European Emissions of Halogenated Greenhouse Gases Inferred from

ARTICLE pubs.acs.org/est

European Emissions of Halogenated Greenhouse Gases Inferred from Atmospheric Measurements Christoph A. Keller,*,† Matthias Hill,† Martin K. Vollmer,† Stephan Henne,† Dominik Brunner,† Stefan Reimann,† Simon O’Doherty,‡ Jgor Arduini,§ Michela Maione,§ Zita Ferenczi,|| Laszlo Haszpra,|| Alistair J. Manning,^ and Thomas Peter# †

)

Laboratory for Air Pollution/Environmental Technology, Swiss Federal Laboratories for Materials Science and Technology (Empa), Duebendorf, Switzerland ‡ Atmospheric Chemistry Research Group, University of Bristol, Bristol, United Kingdom § Department of Basic Sciences and Fundamentals, University of Urbino, Urbino, Italy Hungarian Meteorological Service, Budapest, Hungary ^ Met Office, Exeter, United Kingdom # Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland

bS Supporting Information ABSTRACT: European emissions of nine representative halocarbons (CFC-11, CFC12, Halon 1211, HCFC-141b, HCFC-142b, HCFC-22, HFC-125, HFC-134a, HFC152a) are derived for the year 2009 by combining long-term observations in Switzerland, Italy, and Ireland with campaign measurements from Hungary. For the first time, halocarbon emissions over Eastern Europe are assessed by top-down methods, and these results are compared to Western European emissions. The employed inversion method builds on least-squares optimization linking atmospheric observations with calculations from the Lagrangian particle dispersion model FLEXPART. The aggregated halocarbon emissions over the study area are estimated at 125 (106
150) Tg of CO2 equiv/y, of which the hydrofluorocarbons (HFCs) make up the most important fraction with 41% (31
52%). We find that chlorofluorocarbon (CFC) emissions from banks are still significant and account for 35% (27
43%) of total halocarbon emissions in Europe. The regional differences in per capita emissions are only small for the HFCs, while emissions of CFCs and hydrochlorofluorocarbons (HCFCs) tend to be higher in Western Europe compared to Eastern Europe. In total, the inferred per capita emissions are similar to estimates for China, but 3.5 (2.3
4.5) times lower than for the United States. Our study demonstrates the large benefits of adding a strategically well placed measurement site to the existing European observation network of halocarbons, as it extends the coverage of the inversion domain toward Eastern Europe and helps to better constrain the emissions over Central Europe.

’ INTRODUCTION Anthropogenic halogenated hydrocarbons are used in a wide range of applications such as air conditioning, refrigeration, foam blowing, and fire extinction, in the solvent industry, and as propellants.1 However, these compounds are potent greenhouse gases, and those containing chlorine or bromine contribute to anthropogenic stratospheric ozone depletion.2,3 Therefore, international treaties have been negotiated to control their usage. The production and consumption of ozone-depleting substances (ODSs) is regulated by the Montreal Protocol and its subsequent amendments, imposing a complete ban on chlorofluorocarbons (CFCs) for Annex-1 (developed) and non-Annex-1 (developing) countries by 1996 and 2010, respectively. For the first-generation replacement products, the hydrochlorofluorocarbons (HCFCs), a less stringent phase-out is in force, with a stepwise consumption and production reduction between 2004 and 2030 for Annex-1 r 2011 American Chemical Society

countries and between 2013 and 2040 for non-Annex-1 countries. The chlorine-free second-generation replacement products, the hydrofluorocarbons (HFCs), are characterized by high global warming potentials (GWPs) on the 100 y time horizon and are subject to the Kyoto Protocol.4 The effectiveness of the global phase-out of CFCs is verified by atmospheric measurements, which have shown slowly decreasing or at least stabilizing trends in background concentrations over the past decade.5 Atmospheric abundances of HCFCs and HFCs, on the other hand, are still rising, reflecting the ongoing production and release of these compounds on a global scale.5 These Received: July 16, 2011 Accepted: November 16, 2011 Revised: November 8, 2011 Published: December 16, 2011 217

