Publications and DataBelow is a listing of Jürgen's first- and co-authored publications available for download. For now, only the most important papers are included; if you don't see a particular publication here, it is not yet available. Also, some journals do not allow electronic distribution of their papers, hence those papers will not appear here. In either case, if you click on their link, you will get a note to request a paper copy. Please follow the legal notice, do not post any of these papers on the web and do not distribute any further. Refer interested people to this website, instead. Papers are available in Acrobat TM
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Importance of biomass burning in the atmospheric budgets of nitrogen-containing gases.
Jürgen M. Lobert, Dieter H. Scharffe, Wei M. Hao & Paul J. Crutzen Abstract: Biomass burning is a primary source of many trace substances that are important in atmospheric chemistry. More than 80% of the world's biomass burning takes place in the tropics as a result of savanna fires, forest-clearing activity, and the burning of agricultural waste and wood. Here we report results from laboratory studies on the emissions of nitrogen-containing compounds from the burning of dry vegetation. We find that the emission rates of NOX, HCN, CH3CN are sufficient to contribute signficantly to the global budget of the compounds. Furthermore, possibly up to half of the biomass nitrogen can be converted to molecular nitrogen, N2, leading to an estimated anniual loss of 12-28x1012 g of biomass nitrogen ('pyrodenitrification'), equal to ~9-20% of the estimated global rate of terrestrial nitrogen fixation. Reprinted with permission from Nature 346, 6284, 552-554, 1990. Copyright © 1990 Nature Publishing Group.
EXPERIMENTAL EVALUATION OF BIOMASS BURNING EMISSIONS:
NITROGEN AND CARBON CONTAINING COMPOUNDS.
Jürgen M. Lobert, Dieter H. Scharffe, Wei-Min Hao, Thomas A. Kuhlbusch,
Ralph Seuwen, Peter Warneck & Paul J. Crutzen Abstract:
Today biomass burning is accepted to be an important source of many trace gases affecting atmospheric chemistry. Despite its global significance and in contrast to fossil fuel use, where detailed investigations on global amounts and their distributions are available, still little quantitative information is known about the emissions of some of the compounds emitted and the global amounts consumed by biomass burning. Estimates of these global quantities are difficult to derive because of a very uncertain database. The most recent values published by Crutzen et al. indicate that 1900-5000 Tg biomass carbon is released annually.
Emissions From the Combustion Process in Vegetation
Jürgen M. Lobert and Jürgen Warnatz Abstract:
A detailed description of the processes involved in vegetation fires is given, emphasizing the flaming stage and the smoldering stage of biomass burning. The major factors influencing the appearance of the single stages are discussed as well as their impact on emissions from fires. General production patterns, especially the importance of the ratio of flaming to smoldering combustion, for several classes of compounds are outlined and some specific reaction paths are discussed which are likely to dominate certain emission formations. A summary of global estimates of the most important emissions is added in the end. A proposition is made to simplify the complex nature of vegetation fires to enable reliable predictions of the emissions from biomass burning in a global scientific effort.
A Net Sink for Atmospheric CH3Br in the East Pacific
Ocean
Jürgen M. Lobert, James H. Butler, Stephen A. Montzka, Laurie
S. Geller, Richard C. Myers, and James W. Elkins Abstract:
Surface waters along a cruise track in the East Pacific ocean were undersaturated in methyl bromide (CH3Br) in most areas except for coastal and upwelling regions, with saturation anomalies ranging from +100% in coastal waters to -50% in open ocean areas, representing a regionally weighted mean of -16 (-13 to -20) percent. The partial lifetime of atmospheric CH3Br with respect to calculated oceanic degradation along this cruise track is 3.0 (2.9 to 3.6) years. The global, mean dry mole fraction of CH3Br in the atmosphere was 9.8±0.6 parts per trillion (ppt) with an interhemispheric ratio of 1.31±0.08. These data indicate that ~8 percent (0.2 ppt) of the observed interhemispheric difference in atmospheric CH3Br could be attributed to an uneven global distribution of oceanic sources and sinks.
Reprinted with permission from Science
267, 1002-1005, 1995. Copyright ©1995 American Association for the Advancement of Science.
