Large-Volume Injection and Assessment of Reference Standards for n-Alkane δD and δC Analysis via Gas Chromatography Isotope Ratio Mass Spectrometry.

Rationale: Compound-specific stable isotope analysis of hydrogen (δD) and carbon (δC) in organic compounds is a valuable tool in biogeochemical research. A key limitation of this method is the relatively large amount of sample required to achieve desirable precision.

Methods: We developed a large-volume (20 μL) injection method that allows for high throughput analysis of less concentrated samples and tested it for δC and δD measurements of n-alkanes.

Analytical improvements and assessment of long-term performance of the oxidation-denitrifier method.

Unlabelled: The analysis of the nitrogen (N) isotopic composition of organic matter bound to fossil biomineral structures (BB-δ N) using the oxidation-denitrifier (O-D) method provides a novel tool to study past changes in N cycling processes.

Methods: We report a set of methodological improvements to the O-D method, including (a) a method for sealing the reaction vials in which the oxidation of organic N to NO takes place, (b) a recipe for bypassing the pH adjustment step before the bacterial conversion of NO to N O, and (c) a method for storing recrystallized dipotassium peroxodisulfate (K S O ) under Ar atmosphere.

Results: The new sealing method eliminates the occasional contamination and vial breakage that occurred previously while increasing sample throughput.

Parameterization of thermal properties of aging secondary organic aerosol produced by photo-oxidation of selected terpene mixtures.

Formation and evolution of secondary organic aerosols (SOA) from biogenic VOCs influences the Earth's radiative balance. We have examined the photo-oxidation and aging of boreal terpene mixtures in the SAPHIR simulation chamber. Changes in thermal properties and chemical composition, deduced from mass spectrometric measurements, were providing information on the aging of biogenic SOA produced under ambient solar conditions.

A large source of low-volatility secondary organic aerosol.

Forests emit large quantities of volatile organic compounds (VOCs) to the atmosphere. Their condensable oxidation products can form secondary organic aerosol, a significant and ubiquitous component of atmospheric aerosol, which is known to affect the Earth's radiation balance by scattering solar radiation and by acting as cloud condensation nuclei. The quantitative assessment of such climate effects remains hampered by a number of factors, including an incomplete understanding of how biogenic VOCs contribute to the formation of atmospheric secondary organic aerosol.