[show abstract][hide abstract] ABSTRACT: Methane (CH4), carbon dioxide (CO2), carbon monoxide (CO), and C2–C5 alkanes were measured throughout the Los Angeles (L.A.) basin in May and June 2010. We use these data to show that the emission ratios of CH4/CO and CH4/CO2 in the L.A. basin are larger than expected from population-apportioned bottom-up state inventories, consistent with previously published work. We use experimentally determined CH4/CO and CH4/CO2 emission ratios in combination with annual State of California CO and CO2 inventories to derive a yearly emission rate of CH4 to the L.A. basin. We further use the airborne measurements to directly derive CH4 emission rates from dairy operations in Chino, and from the two largest landfills in the L.A. basin, and show these sources are accurately represented in the California Air Resources Board greenhouse gas inventory for CH4. We then use measurements of C2–C5 alkanes to quantify the relative contribution of other CH4 sources in the L.A. basin, with results differing from those of previous studies. The atmospheric data are consistent with the majority of CH4 emissions in the region coming from fugitive losses from natural gas in pipelines and urban distribution systems and/or geologic seeps, as well as landfills and dairies. The local oil and gas industry also provides a significant source of CH4 in the area. The addition of CH4 emissions from natural gas pipelines and urban distribution systems and/or geologic seeps and from the local oil and gas industry is sufficient to account for the differences between the top-down and bottom-up CH4 inventories identified in previously published work
Journal of Geophysical Research 04/2013; · 3.17 Impact Factor
[show abstract][hide abstract] ABSTRACT: A robust in situ CO2 and CO analysis system has been
developed and deployed at eight sites in the NOAA Earth System Research
Laboratory's (ESRL) Tall Tower Greenhouse Gas Observing Network. The
network uses very tall (> 300 m) television and radio transmitter
towers that provide a convenient platform for mid-boundary layer trace
gas sampling. Each analyzer has three sample inlets for profile
sampling, and a complete vertical profile is obtained every 15 min. The
instrument suite at one site has been augmented with a cavity ring-down
spectrometer for measuring CO2 and CH4. The
long-term stability of the systems in the field is typically better than
0.1 ppm for CO2, 6 ppb for CO, and 0.5 ppb for
CH4, as determined from repeated standard gas measurements.
The instrumentation is fully automated and includes sensors for
measuring a variety of status parameters, such as temperatures,
pressures and flow rates that are inputs for automated alerts and
quality control algorithms. These algorithms provide detailed and
time-dependent uncertainty estimates for all of the gases and could be
adapted to other species or analysis systems. The design emphasizes use
of off the shelf parts and modularity to facilitate network operations
and ease of maintenance. The systems report high-quality data with >
93% uptime. Recurrent problems and limitations of the current system are
discussed along with general recommendations for high accuracy trace-gas
monitoring. The network is a key component of the North American Carbon
Program and a useful model for future research-grade operational
greenhouse gas monitoring efforts.
[show abstract][hide abstract] ABSTRACT: The multispecies analysis of daily air samples collected at the NOAA
Boulder Atmospheric Observatory (BAO) in Weld County in northeastern
Colorado since 2007 shows highly correlated alkane enhancements caused
by a regionally distributed mix of sources in the Denver-Julesburg
Basin. To further characterize the emissions of methane and non-methane
hydrocarbons (propane, n-butane, i-pentane, n-pentane and benzene)
around BAO, a pilot study involving automobile-based surveys was carried
out during the summer of 2008. A mix of venting emissions (leaks) of raw
natural gas and flashing emissions from condensate storage tanks can
explain the alkane ratios we observe in air masses impacted by oil and
gas operations in northeastern Colorado. Using the WRAP Phase III
inventory of total volatile organic compound (VOC) emissions from oil
and gas exploration, production and processing, together with flashing
and venting emission speciation profiles provided by State agencies or
the oil and gas industry, we derive a range of bottom-up speciated
emissions for Weld County in 2008. We use the observed ambient molar
ratios and flashing and venting emissions data to calculate top-down
scenarios for the amount of natural gas leaked to the atmosphere and the
associated methane and non-methane emissions. Our analysis suggests that
the emissions of the species we measured are most likely underestimated
in current inventories and that the uncertainties attached to these
estimates can be as high as a factor of two.