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global emissions can be quantified using simple box models in combination with measured accumulation rates and estimated atmospheric lifetimes.6,7 To derive spatially and temporally more explicit emission estimates, though, more sophisticated approaches incorporating atmospheric transport models are required.8
10 Such “top-down” estimates provide a unique tool to screen official emission inventories, such as those reported to the United Nations Framework Convention on Climate Change (UNFCCC; http://unfccc.org). The latter are compiled from statistical data on production and consumption/usage (“bottom-up”) and may carry significant uncertainties.11
13 While comprehensive top-down emission estimates of halocarbons have recently been derived for various regions in the world, including Western Europe,14
18 North America,8,19 Eastern Asia,20
22 and Australia,23 the magnitude and share of Central and Eastern European halocarbon emissions remain subject to some speculation due to scattered atmospheric observations in these areas.24 To help fill in this gap, a half-year measurement campaign was conducted at K-Puszta, Hungary. These data were combined with continuous measurements from Western Europe to derive top-down emission estimates of CFC-11, CFC-12, Halon 1211, HCFC-141b, HCFC-142b, HCFC-22, HFC-125, HFC-134a, and HFC-152a over Europe. The selected CFCs, Halons, and HCFCs account for more than 90% of total emissions of the respective compound family5,25 and are therefore considered to be representative. For the HFCs, some important gases, including HFC-143a, HFC-23, HFC-32, and HFC-365mfc, were not measured, and the derived HFC emissions are therefore representative of approximately 70% of the total HFC emissions.5,25

spatial coverage of our emission estimates, but also reduces the uncertainties in regions where the areas of influence of the different sites overlap. Lagrangian Backward Modeling. The Lagrangian particle dispersion model FLEXPART, version 8.1,30 was used to obtain the source
receptor relationship (SRR, or “footprint”), providing a 5 day transport history of the air masses arriving at the measurement sites. The SRR is defined here as the particle residence time below 100 m above the model ground, divided by the air density of this subcolumn. The FLEXPART model was driven by 3 hourly wind fields (alternating analysis and 3 h forecasts) of the European Centre for Medium-Range Weather Forecasts (ECMWF) with 91 vertical levels and a horizontal resolution of 1  1 globally and 0.2  0.2 resolution within Central Europe (4.0 E to 16 E, 39.0 N to 51.0 N). This nested highresolution grid improves the representation of transport in particular over mountainous terrain, increasing the quality of the simulations for Jungfraujoch and Monte Cimone.11,31 Following the approach of ref 32, the particle release heights of the two high-altitude stations Jungfraujoch and Monte Cimone were set to 3000 and 2000 m asl, respectively. These heights were determined on the basis of a comparison of specific humidity measurements at these sites with vertical profiles acquired from routinely launched soundings in Payerne, Switzerland, and Milano, Italy, respectively, showing the best agreement around the chosen heights. Inversion Method. A Bayesian optimization technique was employed to estimate the spatial emission pattern over the area influencing the four measurement sites (see the Supporting Information, Figure S1). It finds the optimal solution to the following system of linear equations:10

’ MATERIALS AND METHODS


1 T
1 ðHT σ
1 z H þ σ prior Þðx post
x prior Þ ¼ H σ z ðz
Hx post Þ

Hungarian Measurement Site. Observations were conduc-

ted between April 2009 and October 2009 at K-Puszta (46580 N, 19330 E, 125 m above sea level (asl)), a regional air pollution background monitoring site located in a moderately populated area approximately 70 km southeast of Budapest (Hungary).26 Being part of the Global Atmospheric Watch (GAW) network and the European Monitoring and Evaluation Programme (EMEP), meteorological data including air temperature (2 m above the surface), surface pressure, and wind speed and direction (at a height of 9.4 m) are measured every hour by the Hungarian Meteorological Service.27 Analytical Technique. In situ measurements of nine principal halocarbons were performed by a gas chromatograph/mass spectrometer (Agilent 6890/5973) coupled to an adsorption
desorption system (ADS), identical to those systems formerly used in the Advanced Global Atmospheric Gases Experiment (AGAGE) network.28 Air samples were taken every 2 h at a height of 9.4 m above ground. To detect and correct for drift in detector sensitivity, every 11th sample was taken from a real-air calibration standard. Concentrations are reported as dry air mole fraction (parts per trillion, ppt) on the SIO-2007 calibration scale,29 and measurement precision is estimated to be 10% for CFCs, 5% for HCFCs and Halon 1211, and 3% for HFCs. Continuous European Measurement Sites. To further constrain European emissions, the simultaneous measurements from the measurement sites Jungfraujoch (Switzerland; 46330 N, 7590 E, 3580 m asl), Mace Head (Ireland; 53200 N, 9540 W, 15 m asl), and Monte Cimone (Italy; 44120 N, 10420 E, 2165 m asl) were added to the inversion system. The inclusion of these additional measurements not only significantly increases the

