On Aethalometer measurement uncertainties and multiple scattering enhancement in the Arctic

Other literature type English OPEN
Backman, John ; Schmeisser, Lauren ; Virkkula, Aki ; Ogren, John A. ; Asmi, Eija ; Starkweather, Sandra ; Sharma, Sangeeta ; Eleftheriadis, Konstantinos ; Uttal, Taneil ; Jefferson, Anne ; Bergin, Michael ; Makshtas, Alexander (2016)

Several types of filter-based instruments are used to estimate aerosol light absorption coefficients.Two significant results are presented based on Aethalometer measurements at six Arctic station from 2012&ndash;2014. First, an alternative method of post-processing the Aethalometer data is presented which reduces measurement noise and lowers the detection limit of the instrument more effectively than boxcar averaging. The biggest benefit of this approach can be achieved if instrument drift is minimized. Moreover, by using an attenuation threshold criterion for data post-processing, the relative uncertainty from the electronic noise the instrument is kept constant. This approach results in a time series with a variable collection time (Δ<i>t</i>), but with a constant relative uncertainty with regard to electronic noise in the instrument. An additional advantage of this method is that the detection limit of the instrument will be lowered at small aerosol concentrations at the expense of temporal resolution, whereas there is little to no loss in temporal resolution at high aerosol concentrations (>2.1&ndash;6.7 Mm<sup>&minus;1</sup> as measured by the Aethalometers). At high aerosol concentrations, minimizing the detection limit of the instrument is less critical. Second, utilizing co-located reference methods of aerosol absorption, a multiple cattering enhancement factor (<i>C</i></sub>ref</sub>) of 3.10 specific to low elevation Arctic stations is found. <i>C</i></sub>ref</sub> is a fundamental part of most of the Aethalometer corrections available in literature, and this is the first time a <i>C</i></sub>ref</sub> value has been obtained for the Arctic.
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