Determination of atmospheric soot carbon with a simple thermal method

Abstract

The dark component of carbonaceous aerosols is often referred to as "soot carbon". Soot consists of pure elemental carbon along with highly polymerized organic matter. An accurate discrimination between the soot carbon and the other components of carbonaceous aerosols is difficult to obtain by thermal analytical processes. Here, we report an optimization of a 2-step thermal method focused on the soot carbon determination of atmospheric particles. The organic material which does not absorb visible light is removed from the collection substrate under a pure oxygen flow during a precombustion step which has been carefully optimized in terms of temperature (340°C) and duration (2 h). The remaining carbon content is determined by coulometric titration of the C 0 2 evolved from the combustion of the samples. The method has been tested quantitatively for analytical artefacts (e.g., "soot" production due to the charring of organics; soot losses during the preheating step) by using various standards such as pure graphite, pure organic and natural biogenic compounds and replicates of ambient air samples collected in urban, rural and forested areas in France. The results obtained so far indicate that this approach satisfactorily distinguishes between organic and soot carbon and allows reliable soot carbon determination at the pg level in atmospheric samples from a wide variety of environments. This study confirms that soot carbon is not composed primarily of elemental carbon. It appears to be a variable mixture of highly condensed organic compounds. These compounds may be either combustion-derived material or the result of low-temperature gas-to-particle conversion processes.

Relationships between cloud condensation nuclei spectra and aerosol particles on a south‐north transect of the Indian Ocean

“…Mean sample duration was about 24 hours (this time interval appeared to be necessary for the clean conditions in the Southern Hemisphere). Analyses were conducted following the laboratory thermal protocol [Cachier et al, 1989] including a predecarbonation step. In short, half of each sample is analyzed directly and gives the so-called total carbon content.…”

Airborne aerosols over central Africa during the Experiment for Regional Sources and Sinks of Oxidants (EXPRESSO)

“…This choice was dictated by our concern for the highest possible flow rate and for minimizing positive artifacts during samplings. The analytical protocol routinely applied in our laboratory [Cachier et al, 1989] comprises a decarbonatation before carbon analysis. Black carbon (BC) and organic carbon (OC) are separated during a thermal pretreatment (340øC during 2 hours under oxygen).…”

Radiocarbon Analysis of Carbonaceous Aerosols: Recent Developments

“…[20,21] Although the helium-based method is widely applied for the determination of OC and EC concentrations, it is inappropriate for the isolation of both fractions for 14 C analysis, as this technique substantially produces charring during the evaporation of OC in helium. For the determination of OC and EC concentrations, an optical on-line monitoring is used to correct for this artifact.…”

“…[22] Therefore, the two-step oxidation of OC and EC in pure oxygen is the method of choice, as it is much less prone to charring. [20,22] Further reduction of charring for the isolation of EC is achieved by water extraction of the filters prior to the thermal treatment. [10,14,22] This allows the removal of water-soluble inorganic and organic compounds from the filters, which support the artificial production of EC from OC during analysis, whereas EC remains completely on the filter.…”