Advances in reference materials and measurement techniques for greenhouse gas atmospheric observations

The Global Atmosphere Watch (GAW) Programme was established in 1989 in recognition of the need for improved scientific understanding of the increasing influence of human activities on atmospheric composition and subsequent societal impacts. It is implemented as an activity of the World Meteorological Organization, a specialized agency of the United Nations system, and is funded by the organization member countries.As an international programme, GAW supports a broad spectrum of applications from atmospheric composition-related services to contribution to environmental policy. The examples of the later include provision of a comprehensive set of high quality and long-term globally harmonized observations and analysis of atmospheric composition for the United Nations Framework Convention on Climate Change (UNFCCC), the Montreal Protocol on Substances that Deplete the Ozone Layer and follow-up amendments, and the Convention on Long-Range Transboundary Air Pollution (CLRTAP).The programme includes six focal areas: Greenhouse Gases, Ozone, Aerosols, Reactive Gases, Total Atmospheric Deposition and SolarUltraviolet Radiation.The surface-based observational network of the programme includes Global (31 stations) and Regional (about 400 stations) stations where observations of various GAW parameters occur. These stations are complemented by regular ship cruises and various contributing networks. All observations are linked to common reference standards and the observational data are made available at seven designated World Data Centres (WDC).Surface-based observations are complemented by airborne and space-based observations that help to characterize the upper troposphere and lower stratosphere, with regards to ozone, solar radiation, aerosols, and certain trace gases.Requirements to become a GAW station are detailed in the GAW Implementation Plan 2016-2023 (WMO, 2017). A new IP is in preparation, the four strategic objectives will be presented.The GAW Quality Management comprises: Data Quality Objectives, Measurement Guidelines, Standard Operating Procedures and Data Quality Indicators. Throughout the programme the common quality assurance principles apply, that include requirements for the long-term sustainability of the observations, use of one network standard for each variable and implementation of the measurement practices that satisfy the set data quality objectives. GAW implements open data policy and requires observational data be made available in the dedicated data centers operated by WMO Member countries. The programme relies on different types of central facilities: Central Calibration Laboratories, Quality Assurance/Science Activity Centres, World and Regional Calibration Centres, which are also directly supported and implemented by the individual Member countries for the global services.Majority of the recommendations regarding measurement and quality assurance procedures are developed by the expert and advisory groups within the programme, often those rely on the expertise withing the contributing networks and collaborating organizations, like the Aerosol, Clouds and Trace Gases Research Infrastructure (ACTRIS) or the Integrated Carbon Observation System (ICOS).One of the GAW priorities is to expand and strengthen partnerships with contributing networks, through development of statements and strategies to articulate the mutual benefits for the collaborations and stream-line processes of data reporting and exchange of QA standards and metadata. This involves collaboration with national and regional environmental protection agencies and the development of harmonized metadata and data exchange and quality information.

<p>The Global Atmosphere Watch (GAW) Programme of the World Meteorological Organization (WMO) is driven by the need to understand the variability and trends in atmospheric composition and the related physical parameters, and to assess the consequences thereof. GAW provides reliable scientific information for a broad spectrum of users, including policymakers, on topics related to atmospheric chemical composition. The programme supports international environmental and climate agreements and improves our understanding of climate change and long-range transboundary air pollution through its work on greenhouse gases, aerosols, reactive gases, atmospheric deposition, stratospheric ozone, and ultraviolet radiation. GAW provides information based on combinations of observations, data analysis and modelling activities, and supports a number of applications at the global, regional and urban scale. This implies a variety of target groups and communication vectors. Due to the complexity and interrelations of the different constituents in atmospheric chemistry and the diversity of the target audience, communication of the related issues represents a substantial challenge. Some examples are questions like “If greenhouse gas emissions are falling, why do concentrations not decrease?”, “if satellite data show pollution reductions, why can’t we say that it is due to emission reductions?” etc.  </p><p>To sustain the credibility and increase the visibility of GAW within the WMO community and other national/international bodies, the broader scientific and policy communities, as well as the general public, increasing efforts towards “communicating GAW” are taken. The global pandemic related to COVID-19 was the dominating topic around the globe in 2020. This required adjustments to communication efforts. Due to in-person meetings being impossible, all communication efforts required delivery and engagement through virtual formats.</p><p>While emissions of carbon dioxide (among others) have decreased temporarily in 2020 due to COVID-19 restrictions, concentrations have continued to increase. This has led to confusion among many non-scientists who were surprised that the restrictions they were experiencing did not even have the effect of decreasing atmospheric concentrations of carbon dioxide. Thereby, the crisis has provided an opportunity to explain the difference between emissions and concentrations, emphasizing that carbon dioxide (and other greenhouse gases) are long-lived and remain in the atmosphere for a long time, and highlighting the importance to reach net-zero emissions. Similar confusion was related to the interpretation of the pollution levels and also required additional communication efforts.</p><p>Reflections on communication of atmospheric composition in the framework of WMO/GAW, including challenges and opportunities during the public health crisis will be presented.</p>

