Sensitivity of the Single Particle Soot Photometer to different black carbon types

Abstract

Black carbon (BC) is now mainly of anthropogenic origin. It is the dominant light absorbing component of atmospheric aerosols, playing an important role in the earth's radiative balance and therefore relevant to climate change studies. In addition, BC is known to be harmful to human beings making it relevant to policy makers. Nevertheless, the measurement of BC remains biased by the instrument-based definition of BC. The Single Particle Soot Photometer (SP2), allows the measurement of the refractory BC (rBC) mass of individual particles using laser-induced incandescence. However, the SP2 needs an empirical calibration to retrieve the rBC mass from the incandescence signal and the sensitivity of the SP2 differs between different BC types. Ideally, for atmospheric studies, the SP2 should be calibrated using ambient particles containing a known mass of ambient rBC. However, such "ambient BC" calibration particles cannot easily be obtained and thus commercially available BC particles are commonly used for SP2 calibration instead. In this study we tested the sensitivity of the SP2 to different BC types in order to characterize the potential error introduced by using non-ambient BC for calibration. The sensitivity of the SP2 was determined, using an aerosol particle mass analyzer, for rBC from thermodenuded diesel exhaust, wood burning exhaust and ambient particles as well as for commercially available products: Aquadag<sup>®</sup> and fullerene soot. <br><br> Thermodenuded, fresh diesel exhaust has been found to be ideal for SP2 calibration for two reasons. First, the small amount of non-BC matter upon emission reduces the risk of bias due to incomplete removal of non-BC matter and second, it is considered to represent atmospheric rBC in urban locations where diesel exhaust is the main source of BC. The SP2 was found to be up to 16% less sensitive to rBC from thermodenuded ambient particles (≤15 fg) than rBC from diesel exhaust, however, at least part of this difference can be explained by incomplete removal of non-refractory components in the thermodenuder. The amount of remaining non-refractory matter was estimated to be below 30% by mass, according to a comparison of the scattering cross sections of the whole particles with that of the pure BC cores. The SP2 sensitivity to rBC from wood burning exhaust agrees with the SP2 sensitivity to rBC from diesel exhaust within an error of less than 14% (≤40 fg). <br><br> If, due to experimental restrictions, diesel exhaust cannot be used, untreated fullerene soot was found to give an SP2 calibration curve similar to diesel exhaust and ambient rBC (within ±10% for a rBC mass ≤15 fg) and is therefore recommended although two different batches differed by ~14% between themselves. In addition, the SP2 was found to be up to 40% more sensitive to Aquadag<sup>®</sup> than to diesel exhaust rBC. Therefore Aquadag<sup>®</sup> cannot be recommended for atmospheric application without accounting for the se...

Soot reference materials for instrument calibration and intercomparisons: a workshop summary with recommendations

“…The community of SP2 users, in concurrence with recent publications Gysel et al, 2011;Laborde, et al, 2012a), have identified fullerene soot as the best SRM for calibrating and comparing the SP2s because of its similarity to ambient refractory black carbon (Fig. 5).…”

“…Hence, the established calibration method is to use a differential mobility analyzer (DMA) to select the particles by their mobility diameter. This requires knowledge of the calibration materials effective density (mass -mobility relationship), which may vary from batch to batch (Laborde et al, 2012a). Therefore a central source of well characterized fullerene soot is needed to assure reproducibility and accuracy of SP2 measurements by different research groups.…”

Airborne observations of IEPOX-derived isoprene SOA in the Amazon during SAMBBA

“…This is the same instrument that was used in previous FAAM publications (McMeeking et al, 2010). It was calibrated using monodisperse AquaDAG (Acheson Industries), with a correction of 0.75 applied according to Laborde et al (2012a). The instrument measures refractory black carbon, denoted as rBC according to the definitions recommended by Petzold et al (2013).…”

Black carbon physical properties and mixing state in the European megacity Paris

“…The incandescence signal was calibrated (three times, at the beginning, half way through and at the end of the measurement campaign) using mobility size selected fullerene soot particles (Alpha Aesar; #FS12S011) which is recommended for SP2 calibration as it gives similar SP2 responses as ambient rBC Baumgardner et al, 2012;Laborde et al, 2012a). The fullerene soot particles were selected by mobility diameter using a differential mobility analyser (DMA) and the corresponding particle masses were calculated using the effective density data provided in .…”