iSpex is a plastic contraption that can be clipped on top of a smartphone’s camera. In this simple slit spectrograph light is defracted and polarized by shining through birefringent plastic sheets and a polarisation film. iSpex measures how aerosoles – microscopic or nanoscopic particles hovering in the athmosphere – change the polarization of the highly polarized light that shines from an unclowded, blue sky. This change in polarization renders a distinct pattern in the spectrum, that is cast by the iSpex-device into the phone’s camera. By this approach, iSpex can measure how the air is polluted with particulate dust, which is regarded especially unhealthy and has become topic of fierce political discussions, when the EU ordered city governments to regulate and even lock out automotive traffic.

Behind iSpex stands a consortium of the Netherlands Research School for Astronomy at University of Leiden, Netherlands Institute for Space Research (SRON), National Institute for Public Health and the Environment (RIVM), and the Royal Netherlands Meteorological Institute (KNMI).

Over the course of summer and autumn 2013, thousands of people in the Netherlands participated in “national iSpex days”, jointly measuring particulate dust. The first results of this awesome social effort are published, and we can hope this project will find epigones in other countries.

iSpex website:
Measuring aerosols with spectropolarimetry