Kieran M. Stanley

Atmospheric measurements of greenhouse gases (GHG), including carbon dioxide (CO ₂ ), methane (CH ₄ ) and nitrous oxide (N ₂ O) are essential for assessing climate change and verifying national emission inventories. As global networks rely on high-precision observations of GHGs, ensuring accuracy between observation stations is essential. Maintaining accuracy within a network requires the use of whole air reference materials (RMs) with well-defined calibration scales, such as those maintained by the National Oceanic and Atmospheric Administration (NOAA) for the World Meteorological Organisation (WMO). With the global expansion of atmospheric monitoring networks there is a growing need for readily available RMs, stimulating the development of complementary alternatives such as synthetic air RMs traceable to the International System of Units (SI). In the United Kingdom (UK) and Ireland, the atmospheric GHG monitoring network, comprising long-term atmospheric monitoring stations, is equipped with high precision in situ GHG analysers. These observations are used to verify bottom-up assessments of national emissions. Here, a case study is presented which provides the first direct, network-wide evaluation of whole air versus synthetic air RMs under routine field conditions, allowing an assessment of the implications of SI-traceable RMs within an active national atmospheric monitoring system. We assess the UK and Ireland's network consistency and performance using WMO-NOAA scale-traceable whole air RMs and SI-traceable synthetic air RMs, through a blind multi-site round-robin intercomparison. Between 2021 and 2022, measurements were made of CO ₂ , CH ₄ and N ₂ O in whole and synthetic air RMs at six sites using a range of instruments and the results were used to assess consistency between sites. The measured mole fractions for each cylinder, at each site were then compared with the assigned value on the WMO-NOAA scale and the SI-traceable values for the whole air and synthetic air RMs, respectively. Weighted residual analysis reveals that whole air RMs generally meet the WMO/Global Atmosphere Watch (GAW) compatibility goals for CO ₂ and CH ₄ , while N ₂ O remains more difficult as its relatively small atmospheric variability requires measurement biases to be minimised to resolve meaningful atmospheric differences. Synthetic SI-traceable RMs have associated absolute uncertainties on their assigned values for CH ₄ that are comparable to the extended WMO compatibility goals. However, absolute uncertainties for CO ₂ and N ₂ O remain significantly larger than both the compatibility and extended compatibility goals, which is consistent with previous studies. Overall, these results indicate that while scale-traceable whole air RMs remain essential for achieving the highest level of network compatibility required for atmospheric monitoring, SI-traceable synthetic RMs could play a valuable complementary role, particularly for CH ₄ . However, it is first critical that improved characterisation and compensation of matrix effects arising from instrument-specific responses to differences in RM composition, non-linear instrument response across the relevant mole fraction range, and long-term stability, are achieved for them to become suitable for use in high-precision atmospheric monitoring.

Atmospheric greenhouse gas (GHG) measurements are essential for assessing climate change and verifying national emission inventories. As global networks rely on high-precision observations of potent GHGs such as carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O), ensuring accuracy between observation stations is essential. Maintaining accuracy within a network requires the use of whole air reference materials (RMs) with well-defined calibration scales, such as those maintained by the National Oceanic and Atmospheric Administration (NOAA) for the World Meteorological Organisation (WMO). With the global expansion of atmospheric monitoring networks there is a growing need for readily available RMs, stimulating the development of complementary alternatives such as synthetic air RMs traceable to the International System of Units (SI). In the United Kingdom (UK) and Ireland, the atmospheric GHG monitoring network, comprising long-term atmospheric monitoring stations, is equipped with high precision in situ GHG analysers. These observations are used to verify bottom-up assessments of national emissions. Here, a case study is presented which provides the first direct, network‑wide evaluation of whole air versus synthetic air RMs under routine field conditions, allowing an assessment of the implications of SI‑traceable RMs within an active national atmospheric monitoring system. We assess the UK and Ireland’s network accuracy using WMO-NOAA scale-traceable whole air RMs and SI-traceable synthetic air RMs, through a blind multi-site round-robin intercomparison. Between 2021 and 2022, measurements were made of CO₂, CH₄ and N₂O in whole and synthetic air RMs at six sites using a range of instruments and the results were used to assess biases between sites. The measured mole fractions for each cylinder, at each site were then compared with the assigned value on the WMO-NOAA scale and the SI-traceable values for the whole air and synthetic air RMs, respectively. Weighted residual analysis reveals that whole air RMs generally meet the WMO/Global Atmospheric Watch (GAW) compatibility goals for CO₂ and CH₄, while N₂O remains more difficult due to its small atmospheric variability and instrument performance. Synthetic SI-traceable RMs have associated absolute uncertainties on their assigned values for CH₄ that are comparable to the extended WMO compatibility goals. However, absolute uncertainties for CO₂ and N₂O remain significantly larger than both the compatibility and extended compatibility goals, which is consistent with previous studies. Overall, these results indicate that while scale-traceable whole air RMs remain essential for achieving the highest level of network compatibility required for atmospheric monitoring, SI-traceable synthetic RMs could play a valuable complementary role, particularly for CH₄. However, it is first critical that improved characterisation of matrix effects, mole fraction dependant instrument responses, and long-term stability, are achieved for them to become suitable for high-precision atmospheric monitoring.

