Comparison of integrated filter and automated carbon aerosol measurements at Research Triangle Park, North Carolina

Abstract

Carbon aerosol measurements from the Rupprecht & Patashnick Series 5400 carbon analyzer, the Magee Scientific AE-21 Aethalometer and a filter-based Andersen RAAS2.5-410 Chemical Speciation sampler with quartz filters analyzed by Thermal Optical Transmittance (TOT) were compared. The Series 5400 total carbon (TC) and organic carbon (OC) were moderately correlated (r = 0.64 and 0.67) with the RAAS TOT method and the elemental carbon (EC) was poorly correlated (r = 0.37). The 5400 underestimated the RAAS TC and OC by 64% and 78%, respectively. The underestimate is attributed in part to the positive OC artifact of the filter-based sampling method. Another difference between the 5400 measurements and the RAAS TOT is a correction for char. The lack of correction for any char that occurs in the 5400 could cause and underestimate of OC and an overestimate of EC. The 5400 overestimated RAAS EC by 89%. The Aethalometer black carbon (BC) was compared to the 5400 EC and the RAAS TOT EC measured. The Aethalometer BC correlated well (r = 0.86) with the RAAS EC, but the Aethalometer overestimated the RAAS EC by 30%. The 5400 EC was compared to Aethalometer BC both with and without a PM2.5 size selective inlet. The correlations were 0.92 (inlet) and 0.55 (no inlet). The 5400 overestimated the mean Aethalometer BC by 17% with the inlet and 39% without. The improvement in results may not be due to the addition of the PM2.5 inlet, but instead may be due to a difference in the amount of char formed by the 5400. Factors contributing to the differences in these results are discussed.