OAXTC 92: OCEAN / ATMOSPHERE EXCHANGE OF TRACE COMPOUNDS 1992 Jürgen M. Lobert, Thomas J. Baring, James H. Butler, Stephen A. Montzka, Richard C. Myers, James W. Elkins Abstract:
CFC-11 (CCl3F), CFC-12 (CCl2F2), CFC-113 (CCl2FCClF2), methyl chloroform (CH3CCl3), carbon tetrachloride (CCl4), nitrous oxide (N2O) and HCFC-22 (CHClF2) were measured in the air and surface waters of the Pacific Ocean between 55°N and 22°S during the late summer and early fall of 1992. Atmospheric measurements of all gases agreed well with results from NOAA fixed stations at similar latitudes. CFC-11, CFC-12, and CFC-113, which have long atmospheric lifetimes and are essentially inert in seawater, responded mainly to physical processes in the air and water. The first two gases were supersaturated by 2-6% at higher, northern latitudes, reflecting the effects of radiative warming. Their saturation anomalies declined southward through the tropics and ultimately became slightly negative in the southern hemisphere. HCFC-22 showed signs of small losses in the tropics and subtropics, a sink that may account for 2% of the losses of this gas from the atmosphere. CH3CCl3 showed a similar pattern, with only a tropical sink, which is consistent with hydrolysis and, together with data from an earlier expedition, implies that about 6% of atmospheric CH3CCl3 is lost to the ocean. The net saturation anomaly for CCl4 was virtually negative everywhere and only slightly dependent upon latitude. This would be expected for a sink that was not particularly temperature dependent and it is consistent with evidence from deepwater profiles that indicate a sink at depth. Fluxes calculated from CCl4 saturation anomalies indicate that 15-35% of atmospheric CCl4 is lost to the ocean. N2O surface water data indicated weak equatorial upwelling. Saturation anomalies ranged from 1-6%, which would be consistent with a small source in the W. Pacific.
BLAST 94: Bromine Latitudinal Air/Sea Transect 1994. Jürgen M. Lobert, Laurie S. Geller, Shari A. Yvon, Andrew D. Clarke, James H. Butler, Stephen A. Montzka, Richard C. Myers, James W. Elkins, Abstract:
The Nitrous Oxide And Halocompounds (NOAH) division of NOAA/CMDL
participated in two research cruises in 1994 for the Bromine
Latitudinal Air/Sea Transect project. Frequently collected
CH3Br data from these expeditions constitute the largest
data set for oceanic CH3Br to date, and the first solid
estimate of oceanic emission, production and degradation of the
compound. Our conclusion from these studies is that the ocean
is probably not a net source of CH3Br, but rather a
net sink. Although CH3Br is both produced and consumed
everywhere in the surface ocean, the rate of consumption exceeds
that of production in most waters sampled. Exceptions were coastal
and coastally influenced waters, which were typically supersaturated,
and areas of open ocean upwelling, where CH3Br saturations
were close to zero. About 80% of the oceans are undersaturated
in CH3Br, representing a net annual sink of 8-22 Gg
y-1.
In addition to conducting two research cruises, we investigated
potential contamination effects from sampling flasks and potential
analytical artifacts from GC/ECD systems, developed a calibration
scale for atmospheric and oceanic CH3Br and a global,
finite-increment model for more precisely estimating the partial
lifetime of atmospheric CH3Br with respect to oceanic
losses.
CH3Br data from the second cruise indicate that our
conclusions from the first expedition were qualitatively and quantitatively
accurate. The latter results give greater strength to the global
extrapolations of the first data set. Our best estimate of the
partial lifetime of atmospheric CH3Br with respect
to oceanic losses is 2.7 (2.4-6.5) y. This range was derived from
a 40 year, global data set of sea surface temperatures and windspeeds.
Data from the two expeditions suggest a shorter lifetime of CH3Br
on the order of 2.4 y. The difference between the two estimates
is due to the high windspeeds encountered during the cruises.
Our estimate of the atmospheric lifetime, based upon combined
atmospheric and oceanic losses, is now 1.0-1.1 y, compared to
earlier estimates of 1.82.1 y when the ocean was considered
an insignificant sink and tropospheric OH concentrations were
underestimated by 15%. The oceanic sink correspondingly lowers
the ODP for CH3Br by about one-third.
