Modern Records of Radiatively Important Halogenated Compounds in the Atmosphere
This page provides links to modern instrumental data for a wide variety of radiatively important halogenated compounds. (Data on some other compounds can also be found at these links; gateway pages giving more complete sets of links to records of carbon dioxide, methane and nitrous oxide are available from CDIAC.) Records extend from the beginning of measurements to the most recent data available for each species. There are two programs that include multiple stations with current records derived from flask samples or in-situ measurements of ambient air. These are: (1) the Advanced Global Atmospheric Gases Experiment (AGAGE) or, its predecessors, the Atmospheric Lifetime Experiment (ALE) and the Global Atmospheric Gases Experiment (GAGE), and its collaborators including the System for Observation of halogenated Greenhouse gases in Europe (SOGE), and (2) the Earth System Research Laboratory, Global Monitoring Division, National Oceanic and Atmospheric Administration (NOAA). The World Data Center for Greenhouse Gases (WDCGG) also provides data on several halogenated species for stations around the world. While this site provides the greatest geographical coverage, data may not always be as current as from the individual sources listed above.
A brief history of the ALE/GAGE/AGAGE program, which began in 1978, can be found here. The NOAA Halocarbons and other Atmospheric Trace Species (HATS) program began with flask measurements in 1977. About 10 years later in situ measurements were begun at some stations under a program called Radiatively Important Trace Species (RITS) which later became the Chromatograph for Atmospheric Trace Species (CATS) program which has newer, custom built, gas chromatographs. CATS data are available from six locations and include the same compounds as did the RITS program, plus additional trace gases including carbonyl sulfide (COS), halon-1211 (CBrClF2), HCFC-22 (CHClF2), HCFC-142b (CH3CClF2) and methyl chloride (CH3Cl). Both the AGAGE and NOAA programs measure sulfur hexafluoride (SF6).
The following organizations have current data from multiple sites.
- Investigators participating in the Advanced Global Atmospheric Gases Experiment (AGAGE).
- Research staff at the Earth System Research Laboratory, Global Monitoring Division, NOAA.
- The world data center for greenhouse gases (WDCGG) archives data on several halogenated species from sources around the world
- CDIAC also maintains some otherwise unavailable records.
Period of Record
1977-current depending on species and location.
- AGAGE and NOAA: Station locations are indicated on the maps below.
- WDCGG: Select a species (e.g. SO2F2) or species group (e.g., CFCs) from the parameter list.
- AGAGE:: Thumbnails of graphs for all AGAGE species
- (NOAA introductory material): Trends for the halogenated species CFC-11, CFC-12, SF6 (and also for N2O) can be found from the HATS introductory page. In the left hand column under "data", select a species, and introductory material including a comprehensive set of graphics for that species will appear, as will a link to the underlying data.
Another graphic, along with a good introduction to ozone-depleting substances, is located here.
- NOAA in situ measurements (CATS program): NOAA in situ measurements. For any of the six in-situ sites, select a compound and graphics will appear depicting time series for: (1) the selected station, (2) the selected station compared with other stations and (3) Northern Hemisphere, Southern Hemisphere and global averages.
- AGAGE: Data may be obtained directly from the AGAGE home page or from the CDIAC website.
- NOAA: Go to the general page for all atmospheric species and select halocompounds from the left hand column, or go directly to halocompounds and select in situ or Flask. Select combined for total bromine, total chlorine and equivalent effective chlorine data from one or both sampling methods at 14 sites (the 15 listed on the map above, minus the Wisconsin site). The 3-letter code for each station is given on the map above.
- In situ SF6 data are available from the CATS program, and monthly flask SF6 data for 13 stations (Harvard Forest and Park Falls Wisconsin not included) are available from the HATS program. The general ftp data directory for the HATS program provides quick ftp access to NOAA data on halogenated species.
- WDCGG: Select a species or species group from the parameter list.
- In situ data (1996-2005) from Harvard Forest are also available.
- CDIAC: Data and graphics for individual locations covering limited time periods in recent decades are also available at CDIAC sites:
- Methane, Nonmethane Hydrocarbons, Alkyl Nitrates, and Chlorinated Carbon Compounds including three Chlorofluorocarbons (CFC-11, CFC-12, and CFC-113) in Whole-air Samples.
- Atmospheric CFC-11, CFC-12, CFC-113, CCl4 and SF6 Histories (1910-2011).
- Mixing Ratios of CO, CO2, CH4, and Isotope Ratios of Associated 13C, 18O, and 2H in Air Samples from Niwot Ridge, Colorado, and Montaña de Oro, California, USA (January 2004).
