Well, I think what Jumbodriver was trying to say was if the concentration, I guess the ppm of airborne minerals, was extremely low in general for the Icelandic volcano compared with the Indonesia BA09 event. They are really two different kettle of fish in many ways. Entirely different type of volcano too.

The impression I got was, and I could be wrong, that it was more of a problem determining where the higher concentrations are going to be at a given moment in time as it is constantly on the move in a three-dimensional fashion? After all, models are just digital crystal balls.

Also the make up of volcanic ash varies from one place to another, and in time at the same place - this can affect concentration and composition of the ash overhead on distant lands.

Plenty of variables to wrestle with, so I can why one or several might have erred on the side of caution.