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Production and consumption of CFC-11 (trichlorofluoromethane, CCl3F), CFC-12 (dichlorodifluoromethane, CCl2F2) and CCl4 (carbon tetrachloride) are controlled under the regulations of the Montreal Protocol and have been phased out globally since 2010. Only CCl4 is still widely produced as a chemical feedstock. After 2010, emissions of CFC-11 and CFC-12 should therefore mostly originate from existing banks (e.g. from foams, mobile air conditioning units and refrigerators); however evidence has emerged of an increase in global emissions of CFC-11 in the last decade, some of which has not been fully accounted for. The motivation for this work was to assess the emissions of CFC-11, CFC-12 and CCl4 from western Europe. All countries in this region have been subject to the controls of the Montreal Protocol since the late 1980s and, as non-Article 5 Parties, have been prohibited from producing CFCs and CCl4 for dispersive use since 1996. Four different inverse modelling systems are used to estimate emissions of these gases from 2008 to 2021 using data from four atmospheric measurement stations: Mace Head (Ireland), Jungfraujoch (Switzerland), Monte Cimone (Italy) and Tacolneston (UK). The average of the four model studies found that western European emissions of CFC-11, CFC-12 and CCl4 between 2008 and 2021 were declining at 3.5 % yr−1 (2.7 % yr−1–4.8 % yr−1), 7.7 % yr−1 (6.3 % yr−1–8.0 % yr−1) and 4.4 % yr−1 (2.6 % yr−1–6.4 % yr−1), respectively. Even though the emissions were declining throughout the period, the area including northern France, Belgium, the Netherlands and Luxembourg showed consistently elevated emissions of CFC-11 compared with the surrounding regions. Emissions of CFC-12 were slightly elevated in the same region. CCl4 emissions were the highest in the south of France. France had the highest emissions of all three gases over the period 2008–2021. Emissions from western Europe (2008–2021) were on average 2.4 ± 0.4 Gg (CFC-11), 1.3 ± 0.3 Gg (CFC-12) and 0.9 ± 0.2 Gg (CCl4). Our estimated decline in emissions of CFC-11 is consistent with a western European bank release rate of 3.4 % (2.6 %–4.5 %). This study concludes that emissions of CFC-11, CFC-12 and CCl4 have all declined from 2008 to 2021 in western Europe. Therefore, no evidence is found that western European emissions contributed to the unexplained part of the global increase in atmospheric concentrations of CFC-11 observed in the last decade.

Long term measurement activities carried out at the WMO GAW global station of Monte Cimone (CMN) provide a useful insight into the characterization of the composition of the Southern European atmosphere. Since 2003, ozone depleting substances (ODSs) and halogenated Greenhouse Gases (GHGs) have been measured at CMN in the frame of the AGAGE (Advanced Global Atmospheric Gases Experiment) programme, with the aim of tracking progress towards the implementation of the international treaties on stratospheric ozone depletion and climate, and getting a better understanding of emissions both in terms of magnitude and localisation at the regional (EU) scale. CMN is often influenced by the advection of polluted air masses from the Po basin, one of the most polluted areas in Europe, as well as by the transport from other highly anthropised regions in Central EU. However, during the cold months and at night-time in the warm season, the site is representative of the free troposphere.By providing high quality, high frequency, continuous -almost uninterrupted- observations of ODSs (chlorofluorocarbons and hydrochlorofluorocarbons) and their radiatively active substitutes (hydrofluorocarbons) to modellers, the monitoring activities at CMN are crucial for improving the overall sensitivity of the inverse modelling techniques used to derive emissions through the so called “top-down” approach. Such approach represents an important quasi-independent cross-check of national GHG emission inventories submitted annually by the parties to the United Nations Framework Convention on Climate Change (UNFCCC). Here we will present results of the Bayesian inverse modelling technique used to derive emissions at the EU national scale based on the observations described above.

Global emissions of the ozone depleting gas 1,1-dichloro-1-fluoroethane (HCFC-141b, CH3CCl2F), derived from measurements of atmospheric mole fractions, have been rising between 2017–2021 despite a fall in reported production and consumption for dispersive uses. This study evaluates the possible drivers behind this renewed rise in emissions. HCFC-141b is a controlled substance under the Montreal Protocol, and its phase-out is currently underway, after a peak in reported consumption and production in developing countries (Article 5) in 2013. If reported production and consumption are correct, it suggests that the 2017–2021 rise is due to an increase in emissions from the bank when HCFC-141b containing appliances reach the end of their life, or from production of HCFC-141b not reported for dispersive uses. Regional emissions have been estimated between 2017–2020 for all regions where measurements have sufficient sensitivity to emissions. This includes the regions of northwestern Europe, east Asia, the USA and Australia, where emissions decreased by a total of 1.6 ± 3.9 Gg yr−1, compared to a mean global increase of 3.0 ± 1.2 Gg yr−1 over the same period. Collectively these regions only account for around a third of global emissions in 2020. Therefore we are not able to pinpoint the source regions or specific activities responsible for the recent global emission rise.

National greenhouse gas inventories (GHGIs) are submitted annually to the United Nations Framework Convention on Climate Change (UNFCCC). They are estimated in compliance with Intergovernmental Panel on Climate Change (IPCC) methodological guidance using activity data, emission factors and facility-level measurements. For some sources, the outputs from these calculations are very uncertain. Inverse modelling techniques that use high-quality, long-term measurements of atmospheric gases have been developed to provide independent verification of national GHGIs. This is considered good practice by the IPCC as it helps national inventory compilers to verify reported emissions and to reduce emission uncertainty. Emission estimates from the InTEM (Inversion Technique for Emission Modelling) model are presented for the UK for the hydrofluorocarbons (HFCs) reported to the UNFCCC (HFC-125, HFC-134a, HFC-143a, HFC-152a, HFC-23, HFC-32, HFC-227ea, HFC-245fa, HFC-43-10mee and HFC-365mfc). These HFCs have high global warming potentials (GWPs), and the global background mole fractions of all but two are increasing, thus highlighting their relevance to the climate and a need for increasing the accuracy of emission estimation for regulatory purposes. This study presents evidence that the long-term annual increase in growth of HFC-134a has stopped and is now decreasing. For HFC-32 there is an early indication, its rapid global growth period has ended, and there is evidence that the annual increase in global growth for HFC-125 has slowed from 2018. The inverse modelling results indicate that the UK implementation of European Union regulation of HFC emissions has been successful in initiating a decline in UK emissions from 2018. Comparison of the total InTEM UK HFC emissions in 2020 with the average from 2009–2012 shows a drop of 35 %, indicating progress toward the target of a 79 % decrease in sales by 2030. The total InTEM HFC emission estimates (2008–2018) are on average 73 (62–83) % of, or 4.3 (2.7–5.9) Tg CO2-eq yr−1 lower than, the total HFC emission estimates from the UK GHGI. There are also significant discrepancies between the two estimates for the individual HFCs.