The National Institute of Standards and Technology (NIST) recently began to develop standard mixtures of greenhouse gases as part of a broad program mandated by the 2009 United States Congress to support research in climate change. To this end, NIST developed suites of gravimetrically assigned primary standard mixtures (PSMs) comprising carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) in a dry-natural air balance at ambient mole fraction levels. In parallel, the National Oceanic and Atmospheric Administration (NOAA) in Boulder, Colorado, charged 30 aluminum gas cylinders with northern hemisphere air at Niwot Ridge, Colorado. These mixtures, which constitute NIST Standard Reference Material (SRM) 1720 Northern Continental Air, were certified by NIST for ambient mole fractions of CO2, CH4, and N2O relative to NIST PSMs. NOAA-assigned values are also provided as information in support of the World Meteorological Organization (WMO) Global Atmosphere Watch (GAW) Program for CO2, CH4, and N2O, since NOAA serves as the WMO Central Calibration Laboratory (CCL) for CO2, CH4, and N2O. Relative expanded uncertainties at the 95% confidence interval are <±0.06% of the certified values for CO2 and N2O and <0.2% for CH4, which represents the smallest relative uncertainties specified to date for a gaseous SRM produced by NIST. Agreement between the NOAA (WMO/GAW) and NIST values based on their respective calibration standards suites is within 0.05%, 0.13%, and 0.06% for CO2, CH4, and N2O, respectively. This collaborative development effort also represents the first of its kind for a gaseous SRM developed by NIST.

In Indonesia, the monitoring of Greenhouse Gases (GHGs) is a vital part of the nation's planning strategy, primarily spearheaded by the Meteorological, Climatological, and Geophysical Agency (BMKG) in response to the World Meteorological Organization's (WMO) mandate through the Global Atmosphere Watch (GAW) program. This initiative is of paramount importance as it aims to provide comprehensive and robust GHG monitoring to support global and national efforts in understanding and combating climate change. Despite existing efforts, there remains a pressing need to expand these services to ensure more accurate and extensive data collection, which is crucial for informing government policies and international climate negotiations. Indonesia's approach to GHG monitoring is multifaceted, encompassing global, national, and sub-national strategies to provide a comprehensive understanding of GHG dynamics and contribute effectively to global efforts. At a global and regional level, Indonesia boasts the longest GHG dataset in Southeast Asia, as well as in the equatorial region, from Bukit Kototabang. This data is invaluable, feeding into the WMO GAW international network and providing insights that aid in refining GHG inventories worldwide. It represents a significant contribution to the global understanding of GHG trends and helps position Indonesia as a critical player in international climate dialogues, especially concerning carbon budgeting and emission reduction strategies. Additionally, the implementation plan for the Global Greenhouse Gas Watch (G3W) program, a WMO initiative for a GHG monitoring effort worldwide, &amp;#160;is incorporated in the nation&amp;#8217;s GHG monitoring plan, aiming for a more inclusive and extensive GHG monitoring network. Nationally, Indonesia's strategy leverages the potential of satellite-driven information.&amp;#160; This approach can be considered as complementary as it offers an advantage in providing better spatial resolution, and fully representing the differences in land-cover types. At a sub-national level, the focus is on atmospheric-based monitoring to provide localized GHG estimates through a roadmap for the adoption of the Integrated Global Greenhouse Gas Information System (IG3IS). This ambitious program aims to monitor atmospheric GHGs in an integrated manner, combining this with atmospheric modeling to yield a range of benefits. It enables the estimation of carbon emissions across various sectors and complement in calculating carbon sequestration, particularly in forestry initiatives. Together, these strategies illustrate Indonesia's nuanced and robust approach to GHG monitoring. By continuously enhancing its GHG monitoring plans, adopting advanced satellite technology, and focusing on localized atmospheric monitoring, Indonesia not only contributes valuable data to the global scientific community but also strengthens its own capacity to address climate change. This integrated approach is crucial for developing a comprehensive understanding of GHG dynamics, informing policy and international negotiations, and ultimately guiding the nation towards a sustainable and resilient future in the face of global environmental challenges.&amp;#160;

