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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.

Hydrochlorofluorocarbon HCFC-133a (CF3CH2Cl) is an anthropogenic compound whose consumption for emissive use is restricted under the Montreal Protocol. A recent study showed rapidly increasing atmospheric abundances and emissions. We report that, following this rise, the at- mospheric abundance and emissions have declined sharply in the past three years. We find a Northern Hemisphere HCFC-133a increase from 0.13 ppt (dry air mole fraction in parts-per-trillion) in 2000 to 0.50 ppt in 2012–mid-2013 followed by an abrupt reversal to 0.44 ppt by early 2015. Global emissions derived from these observations peaked at 3.1 kt in 2011, followed by a rapid decline of 0.5 kt yr−2 to 1.5 kt yr−1 in 2014. Sporadic HCFC-133a pollution events are detected in Europe from our high-resolution HCFC-133a records at three European stations, and in Asia from sam- ples collected in Taiwan. European emissions are estimated to be

We report the first multiyear atmospheric record of HCFC-31 (CH2ClF), based on flask samples and in situ analyses of air from both hemispheres. Although HCFC-31 has never been produced in large amounts, observed mole fractions in the Northern Hemisphere increased from 2000 onward, reaching 170 ppq (parts per quadrillion, 10−15) in 2011–2012 before decreasing rapidly. By combining our observations with a two-dimensional atmospheric chemistry-transport model, we infer an increase in global emissions from 240 t yr−1 in 2000 to 840 t yr−1 in 2011–2012, followed by a relatively fast decline to 570 t yr−1 in 2014. Emissions of HCFC-31 originate most probably from intermediate product release during the manufacturing process of HFC-32 (CH2F2). The rapid decline in recent years could be due to changes in production methods rather than declines in diffusive sources such as landfills or HCFC-31 contaminations in merchandised HFC-32.

©2015. The Authors. We have developed a chemical mechanism describing the tropospheric degradation of chlorine containing very short-lived substances (VSLS). The scheme was included in a global atmospheric model and used to quantify the stratospheric injection of chlorine from anthropogenic VSLS (ClyVSLS) between 2005 and 2013. By constraining the model with surface measurements of chloroform (CHCl3), dichloromethane (CH2Cl2), tetrachloroethene (C2Cl4), trichloroethene (C2HCl3), and 1,2-dichloroethane (CH2ClCH2Cl), we infer a 2013 ClyVSLS mixing ratio of 123 parts per trillion (ppt). Stratospheric injection of source gases dominates this supply, accounting for ∼83% of the total. The remainder comes from VSLS-derived organic products, phosgene (COCl2, 7%) and formyl chloride (CHClO, 2%), and also hydrogen chloride (HCl, 8%). Stratospheric ClyVSLS increased by ∼52% between 2005 and 2013, with a mean growth rate of 3.7 ppt Cl/yr. This increase is due to recent and ongoing growth in anthropogenic CH2Cl2 - the most abundant chlorinated VSLS not controlled by the Montreal Protocol.

Carbon tetrachloride (CCl4) is a major anthropogenic ozone-depleting substance and greenhouse gas and has been regulated under the Montreal Protocol. However, the near-zero 2007–2012 emissions estimate based on the UNEP reported production and feedstock usage cannot be reconciled with the observed slow decline of atmospheric concentrations and the inter-hemispheric gradient (IHG) for CCl4. Our 3-D model simulations suggest that the observed IHG (1.5 ± 0.2 ppt for 2000–2012) is primarily caused by ongoing current emissions, while ocean and soil losses and stratosphere-troposphere exchange together contribute a small negative gradient (~0 – −0.3 ppt). Using the observed CCl4 global trend and IHG, we deduce that the mean global emissions for the 2000–2012 period are 393445 Gg/yr (~30% of the peak 1980s emissions) and a corresponding total lifetime of 353732 years.

