Methane emissions associated with the production, transport, and
use of oil and natural gas increase the climatic impacts of energy use;
however, little is known about how emissions vary temporally ...and with
commodity prices. We present airborne and ground-based data, supported by
satellite observations, to measure weekly to monthly changes in total
methane emissions in the United States' Permian Basin during a period of
volatile oil prices associated with the COVID-19 pandemic. As oil prices
declined from ∼ USD 60 to USD 20 per barrel, emissions changed
concurrently from 3.3 % to 1.9 % of natural gas production; as prices
partially recovered, emissions increased back to near initial values.
Concurrently, total oil and natural gas production only declined by
∼ 10 % from the peak values seen in the months prior to the
crash. Activity data indicate that a rapid decline in well development and
subsequent effects on associated gas flaring and midstream infrastructure
throughput are the likely drivers of temporary emission reductions. Our
results, along with past satellite observations, suggest that under more
typical price conditions, the Permian Basin is in a state of overcapacity in
which rapidly growing associated gas production exceeds midstream capacity
and leads to high methane emissions.
Methane is an important greenhouse gas and tropospheric ozone precursor. Simultaneous observation of ethane with methane can help identify specific methane source types. Aerodyne Ethane-Mini ...spectrometers, employing recently available mid-infrared distributed feedback tunable diode lasers (DFB-TDL), provide 1 s ethane measurements with sub-ppb precision. In this work, an Ethane-Mini spectrometer has been integrated into two mobile sampling platforms, a ground vehicle and a small airplane, and used to measure ethane/methane enhancement ratios downwind of methane sources. Methane emissions with precisely known sources are shown to have ethane/methane enhancement ratios that differ greatly depending on the source type. Large differences between biogenic and thermogenic sources are observed. Variation within thermogenic sources are detected and tabulated. Methane emitters are classified by their expected ethane content. Categories include the following: biogenic (<0.2%), dry gas (1–6%), wet gas (>6%), pipeline grade natural gas (<15%), and processed natural gas liquids (>30%). Regional scale observations in the Dallas/Fort Worth area of Texas show two distinct ethane/methane enhancement ratios bridged by a transitional region. These results demonstrate the usefulness of continuous and fast ethane measurements in experimental studies of methane emissions, particularly in the oil and natural gas sector.
Cities around the world have introduced initiatives to reduce CO2 emissions. Atmospheric observations can provide evaluation and assessment of these initiatives by quantifying emissions, considering ...local sources and sinks. The relative importance of the urban biosphere, which can act as both a source (respiration) and sink (photosynthesis) of CO2, has previously been suggested to strongly impact urban CO2 measurements, confounding the ability to use observations to study fossil emissions. However, if using an observing framework that measures a local urban background and the direct urban core outflow, for example, along a downwind airborne transect, the biosphere’s role may be minimized. Here, we combine real, airborne observations of CO2 downwind of select cities in the Northeast US with high‐resolution, back‐trajectory modeling and spatially and temporally resolved surface biosphere and fossil fuel fluxes to characterize the relative biosphere importance to urban CO2 profiles. We show the biosphere influence using this urban observing system to be small, averaging only 15% of the local CO2 enhancement annually, <10% outside of summer, and with a maximum influence of 29% in summer when the biosphere drawdown is most pronounced. Furthermore, when considering two biosphere models that differ by >80%, the impact on observed urban CO2 signals is reduced to only 12% on average. Urban observing frameworks that utilize this local background approach—including those via aircraft or satellite observations—can minimize the biosphere's influence and thus help facilitate robust assessments of urban fossil fuel CO2 emissions.
Plain Language Summary
Cities around the world have announced plans to reduce CO2 emissions. Atmospheric CO2 observations provide a potential pathway toward independent assessment of implemented policies. However, these measurements can be strongly influenced by the urban biosphere, which can act as both a source (respiration) and sink (photosynthesis) of CO2. If using an observing approach that introduces a local, urban background—for example, observations via a downwind airborne transect that captures an entire urban outflow—the relative role of the biosphere may be minimized. Here, we combine back trajectory modeling with high‐resolution surface fossil fuel and biosphere CO2 fluxes across six cities and one powerplant in the NE US to demonstrate that observing strategies using this approach can greatly reduce biosphere interferences in studies of urban CO2 (<10% biosphere interference outside of summer months, on average) and pave the way to conduct robust studies of urban fossil fuel CO2 emissions.
Key Points
Urban fossil CO2 emissions can be isolated from biosphere influences using observation approaches that define a local background
High variability of biosphere representation has minimal influence on bio contribution to urban CO2 using local background framework
We present improved estimates of air-sea CO
exchange over three latitude bands of the Southern Ocean using atmospheric CO
measurements from global airborne campaigns and an atmospheric 4-box inverse ...model based on a mass-indexed isentropic coordinate (M
). These flux estimates show two features not clearly resolved in previous estimates based on inverting surface CO
measurements: a weak winter-time outgassing in the polar region and a sharp phase transition of the seasonal flux cycles between polar/subpolar and subtropical regions. The estimates suggest much stronger summer-time uptake in the polar/subpolar regions than estimates derived through neural-network interpolation of pCO
data obtained with profiling floats but somewhat weaker uptake than a recent study by Long et al.
