On the measurement of absorption with an OC/EC analyser
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We present a novel methodology to measure aerosol absorbing properties and mass metric quantities simultaneous in a single instrument. The laser in an OC/EC analyser, which measures organic carbon (OC) and elemental carbon (EC), is used to measure the attenuation coefficient of a filter laden with aerosol. A single calibration to the Multi-Angle Absorption Photometer (MAAP), which is in our study used as a reference method, is needed to link the attenuation by aerosol on the filter to the absorption coefficient of the aerosol in ambient air. We show that the attenuation coefficient with this method can be determined within a precision of 9.6%. The results of an independent data set show that the results of this methodology are comparable to widely distributed commercial absorption photometers. We further demonstrate that an unstable laser transmission signal in the Sunset Thermal/Optical Carbon Analyser possibly causes a bias in the fractioning of total carbon (TC) into OC and EC. The laser transmission signal during the analysis of instrument blank filters can give an indication of the possible bias. A deviation of the laser transmission signal of 10% leads to a substantial bias in EC content. It is therefore important to monitor the stability of the laser transmission signal during an instrument blank analysis frequently.