&amp;lt;p&amp;gt;The Global Atmosphere Watch (GAW) Programme of the World Meteorological Organization (WMO) is driven by the need to understand the variability and trends in the composition of the global atmosphere and the related physical parameters, and to assess the consequences thereof. GAW provides reliable scientific information for a broad spectrum of users, including policymakers, on topics related to atmospheric chemical composition. The programme supports international environmental and climate agreements and improves our understanding of climate change and long-range transboundary air pollution through its work on greenhouse gases, aerosols, reactive gases, atmospheric deposition, stratospheric ozone, and ultraviolet radiation. GAW provides information based on combinations of observations, data analysis and modelling activities, and supports a number of applications at the global, regional and urban scale. This implies a variety of target groups and communication vectors.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;To sustain the credibility and increase the visibility of GAW within the WMO community and other national/international bodies, the broader scientific and policy communities, as well as the general public, communication efforts are required. Several activities during the EGU General Assembly 2019 have been carried out to celebrate the 30&amp;lt;sup&amp;gt;th&amp;lt;/sup&amp;gt; anniversary of GAW.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;For instance, a Union Symposium explored the 30 year journey from fundamental Atmospheric Composition Research to Societal Services. It showcased the importance of atmospheric composition research to climate, weather forecasting, human health, agricultural productivity and food security. The session highlighted the progress made in translating research into services, but stressed that much more needs to be done. A mentimeter survey during this Union Symposium revealed that among the scientific community GAW is valued for its coordination, observations, capacity building, outreach and its global focus.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Reflections on communication of atmospheric composition and outcomes from the 30&amp;lt;sup&amp;gt;th&amp;lt;/sup&amp;gt; anniversary celebration of GAW will be presented.&amp;lt;/p&amp;gt;

This paper highlights the main findings of the twentieth annual Greenhouse Gas Bulletin (https://library.wmo.int/records/item/69057-no-20-28-october-2024) of the World Meteorological Organization (WMO). The results are based on research and observations performed by laboratories contributing to the WMO Global Atmosphere Watch (GAW) Programme (https://community.wmo.int/activity-areas/gaw).The Bulletin presents global analyses of observational data collected according to GAW recommended practices and submitted to the World Data Center for Greenhouse Gases (WDCGG). Bulletins are prepared by the WMO/GAW Scientific Advisory Group on Greenhouse Gases in collaboration with WDCGG.Observations used for the global analysis are from 146 marine and terrestrial sites for CO2, 153 for CH4 and 112 for N2O. The globally averaged surface mole fractions calculated on the basis of these observations reached new highs in 2023, with CO2 at 420.0&amp;#177;0.1 ppm, CH4 at 1934&amp;#177;2 ppb and N2O at 336.9&amp;#177;0.1 ppb. These values constitute, respectively, increases of 151%, 265% and 125% relative to pre-industrial (before 1750) levels. The increase in CO2 from 2022 to 2023 (2.3 ppm) was slightly higher than the increase observed from 2021 to 2022 and slightly lower than the average annual growth rate over the last decade, which was most likely partly caused by natural variability, as fossil fuel CO2 emissions have continued to increase. This increase marked the twelfth consecutive year with an increase greater than 2 ppm.The Bulletin reports that within-year variability of CO2 was 2.8 ppm in 2023, the fourth largest within-year annual increase since modern CO2 measurements started in the 1950s. Such increase may be a result of enhanced fire emissions and reduced net terrestrial carbon sinks. The CO2 growth rate varies from year to year (between 2.1 and 3.2 ppm during 2014-2023), with the variability mostly driven by the terrestrial biosphere exchange of CO2, as confirmed by measurements of the stable carbon isotopes ratio, 13C:12C in atmospheric CO2. Coincidental with the large CO2 increase during 2023 was the largest increase in atmospheric carbon monoxide (CO) in the past two decades, suggesting enhanced CO2 emissions from fires.The increase of CH4 mole fraction from 2022 to 2023 (11 ppb) was lower than that observed from 2021 to 2022 but still slightly higher than the average annual growth rate over the last decade. The record rise in atmospheric CH4 from 2020 to 2022 was accompanied by a significant drop in atmospheric &amp;#948;13CCH4. The unexpected change in the amount of atmospheric &amp;#948;13CCH4 is best explained by a transition from fossil fuels to microbial emissions as the dominant driver of increasing CH4. Moreover, the geographic distribution of CH4 growth from 2020 to 2022 suggest strong increases in isotopically light emissions from tropical and boreal wetland areas, which is indicative of positive climate feedback on CH4 emissions in response to climate transition to an El Ni&amp;#241;o phase in 2023.In the near future, climate change itself could cause ecosystems to become larger sources or sinks of GHGs. Identifying and tracking the potential climate feedbacks require continued high accuracy observations also at currently undersampled regions.

