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

摘要

pstrongAbstract./strong 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 637span class="thinspace"/spannm. 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 (Junea??September??2014). The mean absorption coefficient (at 637span class="thinspace"/spannm) during this period was 1.8span class="thinspace"/span?±span class="thinspace"/span2.1span class="thinspace"/spanMmsupa??1/sup, with a maximum of 15.9span class="thinspace"/spanMmsupa??1/sup. 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 ??ngstr??m exponent (i?￥/isubABS/sub) retrievals. Proper Aethalometer data compensation schemes are crucial to retrieve the correct i?￥/isubABS/sub, 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 i?￥/isubABS/sub retrieved from offline MWAA measurements./p.