Journal of Geophysical Research 02/2012; 117(D4):4304-. · 3.17 Impact Factor
[show abstract][hide abstract] ABSTRACT: This paper compares two global inversions to estimate carbon monoxide (CO) emissions for 2004. Either surface flask observations from the National Oceanic and Atmospheric Administration Earth System Research Laboratory (NOAA/ESRL) Global Monitoring Division (GMD) or CO total columns from the Measurement of Pollution in the Troposphere (MOPITT) instrument are assimilated in a 4D-Var framework. Inferred emission estimates from the two inversions are consistent over the Northern Hemisphere (NH). For example, both inversions increase anthropogenic CO emissions over Europe (from 46 to 94 Tg CO/yr) and Asia (from 222 to 420 Tg CO/yr). In the Southern Hemisphere (SH), three important findings are reported. First, due to their different vertical sensitivity, the stations-only inversion increases SH biomass burning emissions by 108 Tg CO/yr more than the MOPITT-only inversion. Conversely, the MOPITT-only inversion results in SH natural emissions (mainly CO from oxidation of NMVOCs) that are 185 Tg CO/yr higher compared to the stations-only inversion. Second, MOPITT-only derived biomass burning emissions are reduced with respect to the prior which is in contrast to previous (inverse) modeling studies. Finally, MOPITT derived total emissions are significantly higher for South America and Africa compared to the stations-only inversion. This is likely due to a positive bias in the MOPITT V4 product. This bias is also apparent from validation with surface stations and ground-truth FTIR columns. Our results show that a combined inversion is promising in the NH. However, implementation of a satellite bias correction scheme is essential to combine both observational data sets in the SH.
Journal of Geophysical Research 01/2012; 117(D06309). · 3.17 Impact Factor
[show abstract][hide abstract] ABSTRACT: Airborne and ground-based measurements during the CalNex (California Research at the Nexus of Air Quality and Climate Change) field study in May/June 2010 show a weekend effect in ozone in the South Coast Air Basin (SoCAB) consistent with previous observations. The well-known and much-studied weekend ozone effect has been attributed to weekend reductions in nitrogen oxide (NOx = NO + NO2) emissions, which affect ozone levels via two processes: (1) reduced ozone loss by titration and (2) enhanced photochemical production of ozone due to an increased ratio of non-methane volatile organic compounds (VOCs) to NOx. In accord with previous assessments, the 2010 airborne and ground-based data show an average decrease in NOx of 46 +/- 11% and 34 +/- 4%, respectively, and an average increase in VOC/NOx ratio of 48 +/- 8% and 43 +/- 22%, respectively, on weekends. This work extends current understanding of the weekend ozone effect in the SoCAB by identifying its major causes and quantifying their relative importance from the available CalNex data. Increased weekend production of a VOC-NOx oxidation product, peroxyacetyl nitrate, compared to a radical termination product, nitric acid, indicates a significant contribution from increased photochemical production on weekends. Weekday-to-weekend differences in the products of NOx oxidation show 45 +/- 13% and 42 +/- 12% more extensive photochemical processing and, when compared with odd oxygen (O-x = O-3 + NO2), 51 +/- 14% and 22 +/- 17% greater ozone production efficiency on weekends in the airborne and ground-based data, respectively, indicating that both contribute to higher weekend ozone levels in the SoCAB.
Journal of Geophysical Research-Atmospheres. 01/2012; 117.
[show abstract][hide abstract] ABSTRACT: 1] We present the first inverse modeling study to estimate CO emissions constrained by both surface and satellite observations. Our 4D-Var system assimilates National Oceanic and Atmospheric Administration Earth System Research Laboratory (NOAA/ESRL) Global Monitoring Division (GMD) surface and Measurements Of Pollution In The Troposphere (MOPITT) satellite observations jointly by fitting a bias correction scheme. This approach leads to the identification of a positive bias of maximum 5 ppb in MOPITT column-averaged CO mixing ratios in the remote Southern Hemisphere (SH). The 4D-Var system is used to estimate CO emissions over South America in the period 2006–2010 and to analyze the interannual variability (IAV) of these emissions. We infer robust, high spatial resolution CO emission estimates that show slightly smaller IAV due to fires compared to the Global Fire Emissions Database (GFED3) prior emissions. South American dry season (August and September) biomass burning emission estimates amount to 60, 92, 42, 16 and 93 Tg CO/yr for 2006 to 2010, respectively. Moreover, CO emissions probably associated with pre-harvest burning of sugar cane plantations in São Paulo state are underestimated in current inventories by 50–100%. We conclude that climatic conditions (such as the widespread drought in 2010) seem the most likely cause for the IAV in biomass burning CO emissions. However, socio-economic factors (such as the growing global demand for soy, beef and sugar cane ethanol) and associated deforestation fires, are also likely as drivers for the IAV of CO emissions, but are difficult to link directly to CO emissions.