Abstract. We thoroughly evaluate the performance of a multi-species, in situ Fourier transform infrared (FTIR) analyser with respect to high-accuracy needs for greenhouse gas monitoring networks. The in situ FTIR analyser is shown to measure CO2, CO, CH4 and N2O mole fractions continuously, all with better reproducibility than the inter-laboratory compatibility (ILC) goals, requested by the World Meteorological Organization (WMO) for the Global Atmosphere Watch (GAW) programme. Simultaneously determined δ13CO2 reaches reproducibility as good as 0.03‰. Second-order dependencies between the measured components and the thermodynamic properties of the sample, (temperature, pressure and flow rate) and the cross sensitivities among the sample constituents are investigated and quantified. We describe an improved sample delivery and control system that minimises the pressure and flow rate variations, making post-processing corrections for those quantities non-essential. Temperature disequilibrium effects resulting from the evacuation of the sample cell are quantified and improved by the usage of a faster temperature sensor. The instrument has proven to be linear for all measured components in the ambient concentration range. The temporal stability of the instrument is characterised on different time scales. Instrument drifts on a weekly time scale are only observed for CH4 (0.04 nmol mol−1 day−1) and δ13CO2 (0.02‰ day−1). Based on 10 months of continuously collected quality control measures, the long-term reproducibility of the instrument is estimated to ±0.016 μmol mol−1 CO2, ±0.03‰ δ13CO2, ±0.14 nmol mol−1 CH4, ±0.1 nmol mol−1 CO and ±0.04 nmol mol−1 N2O. We propose a calibration and quality control scheme with weekly calibrations of the instrument that is sufficient to reach WMO-GAW inter-laboratory compatibility goals.

Carbon monoxide (CO) is reported to mainly be emitted from industries, transportation, and burnings for various usages. Its atmospheric lifetime varies from weeks to months, depending on the mixing ratio of the highly reactive hydroxyl radical. Even though the ambient level of CO varies as a function of regional sources, the mixing ratio ranges from 30 nmol/mol to 300 nmol/mol at the marine boundary layers and from 100 nmol/mol to more than 500 nmol/mol in urban areas(1). In order to study temporal trends and regional variations of the level of CO, the National Oceanic & Atmospheric Administration/Earth System Research Laboratory-Global Monitoring Division (NOAA/ESRL-GMD(2)) has played a key role as the designated Central Calibration Laboratory (CCL) within the frame of the World Meteorological Organization (WMO) Global Atmosphere Watch (GAW) program. NOAA/ESRL-GMD provides natural air standards, analyzed for CO, to WMO GAW participants. Since the structure of WMO traceability chain appears hierarchical and explicit all over the world, WMO intends to improve the CO measurement compatibility to up to 2 ppb (in case of extensive compatibility goal: 5 ppb, GAW report No. 213(3)) in order to ensure compatibility through the GAW network. Nevertheless, accurate measurement of CO at an ambient level has proven to be difficult due to the lack of stability in cylinders. For these reasons, it is necessary that measured results are compared among the values assigned by various NMIs.This key comparison was initially proposed to be aimed at a CO/N2 standard in the 2010 CCQM meeting by KRISS. With participation of FMI, NOAA, and Empa, a modified scheme of CO/air standards was developed for the purpose of atmospheric observations and co-operative support to WMO/GAW activities. Therefore, the purpose of the comparison is to support the measurement capability of CO at an ambient level of 350 nmol/mol. Further, this key comparison is expected to contribute to the establishment of traceability to a single scale of CO between NMIs by means of harmonizing the results from different national standards. The Empa result lies in a different report.Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