Perfluorocarbons (PFCs) are amongst the most potent greenhouse gases listed under the United Nations Framework Convention on Climate Change (UNFCCC). With atmospheric lifetimes in the order of thousands to tens of thousands of years, PFC emissions represent a permanent alteration to the global atmosphere on human timescales. While the industries responsible for the vast majority of these emissions – aluminium smelting and semi-conductor manufacturing – have made efficiency improvements and introduced abatement measures, the global mean mole fractions of three PFCs, namely tetrafluoromethane (CF4, PFC-14), hexafluoroethane (C2F6, PFC-116) and octafluoropropane (C3F8, PFC-218), continue to grow. In this study, we update baseline growth rates using in-situ high-frequency measurements from the Advanced Global Atmospheric Gases Experiment (AGAGE) and, using data from four European stations, estimate PFC emissions for northwest Europe. The global growth rate of CF4 decreased from 1.3 ppt yr−1 in 1979 to 0.6 ppt yr−1 around 2010 followed by a renewed steady increase to 0.9 ppt yr−1 in 2018. For C2F6, the growth rate grew to a maximum of 0.125 ppt yr−1 around 1999, followed by a decline to a minimum of 0.075 ppt yr−1 in 2009, followed by weak growth thereafter. The C3F8 growth rate was around 0.007 ppt yr−1 until the early 1990s and then quickly grew to a maximum of 0.03 ppt yr−1 in 2003/04. Following a period of decline until 2012 to 0.015 ppt yr−1, the growth rate slowly increased again to ~ 0.017 ppt yr−1 in 2019. Unlike CF4 (and to a lesser extent C2F6), we observed no clear minimum associated with the 2008 financial crisis for C3F8. We used an inverse modelling framework to infer PFC emissions for northwest Europe. No statistically significant trend in regional emissions was observed for any of the PFCs assessed. For CF4, European emissions in early years were linked predominantly to the aluminium industry. However, we link large emissions in recent years to a chemical manufacturer in northwest Italy. Emissions of C2F6 are linked to a range of sources, including a semi-conductor manufacturer in Ireland and a cluster of smelters in Germany's Ruhr valley. In contrast, northwest European emissions of C3F8 are dominated by a single source in northwest England, raising the possibility of using emissions from this site for a tracer release experiment.

Air pollution is one of the primary concerns of our society for its effect on human health and the environment. Among the policy measures that can be put in place to limit air pollutant emissions, end-of-pipe technologies and/or regulatory instruments may be implemented through legislative acts. Also, equally important are behavioural measures, requiring citizens’ active involvement. The success of any measure to limit pollutant emissions requires the acceptance by the citizens that, in turn, implies a correct perception of the main pollutant emission drivers. We present here the comparison between the public perception of air pollution sources and the real-world situation through a survey carried out in seven European countries and involving 16 101 respondents. Our study shows a dramatic underestimation of the contribution of the agri-food sector to air pollution. This result is common to all respondents in the seven countries examined and only to a small extent depends on gender, age and socio-economic status of the respondents.

We report a 40-year history of SF6 atmospheric mole fractions measured at the Advanced Global Atmospheric Gases Experiment (AGAGE) monitoring sites, combined with archived air samples, to determine emission estimates from 1978 to 2018. Previously we reported a global emission rate of 7.3±0.6 Gg yr−1 in 2008 and over the past decade emissions have continued to increase by about 24 % to 9.04±0.35 Gg yr−1 in 2018. We show that changing patterns in SF6 consumption from developed (Kyoto Protocol Annex-1) to developing countries (non-Annex-1) and the rapid global expansion of the electric power industry, mainly in Asia, have increased the demand for SF6-insulated switchgear, circuit breakers, and transformers. The large bank of SF6 sequestered in this electrical equipment provides a substantial source of emissions from maintenance, replacement, and continuous leakage. Other emissive sources of SF6 occur from the magnesium, aluminium, and electronics industries as well as more minor industrial applications. More recently, reported emissions, including those from electrical equipment and metal industries, primarily in the Annex-1 countries, have declined steadily through substitution of alternative blanketing gases and technological improvements in less emissive equipment and more efficient industrial practices. Nevertheless, there are still demands for SF6 in Annex-1 countries due to economic growth, as well as continuing emissions from older equipment and additional emissions from newly installed SF6-insulated electrical equipment, although at low emission rates. In addition, in the non-Annex-1 countries, SF6 emissions have increased due to an expansion in the growth of the electrical power, metal, and electronics industries to support their continuing development. There is an annual difference of 2.5–5 Gg yr−1 (1990–2018) between our modelled top-down emissions and the UNFCCC-reported bottom-up emissions (United Nations Framework Convention on Climate Change), which we attempt to reconcile through analysis of the potential contribution of emissions from the various industrial applications which use SF6. We also investigate regional emissions in East Asia (China, S. Korea) and western Europe and their respective contributions to the global atmospheric SF6 inventory. On an average annual basis, our estimated emissions from the whole of China are approximately 10 times greater than emissions from western Europe. In 2018, our modelled Chinese and western European emissions accounted for ∼36 % and 3.1 %, respectively, of our global SF6 emissions estimate.

