NOAA logo National Oceanic and Atmospheric Administration (NOAA),
Earth System Research Laboratory (ESRL)

What does this program measure?

The Mauna Loa Halocarbon and Trace Species (HATS) program is a cornerstone to NOAA's efforts to monitor ozone-depleting gases across the globe at remote sites. The NOAA record of ozone-depleting gases is one of the world's most reliable and complete records of atmospheric changes in ozone-depleting gases, and their replacements. Many gases measured in the HATS group also influence climate, such as N2O and SF6, among others. And many are considered hazardous air pollutants.

The table below contains a list of chemicals for which data is currently being obtained from the HATS flask sampling program. The column labeled "DL" denotes the detection limit measured in parts-per-trillion (ppt). The column labeled "Relevance" is clarified by the footnotes below the table.

CFCs Chlorofluorocarbons Relevance* DL
CFC-11 - Trichloro(mono)fluoromethane 1,2 0.5
CFC-12 - Dichlorodifluoromethane 1,2 0.5
CFC-113 - Trichlorotrifluoroethane 1,2 0.5
CFC-114 / CFC-114a § 1 <0.5
HCFCs Hydrochlorofluorocarbons Relevance* DL
HCFC-22 - Chlorodifluoromethane 1,2,3 <0.5
HCFC-141a - Dichlorofluoroethane 1,2 0.15
HCFC-142b - Chlorodiflouroethane 1,2 <0.5
HCFC-124 § 1,3 <0.5
HFCs Relevance* DL
HFC-134a 2,3 <0.25
HCFC-152a 3 0.5
Methyl Halides Relevance* DL
CH3Cl 1,4 0.5
CH3Br - Methyl Bromide 1,4 0.1
CH3I 4 0.1
Other Chlorinated Hydrocarbons Relevance* DL
CCl 4 - Carbon Tetrachloride 1,4 0.5
CH 3CCl 3 - Methyl Chloroform 1,4 0.25
CH2Cl2 - Dichloromethane 4 0.5
CHCl3 - Chloroform 4 0.5
C2Cl4 - Tetrachloroethylene 4 <0.25
C2HCl3 - Trichloroethylene 4,5 <0.5
Other Brominated Hydrocarbons Relevance* DL
Halon 1211 1 0.1
Halon 1301 1,5 0.1
Halon 2402 1,5 0.1
CHBr3 - Bromoform 4 0.1
CH2Br2 4,5 <0.2
Miscellaneous Relevance* DL
C6H6 - Benzene 4 <0.5
COS - Carbonyl Sulfide 4 1.0
CS2 4 <0.5
N2O - Nitrous Oxide 1,2 n.d.
SF6 2 n.d.

§ = Not well calibrated
*1 = Primary ozone-depleting gas, production regulated by the Montreal Protocol (with the exception of CH3Cl and N2O)
*2= Radiatively important gas
*3 = Replacement for ozone-depleting gases
*4 = Hazardous Air Pollutant
*5 = Measured from a subset of samples collected

How does this program work?

Flasks are sampled with air from atop MLO and at other sites across the globe. These flasks are then sent to Boulder and are analyzed by gas chromatography with electron capture and mass spectrometric detection techniques

The table below lists the instruments, frequency and location of the specific compounds measured.

Measurements Instruments Frequency Site
N2O, CFC-11, CFC-12, CFC-113, CH3CCl3, CCl4 300-mL stainless steel flasks 1/week MLO
N2O, CFC-11, CFC-12, CFC-113, CH3CCl3, CCl4, SF6, HCFC-22, HCFC-141b, HCFC-142b, CH3Br, CH3Cl, CH2Cl2, CHCl3, C2HCl3, C2Cl4, H-1301, H-1211, H-2402, HFC-134a 850-mL stainless steel flasks 1/week MLO & Kumukahi
N2O, CFC-11, CFC-12, CFC-113, CH3CCl3, CCl4 HP5890 automated GC 1/hour MLO
N2O Shimadzu automated GC 1/hour MLO

Why is this research important?

This program provides the basis for understanding changes in the depletion of the stratospheric ozone layer. The data is heavily relied upon by nations across the globe to understand if policy decisions have had the desired effect in reducing atmospheric amounts of chemicals that deplete the ozone layer. Nearly all the chemicals measured are also strong greenhouse gases and influence climate. The results are also important for understanding the concentrations of hazardous air pollutants being transported from other countries to the US.

