NIST Database for the Isotopic Composition of Selected Atmospheric Constituents

Standard Reference Database Number 77

© 1999 Copyright by the U.S. Secretary of Commerce on behalf of the United States of America. All rights reserved.

NIST reserves the right to charge for these data in the future.

The National Institute of Standards and Technology (NIST) uses its best efforts to deliver a high quality copy of the Database and to verify that the data contained therein have been selected on the basis of sound scientific judgement. However, NIST makes no warranties to that effect, and NIST shall not be liable for any damage that may result from errors or omissions in the database.

Importance of Isotopic Data in Atmospheric Studies

The proportions of the less abundant stable isotopes such as deuterium (²H) and carbon-13 (¹³C) in atmospheric species are controlled by various factors. The main factors are the isotopic composition of precursor molecules, the kinetics of production at sources, and the kinetics of removal at sinks. These kinetic processes are known as kinetic isotope effects. For the radioactive isotopes such as tritium (³H) and carbon-14 (¹⁴C) in atmospheric species, proportions are controlled primarily by cosmogenic production rates, emissions from nuclear reactors, and radioactive decay processes.

As a result of these processes, the sources and sinks of atmospheric species are encoded in their isotopic compositions. With atmospheric methane, for example, large ¹⁴CH₄ levels in ambient air may indicate the predominance of methane from modern sources such as wetlands, rice paddies and ruminates.

The Isotopic Database for Atmospheric Methane and its Sources

The existing database contains over a thousand reported measurements of CH₃D, ¹³CH₄, and ¹⁴CH₄ at sources and in tropospheric air. These isotopic data are useful to modelers who quantify the global or regional methane budgets by comparing the isotopic compositions of methane in ambient air with the isotopic compositions of the aggregate of flux-weighted sources. Temporal and spatial isotopic variations in the database are also useful for distinguishing the types of methane in subsurface natural gas exploration and for understanding wetland methanogenic pathways.

The methane isotopic database contains numeric and text information on

• methane source types
• sampling times, locations, collection procedures and measurement procedures
• sampling and measurement uncertainties
• isotopic measurements and associated statistics
• data interpretation
• references and personnel involved in data collection

In the following pages, you will be able to search for specific isotopic information by

• methane source type
• years or seasons when samples were collected
• latitude and longitude or latitudinal zone for locations of samples

You will also be able to search on a specific database record number. A database record contains all of the information on a specific sample: numeric information such as measured values and sampling/measurement uncertainties as well as ancillary text information such as collection/measurement procedures and how the data were interpreted when first reported.

Isotopic Database for Other Atmospheric Species

NIST is planning to expand this database to include isotopic compositions of additional trace atmospheric species, primarily in the troposphere. Candidate species are carbonaceous, sulfate and nitrate aerosols, carbon monoxide, reduced sulfur compounds (e.g., H₂S, CH₃SCH₃) and sulfur dioxide, and reduced nitrogen (e.g., N₂, NH₄⁺/NH₃) and nitrogen oxides.

We invite your comments - see email address below - on the need for additions to this database.

Press here for information on how isotopic measurements and standards are defined.

Press here to start search.

This database was created by Joseph M. Conny. The search engine was written by Tatiana Levitsky.

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