We report in situ atmospheric measurements of hydrofluorocarbon HFC-43-10mee (C5H2F10; 1,1,1,2,2,3,4,5,5,5-decafluoropentane) from seven observatories at various latitudes, together with measurements of archived air samples and recent Antarctic flask air samples. The global mean tropospheric abundance was 0.21 ± 0.05 ppt (parts per trillion, dry air mole fraction) in 2012, rising from 0.04 ± 0.03 ppt in 2000. We combine the measurements with a model and an inverse method to estimate rising global emissions—from 0.43 ± 0.34 Gg yr−1 in 2000 to 1.13 ± 0.31 Gg yr−1 in 2012 (~1.9 Tg CO2-eq yr−1 based on a 100 year global warming potential of 1660). HFC-43-10mee—a cleaning solvent used in the electronics industry—is currently a minor contributor to global radiative forcing relative to total HFCs; however, our calculated emissions highlight a significant difference from the available reported figures and projected estimates.

This work reassesses the global atmospheric budget of H2 with the TM5 model. The recent adjustment of the calibration scale for H2 translates into a change in the tropospheric burden. Furthermore, the ECMWF Reanalysis-Interim (ERA-Interim) data from the European Centre for Medium-Range Weather Forecasts (ECMWF) used in this study show slower vertical transport than the operational data used before. Consequently, more H2 is removed by deposition. The deposition parametrization is updated because significant deposition fluxes for snow, water, and vegetation surfaces were calculated in our previous study. Timescales of 1-2h are asserted for the transport of H2 through the canopies of densely vegetated regions. The global scale variability of H2 and [DH2] is well represented by the updated model. H2 is slightly overestimated in the Southern Hemisphere because too little H2 is removed by dry deposition to rainforests and savannahs. The variability in H2 over Europe is further investigated using a high-resolution model subdomain. It is shown that discrepancies between the model and the observations are mainly caused by the finite model resolution. The tropospheric burden is estimated at 165 +/- 8TgH2. The removal rates of H2 by deposition and photochemical oxidation are estimated at 53 +/- 4 and 23 +/- 2TgH2/yr, resulting in a tropospheric lifetime of 2.2 +/- 0.2year.

[1] Western European emission inventories of the potent greenhouse gas trifluoromethane (HFC-23) are validated at a country level by combining 2-hourly atmospheric in-situ measurements at Jungfraujoch (Switzerland) and Mace Head (Ireland) with Lagrangian transport simulations. HFC-23 has an atmospheric lifetime of ∼270 yr and a 100-yr global warming potential (GWP) of 14,800 and is unintentionally produced during the manufacture of chlorodifluoromethane (HCFC-22). For the study region we derive emissions of 144–216 Mg/yr for July 2008–July 2010, which are 60–140% higher than the official emissions gathered from the national reports for the year 2009. The largest discrepancy is found for Italy, where our estimate of 26–56 Mg/yr exceeds the national inventory (2.6 Mg/yr) by more than an order of magnitude. These findings suggest that non-reported emissions from Annex 1 countries partly explain the recently derived gap between global bottom-up and top-down HFC-23 emission estimates. The results presented here provide independent information to relevant authorities on effective reporting of HFC-23 emissions, and demonstrate the potential of atmospheric measurements for real-world verification of greenhouse gas emissions.

[1] High-frequency, in situ observations from the Advanced Global Atmospheric Gases Experiment (AGAGE) and System for Observation of halogenated Greenhouse gases in Europe (SOGE) networks for the period 1998 to 2008, combined with archive flask measurements dating back to 1978, have been used to capture the rapid growth of HFC-125 (CHF2CF3) in the atmosphere. HFC-125 is the fifth most abundant HFC, and it currently makes the third largest contribution of the HFCs to atmospheric radiative forcing. At the beginning of 2008 the global average was 5.6 ppt in the lower troposphere and the growth rate was 16% yr−1. The extensive observations have been combined with a range of modeling techniques to derive global emission estimates in a top-down approach. It is estimated that 21 kt were emitted globally in 2007, and the emissions are estimated to have increased 15% yr−1 since 2000. These estimates agree within approximately 20% with values reported to the United Nations Framework Convention on Climate Change (UNFCCC) provided that estimated emissions from East Asia are included. Observations of regionally polluted air masses at individual AGAGE sites have been used to produce emission estimates for Europe (the EU-15 countries), the United States, and Australia. Comparisons between these top-down estimates and bottom-up estimates based on reports by individual countries to the UNFCCC show a range of approximately four in the differences. This process of independent verification of emissions, and an understanding of the differences, is vital for assessing the effectiveness of international treaties, such as the Kyoto Protocol.