Are there any trends in the data?

The results from this program were the first to show that the overall abundance of ozone-depleting gases peaked in the early-mid 1990s and has since declined. This bodes well for the ozone layer--if these declines continue, scientists expect that the ozone layer will ultimately recover. Despite a decline in the ozone-depleting power of these gases, their influence on warming the climate continues to increase.

Note: For more information and results, please read Halocarbons and Other Atmpsoheric Trace Species (HATS) Trends in the Troposphere (pdf)

Global CFC Decreases
solf 2006
Halons 2006
Substitude Halocarbons

How does this program fit into the big picture?

What is it's role in global climate change?

This measurement program supplies unique and important information that enables humans everywhere to understand how the threat that human actions have posed to the ozone layer and climate are changing over time.

Comments and References

  • Butler, J.H., K.B. Egan, T.M. Thompson, and J.W. Elkins, Nitrous oxide in the atmosphere, surface water, and at depth for the western Pacific and Eastern Indian Oceans, in EOS, pp. 1220, 1987.
  • Butler , J.H., J.W. Elkins, B.D. Hall, S.O. Cummings, and S.A. Montzka, A decrease in the growth rates of atmospheric halon concentrations, Nature, 359, 403-405, 1992.
  • Butler, J.H., J.W. Elkins, T.M. Thompson, and K.B. Egan, Tropospheric and dissolved N2O of the west Pacific and east Indian Oceans during the El Niño-Southern Oscillation event of 1987, J. Geophys. Res. , 94 (D12), 14865-14877, 1989.
  • Butler, J.H., S.A. Montzka, A.D. Clarke, J.M. Lobert, and J.W. Elkins, Growth and distribution of halons in the atmosphere, J. Geophys. Res. , 103 (D1), 1503-1511, 1998.
  • Elkins, J.W., T.M. Thompson, T.H. Swanson, J.H. Butler, B.D. Hall, S.O. Cummings, D.A. Fisher, and A.G. Raffo, Decrease in the growth rates of atmospheric chlorofluorocarbons
  • Montzka, S.A, J.H. Butler, B.D. Hall, J.W. Elkins, D.J. Mondeel, A decline in tropospheric organic bromine, Geophy. Res. Lett., 30(15), 1826, doi:10.1029/2003GL017745, 2003.
  • Montzka, S.A., J.H. Butler, J.W. Elkins, T.M. Thompson, A.D. Clarke, and L.T. Lock, Present and future trends in the atmospheric burden of ozone-depleting halogens, Nature, 398, 690-694, 1999.
  • Montzka, S.A., J.H. Butler, R.C. Myers, T.M. Thompson, T.H. Swanson, A.D. Clarke, L.T. Lock, J.W. Elkins, Decline in the tropospheric abundance of halogen from halocarbons: Implications for stratospheric ozone depletion, Science, 272, 1318-1322, 1996 (received NOAA Outstanding Scientific Paper of the Year Award).
  • Montzka, S.A., R.C. Myers, J.H. Butler, J.W. Elkins, L. Lock, A. Clarke, and A.H. Goldstein, Observations of HFC-134a in the remote troposphere, Geophys Res. Lett., 23, 169-172, 1996.
  • Montzka, S.A., R.C. Myers, J.H. Butler, and J.W. Elkins, Early trends in the global tropospheric abundance of hydrochlorofluorocarbon-141b and -142b, Geophys. Res. Lett., 21, 2483-2486, 1994.
  • Montzka, S.A., R.C. Myers, J.H. Butler, J.W. Elkins, and S.O. Cummings, Global tropospheric distribution and calibration scale of HCFC-22, Geophys Res. Lett., 20, 703-706, 1993.
Lead Investigator(s):

James W. Elkins
Stephen A. Montzka
Debbie Modeel

MLO Contact(s):

Aidan Colton
808-933-6965 (x233)
Paul Fukumura
808-933-6965 (x223))

Web Site(s)
Halocarbons and Other Atmpsoheric Trace Species (HATS) Trends in the Troposphere (pdf)

Date Started


Related Programs

Stealth Gas Chromatograph
Cooperative Global Air Sampling
Greenhouse Gases

Stainless Steel Flasks