Aliso Canyon Research Articles

Investigating the Aliso Canyon Gas Blowout Disaster and Adverse Birth Outcomes: A Quasi Experimental Approach

Investigating the Aliso Canyon Gas Blowout Disaster and Adverse Birth Outcomes: A Quasi Experimental Approach

Underground natural gas storage facility operations and well leakage events in the United States

Federal minimum safety standards for underground natural gas storage (UNGS) operations in the United States (U.S.) were set by the Pipeline and Hazardous Materials Safety Administration (PHMSA) in the aftermath of the 2015 Aliso Canyon well leakage incident. Beginning in 2017, these standards required operators of U.S. UNGS facilities to publicly report: 1) leakage events that meet established criteria for incidents; 2) annual details of well construction, maintenance, and integrity testing activities; and 3) the occurrence of leading indicators of leakage (i.e., safety-related conditions). We reviewed both PHMSA reports and previously published studies to compile a dataset of 53 well leakage events at UNGS facilities in the U.S. that align with the PHMSA reporting requirements. Casings (55.0%) and wellheads (32.5%) were the most common failed well components identified. Human intervention through incorrect operation or outside force damage was the most common (39.3%) cause of well leakage events. Well leakage events caused by corrosion resulted in significantly greater emissions than those with other causes. UNGS annual reports detailed operations at 406 UNGS facilities with 17,993 wells—14,469 were injection and the remainder monitoring. Of these wells, 11,446 (63.6%) were reported to have a design that is potentially susceptible to a single point of failure, which is more than three times the previous estimate. Additional information about the status and construction of individual wells is needed to confirm the number of operational wells with a single-point-of-failure design. These data would help regulators identify single-point-of-failure wells and ensure the elevated risks associated with them are appropriately mitigated by proposed risk management plans. Statistically significant differences in the characteristics of UNGS facilities that have and have not experienced well leakage events were observed among those operating in depleted hydrocarbon reservoirs. Depleted hydrocarbon UNGS facilities that experienced well leakage events were generally larger, which suggests that focusing regulatory inspections and reviews on these facilities may be justified. The UNGS data reported were not sufficient to build a predictive model that forecasts well leakage events. Modeling efforts were limited by the data reporting format, which requires UNGS operators to aggregate data by facility in their annual reports. Gathering and evaluating information for individual wells at UNGS facilities would be valuable and may provide additional insights into well leakage risks to better inform risk management planning efforts.

The effects of air quality on housing prices: Evidence from the Aliso Canyon gas leak

Causal studies on the effect of air quality on house prices, specifically focusing on a large metropolitan area, are rare and difficult to obtain because of potential endogeneity from residential sorting. In this study, we use the Aliso Canyon gas leak as a natural experiment to examine the effect of air quality on housing prices of Los Angeles City. Using a spatial difference-in-differences model, we estimate that houses within the 5-mile radius of the gas well experienced a 8.6% discount in price during the leak, and an additional 13.1% discount after the well was sealed and the air quality was restored. The decrease in price lasted beyond 18 months, with houses closer to the leak suffering higher discounts. We conclude that air quality degradation has a direct and longer term negative impact on house prices.

A national estimate of U.S. underground natural gas storage incident emissions

The 2015 Aliso Canyon storage well blowout was widely reported as the worst natural gas leak in the history of the United States (U.S.) and released ∼0.1 million metric tons of methane (CH4), a potent greenhouse gas. Although storage well fugitive emissions are estimated in the U.S. Environmental Protection Agency’s annual Greenhouse Gas Inventory, the inventory does not include historical estimates of anomalous large emission events other than Aliso Canyon or smaller incident related CH4 releases. A total of 129 underground natural gas storage (UGS) incident-related events between 1940 and 2016 were compiled from various federal/state agencies and literature reviews. Incident emissions were estimated based on best available information, such as direct operator reports, the monetary cost of gas lost, or modeling of the escaping gas at sonic speeds. There are 387 active UGS fields in three types of reservoirs: salt caverns, aquifers, and depleted oil and gas (O&G) fields. 65% of events were in the depleted O&G fields, which account for 79% of storage fields. Texas recorded the highest number of incidents (20), 14 of which were in salt dome reservoirs. The incident emissions showed a heavy-tailed emission pattern with CH4 releases up to 29 billion cubic feet (8.2 × 108m3). The top seven events contributed 98% of the total estimated/measured CH4 emissions.

Quantitative assessment approach to assess benefits of subsurface safety valves and tubing and packer systems in depleted reservoir and aquifer gas storage wells

The Battelle Memorial Institute, Sandia National Laboratory, and Nova Northstar LLC, jointly carried out two projects, sponsored by the Pipeline and Hazardous Materials Safety Administration, assessing the roles of subsurface safety valves and tubing and packer systems in depleted reservoir or aquifer wells used for underground gas storage. The assessment was based on the American Petroleum Institute 581 method and on the storage well-specific model created by the 2017 Joint Industry Task Force organized by the UGS industry in response to the Aliso Canyon gas leak. The model was expanded to capture the specific functionalities of safety valves and tubing and packers, as well as to account for workover risk associated with monitoring and maintenance of such devices. The main conclusion of the two projects is that the application of safety valves and/or tubing and packer systems can reduce risk in some, but not all, gas storage wells. Gas storage wells with low initial risk, as measured by a likelihood of a loss of control event and by a projected consequence of such event, would generally not benefit from installation of new safety systems. In fact, the risk may be increased due to risk of more frequent and more complex workover operations or due to deliverability impairments. For some wells, the initial risk is such that the application of a safety valve or a tubing and packer can substantially decrease risk, specifically reduce consequences of loss of control events. Wells with inherent or initial risk, particularly driven by high likelihood of failure, would see risk reduced by the application of a safety valve or a tubing and packer, however, remaining risk are unacceptably high. An effective way to assess the applicability of these safety devices is to apply quantitative risk models, specifically models that evaluate probabilities/likelihood and consequence of accidents. • Broader use of quantitative risk models should be promoted in the UGS industry. • Tubing and packer systems can reduce risk in some but not all gas storage wells. • Sub surface safety valves can reduce risk in some but not all gas storage wells. • Workover risk should be included in the overall risk model. • Human factors may substantially affect the risk assessment.

The Role of Natural Gas Utilities and Pipeline Operators in a Decarbonized Economy

The natural gas industry has a track record of sharing lessons learned from unfortunate events, leading to initiatives and investments to improve resiliency and reliability. The Columbia Gas of Massachusetts over‐pressurization incident in 2018, led to industry‐wide improvements in natural gas pipeline safety. The Aliso Canyon natural gas storage facility incident resulted in the implementation of American Petroleum Institute (API) storage field standards as regulations. More recently, the industry is still coming to grips with fallout from the February 2021 winter storm events in Texas, when natural gas was unavailable to fuel electricity generation and for residential and commercial/industrial use. Lastly, the May 2021 Colonial Pipeline cyber security breach led to gasoline shortages in downstream markets and will likely lead to new and more comprehensive standards and regulations for pipeline safety and compliance to guard against future cyber‐attacks. While pipeline failures are rare, when they do occur, they are high‐impact events with potentially devastating and costly consequences. According to the Pipeline Hazardous Materials and Safety Administration (PHMSA) trend data, pipeline incidents resulted in 55 fatalities, 272 injuries, and over $3.3 billion in total costs between 2016–2020.

Combustion as a measure to mitigate greenhouse gas emissions from natural gas well blowouts.

Natural gas well blowouts can release a large amount of methane along with other greenhouse gases. According to the Intergovernmental Panel on Climate Change, the global warming potential (GWP) of fossil methane is 30 times higher than that of carbon dioxide in a 100-year time horizon. Here, we show that combustion can be used as a means to significantly reduce the global warming effect of greenhouse emissions from gas well blowouts: up to 90 percent of the effect can be eliminated by combusting the released natural gas. The 2015 Aliso Canyon storage well blowout is used as an example.

DETECTION AND QUANTIFICATION OF INDUSTRIAL METHANE PLUME WITH THE AIRBORNE HYSPEX-NEO CAMERA AND APPLICATIONS TO SATELLITE DATA

Abstract. The control and monitoring of greenhouse gases is an important issue for the study of climate change, for the impact in terms of public health or for the risks related to industry. An algorithm has been developped dedicated to commercial airborne hyperspectral camera as HySpex-NEO for the detection of industrial methane plume and the quantification of the emission source. HySpex-NEO is an imager used in airborne campaign with a spatial resolution of 1.4 m at flight altitude of 2 km, a swath of 650 m and a spectral resolution of 6 nm. This algorithm has been validated over a controlled release less than 100 g/s during an airborne campaign over Lacq (France) industry. It has also been applied to the Aliso Canyon leakage data acquired with AVIRIS JPL (Airborne Visible Infrared Spectrometer) with a spatial resolution of 6.8 m at flight altitude of 6 km, a swath of 5.6 km and a spectral resolution of 10 nm. Application to satellite hyperspectral data is shown on artificial data derived from airborne hyperspectral acquisitions.

Methane emissions from underground gas storage in California

Accurate and timely detection, quantification, and attribution of methane emissions from Underground Gas Storage (UGS) facilities is essential for improving confidence in greenhouse gas inventories, enabling emission mitigation by facility operators, and supporting efforts to assess facility integrity and safety. We conducted multiple airborne surveys of the 12 active UGS facilities in California between January 2016 and November 2017 using advanced remote sensing and in situ observations of near-surface atmospheric methane (CH4). These measurements where combined with wind data to derive spatially and temporally resolved methane emission estimates for California UGS facilities and key components with spatial resolutions as small as 1–3 m and revisit intervals ranging from minutes to months. The study spanned normal operations, malfunctions, and maintenance activity from multiple facilities including the active phase of the Aliso Canyon blowout incident in 2016 and subsequent return to injection operations in summer 2017. We estimate that the net annual methane emissions from the UGS sector in California averaged between 11.0 ± 3.8 GgCH4 yr−1 (remote sensing) and 12.3 ± 3.8 GgCH4 yr−1 (in situ). Net annual methane emissions for the 7 facilities that reported emissions in 2016 were estimated between 9.0 ± 3.2 GgCH4 yr−1 (remote sensing) and 9.5 ± 3.2 GgCH4 yr−1 (in situ), in both cases around 5 times higher than reported. The majority of methane emissions from UGS facilities in this study are likely dominated by anomalous activity: higher than expected compressor loss and leaking bypass isolation valves. Significant variability was observed at different time-scales: daily compressor duty-cycles and infrequent but large emissions from compressor station blow-downs. This observed variability made comparison of remote sensing and in situ observations challenging given measurements were derived largely at different times, however, improved agreement occurred when comparing simultaneous measurements. Temporal variability in emissions remains one of the most challenging aspects of UGS emissions quantification, underscoring the need for more systematic and persistent methane monitoring.

Detection of Methane Emission from a Local Source Using GOSAT Target Observations

Emissions of atmospheric methane (CH4), which greatly contributes to radiative forcing, have larger uncertainties than those for carbon dioxide (CO2). The Thermal And Near-infrared Sensor for carbon Observation Fourier-Transform Spectrometer (TANSO-FTS) onboard the Greenhouse gases Observing SATellite (GOSAT) launched in 2009 has demonstrated global grid observations of the total column density of CO2 and CH4 from space, and thus reduced uncertainty in the global flux estimation. In this paper, we present a case study on local CH4 emission detection from a single-point source using an available series of GOSAT data. By modifying the grid observation pattern, the pointing mechanism of TANSO-FTS targets a natural gas leak point at Aliso Canyon in Southern California, where the clear-sky frequency is high. To enhance local emission estimates, we retrieved CO2 and CH4 partial column-averaged dry-air mole fractions of the lower troposphere (XCO2 (LT) and XCH4 (LT)) by simultaneous use of both sunlight reflected from Earth’s surface and thermal emissions from the atmosphere. The time-series data of Aliso Canyon showed a large enhancement that decreased with time after its initial blowout, compared with reference point data and filtered with wind direction simulated by the Weather Research and Forecasting (WRF) model.

Satellite observations reveal extreme methane leakage from a natural gas well blowout

Methane emissions due to accidents in the oil and natural gas sector are very challenging to monitor, and hence are seldom considered in emission inventories and reporting. One of the main reasons is the lack of measurements during such events. Here we report the detection of large methane emissions from a gas well blowout in Ohio during February to March 2018 in the total column methane measurements from the spaceborne Tropospheric Monitoring Instrument (TROPOMI). From these data, we derive a methane emission rate of 120 ± 32 metric tons per hour. This hourly emission rate is twice that of the widely reported Aliso Canyon event in California in 2015. Assuming the detected emission represents the average rate for the 20-d blowout period, we find the total methane emission from the well blowout is comparable to one-quarter of the entire state of Ohio's reported annual oil and natural gas methane emission, or, alternatively, a substantial fraction of the annual anthropogenic methane emissions from several European countries. Our work demonstrates the strength and effectiveness of routine satellite measurements in detecting and quantifying greenhouse gas emission from unpredictable events. In this specific case, the magnitude of a relatively unknown yet extremely large accidental leakage was revealed using measurements of TROPOMI in its routine global survey, providing quantitative assessment of associated methane emissions.

Satellite Discovery of Anomalously Large Methane Point Sources From Oil/Gas Production

AbstractRapid identification of anomalous methane sources in oil/gas fields could enable corrective action to fight climate change. The GHGSat‐D satellite instrument measuring atmospheric methane with 50‐meter spatial resolution was launched in 2016 to demonstrate space‐based monitoring of methane point sources. Here we report the GHGSat‐D discovery of an anomalously large, persistent methane source (10–43 metric tons per hour, detected in over 50% of observations) at a gas compressor station in Central Asia, together with additional sources (4–32 metric tons per hour) nearby. The TROPOMI satellite instrument confirms the magnitude of these large emissions going back to at least November 2017. We estimate that these sources released 142 ± 34 metric kilotons of methane to the atmosphere from February 2018 through January 2019, comparable to the 4‐month total emission from the well‐documented Aliso Canyon blowout.

Associations among particulate matter, hazardous air pollutants and methane emissions from the Aliso Canyon natural gas storage facility during the 2015 blowout

In October of 2015, a large underground storage well at the Aliso Canyon natural gas storage facility experienced a massive methane leak (also referred to as “natural gas blowout”), which resulted in the largest ever anthropogenic release of methane from a single point source in the United States. Additional sampling conducted during the event revealed unique gas and particle concentrations in ambient air and a characteristic “fingerprint” of metals in the indoor dust samples similar to samples taken at the blowout site. We further investigated the association between the Aliso Canyon natural gas storage site and several measured air pollutants by: (a) conducting additional emission source studies using meteorological data and correlations between particulate matter, methane, and hazardous air pollutants (HAPs) collected during the natural gas blowout at distances ranging from 1.2 to 7.3 km due south of well SS25, (b) identifying the unique i/n-pentane ratio signature associated with emissions from the blowout event, and (c) identifying characteristics unique to the homes that tested positive for air pollutants using data collected from extensive indoor environmental assessment surveys. Results of air quality samples collected near Aliso Canyon during the final weeks of the event revealed that elevated levels of several HAP compounds were likely influenced by the active natural gas blowout. Furthermore, the final attempts to plug the well during the days preceding the well kill were associated with particle emissions likely from the well site. Together, this investigation suggests uncontrolled leaks or blowout events at natural gas storage facilities have the potential to release harmful pollutants with adverse health and environmental consequences into proximate communities. With this evidence, our recommendations include facility-specific meteorological and air quality data-collection equipment installed at natural gas storage facilities and support of environmental surveillance after severe off-normal operation events.

Spatio‐temporally Resolved Methane Fluxes From the Los Angeles Megacity

AbstractWe combine sustained observations from a network of atmospheric monitoring stations with inverse modeling to uniquely obtain spatiotemporal (3‐km, 4‐day) estimates of methane emissions from the Los Angeles megacity and the broader South Coast Air Basin for 2015–2016. Our inversions use customized and validated high‐fidelity meteorological output from Weather Research Forecasting and Stochastic Time‐Inverted Lagrangian model for South Coast Air Basin and innovatively employ a model resolution matrix‐based metric to disentangle the spatiotemporal information content of observations as manifested through estimated fluxes. We partially track and constrain fluxes from the Aliso Canyon natural gas leak and detect closure of the Puente Hills landfill, with no prior information. Our annually aggregated fluxes and their uncertainty excluding the Aliso Canyon leak period lie within the uncertainty bounds of the fluxes reported by the previous studies. Spatially, major sources of CH4 emissions in the basin were correlated with CH4‐emitting infrastructure. Temporally, our findings show large seasonal variations in CH4 fluxes with significantly higher fluxes in winter in comparison to summer months, which is consistent with natural gas demand and anticorrelated with air temperature. Overall, this is the first study that utilizes inversions to detect both enhancement (Aliso Canyon leak) and reduction (Puente Hills) in CH4 fluxes due to the unintended events and policy decisions and thereby demonstrates the utility of inverse modeling for identifying variations in fluxes at fine spatiotemporal resolution.

Detecting Urban Emissions Changes and Events With a Near‐Real‐Time‐Capable Inversion System

AbstractIn situ observing networks are increasingly being used to study greenhouse gas emissions in urban environments. While the need for sufficiently dense observations has often been discussed, density requirements depend on the question posed and interact with other choices made in the analysis. Focusing on the interaction of network density with varied meteorological information used to drive atmospheric transport, we perform geostatistical inversions of methane flux in the South Coast Air Basin, California, in 2015–2016 using transport driven by a locally tuned Weather Research and Forecasting configuration as well as by operationally available meteorological products. We find total‐basin flux estimates vary by as much as a factor of two between inversions, but the spread can be greatly reduced by calibrating the estimates to account for modeled sensitivity. Using observations from the full Los Angeles Megacities Carbon Project observing network, inversions driven by low‐resolution generic wind fields are robustly sensitive (p < 0.05) to seasonal differences in methane flux and to the increase in emissions caused by the 2015 Aliso Canyon natural gas leak. When the number of observing sites is reduced, the basin‐wide sensitivity degrades, but flux events can be detected by testing for changes in flux variance, and even a single site can robustly detect basin‐wide seasonal flux variations. Overall, an urban monitoring system using an operational methane observing network and off‐the‐shelf meteorology could detect many seasonal or event‐driven changes in near real time—and, if calibrated to a model chosen as a transfer standard, could also quantify absolute emissions.

Short-Term Impacts of the Aliso Canyon Natural Gas Blowout on Weather, Climate, Air Quality, and Health in California and Los Angeles.

The Aliso Canyon (Porter Ranch), California, natural gas blowout lasted 112 days, from October 23, 2015 to February 11, 2016, releasing 97 100 metric tonnes of methane, 7300 tonnes of ethane, and a host of other hydrocarbons into the Southern California air. This study estimates the impacts of the leak on transient weather, climate, air quality, and health in California and the Los Angeles Basin using a nested global-through-local weather-climate-air quality computer model. Results suggest that the Aliso Canyon leak may have increased the mixing ratios of multiple emitted hydrocarbon gases throughout California. Subsequent gas-phase photochemistry increased the mixing ratios of additional byproducts, including carbon monoxide, formaldehyde, acetaldehyde, peroxyacetyl nitrate, and ozone. Increases in air temperatures aloft and lesser increases at the surface due to thermal-infrared radiation absorption by methane stabilized the air over much of California, slightly reducing clouds, precipitation, and near-surface wind speed with greater reductions in Los Angeles than in California. The reduction in precipitation, in particular, increased PM2.5 concentration, with a greater increase in Los Angeles than in California. The higher PM2.5 increased estimated premature mortality in California by +32 (9-54) to +43 (15-66), depending on the set of relative risks used. Despite higher PM2.5 in Los Angeles due to the leak, premature mortalities there were more ambiguous, ranging from a mean decrease of -7 to a mean increase of +15, for 2 simulations with different resolution and boundary conditions. The remaining mortalities occurred in the Central Valley and San Francisco Bay Area. Ozone premature mortalities away from the leak increased by <1. The study did not evaluate potential health impacts, including cancers, immediately near the leak. As such, the Aliso Canyon leak affected temperatures, pollution, and health throughout California. Future leaks will also likely have impacts.

Technology Focus: Natural Gas Processing and Handling (April 2019)

Technology Focus To cater to the seasonal highs and lows in demand throughout a year, natural gas is stored in underground storage facilities. The need for such facilities arose because increasing (or decreasing) gas production to mirror changes in demand is neither practical nor economical. Therefore, gas is produced and stored during low-demand times and retrieved to meet the highs during winters. This cyclic trend can be observed also in gas-storage inventories [as reported by the Energy Information Administration (EIA)]. The northeast US has the highest concentration of such storage facilities, close to the biggest market. Most of the underground gas-storage facilities are depleted reservoirs, but aquifers and leached salt caverns are also used. The US and Canada were the pioneers in realizing the potential of depleted reservoirs for gas storage and, hence, have several well-developed facilities. What makes depleted reservoirs attractive is the presence of existing wells used to produce the reservoir, plus the geologic and engineering knowledge acquired during the development of the field. All that information is leveraged when repurposing the field for gas storage. Depleted reservoirs also contain some amount of gas already in the reservoir, which decreases the requirement to inject gas as cushion gas. (Cushion gas is immobile gas that remains in the reservoir and allows the reservoir to be used for storage.) Depleted reservoirs are also the most abundant. I would be remiss not to touch upon the Aliso Canyon incident of 2015. Aliso Canyon was the second-largest storage facility in the US at the time. The industry learned a harsh lesson about the repercussions when containment is lost for such facilities. The loss of containment was because of the casing failure of one of the wells (along with having subsurface safety valves removed in the past). This led to 109,000 tonnes of methane emissions by some estimates. One measure that was proposed to reduce such risks is to use offshore reservoirs nearing abandonment for gas storage (instead of onshore ones that are close to populated urban areas). At the time of this writing, the week-to-week change in the natural gas storage inventory was –237 Bcf, and levels remained lower than the 5-year historical average, according to the EIA. This withdrawal from the inventory was less than most forecasts based on the extreme cold temperatures faced by the US. The Henry Hub natural gas prices reached highs of more than $4.5/million Btu in 2018 because of record gas demand. The price has since dipped to $2.57/million Btu because of abatement in the extreme weather leading to lower demand for heating. To learn more, visit the SPE Annual Technical Conference and Exhibition in Calgary, 30 September–2 October, and the Gastech Exhibition and Conference in Houston, 17–19 September. Recommended additional reading at OnePetro: www.onepetro.org. SPE 190838 Comprehensive Evaluation of the Dynamic Sealing Capacity of Clayey Caprocks in a Large Underground Gas Storage by Junchang Sun, PetroChina, et al. SPE 192961 Maintaining Flare-Tip Health by Venugopal Bakthavachsalam, ADNOC, et al. SPE 192783 Cutting-Edge Solutions for Sour-Gas Treatment: A Retrospective Study by Kuwait Oil Company by Fahad Al-Ghanem, Kuwait Oil Company, et al.

Using Electrical Energy Storage to Mitigate Natural Gas-Supply Shortages

The recent leak of the Aliso Canyon natural gas storage facility calls for coordinated planning of natural gas and electric power systems with specific consideration of electrical energy storage. This paper proposes a coordinated planning model that fills this need. The model is formulated as a two-stage stochastic optimization problem, in which electricity- and natural gas-demand growth and natural gas-supply uncertainties are represented. We analyze the tradeoff between building electrical, natural gas, and electrical energy storage infrastructure. The sensitivity of electrical energy storage investment to the modeling of the operating conditions is also studied. The model is tested using a California-based case study.

Impact of the Aliso Canyon Gas Leak on Respiratory-Related Conditions Among US Department of Veterans Affairs (VA) Users.

The largest gas leak in United States history occurred October 2015 through February 2016 near Porter Ranch (PR), California, and prompted the temporary relocation of nearby residents because of health concerns related to natural gas exposure. A retrospective cohort study was conducted using US Department of Veterans Affairs (VA) administrative and clinical data. On the basis of zip codes, we created two groups: PR (1920 patients) and San Fernando Valley (SFV) (15 260 patients) and examined the proportion of outpatient visits to VA providers with respiratory-related diagnoses between October 2014 and September 2017. We observed an increase in the proportion of visits in the PR group during the leak (7.0% vs 6.1%, P&lt;0.005) and immediately after the leak (7.7% vs 5.3%, P&lt;0.0001). For both groups, we observed a decrease in respiratory diagnoses one year after the leak (7.0% to 5.9%, P&lt;0.05 PR; 6.1% to 5.7%, P&lt;0.01 SFV). Exposure to natural gas likely led to the observed increase in respiratory-related diagnoses during and after the PR gas leak. Early relocation following natural gas leaks may mitigate respiratory exacerbations. (Disaster Med Public Health Preparedness. 2019;13:419-423).

Reducing errors in aircraft atmospheric inversion estimates of point-source emissions: the Aliso Canyon natural gas leak as a natural tracer experiment

Urban greenhouse gas (GHG) flux estimation with atmospheric measurements and modeling, i.e. the ‘top-down’ approach, can potentially support GHG emission reduction policies by assessing trends in surface fluxes and detecting anomalies from bottom-up inventories. Aircraft-collected GHG observations also have the potential to help quantify point-source emissions that may not be adequately sampled by fixed surface tower-based atmospheric observing systems. Here, we estimate CH4 emissions from a known point source, the Aliso Canyon natural gas leak in Los Angeles, CA from October 2015–February 2016, using atmospheric inverse models with airborne CH4 observations from twelve flights ≈4 km downwind of the leak and surface sensitivities from a mesoscale atmospheric transport model. This leak event has been well-quantified previously using various methods by the California Air Resources Board, thereby providing high confidence in the mass-balance leak rate estimates of (Conley et al ), used here for comparison to inversion results. Inversions with an optimal setup are shown to provide estimates of the leak magnitude, on average, within a third of the mass balance values, with remaining errors in estimated leak rates predominantly explained by modeled wind speed errors of up to 10 m s−1, quantified by comparing airborne meteorological observations with modeled values along the flight track. An inversion setup using scaled observational wind speed errors in the model-data mismatch covariance matrix is shown to significantly reduce the influence of transport model errors on spatial patterns and estimated leak rates from the inversions. In sum, this study takes advantage of a natural tracer release experiment (i.e. the Aliso Canyon natural gas leak) to identify effective approaches for reducing the influence of transport model error on atmospheric inversions of point-source emissions, while suggesting future potential for integrating surface tower and aircraft atmospheric GHG observations in top-down urban emission monitoring systems.