The health limit is 50 µg/m3 for a 24 hour average, and on the 13 Feb that was exceeded at the station Grensásvegur, near big traffic streets in Reykjavik.
The measurements are taken every 30 min and the average of the 42 measurements (out of 48) which were recorded was 55 µg/m3 .
Traffic was, without doubt, the main source of PM10. Both emission, but also road wear and re-suspension of particulates on the road.
The wind was very slow, less than 2,5 m/s throughout the day. It was also cold, so a good chance there was a slight temperature inversion. Therefore both NOx emission and PM stayed in the air and build up during the day.
(I made this post originally in Icelandic, so I apoligize for the rough translation)
