Abstract
Abstract. 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 stations from 2012 to 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 minimised. Moreover, by using an attenuation threshold criterion for data post-processing, the relative uncertainty from the electronic noise of the instrument is kept constant. This approach results in a time series with a variable collection time (Δt) 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 ( > 2.1–6.7 Mm−1 as measured by the Aethalometers). At high aerosol concentrations, minimising the detection limit of the instrument is less critical. Additionally, utilising co-located filter-based absorption photometers, a correction factor is presented for the Arctic that can be used in Aethalometer corrections available in literature. The correction factor of 3.45 was calculated for low-elevation Arctic stations. This correction factor harmonises Aethalometer attenuation coefficients with light absorption coefficients as measured by the co-located light absorption photometers. Using one correction factor for Arctic Aethalometers has the advantage that measurements between stations become more inter-comparable.
Highlights
Black carbon (BC) and soot, which originate from incomplete combustion, are potent absorbers of solar radiation and comprise a complex part of the climate system (Bond et al, 2013)
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 (> 2.1–6.7 Mm−1 as measured by the Aethalometers)
The purpose of the correction factor (Cf) values here is to provide a general value that can be used in place of the correction factor (Cref) value for the Arctic, in order to harmonise the determination of σap from Aethalometers in the Arctic with other methods for determining aerosol light absorption coefficients
Summary
Black carbon (BC) and soot, which originate from incomplete combustion, are potent absorbers of solar radiation and comprise a complex part of the climate system (Bond et al, 2013). Weingartner et al, 2003), the particle soot absorption photometer (PSAP; Bond et al, 1999; Virkkula et al, 2005), and the multi-angle absorption photometer (MAAP; Petzold and Schönlinner, 2004; Petzold et al, 2005) These instruments report either equivalent black carbon (eBC) mass concentrations or light absorption coefficients (Petzold et al, 2013). Using the adaptive collection time method of data collection we present an Arctic correction factor (Cf) value to harmonise Aethalometer absorption measurements to other filter-based light absorption photometers. This correction factor can be used in existing Aethalometer correction schemes available in literature
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