Articles | Volume 10, issue 12
Atmos. Meas. Tech., 10, 5039–5062, 2017
Atmos. Meas. Tech., 10, 5039–5062, 2017

Research article 21 Dec 2017

Research article | 21 Dec 2017

On Aethalometer measurement uncertainties and an instrument correction factor for the Arctic

John Backman1, Lauren Schmeisser2,a, Aki Virkkula1,3,4, John A. Ogren2,5, Eija Asmi1, Sandra Starkweather2,5, Sangeeta Sharma6, Konstantinos Eleftheriadis7, Taneil Uttal5, Anne Jefferson2, Michael Bergin8, Alexander Makshtas9, Peter Tunved10, and Markus Fiebig11 John Backman et al.
  • 1Finnish Meteorological Institute, Atmospheric Composition Research, Helsinki, Finland
  • 2University of Colorado Boulder, Cooperative Institute for Research in Environmental Sciences, Boulder, USA
  • 3University of Helsinki, Department of Physics, Helsinki, Finland
  • 4Nanjing University, Joint International Research Laboratory of Atmospheric and Earth System Sciences, Nanjing, China
  • 5National Oceanic and Atmospheric Administration, Earth System Research Laboratory, Boulder, USA
  • 6Environment and Climate Change Canada, Climate Research Division, Downsview, Canada
  • 7Institute of Nuclear and Radiological Science and Technology, Energy and Safety, Environmental Radioactivity Laboratory, NCSR “Demokritos”, Athens, Greece
  • 8Duke University, Civil and Environmental Engineering, Durham, USA
  • 9Russian Federal Service for Hydrometeorology and Environmental Monitoring, Arctic and Antarctic Research Institute, St. Petersburg, Russia
  • 10Stockholm University, Department of Environmental Science and Analytical Chemistry, Stockholm, Sweden
  • 11NILU – Norsk institutt for luftforskning, Dept. Atmospheric and Climate Research (ATMOS), Kjeller, Norway
  • anow at: University of Washington, Department of Atmospheric Sciences, Seattle, USA

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.

Short summary
Light absorption by aerosol particles is of climatic importance. A widely used means to measure aerosol light absorption is a filter-based measurement technique. In remote areas, such as the Arctic, filter-based instruments operate close to their detection limit. The study presents how a lower detection limit can be achieved for one such instrument, the Aethalometer. Additionally, the Aethalometer is compared to similar instruments, thus improving measurement inter-comparability in the Arctic.