Atmospheric greenhouse gas (GHG) measurements are essential for assessing climate change and verifying national emission inventories. As global networks rely on high-precision observations of potent GHGs such as carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O), ensuring accuracy between observation stations is essential. Maintaining accuracy within a network requires the use of whole air reference materials (RMs) with well-defined calibration scales, such as those maintained by the National Oceanic and Atmospheric Administration (NOAA) for the World Meteorological Organisation (WMO). With the global expansion of atmospheric monitoring networks there is a growing need for readily available RMs, stimulating the development of complementary alternatives such as synthetic air RMs traceable to the International System of Units (SI). In the United Kingdom (UK) and Ireland, the atmospheric GHG monitoring network, comprising long-term atmospheric monitoring stations, is equipped with high precision in situ GHG analysers. These observations are used to verify bottom-up assessments of national emissions. Here, a case study is presented which provides the first direct, network‑wide evaluation of whole air versus synthetic air RMs under routine field conditions, allowing an assessment of the implications of SI‑traceable RMs within an active national atmospheric monitoring system. We assess the UK and Ireland’s network accuracy using WMO-NOAA scale-traceable whole air RMs and SI-traceable synthetic air RMs, through a blind multi-site round-robin intercomparison. Between 2021 and 2022, measurements were made of CO₂, CH₄ and N₂O in whole and synthetic air RMs at six sites using a range of instruments and the results were used to assess biases between sites. The measured mole fractions for each cylinder, at each site were then compared with the assigned value on the WMO-NOAA scale and the SI-traceable values for the whole air and synthetic air RMs, respectively. Weighted residual analysis reveals that whole air RMs generally meet the WMO/Global Atmospheric Watch (GAW) compatibility goals for CO₂ and CH₄, while N₂O remains more difficult due to its small atmospheric variability and instrument performance. Synthetic SI-traceable RMs have associated absolute uncertainties on their assigned values for CH₄ that are comparable to the extended WMO compatibility goals. However, absolute uncertainties for CO₂ and N₂O remain significantly larger than both the compatibility and extended compatibility goals, which is consistent with previous studies. Overall, these results indicate that while scale-traceable whole air RMs remain essential for achieving the highest level of network compatibility required for atmospheric monitoring, SI-traceable synthetic RMs could play a valuable complementary role, particularly for CH₄. However, it is first critical that improved characterisation of matrix effects, mole fraction dependant instrument responses, and long-term stability, are achieved for them to become suitable for high-precision atmospheric monitoring.

The perfluorocarbons CF₄ and C₂F₆ are among the most potent greenhouse gases with lifetimes of fifty and ten thousand years, respectively. They are both primarily emitted during aluminum smelting and electronics manufacturing. We perform the first regionally resolved global inversion of CF₄ and C₂F₆, providing atmospheric measurement-based top-down emission estimates for 2006–2023 using the FLEXPART transport model and the FLEXINVERT+ framework. Introducing a global-total constraint to align the inversion results with the relatively accurate global total emissions from the AGAGE 12-box model stabilizes the emissions in poorly monitored regions. Compared to the global bottom-up inventory EDGAR, the inversion increases global CF₄ and C₂F₆ emissions by factors of 2.6 ± 0.3 and 3.1 ± 0.7, respectively, for 2018–2023. China dominates global emissions, contributing 56 % (CF₄) and 58 % (C₂F₆) in 2018–2023. The contribution of South and Southeast Asia to global emissions rose from about 6 % and 10 % in 2006–2011 to 22 % and 18 % by 2018–2023, respectively, though large uncertainties remain due to a lack of measurements in the region itself. European emissions declined until 2010, then stabilized and contribute 2 %–3 % to global emissions by 2018–2023. U.S. CF₄ emissions remain constant and C₂F₆ emissions decreased steadily (reaching 3 %–4 % by 2018–2023), with a temporary drop in 2009 likely linked to the financial crisis. On the global scale, our results suggest a contribution of 81 % by the aluminum industry to total CF₄ emissions and 48 % by the electronics industry to global C₂F₆ emissions.

