Towards the isolation and estimation of elemental carbon in atmospheric aerosols using supercritical fluid extraction and thermo-optical analysis

Abstract

Air-starved combustion of biomass and fossil fuels releases aerosols, including airborne carbonaceous particles, causing negative climatic and health effects. Radiocarbon analysis of the elemental carbon (EC) fraction can help apportion sources of its emission, which is greatly constrained by the challenges in isolation of EC from organic compounds in atmospheric aerosols. The isolation of EC using thermo-optical analysis is however biased by the presence of interfering compounds that undergo pyrolysis during the analysis. EC is considered insoluble in all acidic, basic, and organic solvents. Based on the property of insolubility, a sample preparation method using supercritical CO2 and methanol as co-solvent was developed to remove interfering organic compounds. The efficiency of the method was studied by varying the density of supercritical carbon dioxide by means of temperature and pressure and by varying the methanol content. Supercritical CO2 with 10% methanol by volume at a temperature of 60 °C, a pressure of 350 bar and 20 min static mode extraction were found to be the most suitable conditions for the removal of 59 ± 3% organic carbon, including compounds responsible for pyrolysis with 78 ± 16% EC recovery. The results indicate that the method has potential for the estimation and isolation of EC from OC for subsequent analysis methods and source apportionment studies.

Development of a novel aerosol generation system for conducting inhalation exposures to ambient particulate matter (PM)

“…However, due to the water-insolubility of some PM components (e.g., EC, and some metals and elements), these insoluble fractions of PM were not extracted efficiently during the aqueous extraction, which artificially increased the relative contribution of soluble components, such as WSOM, to total PM 0.18 mass in re-aerosolized (i.e., 53%) versus ambient PM (i.e., 42%) samples. Unlike water-soluble species, the mass fraction of EC was dropped by 75% upon water extraction, since EC is an insoluble species and remains mostly on the filter even after applying the extraction protocol (Azeem et al, 2017;Wallén et al, 2010). Similarly, lower mass fractions were observed for several metals and trace elements in the re-aerosolized samples compared to the ambient samples, which will be discussed in detail in section 3.2.1.…”

Atomic Spectrometry Update – a review of advances in environmental analysis

“…The isolation of elemental C, the commonly used marker for diesel engine exhaust emissions, by thermal-optical analysis can be compromised by the presence of interfering organic carbon compounds that undergo pyrolysis during combustion. This socalled pyrolytic carbon artifact can then be misclassified as elemental C. Researchers in Sweden minimised 52 this effect by initially extracting ~60% of the organic C from filter samples using a 20 minute SCF procedure that involved supercritical CO 2 containing 10%…”