This paper highlights the main findings of the eighteenth annual Greenhouse Gas Bulletin (https://library.wmo.int/index.php?lvl=notice_display&amp;id=22149) of the World Meteorological Organization (WMO). The results are based on research and observations performed by laboratories contributing to the WMO Global Atmosphere Watch (GAW) Programme (https://community.wmo.int/activity-areas/gaw).The Bulletin presents global analyses of observational data collected according to GAW recommended practices and submitted to the World Data Center for Greenhouse Gases (WDCGG). Bulletins are prepared by the WMO/GAW Scientific Advisory Group on Greenhouse Gases in collaboration with WDCGG.Observations used for the global analysis are from more than 100 marine and terrestrial sites worldwide for CO2 and CH4 and at a smaller number of sites for other greenhouse gases. The globally averaged surface mole fractions calculated from this in situ network reached new highs in 2021, with CO2 at 415.7 &amp;#177; 0.2 ppm, CH4 at 1908 &amp;#177; 2 ppb and N2O at 334.0 &amp;#177; 0.1 ppb. These values constitute, respectively, 149%, 262% and 124% of pre-industrial (before 1750) levels. The increase in CO2 from 2020 to 2021 was equal to that observed from 2019 to 2020 and larger than the average annual growth rate over the last decade. For CH4, the increase from 2020 to 2021 was higher than that observed from 2019 to 2020 and considerably higher than the average annual growth rate over the last decade. For N2O, the increase from 2020 to 2021 was slightly higher than that observed from 2019 to 2020 and also higher than the average annual growth rate over the last decade.The Bulletin highlights the exceptional growth of CH4 in 2020 and 2021. The causes of these exceptional increases are still being investigated though analyses of measurements of atmospheric CH4 abundance and its stable carbon isotope ratio 13C/12C indicate that the increase in CH4 since 2007 is associated mostly with biogenic processes, but the relative contributions of anthropogenic and natural sources to this increase are unclear.The Bulletin further highlights that the accuracy of emissions estimates from atmospheric measurements depends on the geometry of the surface network, pointing to the large observational gaps in tropical regions and the interior of the Asian continent. The tropics accommodate not only highly uncertain emissions from natural wetlands, but also the atmospheric hydroxyl radical sink of CH4, which is largest there. Surface measurements provide limited information to distinguish between increasing surface emissions and decreasing atmospheric sinks, which could both explain the increasing atmospheric CH4 abundance.WMO is working with the broader greenhouse gas community to develop a framework for sustained, internationally coordinated global greenhouse gas monitoring. These efforts are envisaged to result in an internationally coordinated approach to observing network design and acquisition, international exchange and use of the observations. It is foreseen that this will result in the expansion of the in-situ network, especially in currently undersampled regions and lead to reduced uncertainties in the quantification of the net atmospheric balance of CH4 and other greenhouse gases.

Many halogenated volatile organic compounds (VOCs) are found in the atmosphere in the pmol/mol range. These halogenated VOCs have negative impacts on the environment as they are strong greenhouse gases and/or contribute to the depletion of the stratospheric ozone layer or their degradation products may have a negative impact on the environment. This underpins the importance to accurately measure the amount fractions of these substances in the atmosphere on the long-term.The Global Atmosphere Watch (GAW) Programme of the World Meteorological Organization (WMO) is a long-term international global programme that coordinates observations and analysis of atmospheric composition changes. The GAW Programme is a collaboration of more than 100 countries and it relies fundamentally on the contributions of its members to help to build a single, coordinated global understanding of atmospheric composition and its change. For most substances there is a Central Calibration Laboratory (CCL) that is responsible for maintaining and distributing the WMO references for instrument calibration for a specified gas in air. However, until summer 2023 there was no CCL for halogenated VOCs. METAS applied successfully for the CCL function for a total of ten halogenated VOCs because METAS' gas analysis laboratory has a decade of experience in the production of reference gas mixtures for halogenated VOCs. Here, we will present our new function as CCL including our services, the work done in the past and the planned work for the next years.