Atmospheric greenhouse gas (GHG) measurements are essential for assessing climate change and verifying national emission inventories. As global networks rely on high-precision observations of potent GHGs such as carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O), ensuring accuracy between observation stations is essential. Maintaining accuracy within a network requires the use of whole air reference materials (RMs) with well-defined calibration scales, such as those maintained by the National Oceanic and Atmospheric Administration (NOAA) for the World Meteorological Organisation (WMO). With the global expansion of atmospheric monitoring networks there is a growing need for readily available RMs, stimulating the development of complementary alternatives such as synthetic air RMs traceable to the International System of Units (SI). In the United Kingdom (UK) and Ireland, the atmospheric GHG monitoring network, comprising long-term atmospheric monitoring stations, is equipped with high precision in situ GHG analysers. These observations are used to verify bottom-up assessments of national emissions. Here, a case study is presented which provides the first direct, network‑wide evaluation of whole air versus synthetic air RMs under routine field conditions, allowing an assessment of the implications of SI‑traceable RMs within an active national atmospheric monitoring system. We assess the UK and Ireland’s network accuracy using WMO-NOAA scale-traceable whole air RMs and SI-traceable synthetic air RMs, through a blind multi-site round-robin intercomparison. Between 2021 and 2022, measurements were made of CO₂, CH₄ and N₂O in whole and synthetic air RMs at six sites using a range of instruments and the results were used to assess biases between sites. The measured mole fractions for each cylinder, at each site were then compared with the assigned value on the WMO-NOAA scale and the SI-traceable values for the whole air and synthetic air RMs, respectively. Weighted residual analysis reveals that whole air RMs generally meet the WMO/Global Atmospheric Watch (GAW) compatibility goals for CO₂ and CH₄, while N₂O remains more difficult due to its small atmospheric variability and instrument performance. Synthetic SI-traceable RMs have associated absolute uncertainties on their assigned values for CH₄ that are comparable to the extended WMO compatibility goals. However, absolute uncertainties for CO₂ and N₂O remain significantly larger than both the compatibility and extended compatibility goals, which is consistent with previous studies. Overall, these results indicate that while scale-traceable whole air RMs remain essential for achieving the highest level of network compatibility required for atmospheric monitoring, SI-traceable synthetic RMs could play a valuable complementary role, particularly for CH₄. However, it is first critical that improved characterisation of matrix effects, mole fraction dependant instrument responses, and long-term stability, are achieved for them to become suitable for high-precision atmospheric monitoring.

Methane is emitted from a range of anthropogenic and natural sources, and identifying these sources is important for emissions monitoring and mitigation. Different sources emit methane with different isotopic signatures. However, these signatures can vary spatially and temporally and are often not well understood. Top-down inverse methods can be used with measurements of methane mole fractions to estimate total emissions of methane from all sources. Here, we present an inverse system for concurrently estimating regional fossil-fuel (FF) and non-fossil-fuel (non-FF) emissions, using isotope ratio observations and considering uncertainty in the isotopic signatures. This method is highly adaptable and could be used to estimate emissions from any number of sources. Synthetic data tests with this method show that this inverse system can accurately estimate FF and non-FF methane emissions across the UK, when isotopic source signatures are fixed at known values. However, emissions estimation becomes less accurate when source signature uncertainties are increased to over approximately 50 % of their likely ranges. In a real-world test of this method, we estimated south-east UK FF and non-FF emissions using high-frequency δ ¹³ C-CH ₄ and δ ² H-CH ₄ observations from one UK site, with source signature uncertainties reflecting our current understanding of these values. Results show only a limited impact on emissions uncertainty and magnitude, when compared with a methane-only inversion. This suggests that both an expansion of the UK network of isotope ratio observations and an improved understanding of isotopic signatures is required for this method to be effective in estimating UK FF and non-FF methane emissions with reduced uncertainty compared to traditional inverse methods.

For the first time, we present long-term, ongoing atmospheric measurements of 1,2-dichloroethane (DCE, CH ₂ ClCH ₂ Cl) from the Advanced Global Atmospheric Gases Experiment (AGAGE) and National Oceanic and Atmospheric Administration (NOAA) global monitoring networks. DCE is an industrially produced, very short-lived chlorinated substance (Cl-VSLS) that has the potential to contribute chlorine to the stratosphere and cause ozone depletion. Compared to other Cl-VSLS, DCE is produced in higher volumes for its primary use as a feedstock in polyvinyl chloride (PVC) manufacture. This production has sustained annual mean mole fractions at the Earth's surface of between 5 and 10 ppt during 2017–2023, making it the third most abundant Cl-VSLS after dichloromethane and chloroform. In this study we estimate mean global emissions for 2017–2023 of 453 ± 185 Gg yr ⁻¹ using the AGAGE observations, and 525 ± 209 Gg yr ⁻¹ using the NOAA observations. We also use AGAGE measurements to estimate regional emissions for northwest Europe (2.06 [1.31, 2.65] Gg yr ⁻¹ ) and California (0.23 [0, 0.37] Gg yr ⁻¹ ), two domains with sufficient observational coverage to enable this approach. Our global emissions estimates are consistent (within uncertainties) with the only previously published estimate by Hossaini et al. (2024), whereas our regional emissions estimates are at least an order of magnitude smaller than those in that study. This suggests global total emissions may be well constrained, but their spatial distribution remains uncertain.

