Accurate and temporally consistent measurements of light absorbing aerosol (LAA) heating rate (HR) and of its source apportionment (fossil-fuel, FF; biomass-burning, BB) and speciation (black and brown Carbon; BC, BrC) are needed to evaluate LAA short-termclimate forcing. For this purpose,wavelength- and time-dependent accurate LAA absorption coefficients are required. HRwas experimentally determined and apportioned (sources/species) 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/AE33multiple-scattering correction factors (C)were determined using two reference systems for the absorption coefficient: 1) 5-wavelength PP_UniMIwith lowtime resolution (12 h, applied to PM2.5 samples); 2) timely-resolved MAAP data at a single wavelength. Using wavelength- and timeindependent C values for the AE31 and AE33 obtainedwith the samereference device, the total HRshowed 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, theHR 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 higherHRFF(+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 inconsistencieswere overcome by introducing awavelength-dependent Cλ for both AE31 and AE33, or usingmulti-wavelength apportionment methods, highlighting the need for further studies on the influence of wavelength corrections for HR determination. Finally, the temporally-resolved determination of C resulted in a diurnal cycle of the HR not statistically different whatever the source- speciation- apportionment used.
Consistent determination of the heating rate of light-absorbing aerosol using wavelength- and time-dependent Aethalometer multiple-scattering correction
Dario Massabò;P. Prati;
2021-01-01
Abstract
Accurate and temporally consistent measurements of light absorbing aerosol (LAA) heating rate (HR) and of its source apportionment (fossil-fuel, FF; biomass-burning, BB) and speciation (black and brown Carbon; BC, BrC) are needed to evaluate LAA short-termclimate forcing. For this purpose,wavelength- and time-dependent accurate LAA absorption coefficients are required. HRwas experimentally determined and apportioned (sources/species) 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/AE33multiple-scattering correction factors (C)were determined using two reference systems for the absorption coefficient: 1) 5-wavelength PP_UniMIwith lowtime resolution (12 h, applied to PM2.5 samples); 2) timely-resolved MAAP data at a single wavelength. Using wavelength- and timeindependent C values for the AE31 and AE33 obtainedwith the samereference device, the total HRshowed 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, theHR 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 higherHRFF(+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 inconsistencieswere overcome by introducing awavelength-dependent Cλ for both AE31 and AE33, or usingmulti-wavelength apportionment methods, highlighting the need for further studies on the influence of wavelength corrections for HR determination. Finally, the temporally-resolved determination of C resulted in a diurnal cycle of the HR not statistically different whatever the source- speciation- apportionment used.
I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