&amp;lt;p&amp;gt;We present results from the sixteenth annual Greenhouse Gas Bulletin (https://library.wmo.int/doc_num.php?explnum_id=10437) of the World Meteorological Organization (WMO). The results are based on research and observations performed by laboratories contributing to the WMO Global Atmosphere Watch (GAW) Programme (https://community.wmo.int/activity-areas/gaw).&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;The Bulletin presents results of global analyses of observational data collected according to GAW recommended practices and submitted to the World Data Center for Greenhouse Gases (WDCGG). Bulletins are prepared by the WMO/GAW Scientific Advisory Group for Greenhouse Gases in collaboration with WDCGG.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Observations used for the global analysis are collected at more than 100 marine and terrestrial sites worldwide for CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; and at a smaller number of sites for other greenhouse gases. The globally averaged surface mole fractions calculated from this in situ network reached new highs in 2019, with CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; at 410.5 &amp;amp;#177; 0.2 ppm, CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; at 1877 &amp;amp;#177; 2 ppb, and N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O at 332.0 &amp;amp;#177; 0.1 ppb. These values constitute, respectively, 148%, 260% and 123% of pre-industrial (before 1750) levels. The increase in CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; from 2018 to 2019 (2.6 ppm) was larger than that observed from 2017 to 2018 and larger than the average annual growth rate over the last decade. For CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt;, the increase from 2018 to 2019 (8 ppb) was slightly smaller than that observed from 2017 to 2018 but still greater than the average annual growth rate over the last decade. For N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O, the increase from 2018 to 2019 (0.9 ppb) was lower than that observed from 2017 to 2018 and practically equal to the average annual growth rate over the past 10 years. The National Oceanic and Atmospheric Administration (NOAA) Annual Greenhouse Gas Index (AGGI) shows that from 1990 to 2019, radiative forcing by long-lived greenhouse gases increased by 45%, with CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; accounting for about 80% of this increase.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;The Bulletin highlights the potential impact of anthropogenic emission reductions due to COVID-19 lockdown measures on the levels of atmospheric concentrations of GHGs. These changes have been especially pronounced in urban areas and were visible in traditional pollutants as well as in greenhouse gases. However, the reduction in anthropogenic emissions due to confinement measures will not have a discernible effect on global mean atmospheric CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; in 2020 as this reduction will be smaller than, or at most, similar in size to the natural year-to-year variability of atmospheric CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;. Direct measurements of the CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; fluxes by ICOS directly demonstrated GHG emission reductions in a number of cities.&amp;amp;#160;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;The Bulletin also describes the emission reduction opportunities related to methane. These opportunities are provided by emerging capabilities of methane observations from space and advances in transport modeling that allow for better source attribution and quantification. Globally averaged methane mole fraction has been increasing since 2007. Long-term observations and analysis of methane isotopic composition shed some light on this increase. The observed trend in &amp;amp;#948;&amp;lt;sup&amp;gt;13&amp;lt;/sup&amp;gt;C-CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; is explained by a combined increase in microbial and fossil emissions. This trend points to the likely scenario that the methane increase is largely driven by the growing demand for energy and food.&amp;lt;/p&amp;gt;

