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 Fiebig11John Backman et al. 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
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
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
Correspondence: John Backman (john.backman@fmi.fi)
Received: 12 Sep 2016 – Discussion started: 08 Dec 2016 – Revised: 08 May 2017 – Accepted: 10 May 2017 – Published: 21 Dec 2017
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.
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.
Light absorption by aerosol particles is of climatic importance. A widely used means to measure...