Work on the sampling and analytical uncertainties has revealed
significant problems with the measurement of CH3Br
in flasks, which have been used historically for virtually all
previous measurements of CH3Br in the atmosphere. Whereas
results from the shipboard system were free of sample storage
effects and both the shipboard and the laboratory-based GC/MS
systems were free of problems with co-eluting compounds, our results
in analyzing flasks from the first expedition show that CH3Br
in flasks often is unstable and will increase or decrease with
time. In addition, we found that results for CH3Br
determined by GC/ECD can be compromised by some GC configurations.
Undersaturations of Methyl Bromide in the Southern Ocean
Jürgen M. Lobert, Shari A. Yvon, James H. Butler, Stephen A. Montzka, and
Richard C. Myers Abstract:
Dry mole fractions of methyl bromide (CH3Br) in marine boundary layer air and in air equilibrated with surface water were measured in the Southern Ocean. Saturation anomalies were consistently negative at -36±7%. The observed undersaturations do not support recently published predictions of highly supersaturated Antarctic waters, but instead suggest a net uptake of atmospheric CH3Br by cold, productive oceans. The observations do not appear to be supported by known chemical degradation rates and present strong evidence for an unidentified, oceanic sink mechanism such as biological breakdown. Our estimate for the global, net, oceanic sink for atmospheric methyl bromide remains negative at -21 (-11 to -32) Gg y-1.
Tropospheric SF6: Observed latitudinal distribution and trends, derived
emissions and interhemispheric exchange time
Geller, L. S., J.W. Elkins, J.M. Lobert, A.D. Clarke, D.F. Hurst, J.H. Butler
and R.C. Myers Abstract:
Sulfur hexafluoride (SF6), an anthropogenically produced compound that is a potent greenhouse gas, has been measured in a number of NOAA CMDL air sampling programs. These include high resolution latitudinal profiles over the Atlantic and Pacific oceans, weekly flask samples from seven remote, globally distributed sites, hourly in situ measurements in rural North Carolina, and a series of archived air samples from Niwot Ridge, Colorado. The observed increase in atmospheric mixing ratio is consistent with an overall quadratic growth rate, at 6.9 ± 0.2% yr-1 (0.24 ± 0.01 ppt yr-1) for early 1996. From these data we derive an early 1996 emission rate of 5.9 ± 0.2 Gg SF6 yr-1 and an interhemispheric exchange time of 1.3 ± 0.1 years.
Carbon monoxide uptake by temperate forest soils: the effects of leaves and humus layers.
E. SANHUEZA, Y. DONG D. SCHARFFE, J.M. LOBERT and P. J. CRUTZEN Abstract:
Carbon monoxide (CO) fluxes between soil and atmosphere were measured between October
1990 and December 1991 in a temperate, deciduous forest near Darmstadt, Germany. Flux
measurements were made with an enclosed chamber technique before and after the removal of
leaves and humus from the forest floor as well as from leaves and humus alone. CO depth
profiles were obtained during the period July to December, 1991. A net uptake of CO was
observed under all conditions with an average of -47.3±24.0 ng CO m-2 s-1 for undisturbed
forest soils, which increased significantly when the leaves or both leaves and humus were
removed from the forest floor. The mean deposition velocity in undisturbed conditions was
0.027±0.008 cm s-1. Our results indicate that CO has a short lifetime within the soil and that
the consumption of atmospheric CO occurs mainly in the top few centimeters of the humus
layer (O horizon). We conclude that temperate forests are a significant net sink for atmospheric
CO and that leaves and humus significantly aVect CO fluxes. The global soil sink for atmospheric
CO was estimated to be 115–230 Tg CO yr-1.
Fluxes of CO2, CH4 and N2O from a temperate forest soil: the effects of leaves and humus layers.
