Accurate and temporally consistent measurements of light absorbing aerosol (LAA) heating rate (HR) and of itssource apportionment (fossil-fuel, FF; biomass-burning, BB) and speciation (black and brown Carbon; BC, BrC) are needed to evaluate LAA short-term climate forcing. For this purpose, wavelength- and time-dependent accu-rate LAA absorption coefficients are required. HR was experimentally determined and apportioned (sources/spe-cies) in the EMEP/ACTRIS/COLOSSAL-2018 winter campaign in Milan (urban-background site). Two Aethalometers (AE31/AE33) were installed together with a MAAP, CPC, OPC, a low volume sampler (PM2.5)and radiation instruments. AE31/AE33 multiple-scattering correction factors (C) were determined using two ref-erence systems for the absorption coefficient: 1) 5-wavelength PP_UniMI with low time resolution (12 h, appliedto PM2.5samples); 2) timely-resolved MAAP data at a single wavelength. Using wavelength- and time-independent C values for the AE31 and AE33 obtained with the same reference device,the total HR showed a consistency (i.e. reproducibility) with average values comparable at 95% probability. However, if different reference devices/approaches are used, i.e.MAAP is chosen as reference instead of a PP_UniMI, the HR can be overestimated by 23–30% factor (by both AE31/AE33). This became more evident focusing on HR apportionment: AE33 data (corrected by a wavelength-and time-independent C) showed higher HRFF(+24± 1%) and higher HRBC (+10±1%) than that of AE31. Conversely, HRBB and HRBrC were −28 ± 1% and −29 ± 1% lower for AE33 compared to AE31. These inconsistencies were overcome by introducing a wavelength-dependent Cλ for both AE31 and AE33,or using multi-wavelength apportionment methods, highlighting the need for further studies on the influence ofwavelength corrections for HR determination.Finally, the temporally-resolved determination of C resulted in a diurnal cycle of the HR not statistically differentwhatever the source- speciation- apportionment used.

Consistent determination of the heating rate of light-absorbing aerosol using wavelength- and time-dependent Aethalometer multiple-scattering correction / L. Ferrero, V. Bernardoni, L. Santagostini, S. Cogliati, F. Soldan, S. Valentini, D. Massabò, G. Močnik, A. Gregorič, M. Rigler, P. Prati, A. Bigogno, N. Losi, G. Valli, R. Vecchi, E. Bolzacchini. - In: SCIENCE OF THE TOTAL ENVIRONMENT. - ISSN 0048-9697. - 791(2021 Oct 15), pp. 148277.1-148277.19. [10.1016/j.scitotenv.2021.148277]

Consistent determination of the heating rate of light-absorbing aerosol using wavelength- and time-dependent Aethalometer multiple-scattering correction

V. Bernardoni
Secondo
;
S. Valentini;G. Valli;R. Vecchi
Penultimo
;
2021

Abstract

Accurate and temporally consistent measurements of light absorbing aerosol (LAA) heating rate (HR) and of itssource apportionment (fossil-fuel, FF; biomass-burning, BB) and speciation (black and brown Carbon; BC, BrC) are needed to evaluate LAA short-term climate forcing. For this purpose, wavelength- and time-dependent accu-rate LAA absorption coefficients are required. HR was experimentally determined and apportioned (sources/spe-cies) in the EMEP/ACTRIS/COLOSSAL-2018 winter campaign in Milan (urban-background site). Two Aethalometers (AE31/AE33) were installed together with a MAAP, CPC, OPC, a low volume sampler (PM2.5)and radiation instruments. AE31/AE33 multiple-scattering correction factors (C) were determined using two ref-erence systems for the absorption coefficient: 1) 5-wavelength PP_UniMI with low time resolution (12 h, appliedto PM2.5samples); 2) timely-resolved MAAP data at a single wavelength. Using wavelength- and time-independent C values for the AE31 and AE33 obtained with the same reference device,the total HR showed a consistency (i.e. reproducibility) with average values comparable at 95% probability. However, if different reference devices/approaches are used, i.e.MAAP is chosen as reference instead of a PP_UniMI, the HR can be overestimated by 23–30% factor (by both AE31/AE33). This became more evident focusing on HR apportionment: AE33 data (corrected by a wavelength-and time-independent C) showed higher HRFF(+24± 1%) and higher HRBC (+10±1%) than that of AE31. Conversely, HRBB and HRBrC were −28 ± 1% and −29 ± 1% lower for AE33 compared to AE31. These inconsistencies were overcome by introducing a wavelength-dependent Cλ for both AE31 and AE33,or using multi-wavelength apportionment methods, highlighting the need for further studies on the influence ofwavelength corrections for HR determination.Finally, the temporally-resolved determination of C resulted in a diurnal cycle of the HR not statistically differentwhatever the source- speciation- apportionment used.
Heating rate; Black carbon; Brown carbon; Fossil fuel
Settore FIS/07 - Fisica Applicata(Beni Culturali, Ambientali, Biol.e Medicin)
Settore CHIM/01 - Chimica Analitica
4-giu-2021
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/849809
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