On a possible bias in elemental carbon measurements with the Sunset thermal/optical carbon analyser caused by unstable laser signal

We present results that demonstrate a possible bias in the fractioning of total carbon (TC) into elemental carbon (EC) and organic carbon (OC) for measurements with the Sunset Laboratory Inc. Thermal/Optical Carbon Aerosol Analyser. The bias is caused by an unstable laser transmission signal. The transmission signal during the analysis of an instrument blank filter can give an indication of the possible bias. If the transmission signal around the OC/EC split point deviates from its initial value, the EC attribution is altered. In a sensitivity study, we show that for a deviation of 10% the EC content is substantially biased.