13C/12C AND D/H ISOTOPIC ANALYSIS OF ATMOSPHERIC METHANE
Impact/Purpose:
This project proposes to estimate various source contributions to the global methane budget by making atmospheric observations of the mean methane isotopic signature and relating these isotopic signals to sources using mass balance.
This project proposes to estimate various source contributions to the global methane budget by making atmospheric observations of the mean methane isotopic signature and relating these isotopic signals to sources using mass balance.
Description:
The magnitudes of the sources and sinks of greenhouse gases like methane need to be better understood to accurately measure changes in emissions and ensure international compliance with global environmental policies such as the Kyoto Protocol.
Record Details:
Record Type:PROJECT(
ABSTRACT
)
Start Date:08/01/2000
Completion Date:08/01/2003
Record ID:
85286
Keywords:
METHANE, ISOTOPES, SPECTROMETER, CARBON, HYDROGEN.,
Related Organizations:
Role
:OWNER
Organization Name
:UNIVERSITY OF COLORADO - BOULDER
Mailing Address
:Campus Box 17
Citation
:Boulder
State
:CO
Zip Code
:80309
Project Information:
Approach
:An infrared absorption spectrometer will be developed that will have sufficient
sensitivity to resolve spatial and temporal trends in both 13C/12C and D/H stable
isotopic ratios. To date, measurements of atmospheric methane 13C/12C and D/H values have
been performed almost exclusively by isotope ratio mass spectrometry. However,
because 13CH4 and
12CH3D have the same
isotopic mass, their measurement requires extensive procedures to convert the
CH4 to CO2 and H2. Infrared absorption spectroscopy offers a simple,
nondestructive way to simultaneously measure the methane, carbon, and hydrogen
isotopic compositions. Samples will be obtained from a global air-sampling
network to provide a good spatial distribution of sites from which to collect
methane variability data and deduce source and sink information. The
spectrometer employs periodically poled lithium niobate (PPLN) to generate
different frequency radiation from two near infrared diode lasers (one at 811 nm
and the other at 1066 nm). This technique yields ~10 microwatts of single mode,
tunable radiation that probes the v3 rotational-vibrational absorption band at
3.4 microns. The radiation is passed through a multipass absorption cell with a
path length of 36 meters and a volume of 0.3 liter. Second harmonic wavelength
modulation is utilized to reduce spectrometer noise. The current detection limit
is 2 ppb of methane. Because the tropospheric mixing ratio of 12CH3D is ~1 ppb and is comparable to
the instrument detection limit, a procedure to concentrate methane samples is
required before isotopic analysis. Methane is
Cost
:$79,280.00
Research Component
:Fellowship - Atmospheric Chemistry
Approach
:
An infrared absorption spectrometer will be developed that will have sufficient
sensitivity to resolve spatial and temporal trends in both 13C/12C and D/H stable
isotopic ratios. To date, measurements of atmospheric methane 13C/12C and D/H values have
been performed almost exclusively by isotope ratio mass spectrometry. However,
because 13CH4 and
12CH3D have the same
isotopic mass, their measurement requires extensive procedures to convert the
CH4 to CO2 and H2. Infrared absorption spectroscopy offers a simple,
nondestructive way to simultaneously measure the methane, carbon, and hydrogen
isotopic compositions. Samples will be obtained from a global air-sampling
network to provide a good spatial distribution of sites from which to collect
methane variability data and deduce source and sink information. The
spectrometer employs periodically poled lithium niobate (PPLN) to generate
different frequency radiation from two near infrared diode lasers (one at 811 nm
and the other at 1066 nm). This technique yields ~10 microwatts of single mode,
tunable radiation that probes the v3 rotational-vibrational absorption band at
3.4 microns. The radiation is passed through a multipass absorption cell with a
path length of 36 meters and a volume of 0.3 liter. Second harmonic wavelength
modulation is utilized to reduce spectrometer noise. The current detection limit
is 2 ppb of methane. Because the tropospheric mixing ratio of 12CH3D is ~1 ppb and is comparable to
the instrument detection limit, a procedure to concentrate methane samples is
required before isotopic analysis. Methane is
Cost
:$79,280.00
Research Component
:Air Quality and Air Toxics
Approach
:
An infrared absorption spectrometer will be developed that will have sufficient
sensitivity to resolve spatial and temporal trends in both 13C/12C and D/H stable
isotopic ratios. To date, measurements of atmospheric methane 13C/12C and D/H values have
been performed almost exclusively by isotope ratio mass spectrometry. However,
because 13CH4 and
12CH3D have the same
isotopic mass, their measurement requires extensive procedures to convert the
CH4 to CO2 and H2. Infrared absorption spectroscopy offers a simple,
nondestructive way to simultaneously measure the methane, carbon, and hydrogen
isotopic compositions. Samples will be obtained from a global air-sampling
network to provide a good spatial distribution of sites from which to collect
methane variability data and deduce source and sink information. The
spectrometer employs periodically poled lithium niobate (PPLN) to generate
different frequency radiation from two near infrared diode lasers (one at 811 nm
and the other at 1066 nm). This technique yields ~10 microwatts of single mode,
tunable radiation that probes the v3 rotational-vibrational absorption band at
3.4 microns. The radiation is passed through a multipass absorption cell with a
path length of 36 meters and a volume of 0.3 liter. Second harmonic wavelength
modulation is utilized to reduce spectrometer noise. The current detection limit
is 2 ppb of methane. Because the tropospheric mixing ratio of 12CH3D is ~1 ppb and is comparable to
the instrument detection limit, a procedure to concentrate methane samples is
required before isotopic analysis. Methane is
Cost
:$79,280.00
Research Component
:Academic Fellowships
Project IDs:
ID Code
:U915835
Project type
:Fellowship