Atmospheric background monitoring refers to the long-term observation of atmospheric composition that is well mixed and not affected by local pollution at a fixed location which is far from the influence of human activities. Atmospheric background monitoring can reflect the long-term changes of atmospheric composition caused by human activities on a global or regional scale. Therefore, it plays a very important role in both socioeconomic development and scientific research. Since the 1950s, some observation stations abroad have carried out background observation of the main atmospheric components such as carbon dioxide, ozone and atmospheric heavy metals. Additionally, the Global Ozone Observing System (GO₃OS) and the Background Air Pollution Monitoring Network (BAPMoN) were established by the World Meteorological Organization (WMO) in 1957 and 1968 to fulfill long-term and continuous observation of the chemical constituents of reactive gases, greenhouse gases, aerosols and acid rain. In 1989, WMO integrated GO₃OS and BAPMoN into the Global Atmosphere Watch (GAW). WMO/GAW has achieved great accomplishments owing to its long-term, systematic and accurate observation of the physical and chemical characteristics of atmospheric composition. During the period of 1981 to 2007, China Meteorological Administration (CMA) has built six representative regional GAW (Global Atmosphere Watch) stations, i.e., Shangdianzi (117.12°E, 40.65°N, <sc>293.3 m</sc> asl), Lin’an (119.75°E, 30.28°N, <sc>138.6 m</sc> asl), Longfengshan (127.60°E, 44. 73°N, <sc>331 m</sc> asl), Akedala (87.93°E, 47.10°N, <sc>562 m</sc> asl), Shangri-La (99.73°E, 28.01°N, <sc>3580 m</sc> asl), and Jinsha (114.2°E, 29.63°N, <sc>750 m</sc> asl), following the construction criteria of the GAW regional background stations. In addition, in accordance with the requirements of GAW global background station site selection, the Chinese government and the UN Global Environmental Facility (GEF) jointly invested and established a global GAW station in China, namely, the China GAW Baseline Observatory (CGAWBO), located at Mt. Waliguan (100.89°E, 36.28°N, <sc>3816 m</sc> asl) in Qinghai Province in 1994. These seven global/regional GAW stations build the current operational network of atmospheric background observation stations in China. Thanks to their long-term continous and precise atmospheric composition monitoring data and special representations, the stations at Mt. Waliguan, Shangdianzi, Lin’an, and Longfengshan were selected as the National Field Scientific Observation and Research Stations by the Ministry of Science and Technology of the People’s Republic of China in 2005. It is well known that the long-time series and excellent data on meteorological and atmospheric composition obtained from these seven global/regional GAW stations have played an unique role in China’s efforts on addressing climate change, climate change diplomacy and negotiation, air pollution control, and scientific research. With China’s socioeconomic development stepping into the new era, however, the deficiencies of the current GAW stations have become increasingly significant. Major problems lie in the unbalanced and insufficient development of these stations, as well as in the lack of innovation and demonstration. In this article, the status and the achievements of these seven stations are reviewed and summarized for the first time, followed by the identification and analysis of major problems of development. At last, it is recommended that future endeavors should be concentrated on enhancing the comprehensive observation capability and international cooperation, as well as further improving the construction and capacities of the national field scientific research stations. Besides, it is also suggested that the development of atmospheric background station shall serve China’s national and local development strategy, as well as strengthen its role in China’s progress of ecological civilization.