Journal of Geophysical Research 01/2012; 117. · 3.17 Impact Factor
[show abstract][hide abstract] ABSTRACT: HIaper Pole to Pole Observations (HIPPO) mission: "To measure cross
sections of atmospheric concentrations approximately pole-to-pole, from
the surface to the tropopause, five times during different seasons over
a three year period..." Results from the NOAA/RSMAS whole air flask
sampler taken during the HIPPO missions provide an unprecedented
snapshot view of ~80 atmospheric trace gas distributions throughout much
of the troposphere. A custom air sampling module aboard the Gulf Stream
V aircraft was used to sample whole air into stainless steel flasks and
glass flask packages. Observed trace gas distributions reflect the
combination of transport, chemistry and/or source/sink distributions and
are evident across hemispheric scales and through atmospheric regimes
that include the open Pacific Ocean and North America and from
near-surface (200 m) up to regions of stratospheric influence (14,400
m). The multitude of measured atmospheric compounds, spanning a wide
range of lifetimes, growth rates and source/sink distributions, provide
insight into chemistry and transport processes. Figure 1. HFC-134a mole
fractions (colorbar in parts per trillion) from the Pacific Ocean
North-South transect. Circles represent coordinates of samples collected
in NOAA's Carbon Cycle Greenhouse Gases group's glass flask packages.
[show abstract][hide abstract] ABSTRACT: Airborne measurements of methane (CH4), carbon dioxide
(CO2), and carbon monoxide (CO) were made aboard the NOAA P-3
during the CalNex (California Research at the Nexus of Air Quality and
Climate Change) field campaign based out of Ontario, California in May
and June, 2010. Additionally, measurements of these three trace gas
species were made twice daily at the Mount Wilson Observatory. The
emission ratio of CH4/CO from observations in the Los Angeles
(L.A.) basin was higher than expected from inventories, consistent with
past published works (Hsu et al., 2009; Wunch et al., 2009). We examine
emission ratios of CH4/CO, CH4/CO2, and
CO/CO2 over time, and conclude that emissions of CO in the
L.A. basin are decreasing faster than emissions of CH4.
CH4 emissions relative to CO2 are decreasing, as
well. We further examine CH4 emissions from point sources in
the L.A. basin and compare these emissions to point source inventories
of the California Air Resources Board.
[show abstract][hide abstract] ABSTRACT: Anthropogenic sources of carbon dioxide represent a significant portion
of the global carbon budget, but partitioning CO2
measurements into their biogenic and anthropogenic sources has been
difficult using only measurements of CO2 abundances and those
of a small number of additional tracers. An intensive field campaign was
conducted in Fall 2010 at the ARM-SGP Central facility near Lamont, OK
to measure CO2 and several tracers for its sources using a
new mobile laboratory. Two trucks carrying over fifteen instruments for
gases and particles were deployed along with a gas-calibration system.
Air was drawn into both trucks from a 10-m tall mast. All measurements
were made either from a common inlet or closely located inlets.
Instruments were selected to provide measurements of tracers of both
biogenic and anthropogenic sources. High-frequency measurements of
abundances of CO2 and its stable isotopologues
(13CO2 and C18OO) were made
simultaneously with measurements of CO, SO2, NOx,
O3, CH4, water vapor isotopologues
(H2O, HDO, and H218O), volatile organic
compounds, black and organic carbon aerosol, and particle count.
