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Recent Research Highlights

  1. Renewed growth of atmospheric methane

  2. Nitrogen trifluoride in the global atmosphere

  3. Global Budget of Hydrogen determined from Measurement and Modeling

  4. HFC-245fa and HFC-365mfc — New foam-blowing hydrofluorocarbons (HFCs) on the horizon

  5. What were the trace gas and particulate emissions from the 2003 southern California wildfires?

  6. Observations of 1,1-difluoroethane (HFC-152a) at AGAGE and SOGE monitoring stations 1994-2004 and derived global and regional emission estimates

  7. Retention behaviour of volatile C1 -C3 fluoroalkanes upon selected preconcentration adsorbents. I. Carbon molecular sieves and activated charcoals

  8. Global trends, seasonal cycles and European emissions of dichloromethane, trichloroethene and tetrachloroethene from the AGAGE observations at Mace Head, Ireland and Cape Grim, Tasmania.

  9. Can recent growth rate anomalies in the greenhouse gases be attributed to large-scale biomass burning events?

  10. What are the lingering U.S. emissions of ozone-depleting gases?

  11. Are there large lingering European emissions of the important ozone-depleting gas methyl chloroform (1,1,1-trichloroethane)?

  12. Is the self-cleansing capacity of the atmosphere changing?

Renewed Growth of Atmospheric Methane

Following almost a decade with little change in global atmospheric methane mole fraction, we present measurements from the Advanced Global Atmospheric Gases Experiment (AGAGE) and the Australian Commonwealth Scientific and Industrial Research Organization (CSIRO) networks that show renewed growth starting near the beginning of 2007. Remarkably, a similar growth rate is found at all monitoring locations from this time until the latest measurements. We use these data, along with an inverse method applied to a simple model of atmospheric chemistry and transport, to investigate the possible drivers of the rise. Specifically, the relative roles of an increase in emission rate or a decrease in concentration of the hydroxyl radical, the largest methane sink, are examined. We conclude that: if the annual mean hydroxyl radical concentration did not change, a substantial increase in emissions was required simultaneously in both hemispheres between 2006 and 2007; 2) if a small drop in the hydroxyl radical concentration occurred, consistent with AGAGE methyl chloroform measurements, the emission increase is more strongly biased to the Northern Hemisphere.

For reprints and further information, please contact: rprinn @ mit. edu

Reference:   Rigby, R. G., Prinn, P. J. Fraser, P. G. Simmonds, R. L. Langenfelds, J. Huang, D. M. Cunnold, L. P. Steele, P. B. Krummel, R. F. Weiss, S. O’Doherty, P. K. Salameh, H. J. Wang, C. M. Harth, J. Mühle, and L. W. Porter, Renewed growth of atmospheric methane, Geophys. Res. Lett., 35, L22805, doi:10.1029/2008GL036037, 2008.

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Nitrogen trifluoride in the global atmosphere

Background atmospheric abundances and trends of nitrogen trifluoride (NF3), a potent anthropogenic greenhouse gas, have been measured for the first time. The mean global tropospheric concentration of NF3 has risen quasi-exponentially from about 0.02 ppt (parts-per-trillion, dry air mole fraction) at the beginning of our measured record in 1978, to a July 1, 2008 value of 0.454 ppt, with a rate of increase of 0.053 ppt yr -1 or about 11% per year, and an interhemispheric gradient that is consistent with these emissions occurring overwhelmingly in the Northern Hemisphere, as expected. This rise rate corresponds to about 620 metric tons of current NF3 emissions globally per year, or about 16% of the poorly-constrained global NF3 production estimate of 4,000 metric tons yr-1. This is a significantly higher percentage than has been estimated by industry, and thus strengthens the case for inventorying NF3 production and for regulating its emissions

For reprints and further information, please contact: rfw @ gaslab. ucsd. edu

Reference:  Weiss, R.F., J. Mühle, P.K. Salameh, and C.M. Harth, Nitrogen trifluoride in the global atmosphere, Geophys. Res. Lett., 35, L20821, doi:10.1029/2008GL035913, 2008.

