A report of the scientific flight from Oberpfaffenhofen/Germany with the research aircraft Falcon 20E D-CMET, that was performed successfully yesterday and took measurements is available.
The report can be downloaded as PDF from
http://www.bmvbs.de/Anlage/original_...April-2010.pdf
Quoting from this
Assuming a particle density of 2 g/cm³ our current best estimate for the particle mass concentration in the ash plume over Leipzig is 60 μg/m³. The error is difficult to estimate without further analysis but at least a factor of 2 uncertainty should be assumed. It is possible that higher concentrations occur in other parts of the plume. In fresh volcanic plumes the concentrations will be much higher.
The cloud was 4-5 days old at this point.