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A method has been developed for the direct determination of the stable chlorine isotope composition ([delta][sup.37]Cl) of organochlorines that eliminates sample preparation, achieves precision comparable to earlier techniques while improving the sensitivity, and makes use of benchtop gas chromatography--quadrupole mass spectrometry instruments (GCqMS). The method is based on the use of multiple injections (n = 8-10) of the sample, bracketed by a molecularly identical isotopic standard with known [delta][sup.37]Cl, determined using off-line thermal ionization mass spectrometry (TIMS). Mass traces of two isotopologues differing by one chlorine isotope were used to calculate [delta][sup.37]Cl values. Optimization of mass spectrometry and peak integration parameters as well as method validation was achieved using tetrachloroethene (PCE), p,p'-dichlorodiphenyl-trichloroethane (DDT), and pentachlorophenol (PCP), spanning a [delta][sup.37]Cl range of -5.5 to +3.2%0 vs SMOC. Injecting 1.6-1100 pmol resulted in standard deviations (1[sigma]) of 0.6-1.3[per thousand], and the [delta][sup.37]Cl results agreed with values independently measured with TIMS. The method was tested by determining the Rayleigh fractionation during evaporation of pure liquid PCE, resulting in a chlorine isotopic enrichment factor of [[epsilon].sub.Cl] = -1.1 [+ or -] 0.4[per thousand]%0. Furthermore, position-specific [delta][sup.37]Cl analysis based on analysis of DDT mass fragments was evaluated. The GCqMS-[delta][sup.37]Cl method offers a simplified yet sensitive approach for compound-specific chlorine isotope analysis. 10.1021/ac902445f

Improved sensitivity in the analysis of stable chlorine isotopes of organochlorines ([[delta].sup.37]C1-OC1) has been established using sealed tube combustion in conjunction with thermal ionization mass spectrometry (TIMS). TIMS of chlorine isotopes was performed on

Polychlorinated dibenzo-p-dioxins (PCDDs) of high concentrations in a ball clay deposit from the Mississippi Embayment were found to be consistent with a natural abiotic and non-pyrogenic origin by investigation with bulk radiocarbon analysis, compound-specific chlorine isotope analysis (CSIA-δ37Cl) of octachlorodibenzo-p-dioxin (OCDD), and black carbon (BC) analysis. The conventional radiocarbon date of total organic carbon from a depth of approximately 10 m in three parallel cores ranged from 14 700 years to >48 000 years, indicating that the strata with elevated levels of PCDDs have remained isolated from recent anthropogenic input in these >40 Ma old clay sediments. The CSIA-δ37Cl of OCDD yielded a δ37Cl of -0.2‰, which is significantly higher than the postulated range for biotic chlorination by chloroperoxidase enzymes, -11 to -10‰, and falls within the known range for abiotic organochlorines, -6 to +3‰. The absence of correlations between concentrations of PCDDs and corresponding pyrogenic black carbon (BC), together with estimations of BC sorptive loadings and the absence of polychlorinated dibenzofurans (PCDFs), suggest that vegetation fires did not form these ball-clay PCDDs. Results from this study indicate that the high levels of the toxic and carcinogenic PCDDs found in kaolinite-bearing clays may result from natural abiotic formation via in situ surface-promoted reactions on the clay mineral, including a so-far unknown organic precursor, rather than being the result of anthropogenic contamination. [ABSTRACT FROM AUTHOR]

A key challenge in climate change research is apportioning the greenhouse gas methane (CH 4 ) between various natural and anthropogenic sources. Isotopic source fingerprinting of CH 4 releases, particularly with radiocarbon analysis, is a promising approach. Here, we establish an analytical protocol for preparing CH 4 from seawater and other aqueous matrices for high-precision natural abundance radiocarbon measurement. Methane is stripped from water in the optionally field-operated system (STRIPS), followed by shore-based purification and conversion to carbon dioxide (CO 2 ) in the CH 4 Isotope Preparation System (CHIPS) to allow Accelerator Mass Spectrometry analysis. The blank (±1σ) of the combined STRIPS and CHIPS is low (0.67 ± 0.12 μg C), allowing natural sample sizes down to 10 μg C-CH 4 (i.e., 30 L samples of 40 nM CH 4 ). The full-system yield is >90% for both CH 4 -spiked seawater and ambient samples from CH 4 hotspots in the Baltic Sea and the Arctic Ocean. Furthermore, the radiocarbon isotope signal of CH 4 remains constant through the multistage processing in the STRIPS and the CHIPS. The developed method thus allows for in-field sampling and sample size reduction followed by precise and CH 4 -specific radiocarbon analysis. This enables powerful source apportionment of CH 4 emitted from aquatic systems from the tropics to the polar regions.

South Asian air is among the most polluted in the world, causing premature death of millions and asserting a strong perturbation of the regional climate. A central component is carbon monoxide (CO), which is a key modulator of the oxidizing capacity of the atmosphere and a potent indirect greenhouse gas. While CO concentrations are declining elsewhere, South Asia exhibits an increasing trend for unresolved reasons. In this paper, we use dual-isotope (δ 13 C and δ 18 O) fingerprinting of CO intercepted in the South Asian outflow to constrain the relative contributions from primary and secondary CO sources. Results show that combustion-derived primary sources dominate the wintertime continental CO fingerprint ( f primary ∼ 79 ± 4%), significantly higher than the global estimate ( f primary ∼ 55 ± 5%). Satellite-based inventory estimates match isotope-constrained f primary -CO, suggesting observational convergence in source characterization and a prospect for model-observation reconciliation. This "ground-truthing" emphasizes the pressing need to mitigate incomplete combustion activities for climate/air quality benefits in South Asia.