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Global Budget of Hydrogen determined from Measurement and Modeling

Hydrogen (H2), a proposed clean energy alternative, warrants detailed investigation of its global budget and future environmental impacts.  The magnitudes and seasonal cycles of the major (presumably microbial) soil sink of hydrogen have been estimated from high-frequency in situ AGAGE H2 observations and also from more geographically extensive but low-frequency flask measurements from CSIRO and NOAA-GMD using the Kalman filter in a two-dimensional (2-D) global transport model.  Hydrogen mole fractions exhibit well-defined seasonal cycles in each hemisphere with their phase difference being only about 3 months.  The global production rate of H2 is estimated to be 103 ± 10 Tg yr-1 with only a small estimated interannual variation.  Soil uptake (84 ± 8 Tg yr-1) represents the major loss process for H2 and accounts for 81% of the total destruction.  Strong seasonal cycles are deduced for the soil uptake of H2.  The soil sink is a maximum over the northern extratropics in summer and peaks only 2 to 3 months earlier in the Northern Hemisphere than in the Southern Hemisphere.  Oxidation by tropospheric OH (18 ± 3 Tg yr-1) accounts for 17% of the destruction, with the remainder due to destruction in the stratosphere.  The calculated global burden is 191 ± 29 Tg, indicating an overall atmospheric lifetime of 1.8 ± 0.3 years.  Hydrogen in the troposphere (149 ± 23 Tg burden) has a lifetime of 1.4 ± 0.2 years.

For reprints and further information, please contact: rprinn @ mit. edu

Reference:   X. Xiao. R. G. Prinn, P. G. Simmonds, L. P. Steele, P. C. Novelli, J. Huang, R. L. Langenfelds, S. O'Doherty, P. B. Krummel, P. J. Fraser, L. W. Porter, R. F. Weiss, P. Salameh, and R. H. J. Wang (2007), Optimal estimation of the soil uptake rate of molecular hydrogen from the Advanced Global Atmospheric Gases Experiment and other measurements, J. Geophys. Res., 112, D07303, doi:10.1029/2006JD007241.

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HFC-245fa and HFC-365mfc — New foam-blowing hydrofluorocarbons (HFCs) on the horizon

The regulations of the Montreal Protocol on Substances that Deplete the Ozone layer and its Amendments and Adjustments has led to the phase-out of chlorofluorocarbons (CFCs) and hydrofluorochlorocarbons (HCFCs) in the rigid foam blowing sector. As a consequence the production of new hydrofluorocarbons (HFCs) has recently begun. Their escape to the atmosphere has led to the first appearance and rapid growth of HFC-245fa (CHF2CH2CF3) and HFC-365mfc (CH3CF2CH2CF3) as observed at the Jungfraujoch SOGE station and now also at AGAGE stations. HFC-365mfc is currently produced in a single plant (France) and exclusively marketed in Europe. HFC-245fa is also produced in a single plant (Geismar, Louisiana) and predominantly marketed in North America.

The atmospheric background concentrations of both substances are very small and in the sub-ppt range. At Jungfraujoch, HFC-245fa has reached ~0.7 ppt at the end of 2005 while HFC-365mfc reached ~0.2 ppt at the end of 2004. HFC-365mfc emissions for central Europe were estimated at 400 - 500 t yr-1 for 2003 and 2004. For HFC-245fa, global emissions increased from 2100 - 2400 t in 2003 to 5100 - 5900 t in 2005. More measurements and improved modeling should help to further our understanding of the atmospheric budgets of these two compounds. Their current southern hemispheric emissions are negligible, suggesting that these new anthropogenic compounds may serve as interhemispheric transport tracers. Alternatively, because their only significant removal process from the atmosphere is OH, these compounds may help in assessing southern hemisphere OH concentrations.

For reprints and further information, please contact: martin.vollmer @ empa.ch

References:

K. Stemmler, D. Folini, S. Ubl, M. K. Vollmer, S. Reimann, S. O'Doherty, B. R. Greally, P. G. Simmonds, A. J. Manning, European emissions of HFC-365mfc, a chlorine-free substitute for the foam blowing agents HCFC-141b and CFC-11, 2007, Environ. Sci. Technol, 41, 1145-1151.

