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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 on 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 2019. 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 2003–2004. 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. 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.

We present a method for estimating fossil fuel methane emissions using observations of methane and ethane, accounting for uncertainty in their emission ratio. The ethane:methane emission ratio is incorporated as a spatially and temporally variable parameter in a Bayesian model, with its own prior distribution and uncertainty. We find that using an emission ratio distribution mitigates bias from using a fixed, potentially incorrect emission ratio and that uncertainty in this ratio is propagated into posterior estimates of emissions. A synthetic data test is used to show the impact of assuming an incorrect ethane:methane emission ratio and demonstrate how our variable parameter model can better quantify overall uncertainty. We also use this method to estimate UK methane emissions from high-frequency observations of methane and ethane from the UK Deriving Emissions linked to Climate Change (DECC) network. Using the joint methane–ethane inverse model, we estimate annual mean UK methane emissions of approximately 0.27 (95 % uncertainty interval 0.26–0.29) Tg yr−1 from fossil fuel sources and 2.06 (1.99–2.15) Tg yr−1 from non-fossil fuel sources, during the period 2015–2019. Uncertainties in UK fossil fuel emissions estimates are reduced on average by 15 % and up to 35 % when incorporating ethane into the inverse model, in comparison to results from the methane-only inversion.

Perfluorocarbons (PFCs) are amongst the most potent greenhouse gases listed under the United Nations Framework Convention on Climate Change (UNFCCC). With atmospheric lifetimes on 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 (CF.sub.4, PFC-14), hexafluoroethane (C.sub.2 F.sub.6, PFC-116) and octafluoropropane (C.sub.3 F.sub.8, 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 CF.sub.4 decreased from 1.3 ppt yr.sup.-1 in 1979 to 0.6 ppt yr.sup.-1 around 2010 followed by a renewed steady increase to 0.9 ppt yr.sup.-1 in 2019. For C.sub.2 F.sub.6, the growth rate grew to a maximum of 0.125 ppt yr.sup.-1 around 1999, followed by a decline to a minimum of 0.075 ppt yr.sup.-1 in 2009, followed by weak growth thereafter. The C.sub.3 F.sub.8 growth rate was around 0.007 ppt yr.sup.-1 until the early 1990s and then quickly grew to a maximum of 0.03 ppt yr.sup.-1 in 2003-2004. Following a period of decline until 2012 to 0.015 ppt yr.sup.-1, the growth rate slowly increased again to â¼ 0.017 ppt yr.sup.-1 in 2019. 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 CF.sub.4, 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 C.sub.2 F.sub.6 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 C.sub.3 F.sub.8 are dominated by a single source in northwest England, raising the possibility of using emissions from this site for a tracer release experiment.

Identification and monitoring of halocarbons in the atmosphere remains important for the purposes of regulation and prediction of stratospheric ozone depletion. Measurements of these and other compounds have created a demand for techniques that improve the number of atmospheric compounds analysable. A prototype time-of-flight gas chromatography-mass spectrometer (GCMS) was characterised for atmospheric measurements. Instrument performance was found to be at the lower end of expectations. A comparison to a quadrupole GC-MS indicated that the TOF GC-MS would be suitable for measurements in polluted environments. As part of this comparison, a number of halocarbons were analysed in London, U.K. as part of the ClearfLo campaign. HCFCs were found at higher concentration than their Northern Hemispheric (NH) baseline values. Furthermore, HFC-134a and HFC-227ea were almost double their NH baseline. CH2Cl2, C2Cl4 and C2HCl3 were encountered at high concentrations and sources of very short-lived bromomethanes (VSLB) were identified close to London. As part of the CARIBIC project, five VSLB were measured in the mid-latitude upper troposphere/ lower stratosphere and tropical troposphere. Higher mixing ratios were encountered over Southeast Asia, likely due to a locally longer CH2Br2 lifetime. Total bromine derived from these five VSLB is at the lower end of the quantity required to balance the stratospheric bromine budget. During the SAMBBA project, biomass burning and natural sources of COS, methyl halides and other halocarbons were assessed over Brazil. Methyl halide emissions from rainforest and savannah fires were quantified. The Cerrado savannah was found to be a strong source of COS. Regional biomass burning emission estimates indicate that this is an important region for emissions of these compounds. Terrestrial, natural sources of CH3Cl, CH3Br and CHCl3 were confirmed over the Amazon rainforest. Emissions from a localised source of CHCl3 were identified and wetlands or agricultural soil disturbance were hypothesised as a likely cause.

As part of the effort to understand volcanic plume composition and chemistry during the eruption of the Icelandic volcano Eyjafjallajökull, the CARIBIC atmospheric observatory was deployed for three special science flights aboard a Lufthansa passenger aircraft. Measurements made during these flights included the collection of whole air samples, which were analyzed for non‐methane hydrocarbons (NMHCs). Hydrocarbon concentrations in plume samples were found to be reduced to levels below background, with relative depletions characteristic of reaction with chlorine radicals (Cl). Recent observations of halogen oxides in volcanic plumes provide evidence for halogen radical chemistry, but quantitative data for free halogen radical concentrations in volcanic plumes were absent. Here we present the first observation‐based calculations of Cl radical concentrations in volcanic plumes, estimated from observed NMHC depletions. Inferred Cl concentrations were between 1.3 × 104 and 6.6 × 104 Cl cm−3. The relationship between NMHC variability and local lifetimes was used to investigate the ratio between OH and Cl within the plume, with [OH]/[Cl] estimated to be ∼37. Key Points Cl chemistry was found to be the dominant sink for NMHCs in the volcanic plume Estimated Cl concentrations were 1.3–6.6 × 104 Cl cm−3 OH within the plume was estimated to be at or below typical background levels