We reconstruct atmospheric abundances of the potent greenhouse gas c - C4F8 (perfluorocyclobutane, perfluorocarbon PFC-318) from measurements of in situ, archived, firn, and aircraft air samples with precisions of ∼1 %–2 % reported on the SIO-14 gravimetric calibration scale. Combined with inverse methods, we found near-zero atmospheric abundances from the early 1900s to the early 1960s, after which they rose sharply, reaching 1.66 ppt (parts per trillion dry-air mole fraction) in 2017. Global c - C4F8 emissions rose from near zero in the 1960s to 1.2±0.1 (1 σ ) Gg yr −1 in the late 1970s to late 1980s, then declined to 0.77±0.03 Gg yr −1 in the mid-1990s to early 2000s, followed by a rise since the early 2000s to 2.20±0.05 Gg yr −1 in 2017. These emissions are significantly larger than inventory-based emission estimates. Estimated emissions from eastern Asia rose from 0.36 Gg yr −1 in 2010 to 0.73 Gg yr −1 in 2016 and 2017, 31 % of global emissions, mostly from eastern China. We estimate emissions of 0.14 Gg yr −1 from northern and central India in 2016 and find evidence for significant emissions from Russia. In contrast, recent emissions from northwestern Europe and Australia are estimated to be small ( ≤1 % each). We suggest that emissions from China, India, and Russia are likely related to production of polytetrafluoroethylene (PTFE, “Teflon”) and other fluoropolymers and fluorochemicals that are based on the pyrolysis of hydrochlorofluorocarbon HCFC-22 ( CHClF2 ) in which c - C4F8 is a known by-product. The semiconductor sector, where c - C4F8 is used, is estimated to be a small source, at least in South Korea, Japan, Taiwan, and Europe. Without an obvious correlation with population density, incineration of waste-containing fluoropolymers is probably a minor source, and we find no evidence of emissions from electrolytic production of aluminum in Australia. While many possible emissive uses of c - C4F8 are known and though we cannot categorically exclude unknown sources, the start of significant emissions may well be related to the advent of commercial PTFE production in 1947. Process controls or abatement to reduce the c - C4F8 by-product were probably not in place in the early decades, explaining the increase in emissions in the 1960s and 1970s. With the advent of by-product reporting requirements to the United Nations Framework Convention on Climate Change (UNFCCC) in the 1990s, concern about climate change and product stewardship, abatement, and perhaps the collection of c - C4F8 by-product for use in the semiconductor industry where it can be easily abated, it is conceivable that emissions in developed countries were stabilized and then reduced, explaining the observed emission reduction in the 1980s and 1990s. Concurrently, production of PTFE in China began to increase rapidly. Without emission reduction requirements, it is plausible that global emissions today are dominated by China and other developing countries. We predict that c - C4F8 emissions will continue to rise and that c - C4F8 will become the second most important emitted PFC in terms of CO2 -equivalent emissions within a year or two. The 2017 radiative forcing of c - C4F8 (0.52 mW m −2 ) is small but emissions of c - C4F8 and other PFCs, due to their very long atmospheric lifetimes, essentially permanently alter Earth's radiative budget and should be reduced. Significant emissions inferred outside of the investigated regions clearly show that observational capabilities and reporting requirements need to be improved to understand global and country-scale emissions of PFCs and other synthetic greenhouse gases and ozone-depleting substances.

Verification of the nationally reported greenhouse gas (GHG) inventories using inverse modelling and atmospheric observations is considered to be best practice by the United Nations Framework Convention on Climate Change (UNFCCC). It allows for an independent assessment of the nationally reported GHG emissions using a comprehensively different approach to the inventory methods. Significant differences in the emissions estimated using the two approaches are a means of identifying areas worthy of further investigation. An inversion methodology called Inversion Technique for Emission Modelling (InTEM) has been developed that uses a non-negative least squares minimisation technique to determine the emission magnitude and distribution that most accurately reproduces the observations. By estimating the underlying baseline time series, atmospheric concentrations where the short-term impact of regional pollution has been removed, and by modelling where the air has passed over on route to the observation stations on a regional scale, estimates of UK emissions are made. In this study we use an extensive network of observations with six stations across the UK and six more in neighbouring countries. InTEM uses information from a Lagrangian dispersion model NAME (Numerical Atmospheric dispersion Modelling Environment), driven by three-dimensional, modelled meteorology, to understand how the air mixes during transport from the emission sources to observation points. The InTEM inversion results are submitted annually by the UK as part of their National Inventory Report to the UNFCCC. They are used within the UK inventory team to highlight areas for investigation and have led to significant improvements to the submitted UK inventory. The latest UK comparisons will be shown along with examples of how the inversion results have informed the inventory.

Significance We demonstrate the need to detect and track unexpected substances in the atmosphere and to locate their sources. Here, we report on three hydrochlorofluorocarbons (HCFCs) that have no known end-uses. HCFC-132b ( C H 2 C l C C l F 2 ) is newly discovered in the global atmosphere. We identify East Asia as the dominant source region for global emissions of this compound and of HCFC-133a ( C H 2 C l C F 3 ). We also quantify global emissions of HCFC-31 ( C H 2 ClF). These compounds are most likely emitted as intermediate by-products of chemical production processes. The early discovery and identification of such unexpected emissions can identify the related industrial practices and help to develop and manage environmental policies to reduce unwanted and potentially harmful emissions before the scale of the problem becomes more costly to mitigate.

The potent greenhouse gas sulfuryl fluoride (SO2F2) is increasingly used as a fumigant, replacing methyl bromide, whose structural and soil fumigation uses have been phased out under the Montreal Protocol. We use measurements on archived air samples and in situ observations from the Advanced Global Atmospheric Gases Experiment (AGAGE) and a box model of the global atmosphere to show a global increase of SO2F2 mole fraction from 0.3 ± 0.02 to 2.5 ± 0.08 ppt along with a global increase in emissions from 0.5 ± 0.4 Gg yr−1 to 2.9 ± 0.4 Gg yr−1 from 1978 to 2019. Based on a hybrid model incorporating bottom-up industry data and a top-down downscaling approach, we estimate the spatial distribution and trend in SO2F2 regional emissions between 2000 and 2019 and propose that the global emissions increase is driven by the growing use of SO2F2 in structural fumigation in North America and in postharvest treatment of grains and other agricultural products worldwide.

Several studies investigated the possible impacts of the restriction measures related to the containment of the spread of the COrona VIrus Disease (COVID-19) to atmospheric ozone (O3) at global, regional, and local scales during 2020. O3 is a secondary pollutant with adverse effects on population health and ecosystems and with negative impacts on climate, acting as greenhouse gas. Most of these studies focused on spring 2020 (i.e. March–May) and on observations in the planetary boundary layer (PBL), mostly in the vicinity of urban agglomerates. Here, we analyzed the variability of O3 above the PBL of northern Italy in 2020 by using continuous observations carried out at a high mountain WMO/GAW global station in Italy (Mt. Cimone–CMN; 44°12' N, 10°42' E, 2165 m a.s.l.). Low O3 monthly anomalies were observed during spring (MAM) and summer (JJA), when periods of low O3 intertwined with periods with higher O3, within climatological ranges. A similar variability was observed for O3 precursors like NO2 and 15 anthropogenic non-methane volatile organic carbons, but the systematic O3 anomalies were not reflected in these variables. The analysis of meteorological variables and diel O3 cycles did not suggest major changes in the vertical transport related to the thermal circulation system in the mountain area. The analysis of five days back-trajectories suggested that the observed O3 anomalies cannot be explained by differences in the synoptic-scale circulation with respect to the previous years alone. On the other hand, the characterization of two transport patterns (i.e. air masses from the regional PBL or from the free troposphere) and the analysis of back-trajectories suggested an important contribution of transport from the continental PBL during the periods with the lowest O3 at CMN. When proxies of air mass transport from the regional PBL are considered, a lower NOx content was pointed out with respect to the previous years, suggesting a lower O3 production in a NOx-limited atmosphere. Our study suggested for the first time that, during MAM and JJA 2020, the reduced anthropogenic emissions related to the COVID-19 restrictions lowered the amount of this short-lived climate forcer/pollutant at remote locations above the PBL over northern Italy. This work suggests the importance of limiting anthropogenic precursor emissions for decreasing the O3 amount at remote locations and in upper atmospheric layers., Environmental Research Letters, 16 (7), ISSN:1748-9326, ISSN:1748-9318

