Refractory black carbon mass concentrations in snow and ice: method evaluation and inter-comparison with elemental carbon measurement

Abstract

Abstract. Accurate measurement of black carbon (BC) mass concentrations in snow and ice is crucial for the assessment of climatic impacts. However, it is difficult to compare methods used to assess BC levels in the literature as they are not the same. The single particle soot photometer (SP2) method appears to be one of the most suitable to measure low concentrations of BC in snow and ice. In this paper, we evaluated a method for the quantification of refractory BC (rBC) in snow and ice samples coupling the SP2 with the APEX-Q nebulizer. The paper reviews all the steps of rBC determination, including SP2 calibration, correction for rBC particle aerosolization efficiency (75 ± 7% using the APEX-Q nebulizer), and treatment of the samples. In addition, we compare the SP2 method and the thermal–optical method – Sunset organic carbon (OC) / elemental carbon (EC) aerosol analyzer with EUSAAR2 protocol – using snow and firn samples with different characteristics from the Greenland Summit, the French Alps, the Caucasus, and the Himalayas. Careful investigation was undertaken of analytical artifacts that potentially affect both methods. The SP2-based rBC quantification may be underestimated when the SP2 detection range does not cover correctly the existing size distribution of the sample. Thermal–optical EC measurements can be underestimated by low filtration efficiency of quartz fiber filter before analysis or dust properties (concentration and type), and overestimated by pyrolyzed OC artifacts during EC analysis. These results underline the need for careful assessment of the analytical technique and procedure for correct data interpretation.

An 800 year high-resolution black carbon ice-core record from Lomonosovfonna, Svalbard

“…35 Whereas the SP2 does not detect rBC particles larger than 500 nm, the optical and thermal-optical methods include a filtration step where the smallest fraction of EC particles is generally lost. Lim et al (2014) reported significant variations of the EC/rBC ratios in snow and ice, ranging from 0.5 to 3.4 according to the sample origin. Furthermore, in the aforementioned studies, most of the EC snow samples from Svalbard were collected in winter/spring, when EC concentrations in fresh snow are higher due to the Arctic Haze and have not experienced yet summer melting of the 40 snowpack, contrary to the LF ice-core samples.…”

“…The autosampler probe was rinsed with ultrapure water during 45 sec between each sample and the waiting time in each vial before data acquisition was set to 1 min 45 sec, which turned out to be sufficient for the background signal to become stable. However, some difficulties arose from the fact that rBC concentrations tend to decrease with time due to particles sticking to the walls and agglomerating beyond the SP2 detection range, which implies that rBC samples have to be measured as fast as possible after sonication (Lim et al, 2014;Wendl et al, 2014). We therefore studied the rBC degradation 10 with time by using 24 ice core samples from Lomonosovfonna and the Swiss Alps (Colle Gnifetti and Fiescherhorn ice cores).…”

“…Losses of rBC from samples which were melted and refrozen in laboratory tests can reach 45 ± 11 % (Lim et al, 2014) or even up to 60 % for a single thaw-freeze-thaw cycle prior to analyses . One possible explanation is the agglomeration of rBC particles to larger sizes during the refreezing process, beyond the SP2 detection 25 range .…”

“…The entire LF-09 core and the LF-11 core were analyzed at PSI in several campaigns between 2012 and 2016 and in AprilMay 2016, respectively, following the procedure established by Wendl et al (2014) for liquid samples and further evaluated by Lim et al (2014). Discrete rBC samples were melted at room temperature, sonicated in a ultrasonic bath for 25 min and immediately analyzed by a Single Particle Soot Photometer (SP2, Droplet Measurement Technologies, USA) (Schwarz et al, 2006;Stephens et al, 2003) coupled with a jet nebulizer (APEX-Q, Elemental Scientific Inc., USA).…”

Real-time analysis of insoluble particles in glacial ice using single-particle mass spectrometry

“…The recent advent of a commercially available intracavity laser-induced incandescence photometer, the Single Particle Soot Photometer (SP2; Droplet Measurement Technologies, Inc., Boulder, CO) has allowed for a new class of online measurements where both concentrations and size distributions of (refractory) carbonaceous particles in snow and ice can be recovered on a per-particle basis (McConnell et al, 2007;Kaspari et al, 2011;Ginot et al, 2014;Lim et al, 2014). McConnell et al (2007) were the first to measure past black carbon deposition continuously along a Greenlandic ice core using SP2 instrumentation.…”