Atmospheric greenhouse gas (GHG) measurements are essential for assessing climate change and verifying national emission inventories. As global networks rely on high-precision observations of potent GHGs such as carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O), ensuring accuracy between observation stations is essential. Maintaining accuracy within a network requires the use of whole air reference materials (RMs) with well-defined calibration scales, such as those maintained by the National Oceanic and Atmospheric Administration (NOAA) for the World Meteorological Organisation (WMO). With the global expansion of atmospheric monitoring networks there is a growing need for readily available RMs, stimulating the development of complementary alternatives such as synthetic air RMs traceable to the International System of Units (SI). In the United Kingdom (UK) and Ireland, the atmospheric GHG monitoring network, comprising long-term atmospheric monitoring stations, is equipped with high precision in situ GHG analysers. These observations are used to verify bottom-up assessments of national emissions. Here, a case study is presented which provides the first direct, network‑wide evaluation of whole air versus synthetic air RMs under routine field conditions, allowing an assessment of the implications of SI‑traceable RMs within an active national atmospheric monitoring system. We assess the UK and Ireland’s network accuracy using WMO-NOAA scale-traceable whole air RMs and SI-traceable synthetic air RMs, through a blind multi-site round-robin intercomparison. Between 2021 and 2022, measurements were made of CO₂, CH₄ and N₂O in whole and synthetic air RMs at six sites using a range of instruments and the results were used to assess biases between sites. The measured mole fractions for each cylinder, at each site were then compared with the assigned value on the WMO-NOAA scale and the SI-traceable values for the whole air and synthetic air RMs, respectively. Weighted residual analysis reveals that whole air RMs generally meet the WMO/Global Atmospheric Watch (GAW) compatibility goals for CO₂ and CH₄, while N₂O remains more difficult due to its small atmospheric variability and instrument performance. Synthetic SI-traceable RMs have associated absolute uncertainties on their assigned values for CH₄ that are comparable to the extended WMO compatibility goals. However, absolute uncertainties for CO₂ and N₂O remain significantly larger than both the compatibility and extended compatibility goals, which is consistent with previous studies. Overall, these results indicate that while scale-traceable whole air RMs remain essential for achieving the highest level of network compatibility required for atmospheric monitoring, SI-traceable synthetic RMs could play a valuable complementary role, particularly for CH₄. However, it is first critical that improved characterisation of matrix effects, mole fraction dependant instrument responses, and long-term stability, are achieved for them to become suitable for high-precision atmospheric monitoring.

Hydrofluorocarbons (HFCs) are potent greenhouse gases widely used in refrigeration, air-conditioning, and heat pump systems. Accurate monitoring of HFC emissions is essential to evaluate compliance with climate regulations and inform mitigation strategies. This study presents trends of HFC emissions across north-western Europe between 2013 and 2024, derived from atmospheric inverse modelling combining atmospheric measurements at eleven monitoring stations with two transport models (NAME and FLEXPART) and three Bayesian inversion systems (InTEM, ELRIS, RHIME). Although global emissions continue to rise for most HFCs, in north-western Europe our results show an overall steady decline in total HFC emissions from 40 ± 3 Tg CO₂-eq yr⁻¹ in 2016 (prior to enhanced regulation) to 29 ± 2 Tg CO₂-eq yr⁻¹ in 2023, following EU F-gas Regulations. This reduction is driven primarily by decreasing emissions of HFC-134a, HFC-143a and HFC-125 despite increasing HFC-32 emissions due to its adoption as a lower-global-warming-potential alternative refrigerant. Comparisons with national inventories reported to the United Nations Framework Convention on Climate Change (UNFCCC) show generally good agreement over north-western Europe but reveal discrepancies for specific compounds and countries, particularly for HFC-134a and HFC-125 in France and Germany during the earlier years of the study period. The recent expansion of the European measurement network demonstrates potential to improve spatial coverage and resolution of inverse emission estimates, especially in southern and central Europe. This study highlights the value of multi-model inversions to provide robust emission estimates with realistic, hence actionable, uncertainty characterisation.