A Simple Procedure for Correcting Loading Effects of Aethalometer Data

TLDR

The study presents a simple method to correct aethalometer loading effects. The correction uses the formula BC_corrected = (1 + k·ATN)·BC_noncorr, applied to data from three Finnish sites and compared with simultaneous aerosol volume measurements. The correction stabilizes the BC‑to‑volume ratio across filter spots, with k values showing a clear seasonal cycle—high in winter and wavelength‑dependent (often negative) in summer—indicating the algorithm effectively adjusts for loading effects.

Abstract

Abstract A simple method for correcting for the loading effects of aethalometer data is presented. The formula BC CORRECTED = (1 + k ATN)∙BC NONCORRECTED, where ATN is the attenuation and BC is black carbon, was used for correcting aethalometer data obtained from measurements at three different sites: a subway station in Helsinki, an urban background measurement station in Helsinki, and a rural station in Hyytiälä in central Finland. The BC data were compared with simultaneously measured aerosol volume concentrations (V). After the correction algorithm, the BC-to-V ratio remained relatively stable between consequent filter spots, which can be regarded as indirect evidence that the correction algorithm works. The k value calculated from the outdoor sites had a clear seasonal cycle that could be explained by darker aerosol in winter than in summer. When the contribution of BC to the total aerosol volume was high, the k factor was high and vice versa. In winter, the k values at all wavelengths were very close to that obtained from the subway station data. In summer, the k value was wavelength dependent and often negative. When the k value is negative, the noncorrected BC concentrations overestimated the true concentrations.