Dichloromethane (CH2Cl2) and perchloroethylene (C2Cl4) are chlorinated very short lived substances (Cl-VSLS) with anthropogenic sources. Recent studies highlight the increasing influence of such compounds, particularly CH2Cl2, on the stratospheric chlorine budget and therefore on ozone depletion. Here, a multiyear global-scale synthesis inversion was performed to optimize CH2Cl2 (2006–2017) and C2Cl4 (2007–2017) emissions. The approach combines long-term surface observations from global monitoring networks, output from a three-dimensional chemical transport model (TOMCAT), and novel bottom-up information on prior industry emissions. Our posterior results show an increase in global CH2Cl2 emissions from 637 ± 36 Gg yr−1 in 2006 to 1,171 ± 45 Gg yr−1 in 2017, with Asian emissions accounting for 68% and 89% of these totals, respectively. In absolute terms, Asian CH2Cl2 emissions increased annually by 51 Gg yr−1 over the study period, while European and North American emissions declined, indicating a continental-scale shift in emission distribution since the mid-2000s. For C2Cl4, we estimate a decrease in global emissions from 141 ± 14 Gg yr−1 in 2007 to 106 ± 12 Gg yr−1 in 2017. The time-varying posterior emissions offer significant improvements over the prior. Utilizing the posterior emissions leads to modeled tropospheric CH2Cl2 and C2Cl4 abundances and trends in good agreement to those observed (including independent observations to the inversion). A shorter C2Cl4 lifetime, from including an uncertain Cl sink, leads to larger global C2Cl4 emissions by a factor of ~1.5, which in some places improves model-measurement agreement. The sensitivity of our findings to assumptions in the inversion procedure, including CH2Cl2 oceanic emissions, is discussed.

We report a 40-year history of SF6 atmospheric mole fractions measured at the Advanced Global Atmospheric Gases Experiment (AGAGE) monitoring sites, combined with archived air samples to determine emission estimates from 1978–2018. Previously we reported a global emission rate of 7.3 ± 0.6 Gigagrams (Gg) yr−1 in 2008 and over the past decade emissions have continued to increase by about 24 % to 9.04 ± 0.35 Gg yr−1 in 2018. We show that changing patterns in SF6 consumption from developed (Kyoto Protocol Annex-1) to developing countries (non-Annex-1) and the rapid global expansion of the electric power industry, mainly in Asia, have increased the demand for SF6-insulated switchgear, circuit breakers and transformers. The large bank of SF6 sequestered in this electrical equipment provides a substantial source of emissions from maintenance, replacement and continuous leakage. Other emissive sources of SF6 occur from the magnesium, aluminium, electronics industries and more minor industrial applications. More recently, reported emissions, including those from electrical equipment and metal industries, primarily in the Annex-1 countries, have steadily declined through substitution of alternative blanketing gases and technological improvements in less emissive equipment and more efficient industrial practices. Conversely, in the non-Annex-1 countries SF6 emissions have increased due to an expansion in the growth of the electrical power, metal and electronics industries to support their development. There is an annual difference of 2.5–5 Gg yr−1 (1990–2018) between our modelled top-down emissions and the UNFCCC reported bottom-up emissions, which we attempt to reconcile through analysis of the potential contribution of emissions from the various industrial applications which use SF6. We also investigate regional emissions in East Asia (China, S. Korea) and Western Europe and their respective contributions to the global atmospheric SF6 inventory. On an average annual basis, our estimated emissions from the whole of China are approximately 10 times greater than emissions from Western Europe. In 2018, our modelled Chinese and Western European emissions accounted for ~ 36 % and 3.1 %, respectively, of our global SF6 emissions estimate.

Methyl Chloride (CH3Cl) is a chlorine-containing trace gas in the atmosphere contributing significantly to stratospheric ozone depletion. While the atmospheric CH3Cl emissions are predominantly caused by natural sources on the global budget, significant uncertainties still remain for the anthropogenic CH3Cl emission strengths. In summer 2007 an intensive field campaign within the ACTRIS-2 Project was hosted at the Mt. Cimone World Meteorological Organization/Global Atmosphere Watch global station (CMN, 44,17&deg, N, 10,68&deg, E, 2165 m a.s.l.). High-frequency and high precision in situ measurements of atmospheric CH3Cl revealed significant high-frequency variability superimposed on the seasonally varying regional background levels. The high-frequency CH3Cl variability was characterized by an evident cycle over 24 h with maxima during the afternoon which points towards a systematic role of thermal vertical transport of air-masses from the regional boundary layer. The temporal correlation analysis with specific tracers of anthropogenic activity (traffic, industry, petrochemical industry) together with bivariate analysis as a function of local wind regime suggested that, even if the role of natural marine emissions appears as predominant, the northern Italy boundary layer could potentially represent a non-negligible source of CH3Cl during summer. Since industrial production and use of CH3Cl have not been regulated under the Montreal Protocol (MP) or its successor amendments, continuous monitoring of CH3Cl outflow from the Po Basin is important to properly assess its anthropogenic emissions.

