Black carbon (BC) is now mainly of anthropogenic origin. It is the dominantlight absorbing component of atmospheric aerosols, playing an important rolein the earth's radiative balance and therefore relevant to climate changestudies. In addition, BC is known to be harmful to human beings making itrelevant to policy makers. Nevertheless, the measurement of BC remains biasedby the instrument-based definition of BC. The Single Particle Soot Photometer(SP2), allows the measurement of the refractory BC (rBC) mass of individualparticles using laser-induced incandescence. However, the SP2 needs anempirical calibration to retrieve the rBC mass from the incandescence signaland the sensitivity of the SP2 differs between different BC types. Ideally,for atmospheric studies, the SP2 should be calibrated using ambient particlescontaining a known mass of ambient rBC. However, such "ambient BC"calibration particles cannot easily be obtained and thus commerciallyavailable BC particles are commonly used for SP2 calibration instead. In thisstudy we tested the sensitivity of the SP2 to different BC types in order tocharacterize the potential error introduced by using non-ambient BC forcalibration. The sensitivity of the SP2 was determined, using an aerosolparticle mass analyzer, for rBC from thermodenuded diesel exhaust, woodburning exhaust and ambient particles as well as for commercially availableproducts: Aquadag? and fullerene soot.Thermodenuded, fresh diesel exhaust has been found to be ideal for SP2calibration for two reasons. First, the small amount of non-BC matter uponemission reduces the risk of bias due to incomplete removal of non-BC matterand second, it is considered to represent atmospheric rBC in urban locationswhere diesel exhaust is the main source of BC. The SP2 was found to be up to16% less sensitive to rBC from thermodenuded ambient particles(≤15 fg) than rBC from diesel exhaust, however, at least part of thisdifference can be explained by incomplete removal of non-refractorycomponents in the thermodenuder. The amount of remaining non-refractorymatter was estimated to be below 30% by mass, according to a comparison ofthe scattering cross sections of the whole particles with that of the pure BCcores. The SP2 sensitivity to rBC from wood burning exhaust agrees with theSP2 sensitivity to rBC from diesel exhaust within an error of less than14% (≤40 fg).If, due to experimental restrictions, diesel exhaust cannot be used,untreated fullerene soot was found to give an SP2 calibration curve similar todiesel exhaust and ambient rBC (within ±10% for a rBC mass≤15 fg) and is therefore recommended although two different batchesdiffered by ~14% between themselves. In addition, the SP2 was foundto be up to 40% more sensitive to Aquadag? than todiesel exhaust rBC. Therefore Aquadag? cannot berecommended for atmospheric application without accounting for thesensitivity difference. These findings for fullerene soot andAquadag? confirm results from previous literature.
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