Automated flask samplers collected whole air samples for off-line
14C analysis using accelerator mass spectrometry. Redundancy
between CO2, CH4, and H2O measurements
provided a valuable crosscheck for the calibrations and the
measurements. Good agreement between CO2 measurements from
four different instruments was attained following careful
post-processing and calibrations. Similarly good agreement was
demonstrated between four instruments that measured water vapor and two
instruments that measured CH4. Correlations between various
tracers and CO2 provide insight into the different sources,
including the anthropogenic component, which includes biomass and fossil
fuel combustion. These results are supported by back-trajectory
[show abstract][hide abstract] ABSTRACT: We present an overview of the background, scientific goals, and execution of the Aerosol, Radiation, and Cloud Processes affecting Arctic Climate (ARCPAC) project of April 2008. We then summarize airborne measurements, made in the troposphere of the Alaskan Arctic, of aerosol particle size distributions, composition, and optical properties and discuss the sources and transport of the aerosols. The aerosol data were grouped into four categories based on gas-phase composition. First, the background troposphere contained a relatively diffuse, sulfate-rich aerosol extending from the top of the sea-ice inversion layer to 7.4 km altitude. Second, a region of depleted (relative to the background) aerosol was present within the surface inversion layer over sea-ice. Third, layers of dense, organic-rich smoke from open biomass fires in southern Russia and southeastern Siberia were frequently encountered at all altitudes from the top of the inversion layer to 7.1 km. Finally, some aerosol layers were dominated by components originating from fossil fuel combustion. Of these four categories measured during ARCPAC, the diffuse background aerosol was most similar to the average springtime aerosol properties observed at a long-term monitoring site at Barrow, Alaska. The biomass burning (BB) and fossil fuel layers were present above the sea-ice inversion layer and did not reach the sea-ice surface during the course of the ARCPAC measurements. The BB aerosol layers were highly scattering and were moderately hygroscopic. On average, the layers produced a noontime net heating of ~0.1 K day-1 between 3 and 7 km and a slight cooling at the surface. The ratios of particle mass to carbon monoxide (CO) in the BB plumes, which had been transported over distances >5000 km, were comparable to the high end of literature values derived from previous measurements in wildfire smoke. These ratios suggest minimal precipitation scavenging and removal of the BB particles between the time they were emitted and the time they were observed in dense layers above the sea-ice inversion layer.
Atmospheric Chemistry and Physics. 01/2011; 11(6):2423-2453.
[show abstract][hide abstract] ABSTRACT: We apply a four-dimensional variational (4D-VAR) data assimilation system to optimize carbon monoxide (CO) emissions for 2003 and 2004 and to reduce the uncertainty of emission estimates from individual sources using the chemistry transport model TM5. The system is designed to assimilate large (satellite) datasets, but in the current study only a limited amount of surface network observations from the National Oceanic and Atmospheric Administration Earth System Research Laboratory (NOAA/ESRL) Global Monitoring Division (GMD) is used to test the 4D-VAR system. By design, the system is capable to adjust the emissions in such a way that the posterior simulation reproduces background CO mixing ratios and large-scale pollution events at background stations. Uncertainty reduction up to 60% in yearly emissions is observed over well-constrained regions and the inferred emissions compare well with recent studies. However, with the limited amount of data from the surface network, the system becomes data sparse. This results in a large solution space and the 4D-VAR system has difficulties in separating anthropogenic and biogenic sources in particular. In addition we show that uncertainties in the model such as biomass burning injection height and the OH distribution largely influence the inversion results. The inferred emissions are validated with NOAA aircraft data over North America and the agreement is significantly improved from prior to posterior simulation. Validation with the Measurements Of Pollution In The Troposphere (MOPITT) instrument version 4 (V4) shows only a slight improved agreement over the well-constrained Northern Hemisphere. However, the model with optimized emissions underestimates MOPITT CO total columns on the remote Southern Hemisphere (SH) by about 40%. This is caused by a reduction in SH CO sources mainly due to surface stations on the high southern latitudes.
ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2011; · 5.51 Impact Factor
[show abstract][hide abstract] ABSTRACT: While the magnitude and direction of changes in tropospheric carbon monoxide (CO) during the past century are still debated; it is most likely that there have been extended periods of increase and decrease, overlaid with much shorter lived changes. The most compelling evidence for a long-term trend in the Northern Hemisphere (NH) comes from a comparison of column measurements determined above the Swiss Alps in the early 1950s and again in the mid-1980s which suggested an increase of ~1% yr-1. Quasi-continuous spectral measurements above Europe and western Russia show increasing column abundances in the 1970s through the mid-1980s, after which CO decreased at a similar rate through the mid-1990s. Several studies have shown declines in NH CO over the past two decades. Carbon monoxide has been measured in air samples collected by the NOAA Cooperative Air Sampling Network since 1988. The results provide a spatial and temporal picture of CO in the marine boundary layer which is used to identify zonal changes. The data suggest a long-term decrease in CO in the NH, with the greatest changes occurring in the 30-90 degree zonal band. Smaller decreases were found in the low Northern and Southern Hemispheres. The primary sources of CO in the NH are roughly evenly distributed between fossil fuel combustion and industrial emissions (FF), oxidation of methane and non-CH4 hydrocarbons, and biomass burning (BB); its major sink is OH. Here we examine how changes in FF and BB emissions have impacted CO in the lower troposphere. A strong decrease in anthropogenic emissions from Annex_1 countries in the early 1990s contributed to a significant decline in its abundance. Continuing declines in their emissions during the late 1990's and 2000's added to the downward trend despite increasing emissions from developing nations. The NH decrease in background CO during 1990-2005 (i.e. change determined without effects of the 1998/2003 fires) compares well with FF emissions inventories. Of the major CO sources only BB exhibits large inter-annual variation. While these variations obscure any trend in emissions, intense periods of biomass burning (such as those which occurred in 1997-1998 and in 2002-2003) are clearly evident in the measurements and are compared to emission estimates. The ability of the atmosphere to remove large pulses of CO suggests the troposphere is well buffered by OH.
[show abstract][hide abstract] ABSTRACT: During April 2008, as part of the International Polar Year (IPY), a number of ground-based and aircraft campaigns were carried out in the North American Arctic region (e.g., ARCTAS, ARCPAC). The widespread presence during this period of biomass burning effluent, both gaseous and particulate, has been reported. Unusually high ozone readings for this time of year were recorded at surface ozone monitoring sites from northern Alaska to northern California. At Barrow, Alaska, the northernmost point in the United States, the highest April ozone readings recorded at the surface (hourly average values >55 ppbv) in 37 years of observation were measured on April 19, 2008. At Denali National Park in central Alaska, an hourly average of 79 ppbv was recorded during an 8-h period in which the average was over 75 ppbv, exceeding the ozone ambient air quality standard threshold value in the U.S. Elevated ozone (>60 ppbv) persisted almost continuously from April 19–23 at the monitoring site during this event. At a coastal site in northern California (Trinidad Head), hourly ozone readings were >50 ppbv almost continuously for a 35-h period from April 18–20. At several sites in northern California, located to the east of Trinidad Head, numerous occurrences of ozone readings exceeding 60 ppbv were recorded during April 2008. Ozone profiles from an extensive series of balloon soundings showed lower tropospheric features at ∼1–6 km with enhanced ozone during the times of elevated ozone amounts at surface sites in western Canada and the U.S. Based on extensive trajectory calculations, biomass burning in regions of southern Russia was identified as the likely source of the observed ozone enhancements. Ancillary measurements of atmospheric constituents and optical properties (aerosol optical thickness) supported the presence of a burning plume at several locations. At two coastal sites (Trinidad Head and Vancouver Island), profiles of a large suite of gases were measured from airborne flask samples taken during probable encounters with burning plumes. These profiles aided in characterizing the vertical thickness of the plumes, as well as confirming that the plumes reaching the west coast of North America were associated with biomass burning events.
[show abstract][hide abstract] ABSTRACT: We present an overview of the background, scientific goals, and
execution of the Aerosol, Radiation, and Cloud Processes affecting
Arctic Climate (ARCPAC) project of April 2008. We then summarize
airborne measurements, made in the troposphere of the Alaskan Arctic, of
aerosol particle size distributions, composition, and optical properties
and discuss the sources and transport of the aerosols. The aerosol data
were grouped into four categories based on gas-phase composition. First,
the background troposphere contained a relatively diffuse, sulfate-rich
aerosol extending from the top of the sea-ice inversion layer to 7.4 km
altitude. Second, a region of depleted (relative to the background)
aerosol was present within the surface inversion layer over sea-ice.