- Globally Averaged Atmospheric CFC-11 Concentrations: Monthly and Annual Data for the Period 1975-1992.
- Atmospheric Methyl Chloride.
- Trifluoromethyl Sulfur Pentafluoride (SF5CF3) and Sulfur Hexafluoride (SF6) from Dome Concordia.
- Atmospheric Fluoroform (CHF3, HFC-23) at Cape Grim, Tasmania.
- Vertical Profiles:
Gas chromatography (GC) is used to separate the species of interest. A sample is injected into a stream of inert carrier gas; the combined gases then move through an "obstacle course" of porous beads, sometimes coated with a liquid, which impede molecular movement so that the exiting molecules are sorted according to size and solubility. For radiatively active halogenated species, the amount of a particular exiting species is then measured by electron capture or mass spectrometry.
Electron Capture (EC) When compounds of a particular species having an enhanced affinity for electrons emerge from the gas chromatograph they enter an electron capture detector, in which an electron source produces a measurable current. The species being measured than absorbs (captures) some of the electrons, reducing the current. The reduction in the current is a measure of the amount of chemical present.
A discussion of how gas chromatography is used in conjunction with electron capture can be found here. (Scroll down to bottom of page.)
Mass spectrometry (MS) Molecules emerging from chromatographic sorting are bombarded with electrons to create ions with particular mass to charge ratios. An electromagnetic field then causes molecules of different mass/charge ratios to follow different paths. The number of ions passing along a particular path is measured by an electronic signal. A nontechnical introduction to mass spectrometry may be found here.
Calibration is accomplished by periodically injecting gas mixtures containing known quantities of the chemicals of interest and measuring their signals.
Information on calibration scales may be found at the following links:
- AGAGE: http://agage.eas.gatech.edu/data_archive/agage/gc-md/readme.scale
- NOAA: http://www.esrl.noaa.gov/gmd/ccl/summary_table.html
- More detailed NOAA calibration information: http://www.esrl.noaa.gov/gmd/ccl/
As a result of The Montreal Protocol on Substances that Deplete the Ozone Level, several halocompounds, identified as both ozone depleting substances and radiatively active ("greenhouse") gases, have been replaced with substitutes selected primarily to reduce destruction of stratospheric ozone. However, many of the replacement compounds are radiatively active, and are increasing. The result is a wide range of trends among the halogenated species in the atmosphere. While major ozone-depleting species such as CFCs 11, 12 and 113 are trending downward, their radiatively active substitutes, are increasing. The net effects on stratospheric ozone and on the "greenhouse" effect are summarized by two indices.
The Ozone Depleting Gas Index (ODGI) for Antarctic regions, and a separate index for mid latitudes of the Southern Hemisphere, provide an overview of the ozone-depleting effects of halocompounds. By 2010, the Antarctic index had decreased by more than 15% of its peak (1994) value and the mid latitude index had decreased by over 30% of its peak (also 1994) value. The ODGI is calculated from surface measurements; effects show up in the Southern Hemispheric stratosphere after about three years in mid latitudes and after about six years in Antarctic regions.
The Annual Greenhouse Gas Index (AGGI) summarizes how trends of the most significant greenhouse gases add up from a radiative standpoint. The overall trend in radiative forcing of the troposphere ("greenhouse effect") continues upward, as does the contribution of halogenated species, which is currently about 12% of the total contribution of all species included. However the collective contribution of halogenated species tended to level off in the early 1990s and is now increasing at a much slower rate, due primarily to the net effect of decreases in CFC-11 and CFC-12 and increases in their substitutes. The rate of radiative forcing increase of all halogenated species included in the index from 2001-2010 was about 12% of the pre-1990 rate of increase for the same species.
Citing This Material
- AGAGE: The general reference for AGAGE data is:
- NOAA: Citations for NOAA data are provided in the readme files (flask data), or in the header of each data file (in situ data). For combined sets use the in situ format.
- WDCGG: Citation instructions are given in red on the WDCGG home page. By use of these data "you accept that an offer of co-authorship will be made through personal contact with the data providers or owners whenever substantial use is made of their data. In all cases, an acknowledgement must be made to the data providers or owners and the data centre when these data are used within a publication."
- If accessing the data from this site: please also cite: Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy.
- If citing material from this page only, cite as: Modern Records of Atmospheric Concentrations of Radiatively Important Halogenated Compounds. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory. http://cdiac.ornl.gov/modern_halogens.html
For particular gases, other appropriate references are given here.