Y. DONG D. SCHARFFE, J.M. LOBERT, P. J. CRUTZEN and E. SANHUEZA Abstract:
Fluxes of CO2, CH4, and N2O from forest soils were measured with an enclosed chamber
technique between October 1990 and December 1991 in a deciduous forest near Darmstadt,
Germany. Flux measurements were made before and after the removal of leaves and humus
layer from the forest floor, and gas fluxes from the leaves and humus alone were also measured
as well as depth profiles of CH4, N2O, and soil moisture. Except for N2O, large seasonal
variations were observed with generally higher gas fluxes during the summer. CO2 and CH4
fluxes were significantly dependent on changes in ambient temperature, whereas N2O fluxes
were more aVected by soil moisture. A good correlation between CO2 production and CH4
uptake was observed, but no relationship was found between N2O emissions and either CO2
or CH4 fluxes. Depth profiles of the CH4 mixing ratio in soil air consistently showed an
exponential decrease with depth, whereas N2O profiles were highly variable and appeared to
be related to changes in soil moisture. The manipulated soil experiments indicate that the leaves
and the humus layers contribute significantly to the soil-atmosphere exchange of trace gases.
Instrumentation For Trace-Level Measurement of Carbon Monoxide in Pristine
Environments
Mark A. Cogan and Jürgen M. Lobert Abstract:
Trace level measurement of carbon monoxide (CO) in air is important to understanding of sources and sinks of CO in the atmosphere. Detection limits of 50 ppb or less are necessary to understanding the creation and propagation of CO in pristine environments. Modifications to existing EPA-type CO monitors to allow such low-level measurements are discussed, along with the comparative increases in detection limits that result from these modifications. Selectivity and possible interferent gases are also discussed.
Global chlorine emissions from biomass burning: Reactive Chlorine Emissions Inventory
J.M. Lobert, W.C. Keene, J.A. Logan, R. Yevich Abstract:
Emissions of reactive chlorine-containing compounds from nine discrete classes of biomass burning were estimated on a 1° latitude by 1° longitude grid based on a biomass burning inventory for carbon emissions. Variations on approaches incorporating both emission ratios relative to CO and CO2 and the chlorine content of biomass burning fuels were used to estimate fluxes and associated uncertainties. Estimated, global emissions are 640 Gg Cl yr-1 for CH3Cl; 49 Gg Cl yr-1 for CH2Cl2; 1.8 Gg Cl yr-1 for CHCl3; 13 Gg Cl yr-1 for CH3CCl3; and 6350 Gg Cl yr-1 for the sum of volatile-inorganic and particulate chlorine. Biomass burning appears to be the single largest source of atmospheric CH3Cl and a significant source of CH2Cl2; contributions of CHCl3 and CH3CCl3 are less than 2% of known sources.
The Indian Ocean Experiment: Widespread Air Pollution from South and Southeast Asia
J. Lelieveld, P.J. Crutzen, V. Ramanathan, M.O. Andreae,
C.A.M. Brenninkmeijer, T. Campos, G.R. Cass,
R.R. Dickerson, H. Fischer, J.A. de Gouw, A. Hansel,
A. Jefferson, D. Kley, A.T.J. de Laat, S. Lal, M.G. Lawrence, J.M. Lobert, O.L. Mayol-Bracero, A.P. Mitra, T. Novakov, S.J. Oltmans, K.A. Prather, T. Reiner, H. Rodhe, H.A. Scheeren, D. Sikka, J. Williams Abstract:
The Indian Ocean Experiment (INDOEX) was an international, multiplatform
field campaign to measure long-range transport of air pollution from South and
Southeast Asia toward the Indian Ocean during the dry monsoon season in
January to March 1999. Surprisingly high pollution levels were observed over
the entire northern Indian Ocean toward the Intertropical Convergence Zone
at about 6¡S. We show that agricultural burning and especially biofuel use
enhance carbon monoxide concentrations. Fossil fuel combustion and biomass
burning cause a high aerosol loading. The growing pollution in this region gives
rise to extensive air quality degradation with local, regional, and global impli-
cations, including a reduction of the oxidizing power of the atmosphere.
Reprinted with permission from Science 291, 1031-1036, 2001. Copyright © 2001 American Association for the
Advancement of Science.
