Abstract
Abstract. We report on an inter-comparison of black-carbon- and aerosol-absorption-measuring instruments with laboratory-generated soot particles coated with controlled amounts of secondary organic matter (SOM). The aerosol generation setup consisted of a miniCAST 5201 Type BC burner for the generation of soot particles and a new automated oxidation flow reactor based on the micro smog chamber (MSC) for the generation of SOM from the ozonolysis of α-pinene. A series of test aerosols was generated with elemental to total carbon (EC / TC) mass fraction ranging from about 90 % down to 10 % and single-scattering albedo (SSA at 637 nm) from almost 0 to about 0.7. A dual-spot Aethalometer AE33, a photoacoustic extinctiometer (PAX, 870 nm), a multi-angle absorption photometer (MAAP), a prototype photoacoustic instrument, and two prototype photo-thermal interferometers (PTAAM-2λ and MSPTI) were exposed to the test aerosols in parallel. Significant deviations in the response of the instruments were observed depending on the amount of secondary organic coating. We believe that the setup and methodology described in this study can easily be standardised and provide a straightforward and reproducible procedure for the inter-comparison and characterisation of both filter-based and in situ black-carbon-measuring (BC-measuring) instruments based on realistic test aerosols.
Highlights
Black-carbon-containing (BC-containing) particles are produced from incomplete combustion of fossil fuels or biomass
Each series consisted of four test aerosols: uncoated soot and soot with three different amounts of secondary organic matter (SOM) coating
The geometric mean mobility diameter (GMDmob) of the soot particles gradually decreased from 92 nm to 83 nm as shown in Fig. 2a, while the EC / TC mass fraction dropped from ∼ 90 % to ∼ 40 % and the single-scattering albedo (SSA) increased from about 0 to ∼ 0.2
Summary
Black-carbon-containing (BC-containing) particles are produced from incomplete combustion of fossil fuels or biomass. Its influence on the radiative balance of the Earth cannot be quantified because BC particles in ambient air are usually internally mixed with organic and/or inorganic species, which may cause absorption enhancement through the socalled “lensing effect” (Cappa et al, 2012; Liu et al, 2015). Despite a plethora of commercially available BCmonitoring instruments based on different measurement techniques, quantification of BC mass concentration remains a challenge to this day. Deviations between 15 % and 30 % among instruments of the same type (Cuesta-Mosquera et al, 2021; Müller et al, 2011a) and up to 50 %–60 % for instruments of different measurement principles (Chirico et al, 2010; Slowik et al, 2007) have been reported.
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