Undersizing of aged African biomass burning aerosol by an ultra-high-sensitivity aerosol spectrometer

Abstract nm aerosols to 15 % for 280 nm particles. Mie scattering calculations show that composition-dependent refractive index of the particles cannot explain the pattern. Heating of brown carbon or tarballs in the beam causing evaporation and shrinking of the particles is the most plausible explanation, though mis-sizing due to non-sphericity cannot be ruled out. A small fraction (10 %–30 %) of the particles were undersized by 25 % to 35 %. Those were apparently the particles containing refractory black carbon. Laboratory calibrations confirm that black carbon is drastically undersized by the UHSAS, because particles heat to their vaporization point and shrink. nm. It raised the median particle diameter by 18 nm, from 163 to 181 nm, during the August 2017 deployment and by smaller amounts during deployments with less intense pollution. Calculated scattering from UHSAS size distributions increased by about 130 %, dramatically improving agreement with scattering measured by nephelometers. The correction is only valid in polluted instances; clean marine boundary layer and free troposphere aerosols behaved more like the calibration spheres. We were unable to directly test the correction between 500 and 1000 nm, though aerodynamic particle sizer (APS) data appear to show that the correction is poor at the largest diameters, which is no surprise as the composition of those particles is likely to be quite different than that of the accumulation mode. This adds to the evidence that UHSAS data must be treated cautiously whenever the aerosol may absorb infrared light. Similar corrections may be required whenever brown carbon aerosol is present.

Object Details

• Location: Deutsche Nationalbibliothek Frankfurt am Main
• Extent: Online-Ressource
• Language: Englisch

References and Relationships

• Bibliographic citation: Undersizing of aged African biomass burning aerosol by an ultra-high-sensitivity aerosol spectrometer ; volume:14 ; number:11 ; year:2021 ; pages:7381-7404 ; extent:24 ; Atmospheric measurement techniques ; 14, Heft 11 (2021), 7381-7404 (gesamt 24)

Contributors, Places and Time

• Creator: Howell, Steven G. ; Freitag, Steffen ; Dobracki, Amie ; Smirnow, Nikolai ; Sedlacek III, Arthur J.

Further information

• DOI: 10.5194/amt-14-7381-2021
• URN: urn:nbn:de:101:1-2021120204442957661066
• Rights: Open Access; Der Zugriff auf das Objekt ist unbeschränkt möglich.
• Last update: 2025-08-15T07:35:15+0200