Single Particle Soot Photometer intercomparison at the AIDA chamber

Abstract

Soot particles, consisting of black carbon (BC), organic carbon (OC), inorganic salts, and trace elements, are emitted into the atmosphere during incomplete combustion. Accurate measurements of atmospheric BC are important as BC particles cause adverse health effects and impact the climate. <br><br> Unfortunately, the accurate measurement of the properties and mass concentrations of BC particles remains difficult. The Single Particle Soot Photometer (SP2) can contribute to improving this situation by measuring the mass of refractory BC in individual particles as well as its mixing state. <br><br> Here, the results of the first detailed SP2 intercomparison, involving 6 SP2s from 6 different research groups, are presented, including the most evolved data products that can presently be calculated from SP2 measurements. <br><br> It was shown that a detection efficiency of almost 100% down to 1 fg BC per particle can readily be achieved, and that this limit can be pushed down to ∼0.2 fg BC with optimal SP2 setup. Number and mass size distributions of BC cores agreed within ±5% and ±10%, respectively, in between the SP2s, with larger deviations in the range below 1 fg BC. <br><br> The accuracy of the SP2's mass concentration measurement depends on the calibration material chosen. The SP2 has previously been shown to be equally sensitive to fullerene soot and ambient BC from sources where fossil fuel was dominant and less sensitive to fullerene soot than to Aquadag. Fullerene soot was therefore chosen as the standard calibration material by the SP2 user community; however, many data sets rely solely on Aquadag calibration measurements. The difference in SP2 sensitivity was found to be almost equal (fullerene soot to Aquadag response ratio of ∼0.75 at 8.9 fg BC) for all SP2s. This allows the calculation of a fullerene soot equivalent calibration curve from a measured Aquadag calibration, when no fullerene soot calibration is available. It could be shown that this approach works well for all SP2s over the mass range of 1–10 fg. This range is suitable for typical BC mass size distributions in the ambient air far from sources. <br><br> The number size distribution of purely scattering particles optically measured by the 6 SP2s also agreed within 15%. Measurements of the thickness of non-refractory coatings (i.e. product from α-pinene ozonolysis) on the BC particles, relying on BC mass optical size and on an additional particle position measurement, also compared well (within ±17%). The estimated coating thickness values were consistent with thermo-optical analysis of OC and elemental carbon (EC) content, though absolutely accurate values cannot be expected given all the assumptions that have to be made regarding refractive index, particle morphology, etc. <br><br> This study showed that the SP2 provides accurate and reproducible data, but also that high data quality is only achieved if the SP2 is carefull...

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

“…Note that the SP2 employs active drying on its sheath air system, so particles are sampled at a low RH. Overall accuracy is estimated at around 20 % with 90 nm sphere equivalent rBC volume necessary for particle detection (Laborde et al, 2012b).…”

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

“…The scattering signal was calibrated twice (at the beginning and half way through the measurement campaign) using spherical polystyrene latex size standards with a diameter of 269 nm (Thermo Scientific, formerly Duke Scientific). More details on SP2 calibration and calibration standard material can be found in Baumgardner et al (2012), Laborde et al (2012b) and .…”

“…It is important to note that this uncertainty refers to the average over many particles, as the coating thickness value determined for an individual particle is associated with additional random noise. Further discussion on the uncertainties associated to the coating thickness is available elsewhere (Schwarz et al, 2008b;Laborde et al, 2012b).…”

“…Prior to the measurement field campaign, the SP2 was adjusted following the recommended adjustments detailed in Laborde et al (2012b). 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).…”

Ambient black carbon particle hygroscopic properties controlled by mixing state and composition

“…The Aquadag was size selected using a differential mobility analyzer (DMA), and the particle mass at each mobility diameter (D mob ) was obtained by assigning an effective density from Gysel et al (2011). The Aquadag mass in single particle was calibrated at ∼0.5-80 fg (D mob ∼80-600 nm), and the calibration curve is further recalculated to be compliant with the physical properties of ambient BC particles by applying a scaling factor of 0.75 according to Baumgardner et al (2012) and Laborde et al (2012). The SP2 measurement is capable of examining whether a single particle contains rBC or not by detecting the ambient incandescence signal.…”