Measured in-situ mass absorption spectra for nine forms of highly-absorbing carbonaceous aerosol

Abstract

Mass absorption coefficient spectra were measured between λ = 500 nm and 840 nm for nine forms of highly-absorbing carbonaceous aerosol: five samples generated from gas-, liquid-and solid-fueled flames; spark-discharge fullerene soot; graphene and reduced graphene oxide (rGO) crumpled nanosheets; and fullerene (C 60 ) assemblies. Aerosol absorption spectra were measured for size-and mass-selected particles and found to be dependent on fuel type and formative conditions. Flame-generated particles had morphologies consistent with freshly emitted black carbon (BC) with mass absorption coefficients (MAC) ranging between 3.8 m 2 g -1 and 8.6 m 2 g -1 at λ = 550 nm. Absorption Ångström exponents (AAE) -i.e. MAC spectral dependence -ranged between 1.0 and 1.3 for flame-generated particles and up to 7.5 for C 60 . The dependence of MAC and AAE on mobility diameter and particle morphology was also investigated. Lastly, the current data were compared to all previously published MAC measurements of highly-absorbing carbonaceous aerosol. Mass absorption coefficient spectra were measured between λ = 500 nm and 840 nm for nine 13 forms of highly-absorbing carbonaceous aerosol: five samples generated from gas-, liquid-and 14 solid-fueled flames; spark-discharge fullerene soot; graphene and reduced graphene oxide (rGO) 15 crumpled nanosheets; and fullerene (C 60 ) assemblies. Aerosol absorption spectra were measured 16 for size-and mass-selected particles and found to be dependent on fuel type and formative 17 conditions. Flame-generated particles had morphologies consistent with freshly emitted black 18 carbon (BC) with mass absorption coefficients (MAC) ranging between 3.8 m 2 g -1 and 8.6 m 2 g -1 19at λ = 550 nm. Absorption Ångström exponents (AAE) -i.e. MAC spectral dependence -ranged 20 between 1.0 and 1.3 for flame-generated particles and up to 7.5 for C 60 . The dependence of MAC 21 and AAE on mobility diameter and particle morphology was also investigated. Lastly, the current 22 M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 2 data were compared to all previously published MAC measurements of highly-absorbing 23 carbonaceous aerosol. 24

Specifying the light-absorbing properties of aerosol particles in fresh snow samples, collected at the Environmental Research Station Schneefernerhaus (UFS), Zugspitze

“…1. A MAC FS of 8.6 m 2 g −1 was measured for the mobility-equivalent diameter of 350 nm, which is still ∼ 40 % larger than the MAC FS given by Zangmeister et al (2018) for the same diameter. However, they used an APM to measure the BC mass, while an SP2 was used here to deduce the refractory BC mass.…”

“…The MAC FS at 532 nm is comparable to the value of 8.84 m 2 g −1 given by Schwarz et al (2012) for fullerene soot (lot no. F12S011) deduced from ISSW measurements, but is significantly higher than the 6.1 ± 0.4 m 2 g −1 (mean ± 2σ ) measured recently by photoacoustic absorption spectroscopy for size-selected fullerene soot particles by Zangmeister et al (2018). The latter authors used a combination of a DMA and an aerosol particle mass analyser (APM) to select fullerene soot particles within a narrow mass range from aerosol generated by an atomizer.…”

“…F12S011 used in the present study. This in turn would increase the MAC FS from 6.1 m 2 g −1 reported by Zangmeister et al (2018) to about 7 m 2 g −1 when using only the refractory BC mass fraction in the calculation of the MAC FS . This assumption reduces the discrepancy between the two MAC FS values to 35 %, which is within the uncertainty range of ±2.2 m 2 g −1 for our 532 nm value.…”

Answer to Reviewer 3

“…Assuming that lot no. W08A039 used in Zangmeister et al (2018) has a similar coating, this would increase the APM mass measurement by about 15 % compared to the SP2-derived BC mass of lot no. F12S011 used in the present study.…”

“…W08A039. Here again, we have to take into account that Zangmeister et al (2018) analysed sizesegregated absorption spectra, and their AAE is given for a mobility-equivalent diameter of 350 nm. Analysing our sizesegregated measurements gives an AAE of 0.82 ± 0.02 for the same mobility-equivalent diameter, which is closer to, but smaller than, the Zangmeister et al value.…”