, 1275-1280 (2021), who used the same airborne data and multiple atmospheric transport models (ATMs) to constrain surface fluxes. Our study also uses moist static energy (MSE) budgets from reanalyses to show that most ATMs tend to have excessive diabatic mixing (transport across moist isentrope, θ
, or M
surfaces) at high southern latitudes in the austral summer, which leads to biases in estimates of air-sea CO
exchange. Furthermore, we show that the MSE-based constraint is consistent with an independent constraint on atmospheric mixing based on combining airborne and surface CO
observations.
We present improved estimates of air–sea CO2 exchange over three latitude bands of the Southern Ocean using atmospheric CO2 measurements from global airborne campaigns and an atmospheric 4-box ...inverse model based on a mass-indexed isentropic coordinate (Mθe). These flux estimates show two features not clearly resolved in previous estimates based on inverting surface CO2 measurements: a weak winter-time outgassing in the polar region and a sharp phase transition of the seasonal flux cycles between polar/subpolar and subtropical regions. The estimates suggest much stronger summer-time uptake in the polar/subpolar regions than estimates derived through neural-network interpolation of pCO2 data obtained with profiling floats but somewhat weaker uptake than a recent study by Long et al. Science 374, 1275–1280 (2021), who used the same airborne data and multiple atmospheric transport models (ATMs) to constrain surface fluxes. Our study also uses moist static energy (MSE) budgets from reanalyses to show that most ATMs tend to have excessive diabatic mixing (transport across moist isentrope, θe, or Mθe surfaces) at high southern latitudes in the austral summer, which leads to biases in estimates of air–sea CO2 exchange. Furthermore, we show that the MSE-based constraint is consistent with an independent constraint on atmospheric mixing based on combining airborne and surface CO2 observations.
We use TROPOMI (TROPOspheric Monitoring Instrument) tropospheric nitrogen dioxide (NO
) measurements to identify cropland soil nitrogen oxide (NO
= NO + NO
) emissions at daily to seasonal scales in ...the U.S. Southern Mississippi River Valley. Evaluating 1.5 years of TROPOMI observations with a box model, we observe seasonality in local NO
enhancements and estimate maximum cropland soil NO
emissions (15-34 ng N m
s
) early in growing season (May-June). We observe soil NO
pulsing in response to daily decreases in volumetric soil moisture (VSM) as measured by the Soil Moisture Active Passive (SMAP) satellite. Daily NO
enhancements reach up to 0.8 × 10
molecules cm
4-8 days after precipitation when VSM decreases to ~30%, reflecting emissions behavior distinct from previously defined soil NO
pulse events. This demonstrates that TROPOMI NO
observations, combined with observations of underlying process controls (e.g., soil moisture), can constrain soil NO
processes from space.
In recent years, space-borne observations of atmospheric carbon dioxide (CO2) have been increasingly used in global carbon-cycle studies. In order to obtain added value from space-borne measurements, ...they have to suffice stringent accuracy and precision requirements, with the latter being less crucial as it can be reduced by just enhanced sample size. Validation of CO2 column-averaged dry air mole fractions (XCO2) heavily relies on measurements of the Total Carbon Column Observing Network (TCCON). Owing to the sparseness of the network and the requirements imposed on space-based measurements, independent additional validation is highly valuable. Here, we use observations from the High-Performance Instrumented Airborne Platform for Environmental Research (HIAPER) Pole-to-Pole Observations (HIPPO) flights from 01/2009 through 09/2011 to validate CO2 measurements from satellites (Greenhouse Gases Observing Satellite – GOSAT, Thermal Emission Sounder – TES, Atmospheric Infrared Sounder – AIRS) and atmospheric inversion models (CarbonTracker CT2013B, Monitoring Atmospheric Composition and Climate (MACC) v13r1). We find that the atmospheric models capture the XCO2 variability observed in HIPPO flights very well, with correlation coefficients (r2) of 0.93 and 0.95 for CT2013B and MACC, respectively. Some larger discrepancies can be observed in profile comparisons at higher latitudes, in particular at 300 hPa during the peaks of either carbon uptake or release. These deviations can be up to 4 ppm and hint at misrepresentation of vertical transport. Comparisons with the GOSAT satellite are of comparable quality, with an r2 of 0.85, a mean bias μ of −0.06 ppm, and a standard deviation σ of 0.45 ppm. TES exhibits an r2 of 0.75, μ of 0.34 ppm, and σ of 1.13 ppm. For AIRS, we find an r2 of 0.37, μ of 1.11 ppm, and σ of 1.46 ppm, with latitude-dependent biases. For these comparisons at least 6, 20, and 50 atmospheric soundings have been averaged for GOSAT, TES, and AIRS, respectively. Overall, we find that GOSAT soundings over the remote Pacific Ocean mostly meet the stringent accuracy requirements of about 0.5 ppm for space-based CO2 observations.
Natural gas infrastructure releases methane (CH4), a potent greenhouse gas, into the atmosphere. The estimated emission rate associated with the production and transportation of natural gas is ...uncertain, hindering our understanding of its greenhouse footprint. This study presents a new application of inverse methodology for estimating regional emission rates from natural gas production and gathering facilities in north-eastern Pennsylvania. An inventory of CH4 emissions was compiled for major sources in Pennsylvania. This inventory served as input emission data for the Weather Research and Forecasting model with chemistry enabled (WRF-Chem), and atmospheric CH4 mole fraction fields were generated at 3 km resolution. Simulated atmospheric CH4 enhancements from WRF-Chem were compared to observations obtained from a 3-week flight campaign in May 2015. Modelled enhancements from sources not associated with upstream natural gas processes were assumed constant and known and therefore removed from the optimization procedure, creating a set of observed enhancements from natural gas only. Simulated emission rates from unconventional production were then adjusted to minimize the mismatch between aircraft observations and model-simulated mole fractions for 10 flights. To evaluate the method, an aircraft mass balance calculation was performed for four flights where conditions permitted its use. Using the model optimization approach, the weighted mean emission rate from unconventional natural gas production and gathering facilities in north-eastern Pennsylvania approach is found to be 0.36 % of total gas production, with a 2σ confidence interval between 0.27 and 0.45 % of production. Similarly, the mean emission estimates using the aircraft mass balance approach are calculated to be 0.40 % of regional natural gas production, with a 2σ confidence interval between 0.08 and 0.72 % of production. These emission rates as a percent of production are lower than rates found in any other basin using a top-down methodology, and may be indicative of some characteristics of the basin that make sources from the north-eastern Marcellus region unique.
Methane (CH4) is a potent greenhouse gas and the primary component of natural gas. The San Juan Basin (SJB) is one of the largest coal-bed methane producing regions in North America and, including ...gas production from conventional and shale sources, contributed ∼2% of U.S. natural gas production in 2015. In this work, we quantify the CH4 flux from the SJB using continuous atmospheric sampling from aircraft collected during the TOPDOWN2015 field campaign in April 2015. Using five independent days of measurements and the aircraft-based mass balance method, we calculate an average CH4 flux of 0.54 ± 0.20 Tg yr–1 (1σ), in close agreement with the previous space-based estimate made for 2003–2009. These results agree within error with the U.S. EPA gridded inventory for 2012. These flights combined with the previous satellite study suggest CH4 emissions have not changed. While there have been significant declines in natural gas production between measurements, recent increases in oil production in the SJB may explain why emission of CH4 has not declined. Airborne quantification of outcrops where seepage occurs are consistent with ground-based studies that indicate these geological sources are a small fraction of the basin total (0.02–0.12 Tg yr–1) and cannot explain basinwide consistent emissions from 2003 to 2015.
At local scales, emissions of methane and carbon dioxide are highly uncertain. Localized sources of both trace gases can create strong local gradients in its columnar abundance, which can be ...discerned using absorption spectroscopy at high spatial resolution. In a previous study, more than 250 methane plumes were observed in the San Juan Basin near Four Corners during April 2015 using the next-generation Airborne Visible/Infrared Imaging Spectrometer (AVIRIS-NG) and a linearized matched filter. For the first time, we apply the iterative maximum a posteriori differential optical absorption spectroscopy (IMAP-DOAS) method to AVIRIS-NG data and generate gas concentration maps for methane, carbon dioxide, and water vapor plumes. This demonstrates a comprehensive greenhouse gas monitoring capability that targets methane and carbon dioxide, the two dominant anthropogenic climate-forcing agents. Water vapor results indicate the ability of these retrievals to distinguish between methane and water vapor despite spectral interference in the shortwave infrared. We focus on selected cases from anthropogenic and natural sources, including emissions from mine ventilation shafts, a gas processing plant, tank, pipeline leak, and natural seep. In addition, carbon dioxide emissions were mapped from the flue-gas stacks of two coal-fired power plants and a water vapor plume was observed from the combined sources of cooling towers and cooling ponds. Observed plumes were consistent with known and suspected emission sources verified by the true color AVIRIS-NG scenes and higher-resolution Google Earth imagery. Real-time detection and geolocation of methane plumes by AVIRIS-NG provided unambiguous identification of individual emission source locations and communication to a ground team for rapid follow-up. This permitted verification of a number of methane emission sources using a thermal camera, including a tank and buried natural gas pipeline.
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