M. K. Vollmer, S. Reimann, D. Folini, L. W. Porter, L. P. Steele, First appearance and rapid growth of anthropogenic HFC-245fa (CHF2CH2CF3) in the atmosphere, 2006, Geophys. Res. Lett., 33, L20806, doi: 10.1029/2006GL026763

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What were the trace gas and particulate emissions from the 2003 southern California wildfires?

In October 2003, thirteen major wildfires in southern California burned more than 300,000 hectares of mainly chaparral biome, strongly impacting an urban area populated by ~20 million people. In situ trace gas and particle measurements of the wildfire plumes in La Jolla, California, showed a high degree of correlation among carbon dioxide (CO2), methane (CH4), nonmethane hydrocarbons (NMHCs), and methyl halide mixing ratios, as well as with particle number concentrations. The chemical compositions of individual particles with aerodynamic diameters of 50-300 nm and 200-2500 nm showed that 70-85% had typical biomass burning signatures with levoglucosan and potassium. Only 5-18% of particles in the 50-300 nm range had vehicle signatures, and C6H6/C7H8 and C6H6/C2H2 ratios confirmed the minor influence of urban pollution.

With the help of trace gas correlations with CO2, a Lagrangian atmospheric transport ”puff” model and a burned area approach, the emissions of the greenhouse gases CO2 and CH4, NMHCs (C2-hydrocarbons, benzene, and toluene), methyl halides (CH3Cl and CH3I), and PM2.5 particulate matter were estimated to have been at least 0.2-3.5% of global annual emissions from extratropical forest fires. CO2 and CH4 emissions over these few days corresponded to 0.2-0.4% of total U.S. emissions in 2003, and 3-7% of total California emissions in 2002. CH4, C6H6, and PM2.5 emissions corresponded to at least 28-36% of total yearly emissions from the San Diego and South Coast Air Basins. PM2.5 considerably exceeded the EPA short-term exposure limit, reaching severely unhealthy levels.

If future winter precipitation in the western U.S. shifts from snow to rain and local climate becomes dryer as predicated by climate models, more pronounced wildfire activity and increased emissions of trace gases and particles with local and global impacts are likely to occur.

For reprints and further information, please contact: jens @ gaslab . ucsd . edu

Reference: J. Mühle, T.J. Lueker, Y. Su, B.R. Miller, K.A. Prather, and R.F. Weiss, (2007), Trace gas and particulate emissions from the 2003 southern California wildfires, J. Geophys. Res., 112, D03307, doi:10.1029/2006JD007350.

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Observations of 1,1-difluoroethane (HFC-152a) at AGAGE and SOGE monitoring stations 1994-2004 and derived global and regional emission estimates

We have taken a 10-year record of observations of a gas used predominantly in hand-held foam blowing canisters and assessed the state of its trends in the atmosphere. This gas (HFC-152a) has a low atmospheric lifetime (approximately 1.5 year) which is evidenced in the observations through a well defined annual cycle consistent with its proposed removal mechanism via reaction with the OH radical in the lower atmosphere. We calculate the rising amount of HFC-152a in the global atmosphere and hence we derive the historical emission of this gas both on a global and regional basis. We estimate that there were approximately 28 ktonnes of HFC-152a emitted in 2004, and of this total European emissions accounted for approximately 5-15%. Australian emissions were neglible, only <0.05% of the global estimate. The observed growth rate for HFC-152a in the atmosphere is steadily increasing in both northern and southern hemispheres as its usage and emission steadily increases.

For reprints and further information, please contact: brian.greally @ bristol. ac. uk

Reference: Greally, B.R., A.J. Manning, S. Reimann, A. McCulloch, J. Huang, B.L. Dunse, P.G. Simmonds, R.G. Prinn, P.J. Fraser, D.M. Cunnold, S. O'Doherty, L.W. Porter, K. Stemmler, M.K. Vollmer, C.R. Lunder, N. Schmidbauer, O. Hermansen, J. Arduini, P.K. Salameh, P.B. Krummel, R.H.J. Wang, D. Folini, R.F. Weiss, M. Maione, G. Nickless, F. Stordal and R.G. Derwent (2007), Observations of 1,1-difluoroethane (HFC-152a) at AGAGE and SOGE monitoring stations 1994-2004 and derived global and regional emission estimates, Journal of Geophysical Research, 112, D06308, doi:10.1029/2006JD007527

