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

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 ( t) but with a

Seasonality of aerosol optical properties in the Arctic

“…The other optical measurements (MAAP and nephelometer) are connected to a 2.5 µm size cut inlet. A more detailed description of aerosol optical measurements and sampling can be found in Lihavainen et al (2015) and in Backman et al (2017). A climatology of aerosol optical properties at PAL is presented by Aaltonen et al (2006) and Lohila et al (2015).…”

“…The Aethalometer absorption data corrected with the Backman et al (2017) correction factor are compared to absorption coefficients from the co-located absorption instruments to ensure that the corrected Aethalometer data are similar to absorption coefficients that are measured by other absorption instruments at the site. Although agreement between Aethalometer measured absorption and co-located instrument absorption is imperfect and variable among stations, corrected Aethalometer data from all sites are utilized in the remainder of this paper for analyses of absorption coefficients at all six Arctic monitoring stations.…”

“…The Magee Aethalometers are the only common absorption instrument among the six stations presented here, and this paper synthesizes the absorption data from Aethalometers across the Arctic. The Aethalometer data are corrected using the new Arctic-specific Aethalometer correction scheme presented by Backman et al (2017). We use the 'reference' co-located absorption instruments to gauge whether the corrected Aethalometer data are similar to what is expected for absorption coefficient values from…”

“…Here we use a new Arctic-specific Aethalometer correction factor from Backman et al (2017) to derive the light absorption coefficient from the Aethalometer data. Backman et al (2017) present an Arctic-specific multiple scattering enhancement factor, C f , derived from Aethalometer data and co-located absorption data from the same sites and time period used in this study. For all 20 wavelengths and for the five low-altitude sites (ALT, BRW, PAL, TIK, ZEP), the value for C f was found to be 3.…”

“…Arctic stations not included in this study 25 either do not measure the parameters presented here, or do not have continuous measurements for the period of interest. This time period was chosen to align with Backman et al (2017), which presents an Arctic-specific correction scheme for aethalometer data, to be used here to describe absorption coefficients at each of the stations.…”