[1] National emission inventories of ozone-depleting substances (ODS) play a key role in the control mechanisms of the Montreal Protocol's emission reduction plans. New quasi-continuous ground-based atmospheric measurements allow us to estimate China's current emissions of the most effective ODS. This serves as an independent validation of China's ODS consumption data reported to the United Nations Environment Programme (UNEP). Emissions of most first-generation ODS have declined in recent years, suggesting compliance with the regulations of China's advanced phase-out program. In contrast the emissions of some second-generation ODS have increased. Because China is currently one of the largest consumers of first generation ODS, the country's upcoming complete phase-out will be crucial for the rate of decline of atmospheric ODS hence the eventual recovery of the stratospheric ozone.

[1] Extensive trace gas measurement campaigns were performed in 2005 at the Swiss high-altitude station Jungfraujoch, including measurements of ozone (O3), carbon monoxide (CO), nitrogen oxides (NOx = NO + NO2), the sum of reactive nitrogen species (NOy), peroxyacetylnitrate (PAN), formaldehyde (HCHO), oxygenated volatile organic compounds (OVOCs), volatile hydrocarbons (HCs), methane (CH4), and nitrous oxide (N2O). The air masses arriving at Jungfraujoch experience particular transport pathways and therefore are expected to have characteristic chemical signatures. These characteristics are often masked by mixing with European planetary boundary layer air. In order to address the influence of European emissions, a method to retrieve “background concentrations” based on backward trajectories and statistics was developed and applied to the trace gas observations at Jungfraujoch. This procedure is important to determine baseline values for subsequent assessment of surface air quality targets. Cluster analysis of backward trajectories for “background conditions” shows that the influence of long-range transport is discernible in most of the clusters. Air masses tend to have lower background concentrations whenever transport conditions favor a higher amount of photochemical degradation (e.g., low latitude or no recent contact to emissions). The results of this study represent an alternative to aircraft measurements which are typically used to determine free tropospheric background conditions. They are valuable for comparison with numerical simulations and for policy making, and provide additional information about free tropospheric chemistry.

This paper presents results from the first large-scale in situ intercomparison of oxygenated volatile organic compound (OVOC) measurements. The intercomparison was conducted blind at the large (270 m(3)) simulation chamber, Simulation of Atmospheric Photochemistry in a Large Reaction Chamber (SAPHIR), in Julich, Germany. Fifteen analytical instruments, representing a wide range of techniques, were challenged with measuring atmospherically relevant OVOC species and toluene (14 species, C-1 to C-7) in the approximate range of 0.5-10 ppbv under three different conditions: (1) OVOCs with no humidity or ozone, (2) OVOCs with humidity added (r.h. approximate to 50%), and (3) OVOCs with ozone (approximate to 60 ppbv) and humidity (r.h. approximate to 50%). The SAPHIR chamber proved to be an excellent facility for conducting this experiment. Measurements from individual instruments were compared to mixing ratios calculated from the chamber volume and the known amount of OVOC injected into the chamber. Benzaldehyde and 1-butanol, compounds with the lowest vapor pressure of those studied, presented the most overall difficulty because of a less than quantitative transfer through some of the participants' analytical systems. The performance of each individual instrument is evaluated with respect to reference values in terms of time series and correlation plots for each compound under the three measurement conditions. A few of the instruments performed very well, closely matching the reference values, and all techniques demonstrated the potential for quantitative OVOC measurements. However, this study showed that nonzero offsets are present for specific compounds in a number of instruments and overall improvements are necessary for the majority of the techniques evaluated here.

