Low blank sampling method for measurement of the nitrogen isotopic composition of atmospheric NOx.

The nitrogen isotopic composition of nitrogen oxide (NOx) is useful for estimating its sources and sinks. Several methods have been developed to convert atmospheric nitric oxide (NO) and/or nitrogen dioxide (NO2) to nitrites and/or nitrates for collection. However, the collection efficiency and blanks are poorly evaluated for many collection methods.

A GC-IRMS method for measuring sulfur isotope ratios of carbonyl sulfide from small air samples.

A new system was developed for measuring sulfur isotopes δ S and δ S from atmospheric carbonyl sulfide (COS) on small air samples of several liters, using pre-concentration and gas chromatography - isotope ratio mass spectrometry (GC-IRMS). Measurements of COS isotopes provide a tool for quantifying the COS budget, which will help towards better understanding climate feedback mechanisms. For a 4 liter sample at ambient COS mixing ratio, ~500 parts per trillion (ppt), we obtain a reproducibility error of 2.

Constraining the atmospheric OCS budget from sulfur isotopes.

Carbonyl sulfide (OCS), the most abundant sulfur-containing gas in the atmosphere, is used as a proxy for photosynthesis rate estimation. However, a large missing source of atmospheric OCS has been inferred. Sulfur isotope measurements (S/S ratio and S) on OCS are a feasible tool to distinguish OCS sources from oceanic and anthropogenic emissions.

Isotopic Fractionation of Sulfur in Carbonyl Sulfide by Carbonyl Sulfide Hydrolase of Thiobacillus thioparus THI115.

Carbonyl sulfide (COS) is one of the major sources of stratospheric sulfate aerosols, which affect the global radiation balance and ozone depletion. COS-degrading microorganisms are ubiquitous in soil and important for the global flux of COS. We examined the sulfur isotopic fractionation during the enzymatic degradation of COS by carbonyl sulfide hydrolase (COSase) from Thiobacillus thioparus THI115.

Automated system measuring triple oxygen and nitrogen isotope ratios in nitrate using the bacterial method and N O decomposition by microwave discharge.

Rationale: Triple oxygen and nitrogen isotope ratios in nitrate are powerful tools for assessing atmospheric nitrate formation pathways and their contribution to ecosystems. N O decomposition using microwave-induced plasma (MIP) has been used only for measurements of oxygen isotopes to date, but it is also possible to measure nitrogen isotopes during the same analytical run.

Methods: The main improvements to a previous system are (i) an automated distribution system of nitrate to the bacterial medium, (ii) N O separation by gas chromatography before N O decomposition using the MIP, (iii) use of a corundum tube for microwave discharge, and (iv) development of an automated system for isotopic measurements.

Sulfur Isotopic Fractionation of Carbonyl Sulfide during Degradation by Soil Bacteria.

We performed laboratory incubation experiments on the degradation of gaseous phase carbonyl sulfide (OCS) by soil bacteria to determine its sulfur isotopic fractionation constants ((34)ε). Incubation experiments were conducted using strains belonging to the genera Mycobacterium, Williamsia, and Cupriavidus isolated from natural soil environments. The (34)ε values determined were -3.