A wide range of anthropogenic halocarbons is released to the atmosphere, contributing to stratospheric ozone depletion and global warming. Using measurements of atmospheric abundances for the estimation of halocarbon emissions on the global and regional scale has become an important top-down tool for emission validation in the recent past, but many populated and developing areas of the world are only poorly covered by the existing atmospheric halocarbon measurement network. Here we present 6 months of continuous halocarbon observations from Finokalia on the island of Crete in the Eastern Mediterranean. The gases measured are the hydrofluorocarbons (HFCs), HFC-134a (CH2FCF3), HFC-125 (CHF2CF3), HFC-152a (CH3CHF2) and HFC-143a (CH3CF3) and the hydrochlorofluorocarbons (HCFCs), HCFC-22 (CHClF2) and HCFC-142b (CH3CClF2). The Eastern Mediterranean is home to 250 million inhabitants, consisting of a number of developed and developing countries, for which different emission regulations exist under the Kyoto and Montreal protocols. Regional emissions of halocarbons were estimated with Lagrangian atmospheric transport simulations and a Bayesian inverse modeling system, using measurements at Finokalia in conjunction with those from Advanced Global Atmospheric Gases Experiment (AGAGE) sites at Mace Head (Ireland), Jungfraujoch (Switzerland) and Monte Cimone (Italy). Measured peak mole fractions at Finokalia showed generally smaller amplitudes for HFCs than at the European AGAGE sites except for periodic peaks of HFC-152a, indicating strong upwind sources. Higher peak mole fractions were observed for HCFCs, suggesting continued emissions from nearby developing regions such as Egypt and the Middle East. For 2013, the Eastern Mediterranean inverse emission estimates for the four analyzed HFCs and the two HCFCs were 13.9 (11.3–19.3) and 9.5 (6.8–15.1) Tg CO2eq yr−1, respectively. These emissions contributed 16.8 % (13.6–23.3 %) and 53.2 % (38.1–84.2 %) to the total inversion domain, which covers the Eastern Mediterranean as well as central and western Europe. Greek bottom-up HFC emissions reported to the UNFCCC were higher than our top-down estimates, whereas for Turkey our estimates agreed with UNFCCC-reported values for HFC-125 and HFC-143a, but were much and slightly smaller for HFC-134a and HFC-152a, respectively. Sensitivity estimates suggest an improvement of the a posteriori emission estimates, i.e., a reduction of the uncertainties by 40–80 % in the entire inversion domain, compared to an inversion using only the existing central European AGAGE observations.

Hydrofluorocarbons (HFCs) are used in a range of industrial applications and have largely replaced previously used gases (CFCs and HCFCs). HFCs are not ozone-depleting but have large global warming potentials and are, therefore, reported to the United Nations Framework Convention on Climate Change (UNFCCC). Here, we use four independent inverse models to estimate European emissions of the two HFCs contributing the most to global warming (HFC-134a and HFC-125) and of SF6 for the year 2011. Using an ensemble of inverse models offers the possibility to better understand systematic uncertainties in inversions. All systems relied on the same measurement time series from Jungfraujoch (Switzerland), Mace Head (Ireland), and Monte Cimone (Italy) and the same a priori estimates of the emissions, but differed in terms of the Lagrangian transport model (FLEXPART, NAME), inversion method (Bayesian, extended Kalman filter), treatment of baseline mole fractions, spatial gridding, and a priori uncertainties. The model systems were compared with respect to the ability to reproduce the measurement time series, the spatial distribution of the posterior emissions, uncertainty reductions, and total emissions estimated for selected countries. All systems were able to reproduce the measurement time series very well, with prior correlations between 0.5 and 0.9 and posterior correlations being higher by 0.05 to 0.1. For HFC-125, all models estimated higher emissions from Spain + Portugal than reported to UNFCCC (median higher by 390 %) though with a large scatter between individual estimates. Estimates for Germany (+140 %) and Ireland (+850 %) were also considerably higher than UNFCCC, whereas the estimates for France and the UK were consistent with the national reports. In contrast to HFC-125, HFC-134a emissions from Spain + Portugal were broadly consistent with UNFCCC, and emissions from Germany were only 30 % higher. The data suggest that the UK over-reports its HFC-134a emissions to UNFCCC, as the model median emission was significantly lower, by 50 %. An overestimation of both HFC-125 and HFC-134a emissions by about a factor of 2 was also found for a group of eastern European countries (Czech Republic + Poland + Slovakia), though with less confidence since the measurement network has a low sensitivity to these countries. Consistent with UNFCCC, the models identified Germany as the highest national emitter of SF6 in Europe, and the model median emission was only 1 % lower than the UNFCCC numbers. In contrast, the model median emissions were 2–3 times higher than UNFCCC numbers for Italy, France, and Spain + Portugal. The country-aggregated emissions from the different models often did not overlap within the range of the analytical uncertainties formally given by the inversion systems, suggesting that parametric and structural uncertainties are often dominant in the overall a posteriori uncertainty. The current European network of three routine monitoring sites for synthetic greenhouse gases has the potential to identify significant shortcomings in nationally reported emissions, but a denser network would be needed for more reliable monitoring of country-wide emissions of these important greenhouse gases across Europe.

Very short‐lived substances (VSLS), including dichloromethane (CH2Cl2), chloroform (CHCl3), perchloroethylene (C2Cl4), and 1,2‐dichloroethane (C2H4Cl2), are a stratospheric chlorine source and therefore contribute to ozone depletion. We quantify stratospheric chlorine trends from these VSLS (VSLCltot) using a chemical transport model and atmospheric measurements, including novel high‐altitude aircraft data from the NASA VIRGAS (2015) and POSIDON (2016) missions. We estimate VSLCltot increased from 69 (±14) parts per trillion (ppt) Cl in 2000 to 111 (±22) ppt Cl in 2017, with >80% delivered to the stratosphere through source gas injection, and the remainder from product gases. The modeled evolution of chlorine source gas injection agrees well with historical aircraft data, which corroborate reported surface CH2Cl2 increases since the mid‐2000s. The relative contribution of VSLS to total stratospheric chlorine increased from ~2% in 2000 to ~3.4% in 2017, reflecting both VSLS growth and decreases in long‐lived halocarbons. We derive a mean VSLCltot growth rate of 3.8 (±0.3) ppt Cl/year between 2004 and 2017, though year‐to‐year growth rates are variable and were small or negative in the period 2015–2017. Whether this is a transient effect, or longer‐term stabilization, requires monitoring. In the upper stratosphere, the modeled rate of HCl decline (2004–2017) is −5.2% per decade with VSLS included, in good agreement to ACE satellite data (−4.8% per decade), and 15% slower than a model simulation without VSLS. Thus, VSLS have offset a portion of stratospheric chlorine reductions since the mid‐2000s., Key Points Stratospheric chlorine from very short‐lived substances increased by 3.8 ppt/year over 2004–2017, with a growth slowdown in 2015–2017Chlorine from short‐lived substances improves model representation of upper stratospheric HCl trendsShort‐lived chlorine offsets the 2004–2017 rate of upper stratospheric HCl decline by 15%

Decision making in the field of air quality and greenhouses gases reductions can nowadays be supported by a clear overall framework and by computer tools that integrate the most relevant aspects of the problem. This approach is particularly important at local scale since new general rules on emission abatement at European level can only marginally modify the most critical hotspots and may be very costly. This paper adapts the general Drivers, Pressures, State, Impacts, Responses (DPSIR) scheme proposed by the European Environment Agency to the specific case of local air quality policies and shows how the most recent scientific developments in impact evaluation and social acceptance can be integrated. The proposed decision framework represents a general methodology to design Integrated Assessment Modelling (IAM) systems aimed at the implementation of effective Air Quality Plans (AQP). An extensive survey across European countries shows the current degree of adoption of these approaches.