Third, layers of dense, organic-rich smoke from open biomass fires in
Southern Russia and Southeastern Siberia were frequently encountered at
all altitudes from the top of the inversion layer to 7.1 km. Finally,
some aerosol layers were dominated by components originating from fossil
fuel combustion. Of these four categories measured during ARCPAC,
the diffuse background aerosol was most similar to the average
springtime aerosol properties observed at a long-term monitoring site at
Barrow, Alaska. The biomass burning (BB) and fossil fuel layers were
present above the sea-ice inversion layer and did not reach the sea-ice
surface during the course of the ARCPAC measurements. The BB aerosol
layers were highly scattering and were moderately hygroscopic. On
average, the layers produced a noontime net heating of ~0.1 K
day-1 between 2 and 7 km and a~slight cooling at the
surface. The ratios of particle mass to carbon monoxide (CO) in the BB
plumes, which had been transported over distances >5000 km, were
comparable to the high end of literature values derived from previous
measurements in fresh wildfire smoke. These ratios suggest minimal
precipitation scavenging and removal of the BB particles between the
time they were emitted and the time they were observed in dense layers
above the sea-ice inversion layer.
Atmospheric Chemistry and Physics 10/2010; 10:27361-27434. · 4.88 Impact Factor
[show abstract][hide abstract] ABSTRACT: Vertical profiles of carbon monoxide (CO) concentration and corresponding total column values derived from measurements made by the Measurements of Pollution in the Troposphere (MOPITT) satellite instrument are now being processed operationally with the ``version 4'' (V4) retrieval algorithm. This algorithm exploits the results of analyses of in situ data, chemical transport modeling, and radiative transfer modeling in the MOPITT postlaunch era. Improvements in the V4 product are evident in both clean and polluted conditions. The new products are validated using CO in situ measurements acquired from aircraft from 2000 to 2007. As determined by both retrieval simulations and observations, retrieval bias drift is typically about 1 ppbv/yr for levels in the middle troposphere and about 2 ppbv/yr in the upper troposphere. Retrieval simulations indicate that observed bias drift may be the result of gradual on-orbit changes in the instrument's modulation cell parameters.
Journal of Geophysical Research 01/2010; 115. · 3.17 Impact Factor
[show abstract][hide abstract] ABSTRACT: Analysis of recent trace gas and aerosol data taken downwind of oil
extraction facilities on the Alaskan North Slope, including Prudhoe Bay,
provides new insights into the chemistry and fate of anthropogenic
industrial emissions at high latitudes, and can better constrain the
anticipated impact of new emissions on air quality and climate in the
Arctic. Three different analyses have been carried out using airborne
data from the NOAA WP-3D and the NASA DC-8 instrumented aircraft during
April 2008, the long-term data set from the NOAA GMD observatory at
Barrow, and the FLEXPART transport model. These analyses include: 1. a
determination of NOx oxidation rates and OH sources downwind of the
Prudhoe Bay, AK oil extraction facilities, and a comparison to
observations in well-mixed continental plumes at lower latitudes. 2. a
new signature of halogen atom chemistry in the alkane-rich Prudhoe Bay
plume. Coupled with transport model age spectra, this analysis provides
a new and unique constraint on the time scales of halogen-catalyzed
ozone depletion in the Arctic. 3. a direct quantification of greenhouse
gas source strengths from oil extraction facilities at Prudhoe Bay in
the Alaskan Arctic, and a comparison to existing global inventories.
[show abstract][hide abstract] ABSTRACT: Carbon monoxide (CO) plays a key role in global atmospheric chemistry by being the main sink of atmospheric hydroxyl radicals (OH). Records of past [CO] from both hemispheres are essential for understanding past changes in atmospheric [OH]. Earlier attempts at reconstruction of northern hemisphere (NH) [CO] suffered from apparent in-situ CO production in ice and firn. We present a record of high-latitude NH [CO] to ~1950 AD, from measurements by four different laboratories of firn air collected from three different boreholes at the NEEM ice core site in Greenland. Procedural blanks indicate no detectable [CO] contamination from sampling. Excellent agreement with a firn air record from another cold Greenland site (NGRIP) is consistent with the NEEM firn CO record being unaltered. A preliminary analysis of our measurements, interpreted using two different firn air diffusion models, suggests that high-latitude NH [CO] 1) was 140 - 150 ppb in the early 1950s, 2) increased from ~1950 to the 1970s, 3) peaked between 157 and 167 ppb in the 1970s, which is earlier than first direct atmospheric measurements suggest, and 4) gradually declined after the 1970s. In addition, we present the NEEM firn record of molecular hydrogen (H2), from measurements by three laboratories. The main features of the [H2] record are similar to those of the [CO] record, with preliminary results suggesting an increase in [H2] from ~1960 to the early 1980s, followed by a gradual decline. This is consistent with early direct atmospheric measurements. The similarity in the main features of [CO] and [H2] records is expected because of broadly similar sources for the two gases. Further work is in progress to improve the firn air diffusion models and reconstruct atmospheric histories with well-defined uncertainty envelopes.