[1] At the high alpine site Jungfraujoch (Switzerland) mixing ratios of 21 oxygenated volatile organic compounds (OVOCs) and selected nonmethane hydrocarbons (NMHCs) have been measured by a newly developed two-stage double adsorbent system coupled to a gas chromatograph–mass spectrometer (GC–MS). In addition, formaldehyde was measured by the Hantzsch technique. Four measurement campaigns were performed once every season in 2005, providing for the first time a unique data set of OVOCs in the free troposphere of central Europe. The dominating OVOCs measured were acetone, methanol, formaldehyde and acetaldehyde, with mean mixing ratios of 622–867 ppt, 362–790 ppt, 303–505 ppt and 310–392 ppt, respectively. These compounds explained 95% of the measured organic compounds in summer and 83% in fall. Elevated mixing ratios in summer were observed for compounds with strong biogenic sources (e.g., methanol and acetone), whereas mainly anthropogenic compounds (e.g., ethanol and benzene) had higher mixing ratios during winter. Potential European source regions were estimated for the organic trace gases by combining the measured data with a statistical trajectory model. Northern Italy, southern France and southern and eastern Germany were identified as the main European contributors to the measured organic compounds at Jungfraujoch.

[1] In this work, a photochemical dispersion model, CAMx (Comprehensive Air quality Model with eXtensions) was used to simulate a high ozone episode observed in the Po basin during the 2003 FORMAT (Formaldehyde as a Tracer of Oxidation in the Troposphere) campaign. The study focuses on formaldehyde and ozone, and a budget analysis was set up for interpreting the importance of different processes, namely emission, chemistry, transport and deposition, for three different areas (urban, downwind, suburban) around the Milan metropolitan region. In addition, a sensitivity study was carried out based on 11 different VOC emission scenarios. The results of the budget study show that the strongest O3 production rate (4 ppbv/hour) occurs in the downwind area of the city of Milan, and that accumulated O3 is transported back to Milan city during nighttime. More than 80% of the HCHO concentration over the Milan metropolitan region is secondary, i.e., photochemically produced from other VOCs. The sensitivity study shows that the emissions of isoprene are not, on average, a controlling factor for the peak concentrations of O3 and HCHO over the model domain because of very few oak trees in this region. Although the paraffinic (PAR) emissions are fairly large, a 20% reduction of PAR yields only 1.7% of HCHO reduction and 2.7% reduction of the O3 peak. The largest reduction of O3 levels can be obtained by reduced xylene (XYL) emissions. A 20% reduction of the total anthropogenic VOC emissions leads to 15.5% (20.3 ppbv) reduction of O3 peak levels over the Milan metropolitan region.

[1] Ground-based in situ measurements of 1,1-difluoroethane (HFC-152a, CH3CHF2) which is regulated under the Kyoto Protocol are reported under the auspices of the AGAGE (Advanced Global Atmospheric Gases Experiment) and SOGE (System of Observation of halogenated Greenhouse gases in Europe) programs. Observations of HFC-152a at five locations (four European and one Australian) over a 10 year period were recorded. The annual average growth rate of HFC-152a in the midlatitude Northern Hemisphere has risen from 0.11 ppt/yr to 0.6 ppt/yr from 1994 to 2004. The Southern Hemisphere annual average growth rate has risen from 0.09 ppt/yr to 0.4 ppt/yr from 1998 to 2004. The 2004 average mixing ratio for HFC-152a was 5.0 ppt and 1.8 ppt in the Northern and Southern hemispheres, respectively. The annual cycle observed for this species in both hemispheres is approximately consistent with measured annual cycles at the same locations in other gases which are destroyed by OH. Yearly global emissions of HFC-152a from 1994 to 2004 are derived using the global mean HFC-152a observations and a 12-box 2-D model. The global emission of HFC-152a has risen from 7 Kt/yr to 28 Kt/yr from 1995 to 2004. On the basis of observations of above-baseline elevations in the HFC-152a record and a consumption model, regional emission estimates for Europe and Australia are calculated, indicating accelerating emissions from Europe since 2000. The overall European emission in 2004 ranges from 1.5 to 4.0 Kt/year, 5–15% of global emissions for 1,1-difluoroethane, while the Australian contribution is negligible at 5–10 tonnes/year

[1] We capture the first atmospheric appearance of HFC-245fa (CHF2CH2CF3), a new foam blowing agent. Our results from the high-altitude observatory at Jungfraujoch, Switzerland, show a rapid growth of this substance in the northern hemispheric troposphere from 0.28 ppt in July 2004 to 0.68 ppt at the end of 2005, which corresponds to an overall increase of >90% per year. By combining our observations with an atmospheric 3-box model we estimate a southern hemispheric trend for this trace gas which we compare to observations at southern hemisphere mid-latitudes. We also estimate a global HFC-245fa emissions increase from 2100–2400 tonnes in 2003 to 5100–5900 tonnes in 2005. Pollution episodes are relatively rare at Jungfraujoch compared to other hydrofluorocarbons thereby confirming the limited use of HFC-245fa in Europe. Back trajectory analysis reveals the largest potential European sources of HFC-245fa in northern Italy and northeastern Spain.