We report ground-based atmospheric measurements and emission estimates for the halons H-1211 (CBrClF2), H-1301 (CBrF3), and H-2402 (CBrF2CBrF2) from the AGAGE (Advanced Global Atmospheric Gases Experiment) and the National Oceanic and Atmospheric Administration global networks. We also include results from archived air samples in canisters and from polar firn in both hemispheres, thereby deriving an atmospheric record of nearly nine decades (1930s to present). All three halons were absent from the atmosphere until ∼1970, when their atmospheric burdens started to increase rapidly. In recent years H-1211 and H-2402 mole fractions have been declining, but H-1301 has continued to grow. High-frequency observations show continuing emissions of H-1211 and H-1301 near most AGAGE sites. For H-2402 the only emissions detected were derived from the region surrounding the Sea of Japan/East Sea. Based on our observations, we derive global emissions using two different inversion approaches. Emissions for H-1211 declined from a peak of 11 kt yr−1 (late 1990s) to 3.9 kt yr−1 at the end of our record (mean of 2013–2015), for H-1301 from 5.4 kt yr−1 (late 1980s) to 1.6 kt yr−1, and for H-2402 from 1.8 kt yr−1 (late 1980s) to 0.38 kt yr−1. Yearly summed halon emissions have decreased substantially; nevertheless, since 2000 they have accounted for ∼30% of the emissions of all major anthropogenic ozone depletion substances, when weighted by ozone depletion potentials.

High frequency, in situ observations from 11 globally distributed sites for the period 1994–2014 and archived air measurements dating from 1978 onward have been used to determine the global growth rate of 1,1-difluoroethane (HFC-152a, CH3CHF2). These observations have been combined with a range of atmospheric transport models to derive global emission estimates in a top-down approach. HFC-152a is a greenhouse gas with a short atmospheric lifetime of about 1.5 years. Since it does not contain chlorine or bromine, HFC-152a makes no direct contribution to the destruction of stratospheric ozone and is therefore used as a substitute for the ozone depleting chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). The concentration of HFC-152a has grown substantially since the first direct measurements in 1994, reaching a maximum annual global growth rate of 0.84 ± 0.05 ppt yr−1 in 2006, implying a substantial increase in emissions up to 2006. However, since 2007, the annual rate of growth has slowed to 0.38 ± 0.04 ppt yr−1 in 2010 with a further decline to an annual average rate of growth in 2013–2014 of −0.06 ± 0.05 ppt yr−1. The annual average Northern Hemisphere (NH) mole fraction in 1994 was 1.2 ppt rising to an annual average mole fraction of 10.1 ppt in 2014. Average annual mole fractions in the Southern Hemisphere (SH) in 1998 and 2014 were 0.84 and 4.5 ppt, respectively. We estimate global emissions of HFC-152a have risen from 7.3 ± 5.6 Gg yr−1 in 1994 to a maximum of 54.4 ± 17.1 Gg yr−1 in 2011, declining to 52.5 ± 20.1 Gg yr−1 in 2014 or 7.2 ± 2.8 Tg-CO2 eq yr−1. Analysis of mole fraction enhancements above regional background atmospheric levels suggests substantial emissions from North America, Asia, and Europe. Global HFC emissions (so called “bottom up” emissions) reported by the United Nations Framework Convention on Climate Change (UNFCCC) are based on cumulative national emission data reported to the UNFCCC, which in turn are based on national consumption data. There appears to be a significant underestimate ( > 20 Gg) of “bottom-up” reported emissions of HFC-152a, possibly arising from largely underestimated USA emissions and undeclared Asian emissions.

Since January 2010 continuous high-frequency in situ measurements of a range of anthropogenic Non-Methane Volatile Organic Compounds (NMVOCs) has been carried out at the World Meteorological Organisation Global Atmospheric Watch observatory at Mt. Cimone, on the highest peak of the Italian Northern Apennines, at the border between the Po Valley and the Mediterranean Basin. Five-year (2010-2014) time series of eleven NMVOCs, including aromatic and aliphatic species, have been analysed in order to derive average mixing ratios and detect annual and seasonal variability. Recent studies conducted in Europe, mainly in urban areas, have reported a decrease in atmospheric NMVOCs. Here we investigate how the decline in emissions, due to the implementation of air pollution policies, is reflected in the annual variability of NMVOC mixing ratios measured at a regional background location. Analysis of temporal trends for wellmixed conditions showed statistically significant decreases in ethyne, n-pentane and ethyl-benzene, while no significant trends were found for propane, butanes, i-pentane, toluene and xylenes. The seasonal variability of NMVOCs has been studied showing clear seasonal cycles for longer lived compounds and cycles with smaller seasonal amplitudes for shorterlived species. We used the propane time series to describe the seasonal cycle and to verify to what extent the mixing ratios of propane have been depleted by OH oxidation. We found that, during the summer, different transport times to the receptors and different source distribution are the main responsible for the relatively low integrated OH concentrations at Mt. Cimone.

HCFC-22 (CHClF2), a stratospherie ozone depleting substance and a powerful greenhouse gas, is the third most abundant anthropogenic halocarbon in the atmosphere. Primarily used in refrigeration and air conditioning systems, its global production and consumption have increased during the last 60 years, with the global increases in the last decade mainly attributable to developing countries. In 2007, an adjustment to the Montreal Protocol for Substances that Deplete the Ozone Layer called for an accelerated phase out of HCFCs, implying a 75% reduction (base year 1989) of HCFC production and consumption by 2010 in developed countries against the previous 65% reduction. In Europe HCFC-22 is continuously monitored at the two sites Mace Head (Ireland) and Monte Cimone (Italy). Combining atmospheric observations with a Bayesian inversion technique, we estimated fluxes of HCFC-22 from Europe and from eight macro-areas within it, over an 11-year period from January 2002 to December 2012, during which the accelerated restrictions on HCFCs production and consumption have entered into force. According to our study, the maximum emissions over the entire domain was in 2003 (38.2 +/- 4.7 Gg yr(-1)), and the minimum in 2012 (12.1 +/- 2.0 Gg yr(-1)); emissions continuously decreased between these years, except for secondary maxima in the 2008 and 2010. Despite such a decrease in regional emissions, background values of HCFC-22 measured at the two European stations over 2002-2012 are still increasing as a consequence of global emissions, in part from developing countries, with an average trend of ca 7.0 ppt yr(-1). However, the observations at the two European stations show also that since 2008 a decrease in the global growth rate has occurred. In general, our European emission estimates are in good agreement with those reported by previous studies that used different techniques. Since the currently dominant emission source of HCFC-22 is from banks, we assess the banks' size and their contribution to the total European emissions up to 2030, and we project a fast decrease approaching negligible emissions in the last five years of the considered period. Finally, inversions conducted over three month periods showed evidence for a seasonal cycle in emissions in regions in the Mediterranean basin but not outside it. Emissions derived from regions in the Mediterranean basin were ca. 25% higher in warmer months than in colder months. (C) 2015 The Authors. Published by Elsevier Ltd.

