Speaker
Description
Light absorbing carbonaceous aerosols (LAC) contribute positive forcing to the Earth radiative budget, which results in atmospheric warming. To determine the actual contribution of LAC aerosols, measurements from across the globe are incorporated into climate models. The most used approach for this measurement is by using filter-photometers (FP), which measure the attenuation of light through a filter where aerosols are being deposited. Of all the possible in-situ surface measurements, the most deployed instrument across measurement networks is the aethalometer AE33 (Aerosol d.o.o.; Drinovec et al., 2015). More sophisticated FP instruments, such as the Multi-Angle Absorption Photometer (MAAP, Thermo Scientific Inc.; Petzold and Schönlinner, 2004) are also deployed in some stations, acting as pseudo-reference instruments.
The use of FPs results in several artifacts, with cross-sensitivity to scattering being most important at high single scattering albedo, with the error exceeding 100%. This cross-sensitivity to scattering has been found to have site-to-site variability (e.g., Bernardoni et al., 2021, Yus-Diez et al., 2021). In Yus-Diez et al. (2021) a compensation scheme was proposed. However, it requires the availability of scattering coefficient measurements, less frequent across networks, and a direct measurement of the aerosol absorption coefficient which can serve as the reference for the measurement with the AE33. In Yus-Diez et al. (2021), a MAAP and a laboratory-based FP, the PP_UniMi, were used as reference instruments, however, although to a lower degree, these are also subject to the same artifacts.
Here we show measurements performed during the AGORA 2023 summer campaign in Granada, with ambient measurements using the AE33 and MAAP filter photometers and a novel reference absorption instrument, the dual-wavelength photo-thermal interferometer (PTAAM-2λ, Haze Instruments d.o.o.; Drinovec et al., 2022). In addition, we also measured scattering coefficients, particle size distribution and other variables that describe the properties of aerosol particles.
Here we present the result of applying the correction scheme described in Yus-Diez et al. (2021) by using the PTAAM-2λ reference, which results in a perfect correction. However, the required instrumentation for this correction is not available in stations where filter photometer measurements are taken. Since we do not have the scattering measurements and/or deploy a PTAAM-2λ everywhere, we resort to Machine Learning (ML) models.
As a proof of concept, we applied a gradient boosting regressor model, where we splited the data into 80% training and 20% prediction. We were able to obtain an excellent correlation (slope=0.98, R2 = 0.96) between the MAAP measurements processed using the ML algorithm and the reference PTAAM’s absorption coefficient (interpolated to the MAAP wavelength). As future work, we plan to further improve the model while also extending it to the AE33 instrument measurements.
References:
- Petzold A and Schönlinner M, The Multi-angle absorption photometer – A new method for the measurement of aerosol light absorption and atmospheric black carbon. Journal of Aerosol Science, 35, 421-441, 2004
- Drinovec, L., Močnik, G., Zotter, P., Prévôt, A.S.H., Ruckstuhl, C., Coz, E., Rupakheti, M., Sciare, J., Müller, T., Wiedensohler, A., Hansen, A.D.A., 2015. The "dual-spot" Aethalometer: an improved measurement of aerosol black carbon with real-time loading compensation, Atmospheric Measurement Techniques, 8, 1965–1979. https://doi.org/10.5194/amt-8-1965-2015
-Bernardoni, V., Ferrero, L., Bolzacchini, E., Forello, A. C., Gregorič, A., Massabò, D., Močnik, G., Prati, P., Rigler, M., Santagostini, L., Soldan, F., Valentini, S., Valli, G., and Vecchi,R.: Determination of Aethalometer multiple-scattering enhancement parameters and impact on source apportionment during the winter 2017/18 EMEP/ACTRIS/COLOSSAL campaign in Milan, Atmos. Meas. Tech., 14, 2919–2940, https://doi.org/10.5194/amt-14-2919-2021, 2021
- Yus-Díez, J., Bernardoni, V., Močnik, G., Alastuey, A., Ciniglia, D.,Ivančič, M., Querol, X., Perez, N., Reche, C., Rigler, M., Vecchi, R., Valentini, S., and Pandolfi, M., 2021. Determination of the multiple-scattering correction factor and its cross-sensitivity to scattering and wavelength dependence for different AE33 Aethalometer filter tapes: A multi-instrumental approach, Atmos. Meas. Tech https://doi.org/10.5194/amt-2021-46 Drinovec, Luka, et al."A dual-wavelength photothermal aerosol absorption monitor: design, calibration and performance." Atmospheric Measurement Techniques 15.12 (2022): 3805-3825.
