PM measurements in ambient aerosol: comparison 2.5 between Harvard impactor žHI/ and the tapered element oscillating microbalance ž TEOM/ system

comparison, based on the regression of 32 daily mean PM2.5 aerosol loadings determined by a tapered element oscillating microbalance ŽTEOM. and by a Harvard impactor ŽHI., is reported for the ambient aerosol of Erfurt ŽGermany.. The PM2.5 concentrations measured by the TEOM were systematically lower then those obtained by the HI. The ratio of the means TEOM HI was 0.74 and the regression equation is TEOM 0.69 HI 0.071. This result is consistent with reports elsewhere suggesting that semi-volatile aerosol material is lost from the heated sample filter on the TEOM. To verify this assertion, a heating system was developed for the HI which was able to keep the HI sample filter at 50 1 C. After the implementation of this heating system, no systematically differences were observed between the TEOM and the heated HI system. The ratio of means was 1.06 and the regression equation TEOM 1.10 HI 0.668. Because the measured levels of ammonium nitrate were very low in Erfurt, we concluded that other compounds like semi-volatile organics were responsible for the loss of particulate material at 50 C.