We present the organization, instrumentation, datasets, data interpretation, modeling, and accomplishments of the multinational global atmospheric measurement program AGAGE (Advanced Global Atmospheric Gases Experiment). AGAGE is distinguished by its capability to measure globally, at high frequency, and at multiple sites all the important species in the Montreal Protocol and all the important non-carbon-dioxide (non-CO[subscript 2]) gases assessed by the Intergovernmental Panel on Climate Change (CO[subscript 2] is also measured at several sites). The scientific objectives of AGAGE are important in furthering our understanding of global chemical and climatic phenomena. They are the following: (1) to accurately measure the temporal and spatial distributions of anthropogenic gases that contribute the majority of reactive halogen to the stratosphere and/or are strong infrared absorbers (chlorocarbons, chlorofluorocarbons – CFCs, bromocarbons, hydrochlorofluorocarbons – HCFCs, hydrofluorocarbons – HFCs and polyfluorinated compounds (perfluorocarbons – PFCs), nitrogen trifluoride – NF[subscript 3], sulfuryl fluoride – SO[subscript 2]F[subscript 2], and sulfur hexafluoride – SF[subscript 6]) and use these measurements to determine the global rates of their emission and/or destruction (i.e., lifetimes); (2) to accurately measure the global distributions and temporal behaviors and determine the sources and sinks of non-CO[subscript 2] biogenic–anthropogenic gases important to climate change and/or ozone depletion (methane – CH[subscript 4], nitrous oxide – N[subscript 2]O, carbon monoxide – CO, molecular hydrogen – H[subscript 2], methyl chloride – CH[subscript 3]Cl, and methyl bromide – CH[subscript 3]Br); (3) to identify new long-lived greenhouse and ozone-depleting gases (e.g., SO[subscript 2]F[subscript 2], NF[subscript 3], heavy PFCs (C[subscript 4]F[subscript 10], C[subscript 5]F[subscript 12], C[subscript 6]F[subscript 14], C[subscript 7]F[subscript 16], and C[subscript 8]F[subscript 18]) and hydrofluoroolefins (HFOs; e.g., CH[subscript 2] = CFCF[subscript 3]) have been identified in AGAGE), initiate the real-time monitoring of these new gases, and reconstruct their past histories from AGAGE, air archive, and firn air measurements; (4) to determine the average concentrations and trends of tropospheric hydroxyl radicals (OH) from the rates of destruction of atmospheric trichloroethane (CH[subscript 3]CCl[subscript 3]), HFCs, and HCFCs and estimates of their emissions; (5) to determine from atmospheric observations and estimates of their destruction rates the magnitudes and distributions by region of surface sources and sinks of all measured gases; (6) to provide accurate data on the global accumulation of many of these trace gases that are used to test the synoptic-, regional-, and global-scale circulations predicted by three-dimensional models; and (7) to provide global and regional measurements of methane, carbon monoxide, and molecular hydrogen and estimates of hydroxyl levels to test primary atmospheric oxidation pathways at midlatitudes and the tropics. Network Information and Data Repository: http://agage.mit.edu/data or http://cdiac.ess-dive.lbl.gov/ndps/alegage.html (https://doi.org/10.3334/CDIAC/atg.db1001)., United States. National Aeronautics and Space Administration (NAG5-12669), United States. National Aeronautics and Space Administration (NNX07AE89G), United States. National Aeronautics and Space Administration (NNX11AF17G), United States. National Aeronautics and Space Administration (NNX16AC98G)

Based on observations of three chlorofluorocarbons, CFC-13 (chlorotrifluoromethane), CFC-114 (dichlorotetrafluoroethane) and CFC-115 (chloropentafluoroethane) in atmospheric and firn samples, we reconstruct records of their tropospheric histories spanning nearly eight decades. These compounds were measured in polar firn air samples, in ambient air archived in canisters, and in-situ at the AGAGE (Advanced Global Atmospheric Gases Experiment) network and affiliated sites. Global emissions to the atmosphere are derived from these observations using an inversion based on a 12-box atmospheric transport model. For CFC-13, we provide the first comprehensive global analysis. This compound increased monotonically from its first appearance in the atmosphere in the late 1950s to a mean global abundance of 3.18 ppt (dry air mole fraction in parts-per-trillion, pmol mol−-1) in 2016. Its growth rate has decreased since the mid 1980s but has remained at a surprisingly high level of 0.02 ppt yr−1 since the late 2000s. CFC-114 increased from its appearance in the 1950s to a maximum of 16.6 ppt in the early 2000s, and has since slightly declined to 16.3 ppt in 2016. CFC-115 increased monotonically from its first appearance in the 1960s and reached a global mean mole fraction of 8.52 ppt in 2016. Growth rates of all three compounds over the past years are significantly larger than would be expected from zero emissions. Under the assumption of unaltered lifetimes and atmospheric transport patterns, we derive global emissions from our measurements, which have remained unexpectedly high in recent years: Mean yearly emissions for the last decade (2007–2016) of CFC-13 are at 0.48 ± 0.15 kt yr−1 (> 15 % of past peak emissions), of CFC-114 at 1.90 ± 0.84 kt yr−1 (~ 10 % of peak emissions), and of CFC-115 at 0.80 ± 0.50 kt yr−1 (> 5 % of peak emissions). Mean yearly emissions of CFC-115 for 2014–2016 are 1.08 ± 0.50 kt yr−1 and have more than doubled compared to 2009. Cumulative global emissions for CFC-114 derived from observations through 2016 exceed the global cumulative production derived from reported inventory data by > 10 % while those for CFC-115 agree well. We find CFC-13 emissions from aluminum smelters and impurities of CFC-115 in the refrigerant HFC-125 (CHF2CF3) but if extrapolated to global emissions neither of them can account for the lingering global emissions determined from the atmospheric observations. We also conduct regional inversions for the years 2012–2016 for the north-east Asian area using observations from the Korean Gosan AGAGE site and find significant emissions for CFC-114 and CFC-115, suggesting that a large fraction of their global emissions currently occur in north-eastern Asia and more specifically on the Chinese mainland.

