Measurement Uncertainty in IMPROVE Aluminum and Silicon Concentrations when Sulfur Concentrations are High

摘要

Experimental results show that Si and Al mass measurements have large uncertainties when sulfur relative to soil content (S/Fe) is high in IMPROVE samples. These uncertainties in Si and Al masses were observed when ambient samples with an IMPROVE range of Si and Al masses and low sulfur content (measured by XRF) were modified by adding additional sulfur and then re-analyzed by XRF. We found that for 50% of IMPROVE data from 2002-2010, the S/Fe is low (less than 8) and the measurement of Si and Al is not impacted by the sulfur content in the sample. However, for samples with higher S/Fe ratios large uncertainties in both Si and Al are observed. The reported mass of Si on the treated samples increases with increasing S/Fe and is higher than the untreated ambient samples by up to 300 %. The enhancement in the Si data is likely due to a spectral interference caused by the large neighboring S peak. Aluminum measurements have increasing uncertainty in the observed mass with increasing S/Fe but no pattern to predict when a result is over or under-reporting the mass. This laboratory study confirms the existence of a sulfur interference in the CNL XRF system that had earlier been suggested and reported to data users in data advisories. The results apply to IMPROVE data from December, 1, 2001 through December 31, 2010. Beginning with January 1, 2011 data, CNL is utilizing new commercial PANalytical Epsilon 5 instruments for XRF analysis. A full report of this work is available online July 5, 2012, in Atmospheric Environment; Experimental characterization of sulfur interference in IMPROVE aluminum and silicon XRF data, Hege Indresand, Ann M. Dillner, http://dx.doi.org/10.1016/j.atmosenv.2012.06.079.