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.
Highlights
Atmospheric aerosols are known to have negative effects on human health
41.2 32.8 24.5 56.0 47.8 removal of measurable pyrolytic organic carbon (OC) from aerosol samples as compared to neat scCO2 since 49–57% OC was removed with 81–88% elemental carbon (EC) recovery when 10% methanol was added (Table 1 shows filter loadings as filter 1)
Values, percentage OC removal, and percentage EC recovery at the eight different treatment conditions applied on filter 1
Summary
Atmospheric aerosols are known to have negative effects on human health. Exposure to aerosols is one of the major causes of lung diseases and cardiovascular morbidity and mortality in the world [1, 2]. The radiocarbon analysis takes advantage of the fact that fossil fuels are completely free from 14C, while modern biomass contains a known amount of naturally produced 14C as well as 14C resulting from atmospheric nuclear tests in the twentieth century [6, 14,15,16,17,18,19,20,21,22,23] This knowledge on relative contribution of emission sources might be valuable for stakeholders and policymakers in order to make scientifically sound decisions regarding mitigation of anthropogenic emissions of EC, taking both climate and health into consideration
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