The aerosol chemical composition at Mt. Cimone has been investigated since 2000 during a series of field campaigns. Starting from 2009, systematic measurements on PM1 filters was conducted as a contribution to the EUSAAR/ACTRIS network. Moreover, first online chemical measurements were conducted at Mt. Cimone (CMN) in summer 2012 using a high-resolution aerosol mass spectrometer (AMS). The analyses show that the concentrations of mineral elements, associated to coarse particles, are largely influenced by long-range transport of desert dust from Africa. The submicron aerosol composition is dominated by sulfate, carbonaceous material and, to a lesser extent, by nitrate. The concentrations of all PM1 major components followed a yearly cycle with maxima in the summer when the station prevalently resides in the planetary boundary layer (PBL). The organic-to-sulfate ratio is smaller in summer then in winter. A meta-analysis of the whole dataset shows evidence of a decrease of sulfate concentrations in PM1 from 2000 to 2010. The sources of organic matter at CMN are still subject of investigation, although biogenic secondary organic aerosol seems to play a role in summertime while biomass burning becomes prevalent in winter.

Naturally-occurring and artificial radionuclides in PM10 aerosol samples have been systematically measured for more than 12 years at the “O. Vittori” observatory, a baseline station located in a crucial position in the middle of the Mediterranean basin under the influence of relevant atmospheric streamers crossing in this area. The database collected and herein described covers PM10 mass load, 7Be and 210Pb, while sporadic samples showed the occurrence of artificial radionuclides as a result of accidents such as the tsunami induced Fukushima nuclear accident or the Algeciras non-nuclear 137Cs release. The principal scope of radioactivity monitoring at CMN has been the study of Stratosphere to Troposphere Exchange, mainly based on the variation of cosmogenic 7Be, while the availability of 210Pb as well of the mass load of PM10 allowed to extend the efficiency of radiotracer data to the identification of continental aerosol sources such as Saharan dust and the Balkan region. Extensive work has been and is still in progress based on the collected dataset concerning the application of global circulation models which rely on the support of objective tracers for their validation.

By this appendix, we provide a set of statistical information about long-term observations of Essential Climate Variables at CMN. We provide a short description of the statistical methods, together with tables and plots describing typical ECV average values and variabilities as a function of seasons and years.

In the past decades, accurate and precise atmospheric measurements of radiatively active gases have been crucial in revealing the rapid and unceasing growth of their global concentrations that has been long recognized as the main driver of climate change. Even if carbon dioxide is the major anthropogenic contributor to radiative forcing, other gases such as methane, nitrous oxide, and halogenated gases are extremely relevant in climate issues because of their very high global warming potential. Continuous measurement programs of these gases are carried out at CMN in the frame of important international programs. This chapter reports an overview of the scientific results obtained based on 15 years of atmospheric measurements. These results have been achieved combining atmospheric data with different modeling approaches, with the aim of understanding the budget of these radiatively active gases and providing emission estimates at the regional scale. Such estimates constitute an important support to improve bottom-up emission data that each country is required to submit every year in the frame of the most important international global protocols aimed at combatting climate change.

The Mediterranean basin represents a global hotspot for climate change, air quality, and anthropogenic contributions to these issues. Since the early 1990s at Mt. Cimone, the highest peak of Italian northern Apennines, an observatory is performing continuous measurements of atmospheric composition. The Italian climate observatory “O. Vittori” is a research infrastructure managed by the Institute for Atmospheric Sciences and Climate (ISAC) of the National Research Council of Italy (CNR) and hosted by the Italian Air Force. It is part of the WMO/GAW global station “Mt. Cimone” (GAW id: CMN). Due to the completely free horizon, high altitude, and great distance from major pollution sources, CMN represents a strategic platform to study the chemical–physical characteristics and climatology of the free troposphere in the South Europe and Mediterranean basin. At this observatory, continuous monitoring of climate-altering compounds (trace gases and aerosol), solar radiation, as well as meteorological parameters is carried out. Besides providing a historical perspective of scientific research at CMN, we characterize the measurement site, and we describe the current observatory technical facilities, including the e-access to data and the services for near-real-time data delivery. Good practices for educational and outreach activities are also presented.

The Mediterranean basin represents a global hot spot for climate change, air quality, and anthropogenic contributions to these issues. In this region, a relevant role is played by reactive gases (RGs), i.e., O3, CO, SO2, NOx, and VOCs. At the “O. Vittori” observatory at Mt. Cimone, a number of RGs are observed since more than 20 years. These observations are carried out within the framework of international program (e.g., WMO/GAW, ACTRIS) representing a valuable resource of information for quantifying the variability of these atmospheric key compounds and for investigating the influence of specific atmospheric processes to this variability (e.g., polluted air mass transport, open fire emissions, mineral dust outbreaks, stratospheric intrusion events). These observations were used to experimental applications like near-real-time data delivery services or model verification and satellite data ground-truthing.

Hydrofluorocarbons are powerful greenhouse gases developed by industry after the phase-out of the ozone depleting chlorofluorocarbons and hydrochlorofluorocarbons required by the Montreal Protocol. The climate benefit of reducing the emissions of hydrofluorocarbons has been widely recognised, leading to an amendment of the Montreal Protocol (Kigali Amendment) calling for developed countries to start to phase-down hydrofluorocarbons by 2019 and in developing countries to follow with a freeze between 2024 and 2028. In this way, nearly half a degree Celsius of warming would be avoided by the end of the century. Hydrofluorocarbons are also included in the basket of gases controlled under the Kyoto Protocol of the United Nations Framework Convention on Climate Change. Annex I parties to the Convention submit annual national greenhouse gas inventories based on a bottom-up approach, which relies on declared anthropogenic activities. Top-down methodologies, based on atmospheric measurements and modelling, can be used in support to the inventory compilation. In this study we used atmospheric data from four European sites combined with the FLEXPART dispersion model and a Bayesian inversion method, in order to derive emissions of nine individual hydrofluorocarbons from the whole European Geographic Domain and from twelve regions within it, then comparing our results with the annual emissions that the European countries submit every year to the United Nations Framework Convention on Climate Change, as well as with the bottom-up Emissions Database for Global Atmospheric Research. We found several discrepancies when considering the specific compounds and on the country level. However, an overall agreement is found when comparing European aggregated data, which between 2008 and 2014 are on average 84.2 +/- 28.0 Tg-CO2-eq.yr(-1) against the 95.1 Tg-CO2-eq.yr(-1) reported by UNFCCC in the same period. Therefore, in agreement with other studies, the gap on the global level between bottom-up estimates of Annex I countries and total global top-down emissions should be essentially due to emissions from non-reporting countries (non-Annex I). (C) 2017 Elsevier Ltd. All rights reserved.