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

TitleComparison of different Aethalometer correction schemes and a reference multi-wavelength absorption technique for ambient aerosol data
Publication TypeJournal Article
Year of Publication2017
AuthorsSaturno J., Pohlker C., Massabo D., Brito J., Carbone S., Cheng Y.F, Chi X.G, Ditas F., de Angelis I.H, Moran-Zuloaga D., Pohlker M.L, Rizzo L.V, Walter D., Wang Q.Q, Artaxo P., Prati P., Andreae M.O
JournalAtmospheric Measurement Techniques
Date Published2017/08
Type of ArticleArticle
ISBN Number1867-1381
Accession NumberWOS:000407382500001
Keywordsangstrom exponent; apportionment; atmospheric black carbon; brown carbon; light-absorption; Meteorology & Atmospheric Sciences; optical-absorption; particulate matter; photoacoustic; source; spectral dependence; spectrometer; wavelength dependence

Deriving absorption coefficients from Aethalometer attenuation data requires different corrections to compensate for artifacts related to filter-loading effects, scattering by filter fibers, and scattering by aerosol particles. In this study, two different correction schemes were applied to seven-wavelength Aethalometer data, using multi-angle absorption photometer (MAAP) data as a reference absorption measurement at 637 nm. The compensation algorithms were compared to five-wavelength offline absorption measurements obtained with a multi-wavelength absorbance analyzer (MWAA), which serves as a multiple-wavelength reference measurement. The online measurements took place in the Amazon rainforest, from the wet-to-dry transition season to the dry season (June-September 2014). The mean absorption coefficient (at 637 nm) during this period was 1.8 +/- 2.1Mm(-1), with a maximum of 15.9Mm(-1). Under these conditions, the filter-loading compensation was negligible. One of the correction schemes was found to artificially increase the short-wavelength absorption coefficients. It was found that accounting for the aerosol optical properties in the scattering compensation significantly affects the absorption Angstrom exponent ((a) over circle (ABS))retrievals. Proper Aethalometer data compensation schemes are crucial to retrieve the correct (a) over circle (ABS), which is commonly implemented in brown carbon contribution calculations. Additionally, we found that the wavelength dependence of uncompensated Aethalometer attenuation data significantly correlates with the (a) over circle (ABS) retrieved from offline MWAA measurements.

Short TitleAtmos. Meas. Tech.
Student Publication: