Quantifying greenhouse-gas emissions from atmospheric measurements: a critical reality check for climate legislation

Sustained growth of sulfur hexafluoride emissions in China inferred from atmospheric observations

Sulfur hexafluoride (SF6) is a potent greenhouse gas. Here we use long-term atmospheric observations to determine SF6 emissions from China between 2011 and 2021, which are used to evaluate the Chinese national SF6 emission inventory and to better understand the global SF6 budget. SF6 emissions in China substantially increased from 2.6 (2.3-2.7, 68% uncertainty) Gg yr-1 in 2011 to 5.1 (4.8-5.4) Gg yr-1 in 2021. The increase from China is larger than the global total emissions rise, implying that it has offset falling emissions from other countries. Emissions in the less-populated western regions of China, which have potentially not been well quantified in previous measurement-based estimates, contribute significantly to the national SF6 emissions, likely due to substantial power generation and transmission in that area. The CO2-eq emissions of SF6 in China in 2021 were 125 (117-132) million tonnes (Mt), comparable to the national total CO2 emissions of several countries such as the Netherlands or Nigeria. The increasing SF6 emissions offset some of the CO2 reductions achieved through transitioning to renewable energy in the power industry, and might hinder progress towards achieving China's goal of carbon neutrality by 2060 if no concrete control measures are implemented.

Lagrangian Particle Dispersion Models in the Grey Zone of Turbulence: Adaptations to FLEXPART-COSMO for Simulations at 1 km Grid Resolution

Lagrangian particle dispersion models (LPDMs) are frequently used for regional-scale inversions of greenhouse gas emissions. However, the turbulence parameterizations used in these models were developed for coarse resolution grids, hence, when moving to the kilometre-scale the validity of these descriptions should be questioned. Here, we analyze the influence of the turbulence parameterization employed in the LPDM FLEXPART-COSMO model. Comparisons of the turbulence kinetic energy between the turbulence schemes of FLEXPART-COSMO and the underlying Eulerian model COSMO suggest that the dispersion in FLEXPART-COSMO suffers from a double-counting of turbulent elements when run at a high resolution of 1 × 1 km 2 . Such turbulent elements are represented in both COSMO, by the resolved grid-scale winds, and FLEXPART, by its stochastic parameterizations. Therefore, we developed a new parametrization for the variations of the winds and the Lagrangian time scales in FLEXPART in order to harmonize the amount of turbulence present in both models. In a case study for a power plant plume, the new scheme results in improved plume representation when compared with in situ flight observations and with a tracer transported in COSMO. Further in-depth validation of the LPDM against methane observations at a tall tower site in Switzerland shows that the model's ability to predict the observed tracer variability and concentration at different heights above ground is considerably enhanced using the updated turbulence description. The high-resolution simulations result in a more realistic and pronounced diurnal cycle of the tracer concentration peaks and overall improved correlation with observations when compared to previously used coarser resolution simulations (at 7 km × 7 km). Our results indicate that the stochastic turbulence schemes of LPDMs, developed in the past for coarse resolution models, should be revisited to include a resolution dependency and resolve only the part of the turbulence spectrum that is a subgrid process at each different mesh size. Although our new scheme is specific to COSMO simulations at 1 × 1 km 2 resolution, the methodology for deriving the scheme can easily be applied to different resolutions and other regional models.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10546-022-00728-3.

Unexpected nascent atmospheric emissions of three ozone-depleting hydrochlorofluorocarbons

Global and regional atmospheric measurements and modeling can play key roles in discovering and quantifying unexpected nascent emissions of environmentally important substances. We focus here on three hydrochlorofluorocarbons (HCFCs) that are restricted by the Montreal Protocol because of their roles in stratospheric ozone depletion. Based on measurements of archived air samples and on in situ measurements at stations of the Advanced Global Atmospheric Gases Experiment (AGAGE) network, we report global abundances, trends, and regional enhancements for HCFC-132b ([Formula: see text]), which is newly discovered in the atmosphere, and updated results for HCFC-133a ([Formula: see text]) and HCFC-31 ([Formula: see text]ClF). No purposeful end-use is known for any of these compounds. We find that HCFC-132b appeared in the atmosphere 20 y ago and that its global emissions increased to 1.1 Gg⋅y-1 by 2019. Regional top-down emission estimates for East Asia, based on high-frequency measurements for 2016-2019, account for ∼95% of the global HCFC-132b emissions and for ∼80% of the global HCFC-133a emissions of 2.3 Gg⋅y-1 during this period. Global emissions of HCFC-31 for the same period are 0.71 Gg⋅y-1 Small European emissions of HCFC-132b and HCFC-133a, found in southeastern France, ceased in early 2017 when a fluorocarbon production facility in that area closed. Although unreported emissive end-uses cannot be ruled out, all three compounds are most likely emitted as intermediate by-products in chemical production pathways. Identification of harmful emissions to the atmosphere at an early stage can guide the effective development of global and regional environmental policy.

Next-Generation Digital Ecosystem for Climate Data Mining and Knowledge Discovery: A Review of Digital Data Collection Technologies

Climate change has been called "the defining challenge of our age" and yet the global community lacks adequate information to understand whether actions to address it are succeeding or failing to mitigate it. The emergence of technologies such as earth observation (EO) and Internet-of-Things (IoT) promises to provide new advances in data collection for monitoring climate change mitigation, particularly where traditional means of data exploration and analysis, such as government-led statistical census efforts, are costly and time consuming. In this review article, we examine the extent to which digital data technologies, such as EO (e.g., remote sensing satellites, unmanned aerial vehicles or UAVs, generally from space) and IoT (e.g., smart meters, sensors, and actuators, generally from the ground) can address existing gaps that impede efforts to evaluate progress toward global climate change mitigation. We argue that there is underexplored potential for EO and IoT to advance large-scale data generation that can be translated to improve climate change data collection. Finally, we discuss how a system employing digital data collection technologies could leverage advances in distributed ledger technologies to address concerns of transparency, privacy, and data governance.

Replacing SF6 in Electrical Gas-Insulated Switchgear: Technological Alternatives and Potential Life Cycle Greenhouse Gas Savings in an EU-28 Perspective

To date, atmospheric concentrations of sulfur hexafluoride (SF6) are the most potent among the greenhouse gases identified by the Intergovernmental Panel on Climate Change (IPCC) and are still rising. In the EU-28, SF6 has been banned from several applications, however, an important exception is gas-insulated electrical switchgear (GIS) for which cost-effective and environmentally sound alternatives were unavailable when the F-Gas regulation was last revised in 2014. To date, after some recent innovations, we argue that the phasing out of SF6 could spur the accelerated development of alternatives with a lower carbon footprint. In the EU-28, the SF6 amount in switchgear is unclear. In this paper, we estimated the SF6 amount to be between 10,800 and 24,700 t (with a mode at 12,700 t) in 2017, resulting in 68 to 140 t of annual emissions from operational leakage only, corresponding to 1.6 to 3.3 Mt of CO2-eq. We additionally calculated the potential greenhouse gas savings over the lifecycle of one exemplary 145 kV gas-insulated switchgear bay upon replacing SF6 by decafluoro-2-methylbutan-3-one (C5-FK) and heptafluoro-2-methylpropanenitrile (C4-FN) mixtures. Projecting these results over the EU-28, a phase-out scenario starting from 2020 onwards could reduce the carbon footprint by a median of 14 Mt of CO2-eq, over a period of 50 years. Extrapolation to medium voltage could be assumed to be of a similar magnitude.

Dissolved methane in the influent of three Australian wastewater treatment plants fed by gravity sewers

Methane (CH₄) is an important anthropogenic greenhouse gas and a by-product of urban sewage management. In recent years and contrary to international (IPCC) consensus, pressurised (anaerobic) sewers were identified as important CH₄ sources, yet relatively little remains known regarding the role of gravity sewers in CH₄ production and conveyance. Here we provide the results of a nine month study assessing dissolved CH₄ levels in the raw influent of three large Australian wastewater treatment plants (WWTPs) fed by gravity sewers. Similar to recent international research and contrary to IPCC guidance, results show that gravity sewered wastewater contains moderate levels of CH₄ (≈1mgL^-1). Dissolved CH₄ concentration correlated negatively with daily sewage flow rate (i.e. inversely proportional to sewer hydraulic residence time), with daily CH₄ mass loads on average some two-fold greater under low flow (dry weather) conditions. Along with sewage hydraulic residence time, sewer sediments are thought to interact with sewage flow rate and are considered to play a key role in gravity sewer CH₄ production. A per capita load of 78gCH₄person^-1y^-1 is offered for gravity sewered wastewater entering WWTPs, with a corresponding emission estimate of up to 62gCH₄person^-1y^-1, assuming 80% water-to-air transfer of inflowing CH₄ in WWTPs with combined preliminary-primary plus secondary treatment. Results here support the emerging consensus view that hydraulic operation (i.e. gravity versus pressurised, sewage flow rate) is a key factor in determining sewer CH₄ production, with gravity sewer segments likely to play a dominant role in total CH₄ production potential for large metropolitan sewer networks. Further work is warranted to assess the scale and temporal dynamics of CH₄ production in gravity sewers elsewhere, with more work needed to adequately capture and assess the scale of diffuse sewer network CH₄ emissions from sprawling urban settlements globally.

Reconciling reported and unreported HFC emissions with atmospheric observations

We infer global and regional emissions of five of the most abundant hydrofluorocarbons (HFCs) using atmospheric measurements from the Advanced Global Atmospheric Gases Experiment and the National Institute for Environmental Studies, Japan, networks. We find that the total CO2-equivalent emissions of the five HFCs from countries that are required to provide detailed, annual reports to the United Nations Framework Convention on Climate Change (UNFCCC) increased from 198 (175-221) Tg-CO2-eq ⋅ y(-1) in 2007 to 275 (246-304) Tg-CO2-eq ⋅ y(-1) in 2012. These global warming potential-weighted aggregated emissions agree well with those reported to the UNFCCC throughout this period and indicate that the gap between reported emissions and global HFC emissions derived from atmospheric trends is almost entirely due to emissions from nonreporting countries. However, our measurement-based estimates of individual HFC species suggest that emissions, from reporting countries, of the most abundant HFC, HFC-134a, were only 79% (63-95%) of the UNFCCC inventory total, while other HFC emissions were significantly greater than the reported values. These results suggest that there are inaccuracies in the reporting methods for individual HFCs, which appear to cancel when aggregated together.

Nitrogen trifluoride global emissions estimated from updated atmospheric measurements

Nitrogen trifluoride (NF(3)) has potential to make a growing contribution to the Earth's radiative budget; however, our understanding of its atmospheric burden and emission rates has been limited. Based on a revision of our previous calibration and using an expanded set of atmospheric measurements together with an atmospheric model and inverse method, we estimate that the global emissions of NF(3) in 2011 were 1.18 ± 0.21 Gg⋅y(-1), or ∼20 Tg CO(2)-eq⋅y(-1) (carbon dioxide equivalent emissions based on a 100-y global warming potential of 16,600 for NF(3)). The 2011 global mean tropospheric dry air mole fraction was 0.86 ± 0.04 parts per trillion, resulting from an average emissions growth rate of 0.09 Gg⋅y(-2) over the prior decade. In terms of CO(2) equivalents, current NF(3) emissions represent between 17% and 36% of the emissions of other long-lived fluorinated compounds from electronics manufacture. We also estimate that the emissions benefit of using NF(3) over hexafluoroethane (C(2)F(6)) in electronics manufacture is significant-emissions of between 53 and 220 Tg CO(2)-eq⋅y(-1) were avoided during 2011. Despite these savings, total NF(3) emissions, currently ∼10% of production, are still significantly larger than expected assuming global implementation of ideal industrial practices. As such, there is a continuing need for improvements in NF(3) emissions reduction strategies to keep pace with its increasing use and to slow its rising contribution to anthropogenic climate forcing.

Compositions and greenhouse gas emission factors of flared and vented gas in the Western Canadian Sedimentary Basin

A significant obstacle in evaluating mitigation strategies for flaring and venting in the upstream oil and gas industry is the lack of publicly available data on the chemical composition of the gas. This information is required to determine the economic value of the gas, infrastructure and processing requirements, and potential emissions or emissions credits, all of which have significant impact on the economics of such strategies. This paper describes a method for estimating the composition of solution gas being flared and vented at individual facilities, and presents results derived for Alberta, Canada, which sits at the heart of the Western Canadian Sedimentary Basin. Using large amounts of raw data obtained through the Alberta Energy Resources Conservation Board, a relational database was created and specialized queries were developed to link production stream data, raw gas samples, and geography to create production-linked gas composition profiles for approximately half of the currently active facilities. These were used to create composition maps for the entire region, to which the remaining facilities with unknown compositions were geographically linked. The derived data were used to compute a range of solution gas composition profiles and greenhouse gas emission factors, providing new insight into flaring and venting in the region and enabling informed analysis of future management and mitigation strategies.

IMPLICATIONS

Accurate and transparent determination of environmental impacts of flaring and venting of gas associated with oil production, and potential benefits of mitigation, is severely hampered by the lack of publicly available gas composition data. In jurisdictions within the Western Canadian Sedimentary Basin, frameworks exist for regulating and trading carbon offset credits but current potential for mitigation is limited by a lack of standardized methods for calculating CO2 equivalent emissions. The composition and emission factor data derived in this paper will be useful to industry, regulators, policy researchers, and entrepreneurs seeking statistically significant and openly available data necessary to manage and mitigate upstream flaring and venting activity and estimate greenhouse gas impacts.

Invited article: A materials investigation of a phase-change micro-valve for greenhouse gas collection and other potential applications

The deleterious consequences of climate change are well documented. Future climate treaties might mandate greenhouse gas (GHG) emissions measurement from signatories in order to verify compliance. The acquisition of atmospheric chemistry would benefit from low cost, small size/weight/power of microsystems. In this paper, we investigated several key materials science aspects of a phase-change microvalve (PCμV) technology with low power/size/weight/cost for ubiquitous GHG sampling. The novel design, based on phase-change material low-melting-point eutectic metal alloys (indium-bismuth, InBi and tin-lead, SnPb), could be actuated at temperatures as low as 72 °C. Valve manufacturing was based on standard thick and thin-film processes and solder technologies that are commonly used in industry, enabling low-cost, high-volume fabrication. Aging studies showed that it was feasible to batch fabricate the PCμVs and store them for future use, especially in the case of SnPb alloys. Hermetic sealing of the valve prototypes was demonstrated through helium leak testing, and Mil spec leak rates less than 1 × 10(-9) atm cm(3)/s were achieved. This confirms that the sample capture and analysis interval can be greatly expanded, easing the logistical burdens of ubiquitous GHG monitoring. Highly conservative and hypothetical CO(2) bias due to valve actuation at altitude in 1 cm(3) microsamplers would be significantly below 1.0 and 2.2 ppmv for heat-treated InBi and SnPb solders, respectively. The CO(2) bias from the PCμV scales well, as a doubling of sampler volume halved the bias. We estimated the shelf life of the SnPb PCμVs to be at least 2.8 years. These efforts will enable the development of low cost, low dead volume, small size/weight microsystems for monitoring GHGs and volatile organic compounds.

Greenhouse gases in the Earth system: setting the agenda to 2030

What do we need to know about greenhouse gases? Over the next 20 years, how should scientists study the role of greenhouse gases in the Earth system and the changes that are taking place? These questions were addressed at a Royal Society scientific Discussion Meeting in London on 22-23 February 2010, with over 300 participants.