Trace Gases and Air Mass Origin over Kaashidhoo, Indian Ocean
J.M. Lobert, J.M. Harris Abstract:
Carbon monoxide (CO) was measured at the Kaashidhoo Climate Observatory (KCO, Republic of Maldives)
between February 1998 and March 2000 to assess the regional pollution of the remote atmosphere in the
northern Indian Ocean. CO showed a distinct annual cycle with maximum daily mixing ratios of around 240
parts per billion (ppb), a seasonal difference of about 200 ppb, and high variability during the dry
seasons. Detailed air mass trajectory analysis for 1998, 1999, and 2000 was used to identify source regions
and to associate them with various levels of pollution encountered at KCO. We conclude that most significant
changes in local pollution throughout the year are caused by changes in air masses. Air at KCO generally
originated from three main regions with decreasing pollution: India and southeast Asia, the Arabian Sea,
and the Southern Hemisphere. We show that isentropic air mass trajectories can be used to predict CO
pollution levels at KCO to a certain extent and vice versa. Nitrous oxide, CFC-11, CFC-12, CCI4,
and SF6 were measured during the Indian Ocean Experiment (February to March 1999) to support
pollution analysis and to confirm that India is the main source for heavy pollution measured at KCO.
Correlations between CO and other gases and aerosol properties measured at the surface illustrate that CO
may also be used as a proxy for aerosol loading and general pollution at the surface.
Emissions of Major Gaseous and Particulate Species During Experimental Burns of Southern African Biomass
William C. Keene, Jürgen M. Lobert, Paul J. Crutzen, John R. Maben, Dieter H. Scharffe, Tobias Landmann, Christelle Hély, and Conrad Brain Abstract:
Characteristic vegetation and biofuels in major ecosystems of southern Africa were sampled during summer and autumn 2000 and
burned under semi-controlled conditions. Elemental compositions of fuels and ash and emissions of CO2, CO, CH3COOH, HCOOH,
NOX, NH3, HONO, HNO3, HCl, total volatile inorganic Cl and Br, SO2 and particulate C, N, and major ions were measured.
Modified combustion efficiencies (MCEs, median = 0.94) were similar to those of ambient fires. Elemental emissions factors
(EFel) for CH3COOH were inversely correlated with MCEs; EFels for heading and mixed grass fires were higher than those for
backing fires of comparable MCEs. NOX, NH3, HONO, and particulate N accounted for a median of 22% of emitted N; HNO3
emissions were insignificant. Grass fires with the highest EFels for NH3 corresponded to MCEs in the range of 0.93; grass
fires with higher and low MCEs exhibited lower EFels. NH3 emissions for most fuels were poorly correlated with fuel N.
Most Cl and Br in fuel was emitted during combustion (median for each = 73%). Inorganic gases and particulate ions accounted
for medians of 53% and 30% of emitted Cl and Br, respectively. About half of volatile inorganic Cl was HCl indicating
significant emissions of other gaseous inorganic Cl species. Most fuel S (median = 76%) was emitted during combustion;
SO2 and particulate SO42- accounted for about half the flux. Mobilization of P by fire (median emission = 82%) implies
large nutrient losses from burned regions and potentially important exogenous sources of fertilization for downwind ecosystems.
Oceanic distributions and emissions of short-lived halocarbons
Butler, J. H., D. B. King, J. M. Lobert, S. A. Montzka, S. A. Yvon-Lewis, B. D. Hall, N. J. Warwick, D. J. Mondeel, M. Aydin, and J. W. Elkins Abstract:
Using data from seven cruises over a 10-year span, we report marine boundary layer
mixing ratios (i.e., dry mole fractions as pmol mol.1 or ppt), degrees of surface seawater
saturation, and air-sea fluxes of three short-lived halocarbons that are significant in
tropospheric and potentially stratospheric chemistry. CHBr3, CH2Br2, and CH3I were all highly supersaturated almost everywhere, all the time. Highest saturations of the
two polybrominated gases were observed in coastal waters and areas of upwelling, such
as those near the equator and along ocean fronts. CH3I distributions reflected the different
chemistry and cycling of this gas in both the water and the atmosphere. Seasonal
variations in fluxes were apparent where cruises overlapped and were consistent among
oceans. Undersaturations of these gases were noted at some locations in the Southern
Ocean, owing to mixing of surface and subsurface waters, not necessarily biological
or chemical sinks. The Pacific Ocean appears to be a much stronger source of CHBr3 to
the marine boundary layer than the Atlantic. The high supersaturations, fluxes, and
marine boundary layer mixing ratios in the tropics are consistent with the suggestion that
tropical convection could deliver some portion of these gases and their breakdown
products to the upper troposphere and lower stratosphere.
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