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Retention behaviour of volatile C1-C3 fluoroalkanes upon selected preconcentration adsorbents. I. Carbon molecular sieves and activated charcoals

This paper describes experimental methods and presents results for the adsorption of atmospherically important gases on carbon-based solid adsorbent materials used principally in our on-site ADS-GCMS instruments. We describe two methods for determination of the "breakthrough" of gases through a tube filled with solid adsorbents, this breakthrough can then be used to calculate the retention behaviour of the test gas on the adsorbent material over a wide temperature range, including at below-ambient temperatures. The methods and results described allows the reader to determine whether a particular adsorbent class will be of use in similar or other instrumental systems used for measuring gases in air samples present in extremely low amounts in the atmosphere.

For reprints and further information, please contact: brian.greally @ bristol .ac .uk

Reference: Greally, B.R., G. Nickless and P.G. Simmonds (2006), Retention behaviour of volatile C1-C3 fluoroalkanes upon selected preconcentration adsorbents. I. Carbon molecular sieves and activated charcoals, Journal of Chromatography A, 1133, 49-57

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Global trends, seasonal cycles and European emissions of dichloromethane, trichloroethene and tetrachloroethene from the AGAGE observations at Mace Head, Ireland and Cape Grim, Tasmania.

Chlorinated hydrocarbons are emitted to the atmosphere from their widespread use as solvents in diverse industrial, commercial and domestic applications. Dichloromethane (CH2Cl2), trichloroethene, (C2HCl3) and tetrachloroethene (C2Cl4) are three important chlorinated solvents that are not regulated by the Montreal Protocol. Due to their short atmospheric lifetimes they have low impacts on stratospheric ozone and are removed from the atmosphere through oxidation by tropospheric OH, in the order of their atmospheric lifetimes C2HCl3-5 days, C2Cl4-100 days, and CH2Cl2-140 days. However, they are classed as hazardous air pollutants and toxic volatile organic compounds in regional air quality inventories.

GC-MS observations of dichloromethane (CH2Cl2), trichloroethene (C2HCl3), and tetrachloroethene (C2Cl4), have been recorded at two AGAGE station, Mace Head, Ireland and Cape Grim, Tasmania. However, trichloroethene is usually below the limit of detection at Cape Grim except during pollution episodes.

At Mace Head CH2Cl2 shows a downward trend from 1995-2004 of 0.7 ± 0.2 ppt yr-1 (ppt: expressed as dry mole fractions in 1012), although from 1998-2004 the decrease has been only 0.3 ± 0.1ppt yr-1.  Conversely, there has been a small but significant growth of 0.05 ± 0.01 ppt yr-1 in CH2Cl2 at Cape Grim (1998-2004). The time series for C2HCl3 and C2Cl4 are relatively short for accurate trend analyses, however, we observe a small but significant decline in C2Cl4. (0.18 ± 0.05 ppt yr-1) at Mace Head.

European emissions inferred from AGAGE measurements of these three solvents are compared to recent estimates from industry data, and show general agreement for C2HCl3. Emissions estimated from observations are lower than industry emission estimates for C2Cl4 and much lower in the case of CH2Cl2.  A study of wildfires in Tasmania, uncontaminated by urban emissions, suggests that the biomass burning source of CH2Cl2 may have been previously overestimated.

There are a number of possible explanations for the disagreement between the European emission estimates for CH2Cl2 by the NAME model and industry. The geographical areas covered by the two estimates are not identical although both methods include the major emitting countries. The calibration scale (UB98) for CH2Cl2 is based on a single primary calibration mixture. Recent comparisons of calibrated AGAGE CH2Cl2 in situ measurements with NOAA flask data at Mace Head show an absolute calibration difference of 8.8 ± 4%, with NOAA data higher. Reporting the AGAGE measurements on the NOAA scale would improve agreement between the two emission estimates in most years.

