Last year we reported on a novel experiment in citizen science (iSPEX) involving a smart phone and a measurement of atmospheric dust levels (here). The official results are now published in Geophysical Research Letters (open access!) and the article has no less than 3203 authors! Must be a world record. OK, that figure is not entirely honest: the article has 16 named authors and mention is made of another 3187 iSPEX citizen scientists. On three sunny measurement days each several thousands of submissions were collected. Basically a measurement involved attaching a small plastic optical device to the camera of the smart phone, taking several photo's of the blue sky at different angles and upload them to the research group.

The aerosol optical thickness results were collected on a map of the Netherlands and compared to that of satellite data provided by MODIS (niche use: tracking wildland fires). Compared to MODIS the resolution of iSPEX was larger (2 km compared to 10-20 km) and overall the researchers state they are happy with agreement between the two methods. A comparison with the AERONET network was also deemed favourable.
On July 8 2013 (measurement day 1) the main source of aerosols in The Netherlands were North-American forest fires. The formation of Cirrus clouds did not help but later in the afternoon wind from the sea started to provide fresh air at least to the northern provinces.