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Inter-laboratory comparison filter weighing 2011

Inter-laboratorium vergelijking filterwegingen 2011


Reference measurements of particulate matter (PM) in ambient air are performed by sampling a known volume of air through a filter for 24 hours. By measuring the mass difference of the filter before and after sampling the concentration of particulate matter may be determined. For this purpose filters are weighed at least twice under strict conditions of temperature and relative humidity, as prescribed in European Standards EN 12341 and EN 14907. In order to investigate whether application of this procedure - when applied by different laboratories - leads to comparable results, an inter-laboratory comparison has been conducted. For this purpose one pilot laboratory has sent sets of 12 filters typically used for low-volume sampling (8 loaded, 4 blanks) to other participating laboratories. After having been weighed by participants the filters have been reweighed by the pilot laboratory. In addition, the weighing conditions in participants' weighing rooms have been monitored using portable temperature/humidity meters. The monitoring results indicate that none of the laboratories has problems in meeting the requirements for weighing conditions given in EN 12341 and EN 14907. Evaluation of the results of the comparison shows that - when average results of the pilot laboratory are used as reference values and En scores are calculated using estimated weighing uncertainties - all results but one correspond with the reference values. From the results the inter-laboratory (reproducibility) uncertainty of the weighing results has been calculated and has been found to be 0,078 mg for a confidence level of 95 % for all filters. This corresponds to a relative uncertainty of 2,8% at the level of daily limit value for PM10.

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