[show abstract][hide abstract] ABSTRACT: The Earth's troposphere contains approximately 160 Tg H2 with an average surface mixing ratio approximately 530 nmole mole(-1) (ppb) and lifetime of 2 years. Atmospheric H2 is typically measured using gas chromatography (GC) followed by hot mercuric oxide reduction detection (GC-HgO). Here we describe an alternate method using GC with a pulsed-discharge helium ionization detector (HePPD). HePPD is a universal detector; when applied to H2, the GC-HePDD provides a wide linear range (0.3% over a range of 2000 ppb), a detection limit of approximately 0.03 pg, high precision (0.12%) and a stable response (+/-1.6% over nearly one year). HePPD is compared to HgO reduction using a suite of gravimetrically prepared reference gases spanning remote to urban concentrations. The method is excellent for atmospheric measurements as it provides a wide linear range with high precision, stability and reproducibility. We suggest these characteristics will improve the ability to maintain reference gases and improve measurements of atmospheric H2, thus providing better constraints on potential future changes in its sources and sinks.
Environmental Science and Technology 05/2009; 43(7):2431-6. · 5.26 Impact Factor
[show abstract][hide abstract] ABSTRACT: CO abundances are retrieved from spectra of atmospheric down-welling radiation measured by the Atmospheric Emitted Radiance Interferometer (AERI) at the Southern Great Plains (SGP) observatory of the Atmospheric Radiation Measurements (ARM) program sponsored by the United States Department of Energy (DOE). These spectra measured every 8 minutes are publicly available for the period between 1997 and the present. The R-branch of the CO fundamental vibration-rotational band between 2135 and 2200 cm-1 is chosen for analysis. Radiative transfer calculations are performed using the k-Compressed Atmospheric Radiative Transfer Algorithm (kCARTA). Atmospheric temperature and water vapor profiles were retrieved from other parts of the AERI spectra using standard software developed by the University of Wisconsin and constrained with SGP Microwave Radiometer total precipitable water retrievals. An a priori constant CO mixing ratio profile is perturbed to minimize the spectral residuals due to CO. A correction for the scattered solar radiance during day-time is applied. Independent measurements of CO boundary layer mixing ratios by the Lawrence Berkeley National Laboratory (LBNL) and free tropospheric CO by the Earth System Research Laboratory (ESRL) of the Global Monitoring Division (GMD) , NOAA provide validation for the AERI retrieval technique.
[show abstract][hide abstract] ABSTRACT: Measurements of atmospheric CH4 from air samples collected weekly at 46 remote surface sites show that, after a decade of near-zero growth, globally averaged atmospheric methane increased during 2007 and 2008. During 2007, CH4 increased by 8.3 ± 0.6 ppb. CH4 mole fractions averaged over polar northern latitudes and the Southern Hemisphere increased more than other zonally averaged regions. In 2008, globally averaged CH4 increased by 4.4 ± 0.6 ppb; the largest increase was in the tropics, while polar northern latitudes did not increase. Satellite and in situ CO observations suggest only a minor contribution to increased CH4 from biomass burning. The most likely drivers of the CH4 anomalies observed during 2007 and 2008 are anomalously high temperatures in the Arctic and greater than average precipitation in the tropics. Near-zero CH4 growth in the Arctic during 2008 suggests we have not yet activated strong climate feedbacks from permafrost and CH4 hydrates.
Geophysical Research Letters 01/2009; 36(18). · 3.98 Impact Factor