Comparison of different Aethalometer correction schemes and a reference multi-wavelength absorption technique for ambient aerosol data

摘要

Deriving absorption coefficients from Aethalometer attenuation datarequires different corrections to compensate for artifacts related tofilter-loading effects, scattering by filter fibers, and scattering byaerosol particles. In this study, two different correction schemes wereapplied to seven-wavelength Aethalometer data, using multi-angle absorptionphotometer (MAAP) data as a reference absorption measurement at 637 nm. Thecompensation algorithms were compared to five-wavelength offline absorptionmeasurements obtained with a multi-wavelength absorbance analyzer (MWAA),which serves as a multiple-wavelength reference measurement. The onlinemeasurements took place in the Amazon rainforest, from the wet-to-drytransition season to the dry season (June–September 2014). The meanabsorption coefficient (at 637 nm) during this period was1.8 ± 2.1 Mm, with a maximum of 15.9 Mm. Under theseconditions, the filter-loading compensation was negligible. One of thecorrection schemes was found to artificially increase the short-wavelengthabsorption coefficients. It was found that accounting for the aerosol opticalproperties in the scattering compensation significantly affects theabsorption Ångström exponent () retrievals.Proper Aethalometer data compensation schemes are crucial to retrieve thecorrect , which is commonly implemented in brown carboncontribution calculations. Additionally, we found that the wavelengthdependence of uncompensated Aethalometer attenuation data significantlycorrelates with the retrieved from offline MWAAmeasurements.