[1] The hydroxyl free radical (OH) is the major oxidizing chemical in the atmosphere, destroying about 3.7 petagrams (Pg) of trace gases each year, including many gases involved in ozone depletion, the greenhouse effect and urban air pollution. Measurements of 1,1,1-trichloroethane (methyl chloroform, CH3CCl3), which reacts with OH, provide the most accurate method currently utilized for determining the global behavior of OH. We report that CH3CCl3 levels rose steadily from 1978 to reach a maximum in 1992 and have since decreased rapidly to levels in 2004 about 30% of the levels when measurements began in 1978. Analysis of these observations shows that global average OH levels had a small maximum around 1989 and a larger minimum around 1998, with OH concentrations in 2003 being comparable to those in 1979. This post-1998 recovery of OH reported here contrasts with the situation 4 years ago when reported OH was decreasing. The 1997–1999 OH minimum coincides with, and is likely caused by, major global wildfires and an intense El Nino event at this time.

[1] The influence of mountain venting over the Alps on ozone (O3) mixing ratios in the lower free troposphere (FT) and on export of European emissions was investigated with a Lagrangian chemical box-model system. During summertime fair-weather conditions mountain venting is an efficient tropospheric lifting mechanism that carries atmospheric boundary layer (ABL) pollutants to the FT. Little is known about the effect of mountain venting on net O3 production in the FT. Chemistry in a FT and an ABL air parcel was initialized with typical European summertime background FT and Alpine ABL mixing ratios, respectively, which were derived from measurements. A parameterization was developed based on previous quantification of mountain venting in the Swiss Alps, describing the injection of air from the ABL into the FT. For simulations at constant altitude (3500 m above mean sea level (MSL)), net O3 production was generally positive for day 0 of the simulation, when mountain venting occurred. Whether O3 was produced or destroyed from day 1 onward critically depended on initial nitrogen oxides (NOx) plus peroxy acetyl nitrates (PANs) mixing ratios in the ABL, and to a smaller extent on initial H2O and O3 mixing ratios, photolysis rates, and PANs chemistry. For a simulation period of 8 days O3 mixing ratios remained higher in the simulations with venting than in simulations for the FT background without venting. Simulations on cluster average forward trajectories initialized over the Alps showed that European emissions vented in the Alps have a strong influence on the Mediterranean region. O3 production on these trajectories was enhanced by the release of NOx from PANs that acted as a reservoir species while the air parcel was descending over the Mediterranean. The O3 production efficiency with regard to NOx was about 20 molecules O3 produced per molecule NOx consumed at 3500 m MSL on day 0 of the venting simulation. On the southward moving trajectories O3 production efficiency was in the range of 6–11 until day 3 of the simulation when all injected NOy was consumed.

Volatile organic compounds (VOCs) include saturated, unsaturated, and other substituted hydrocarbons. VOCs play an important role in the chemistry of the atmosphere by influencing ozone and hydroxyl radical (OH) concentrations, and the conversion rates of nitrogen oxides (NOx). Elevated levels of VOCs and NOx have led to an approximate doubling of ozone in the lower troposphere over the past couple of centuries, making tropospheric ozone the third most important anthropogenic greenhouse gas after carbon dioxide (CO2) and methane. Because of ozone's strong oxidizing properties, increases in tropospheric ozone are a concern for living systems on Earth. Ozone stresses and damages vegetation, resulting in a reduction of terrestrial CO2 sequestration. VOCs also serve as a source of atmospheric secondary organic aerosol (SOA), which influences the solar radiation budget and cloud droplet nucleation. Through these complex interactions, VOCs play an important role in air quality and climate.