Climatology of PM2.5 organic carbon concentrations from a review of ground-based atmospheric measurements by evolved gas analysis

Abstract. Thermal-optical evolved gas analysis (TOEGA) is a conventional method for classifying carbonaceous aerosols as organic carbon (OC) and elemental carbon (EC). Its main source of uncertainty arises from accounting for pyrolized OC (char), which has similar behavior to the EC originally present on the filter. Sample composition can also cause error, at least partly by complicating the charred carbon correction. In this study, lab generated metal salt particles, including alkali (NaCl, KCl, Na2SO4), alkaline-earth (MgCl2, CaCl2) and transition metal salts (CuCl2, FeCl2, FeCl3, CuCl, ZnCl2, MnCl2, CuSO4, Fe2(SO4)3), were deposited on a layer of diesel particles to investigate their effect on EC and OC quantification with TOEGA. Measurements show that metals reduce the oxidation temperature of EC and enhance the charring of OC. The split point used to determine classification of EC vs. OC is more dependent on changes in EC oxidation temperature than it is on charring. The resulting EC/OC ratio is reduced by 0–80% in the presence of most of the salts, although some metal salts increase reported EC/OC at low metal to carbon ratios. The results imply that EC/OC ratios of ambient aerosols quantified with TOEGA have variable low biases due to the presence of metals. In general, transition metals are more active than alkali and alkaline-earth metals; copper is the most active. Copper and iron chlorides are more active than sulfates. The melting point of metal salts is strongly correlated with the increase of OC charring, but not with the reduction of EC oxidation temperature. Other chemistry, such as redox reactions, may affect the EC oxidation. A brief discussion of possible catalytic mechanisms for the metals is provided.

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Detection of organic carbon in Mars-analog paleosols with thermal and evolved gas analysis

10.31223/x50g88 ◽

2021 ◽

Author(s):

Adrian Broz ◽

Joanna Clark ◽

Brad Sutter ◽

Doug Ming ◽

Briony Horgan ◽

...

Keyword(s):

Organic Carbon ◽

Evolved Gas Analysis ◽

Gas Analysis ◽

14C Dating ◽

Mars Rover ◽

Evolved Gas ◽

Near Surface ◽

Carbon Decomposition ◽

Preservation Potential ◽

Mars Analog

Decades of space exploration have shown that surface environments on Mars were habitable billions of years ago. Ancient, buried surface environments, or paleosols, may have been preserved in the geological record on Mars, and are considered high-priority targets for biosignature investigation. Studies of paleosols on Earth that are compositionally similar to putative martian paleosols can provide a reference frame for constraining their organic preservation potential on Mars. However, terrestrial paleosols typically preserve only trace amounts of organic carbon, and it remains unclear whether the organic component of paleosols can be detected with Mars rover-like instruments. Furthermore, the study of terrestrial paleosols is complicated by diagenetic additions of organic carbon, which can confound interpretations of their organic preservation potential. The objectives of this study were a) to determine whether organic carbon in ~30-million-year-old Mars-analog paleosols can be detected with thermal and evolved gas analysis, and b) constrain the age of organic carbon using radiocarbon (14C) dating to identify late diagenetic additions of carbon. Al/ Fe smectite-rich paleosols from the Early Oligocene (33 Ma) John Day Formation in eastern Oregon were examined with a thermal and evolved gas analyzer configured to operate similarly to the Sample Analysis at Mars Evolved Gas Analysis (SAM-EGA) instrument onboard the Mars Science Laboratory Curiosity rover. All samples evolved CO2 with peaks at ~400 °C and ~700° C from the thermal decomposition of refractory organic carbon and small amounts of calcium carbonate, respectively. Evolutions of organic fragments co-occurred with evolutions of CO2 from organic carbon decomposition. Total organic carbon (TOC) ranged from 0.002 - 0.032 ± 0.006 wt. %. Like modern soils, the near-surface horizons of all paleosols had significantly higher TOC relative to subsurface layers. Radiocarbon dating of four samples revealed an organic carbon age ranging between ~6,200 – 14,500 years before present, suggesting there had been inputs of exogenous organic carbon during diagenesis. By contrast, refractory carbon detected with EGA and enrichment of TOC in near-surface horizons of all three buried profiles were consistent with the preservation of trace amounts of endogenous organic carbon. This work demonstrates that near-surface horizons of putative martian paleosols should be considered high priority locations for in-situ biosignature investigation and reveals challenges for examining organic matter preservation in terrestrial paleosols.

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The effect of metal salts on quantification of elemental and organic carbon in diesel exhaust particles using thermal-optical evolved gas analysis

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-10-16941-2010 ◽

2010 ◽

Vol 10 (7) ◽

pp. 16941-16968

Author(s):

Y. Wang ◽

A. Chung ◽

S. E. Paulson

Keyword(s):

Organic Carbon ◽

Alkaline Earth ◽

Metal Salt ◽

Evolved Gas Analysis ◽

Gas Analysis ◽

Diesel Exhaust Particles ◽

Metal Salts ◽

Oxidation Temperature ◽

Carbonaceous Aerosols ◽

Evolved Gas

Abstract. Thermal-optical evolved gas analysis (TOEGA) is a conventional method for classifying carbonaceous aerosols as organic carbon (OC) and elemental carbon (EC). Its main source of uncertainty arises from accounting for pyrolyzed OC (char), which has similar behavior to the EC originally present on the filter. Sample composition can also cause error, at least partly by complicating the charred carbon correction. In this study, lab generated metal salt particles, including alkali (NaCl, KCl, Na2SO4), alkaline-earth (MgCl2, CaCl2) and transition metal salts (CuCl2, FeCl2, FeCl3, CuCl, ZnCl2, MnCl2, CuSO4, Fe2(SO4)3), were deposited on a layer of diesel particles to investigate their effect on EC and OC quantification with TOEGA. Measurements show that metals reduce the oxidation temperature of EC and enhance the charring of OC. The split point used to determine classification of EC vs. OC is more dependent on changes in EC oxidation temperature than it was on charring. The resulting EC/OC ratio is reduced by 0–80% in the presence of most of the salts, although some metal salts increased reported EC/OC at low metal to carbon ratios. In general, transition metals are more active than alkali and alkaline-earth metals; copper is the most active. Copper and iron chlorides are more active than sulfates. The melting point of metal salts is strongly correlated with the increase of OC charring, but not with the reduction of EC oxidation temperature. Other chemistry, such as redox reactions, may affect the EC oxidation. A brief discussion of possible catalytic mechanisms for the metals is provided.

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