Emissions from Europe may be overstated by the industry estimates in a number of ways despite the fact that global emissions from the same database are consistent with our 12-box model results. Emissions are derived from consumption (sales) data and are assumed to occur in the same geographical area. Material shipped directly by producers is assumed as consumption at the destination, but significant exports from Europe of the solvents (by chemical merchants, not producers) or in equipment containing the solvents would result in the true emissions in Europe being lower than derived from consumption data.

There may be seasonal variability in the emissions and the relative loss rates of each individual solvent during transport are uncertain. Furthermore, halocarbons dissolved in surface water might be transported over a significant distance before temperature changes might cause them to be re-emitted to the atmosphere. Notably, of the three solvents CH2Cl2 has the highest water solubility [13.2g/liter @20oC].

There may also be unaccounted for sinks, such as hydrolysis, dry deposition and biodegradation which could perturb the relative emission ratios from the primary source regions. No single factor appears to account for the inconsistencies between industry-derived, NAME model-derived and CO inventory estimated emissions. In order to resolve some of these questions high frequency measurements from additional sites in Europe are required.

For reprints and further information, please contact:  PETERGSIMMONDS @ aol. com

Reference: Simmonds, P.G., A.J. Manning, D. M. Cunnold, P.J. Fraser, A. McCulloch, S. O'Doherty, P.B. Krummel, R.H.J. Wang, L.W. Porter, R.G. Derwent, B. Greally, P. Salameh, B.R. Miller, R.G. Prinn, and R.F. Weiss (2006), Observations of dichloromethane, trichloroethene and tetrachloroethene from the AGAGE stations at Cape Grim, Tasmania, and Mace Head, Ireland, J. Geophys. Res., 111, D18304, doi:10.1029/2006JD007082.

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Can recent growth rate anomalies in the greenhouse gases be attributed to large-scale biomass burning events?

An annual increase in the rate of accumulation of carbon dioxide (CO2) of more than 2 ppm was observed at the AGAGE station at Mace Head, Ireland during 2002-2003, in close agreement with a similar increase in the growth rate of CO2 reported from measurements at the Mauna Loa Observatory, Hawaii. This increase is unexpected, as it did not occur in a major El Niño period, and although CO2 emissions from global fossil fuel increased by more than the recent trend in 2002 and 2003, the additional increase (estimated from data in the BP Statistical Review of World Energy to be about 0.4 GtC in 2003, mainly due to increased coal consumption) is not sufficient to account for the anomaly. Sustained increases in the growth of CO2 above the historical average annual trend are significant, and would imply a positive feedback on global warming thereby accelerating climate change.

Moreover, at Mace Head simultaneous in situ measurements of CO, CH4, H2, O3, and CH3Cl also exhibit similar trends in their annual rates of increase as with CO2 in 1998-99 and 2002-03, both periods with intense global fires. These perturbations demonstrate a causal relationship between large-scale biomass burning events and the interannual variability of these gases, and imply that the recent increase in the rate of accumulation of CO2 is a hemispheric wide phenomenon related to large-scale biomass burning rather than a change in ocean exchange.

For reprints and further information, please contact: PETERGSIMMONDS @ aol. com

Reference: P.G. Simmonds, A.J. Manning, R.G. Derwent, P. Ciais, M. Ramonet, V. Kazan and D. Ryall, (2005), Atmospheric Environment, 39, 2513-2517.

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What are the lingering U.S. emissions of ozone-depleting gases?

AGAGE measurements of pollution events at Trinidad Head (near Eureka) in Northern California have been used to infer decreases of the emissions of CFC-11, CFC-12, CFC-113 and methyl chloroform from 1996 to 2003. It is shown that polluted air masses which reach Trinidad Head have traveled over the major cities in California, Washington and Oregon. As a result emission rates of these gases from California and Washington/Oregon have been estimated. The emissions of all these gases in the US West Coast region decreased from 1998 to 1999 by a factor of two or more, but the emissions of all four gases in 1999-2002 are calculated to have remained fairly constant at 0.016, 0.048, 0.002, and 0.006 kg/person/yr respectively. The emissions per person from California in 1996-1998, are calculated to have been factors of up to 2.2 less than the reported emissions at the same time from the New Jersey area. The methyl chloroform estimates in 1999-2000 are in agreement with the methyl chloroform emission per person averages for the USA estimated by the United Nations Environment Programme (UNEP). If the Trinidad Head and the New Jersey estimates are assumed to be representative of the USA, we estimate methyl chloroform emissions from the USA of 18 Gg/yr in 1996 to 1998 and 2.2 Gg/yr in 2001-2002. In addition we estimate average emissions of CH4, N2O and chloroform from the US West Coast region, in 1996 to 2002, of 44, 3.7 and 0.07 kg/person/year respectively.

