Aerosol optical properties monitoring.

At the Gruvebadet Aerosol Laboratory (GAL) aerosol scattering coefficient is measured at a single wavelength (530 nm) using a Radiance Research nephelometer. Data is acquired continuously at 1-minute time resolution.

For the scattering coefficient the truncation error correction is performed according to Muller et al. (2009) and assuming a scattering angstrom exponent of 1.15 (Schmeisser et al., 2018).

Aerosol light absorption is measured 7 wavelengths (370, 470, 520, 590, 660, 880, 950 nm) measured using an AETHALOMETER AE33 from Aerosol Magee Scientific. Data is acquired continuously at 1-minute time resolution.

We calculated aerosol absorption coefficient at seven wavelengths according to the formula reported by Drinovec et al. (2015). Corrected aerosol absorption coefficient was derived from the increment of aerosol attenuation measured over a time interval of 60 minutes (dATN). The attenuation was normalized by the sampling flow (F), corrected for the leakage factor z (1%), and the filter collection spot area (S=0.785 cm2). To take into account the loading effect, which would lead to an underestimation of aerosol absorption when filter loading increases, the normalized attenuation increment was divided by the factor (1-kATN), where k is derived from the simultaneous attenuation measurements on two different filter spots characterized by different sampling flows (Drinovec et al., 2015). The parameter k in formula (1) is the average value during the 1-hour time interval and it was calculated assuming that it varied linearly in time. The parameter C compensates for the enhancement of aerosol optical absorption due to the scattering of light by the filter fibers and it was equal to 1.39. Black carbon (BC) concentration derived from the aerosol absorption coefficient at 880 nm and assuming a Mass Absorption Cross section of 7.77 m2/g (according to the instrument manufacturer).

Both absorption and scattering coefficient measurements are normalized at standard pressure and temperature conditions (1 atm and 0 degC), averaged over a 1-hour period, and provided at all available wavelengths.

Müller, T., Nowak, A., Wiedensohler, A., Sheridan, P., Laborde, M., Covert, D.S., Marinoni, A., Imre, K., Henzing, B., Roger, J.C., Martins dos Santos, S., Wilhelm, R., Wang, Y.Q., de Leeuw, G. (2009) Angular Illumination and Truncation of Three Different Integrating Nephelometers: Implications for Empirical, Size-Based Corrections, Aerosol Science and Technology, 43:6, 581-586, DOI: 10.1080/02786820902798484;

Schmeisser, L., Backman, J., Ogren, J. A., Andrews, E., Asmi, E., Starkweather, S., Uttal, T., Fiebig, M., Sharma, S., Eleftheriadis, K., Vratolis, S., Bergin, M., Tunved, P., and Jefferson, A.: Seasonality of aerosol optical properties in the Arctic, Atmos. Chem. Phys., 18, 11599-11622, https://doi.org/10.5194/acp-18-11599-2018 , 2018;

Drinovec, L., Močnik, G., Zotter, P., Prévôt, A. S. H., Ruckstuhl, C., Coz, E., Rupakheti, M., Sciare, J., Müller, T., Wiedensohler, A., and Hansen, A. D. A.: The "dual-spot" Aethalometer: an improved measurement of aerosol black carbon with real-time loading compensation, Atmos. Meas. Tech., 8, 1965–1979, https://doi.org/10.5194/amt-8-1965-20 15, 2015.

ISO 19139

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