen science network of thousands of enthusiastic volunteers who actively carry out outdoor measurements. In this way, valuable information can be collected about fine air particles on locations and/or at times that are not covered by professional equipment. Currently is being investigated to what extent more information can be extracted about atmospheric particles from the iSPEX data, as for example their sizes and compositions. Also more measurement days will be organised.
With the help of a grant that supports public activities in Europe during the International Year of Light 2015, the iSPEX team is now preparing for the international expansion of the project. This expansion provides opportunities for national and international parties to join the project. The final goal is to establish a global network of citizen scientists who all contribute measurements to study the sources and societal effects of polluting atmospheric particles.

Strategic Programme RIVM National Institute for Public Health and the Environment (SPR Strategic Programme RIVM )

The iSPEX project provides insight into the possibilities of gathering large amounts of research information with the help of involved citizens at a low cost. RIVM expects many more of these types of citizens’ initiatives to take place in the future. RIVM has the in-house knowledge to support citizen science by calibrating, compiling and interpreting the data, so that the data becomes more valuable for everyone. RIVM’s contribution to the iSPEX project is part of our Strategic Programme RIVM (SPR), which is directed to responding to key future issues and comprises many innovative projects.