A small error in the model equation has been identified and was corrected on 28th April 2009. This error concerned the temperature and pressure correction applied to the reported TEOM concentrations. This resulted in an underestimation of the TEOM_VCM concentration of approximately 4% at background locations; an analysis of the impact of this error on the 2007 AURN measurements can be seen on the graoh to the left.

Concentrations calculated using the VCM before this date should therefore be recalculated. To help with this process the correction xls spreadsheets that have been generated using the VCM Web Portal have been regenerated and can be downloaded from VCM web portal.

Unfortunately, the details for all the corrections made are not available to us, specifically, if you made more than one correction in a visit to the web portal then only the last correction made will have been saved.

We apologise for the inconvenience caused. This error affects the application of the VCM to TEOM measurements through the VCM web portal. It does not affected the underlying basis of the VCM and its proven equivalence to the EU reference method.

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Item date 01/05/2009