&amp;lt;p&amp;gt;We present results from the fifteenth annual Greenhouse Gas Bulletin (https://library.wmo.int/doc_num.php?explnum_id=10100) of the World Meteorological Organization (WMO). The results are based on research and observations performed by laboratories contributing to the WMO Global Atmosphere Watch (GAW) Programme (https://community.wmo.int/activity-areas/gaw).&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;The Bulletin presents results of global analyses of observational data collected according to GAW recommended practices and submitted to the World Data Center for Greenhouse Gases (WDCGG). Bulletins are prepared by the WMO/GAW Scientific Advisory Group for Greenhouse Gases in collaboration with WDCGG.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Observations used for the global analysis are collected at more than 100 marine and terrestrial sites worldwide for CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; and at a smaller number of sites for other greenhouse gases. The globally averaged surface mole fractions calculated from this in situ network reached new highs in 2018, with CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; at 407.8 &amp;amp;#177; 0.1 ppm, CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; at 1869 &amp;amp;#177; 2 ppb and N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O at 331.1 &amp;amp;#177; 0.1 ppb. These values constitute, respectively, 147%, 259% and 123% of pre-industrial (before 1750) levels. The increase in CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; from 2017 to 2018 is very close to that observed from 2016 to 2017 and practically equal to the average growth rate over the last decade. The increase of CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; from 2017 to 2018 was higher than both that observed from 2016 to 2017 and the average growth rate over the last decade. The increase of N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O from 2017 to 2018 was also higher than that observed from 2016 to 2017 and the average growth rate over the past 10 years. The National Oceanic and Atmospheric Administration (NOAA) Annual Greenhouse Gas Index (AGGI) shows that from 1990 to 2018, radiative forcing by long-lived greenhouse gases (GHGs) increased by 43%, with CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; accounting for about 81% of this increase.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;The Bulletin highlights the value of the long-term measurement of the GHGs isotopic composition. In particular, it presents the use of the radiocarbon and &amp;lt;sup&amp;gt;13&amp;lt;/sup&amp;gt;C measurements in atmospheric CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; in discriminating between fossil fuel combustion and natural sources of CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;. The simultaneous decline in both &amp;lt;sup&amp;gt;13&amp;lt;/sup&amp;gt;C and &amp;lt;sup&amp;gt;14&amp;lt;/sup&amp;gt;C content alongside CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; increases can only be explained by the ongoing release of CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; from fossil fuel burning. The Bulletin also articulates how the measurements of the stable isotopes can be used to provide the insights into the renewed growth of methane that started in 2007. Though there are several hypotheses articulated in the peer-reviewed literature, the most plausible is that an increase has occurred in some or all sources of biogenic (wetlands, ruminants or waste) emissions, which contain relatively little &amp;lt;sup&amp;gt;13&amp;lt;/sup&amp;gt;C. An increase in the proportion of global emissions from microbial sources may have driven both the increase in the methane burden and the shift in &amp;amp;#948;&amp;lt;sup&amp;gt;13&amp;lt;/sup&amp;gt;C-CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt;.&amp;lt;/p&amp;gt;

Atmospheric methane is the second most abundant greenhouse gas in the atmosphere after carbon dioxide, and its concentration changes significantly regulate the intensity of the greenhouse effect, thereby exerting a profound influence on global warming and related climate change. Accurately understanding the changing patterns and future trends of atmospheric methane concentrations is of critical importance for elucidating the mechanisms of climate change, developing scientifically sound and effective emission reduction strategies, and advancing the realization of the global carbon neutrality objective. This study aims to construct a statistical model using the ARIMR model by integrating the characteristics of autoregression (AR), moving average (MA), and regression (R) to conduct predictive analysis of monthly changes in global atmospheric methane concentrations. The research data are sourced from monitoring stations under the World Meteorological Organization (WMO) Global Atmospheric Watch (GAW) program, covering monthly atmospheric methane concentration observations from 1994 to 2021. First, the data were subjected to stationarity tests, with the ADF test used to determine stationarity, and non-stationary data were differenced. Subsequently, the autoregressive correlation function (ACF) plot and partial autoregressive correlation function (PACF) plot were used for model order determination, ultimately selecting the ARIMR(0,1,1) model for predictive analysis. The results indicate that the ARIMR(0,1,1) model with a drift term demonstrates good fitting performance and predictive capability when forecasting changes in atmospheric methane concentrations, with small prediction errors and the ability to effectively continue the original trend of the series. Using the ARIMR model with a drift term to forecast atmospheric methane concentrations for 2025, the results show that atmospheric methane concentrations are expected to continue rising in the future.

Long-term observations of reactive gases in the troposphere are important for understanding trace gas cycles and the oxidation capacity of the atmosphere, assessing impacts of emission changes, verifying numerical model simulations, and quantifying the interactions between short-lived compounds and climate change. The World Meteorological Organization’s (WMO) Global Atmosphere Watch (GAW) program coordinates a global network of surface stations some of which have measured reactive gases for more than 40 years. Gas species included under this umbrella are ozone, carbon monoxide, nitrogen oxides, and volatile organic compounds (VOCs). There are many challenges involved in setting-up and maintaining such a network over many decades and to ensure that data are of high quality, regularly updated and made easily accessible to users. This overview describes the GAW surface station network of reactive gases, its unique quality management framework, and discusses the data that are available from the central archive. Highlights of data use from the published literature are reviewed, and a brief outlook into the future of GAW is given. This manuscript constitutes the overview of a special feature on GAW reactive gases observations with individual papers reporting on research and data analysis of particular substances being covered by the program.