For reprints and further information, please contact: cunnold @ eas. gatech. edu

Reference: J. Li, D. M. Cunnold, H. Wang, R.F. Weiss, B.R. Miller, C. Harth, P. Salameh, and J.M. Harris, (2005), Halocarbon emissions estimated from Advanced Global Atmospheric Gases Experiment measured pollution events at Trinidad Head, California, J. Geophys. Res., 110, D14308, doi:10.1029/2004JD005739.

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Are there large lingering European emissions of the important ozone-depleting gas methyl chloroform (1,1,1-trichloroethane)?

Long term data from Mace Head (Ireland) and Jungfraujoch (Switzerland) show that annual European emissions of methyl chloroform did not exceed 3,400 tons between 2000 and 2003, as published in Nature on February 3, 2005. Methyl chloroform is one of the ozone depleting substances phased out under the Montreal Protocol. The data in this manuscript revise published European emission estimates of more than 20,000 tons per year from two short-term campaigns, which had raised questions about the implementation of the Montreal protocol and under-reporting of emissions by the EU member states. Although present emissions are still high for a compound forbidden beginning a decade ago, they can be explained by small-scale illegal usage from storage and potential emissions from waste dumping sites.

Accurate estimation of methyl chloroform emissions is not only important in relation to ozone decline, but also is used for the estimation of the hydroxyl-radical (OH) in the atmosphere, whose average global concentrations cannot be determined by direct measurements. The revised estimated European emissions of methyl chloroform are compatible with fluctuating OH radical concentrations in recent decades but no significant long-term trend.

For reprints and further information, please contact: Stefan. Reimann @ empa. ch

Reference: S. Reimann, A.J. Manning, P.G. Simmonds, D.M. Cunnold, R.H.J. Wang, J. Li, A. McCulloch, R.G. Prinn, J. Huang, R.F. Weiss, P.F. Fraser, S. O'Doherty, B.R. Greally, K. Stemmler, M. Hill, and D. Folini, (2005), Low European methyl chloroform emissions inferred from long-term atmospheric measurements, Nature, 433, 506-508.

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Is the self-cleansing capacity of the atmosphere changing?

The hydroxyl free radical (OH) is the major oxidizing chemical in the atmosphere, destroying about 3.7 petagrams (Pg) of trace gases each year, including many gases involved in ozone depletion, the greenhouse effect and urban air pollution. Measurements of 1,1,1-trichloroethane (methyl chloroform, CH3CCl3), which reacts with OH, provide the most accurate currently utilized method for determining the global behavior of OH. We report that CH3CCl3 levels rose steadily from 1978 to reach a maximum in 1992 and have since decreased rapidly to levels in 2004 less than 30% of the levels when measurements began in 1979. Analysis of these observations shows that global average OH levels had a small maximum around 1989 and a larger minimum around 1998, with OH concentrations in 2003 being comparable to those in 1979 (that is no significant long-term trend). This post-1998 recovery of OH reported here contrasts with the situation 4 years ago when reported OH was decreasing. The 1997-1999 OH minimum coincides with, and is likely caused by, major global wildfires and an intense El Niño event at this time.

For reprints and further information, please contact: rprinn @ mit. edu

Reference: R.G. Prinn, J. Huang, R.F. Weiss, D.M. Cunnold, P.J. Fraser, P.G. Simmonds, A. McCulloch, C. Harth, S. Reimann, P. Salameh, S. O'Doherty, R.H.J. Wang, L. W. Porter, B.R. Miller and P. B. Krummel, (2005), Geophys. Res. Lett., 32, L07809, doi:10.1029/2004 GL022228.

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AGAGE project official: Ron Prinn, curator: Ray H.J. Wang

 Last update: July 2010