where xprior and xpost are the prior and posterior emissions state vectors, respectively, the matrix operator H denotes the SRR as determined by FLEXPART, z denotes the observations, and σprior and σz are the emissions and model-data uncertainties, respectively. For the HFCs, the a priori emissions were compiled from the emission data reported by individual countries to the UNFCCC (http://unfccc.int). Within countries, spatial differences were derived in proportion to population density.33 For the ODSs, we used global and regional emission data together with assumptions on the share of these emissions among the individual countries, again disaggregating these values by population density (see the Supporting Information, Table S1). Uncertainties in the diagonal elements of σprior were defined similarly to those in ref 10, namely, as σi,iprior = max(pxi, pxsurface), with xsurface being the average land surface emissions and p the uncertainty factor. The latter was set to 3 for the HCFCs and CFCs, ensuring that the overall a priori emission uncertainty becomes 50
100% (the exact number depends on the spatial distribution of the emissions), which is a realistic assumption for these compounds.10,14,21,34 The emission numbers compiled from the UNFCCC data are expected to be more accurate, and for the HFCs p was therefore set to 1, resulting in an aggregated uncertainty of 20
30%.9,10,35 The spatial correlation of the emissions was considered by adding a correlation length parameter σi,jprior = exp[
d(i,j)/L] to the nondiagonal elements of σprior, where d(i,j) is the distance between the midpoints of the inversion grid cells i and j and L is 218

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Environmental Science & Technology the spatial correlation length scale. On the basis of results from similar studies, L was set to 400 km.31,36 The model-data uncertainty σz comprises errors in the measurements and the transport model and was determined by iteratively fitting the model-observation residuals to a normal distribution.10 As the SRRs only capture the exposure of the air particles to emissions within the past 5 days, the (large-scale) background signal needs to be superimposed to the model results. For that, the weekly background concentrations were considered as part of the state vector x, with the a priori value derived from a nonparametric method that statistically determines baseline concentrations.37 Note that this procedure introduces a slight dependency of x prior on the observations. The corresponding uncertainties in σprior were therefore generously set to the variance of the a priori background values of the past 7 days, minimizing this dependency. Inversion Grid. The inversion grid consists of cells of variable horizontal resolution of 0.4, 0.8, or 1.6, with each of them contributing at least 16 times (i.e., 2 days in total) with more than 1000 s m3 kg
1 at one of the sites. This definition ensures that each grid box has a discernible effect on one of the sites for more than only one emission event, which could bias the results. Since halocarbon emissions predominantly occur over land, only those cells were included which are covered by land masses by at least 5%. We checked the sensitivity of the inversion to these settings by repeating the calculations with grid thresholds of at least 1 day at 500 s m3 kg
1 and 3 days at 2000 s m3 kg
1, respectively, as well as by including sea cells in the inversion grid. In all cases, only small differences of less than 10% were found compared to the original solution. Settings for K-Puszta. One basic assumption of the inversion is that atmospheric advection and mixing is well reproduced by the transport model and that the air masses are well mixed when they arrive at the measurement site, so that any potential diurnal emission variations are removed. These conditions were found to be not fulfilled at K-Puszta during nighttime, when strong outgoing surface radiation induces the formation of a shallow and persistent stable boundary layer.26 This process is not adequately reproduced by the transport model, and we therefore considered only the afternoon data (12:00 to 18:00 local time) from KPuszta, when the air masses are well mixed26 and air transport is well captured by FLEXPART. This decreases the number of observations from K-Puszta, but it does not introduce a systematic bias as would be the case when considering all data points. A further difficulty arose for HFC-134a and HFC-125, which were found to be employed in some of the cooling systems at the station, resulting in very large concentration variability at K-Puszta (Figure 1). These local emission sources tend to falsify the inversion results, as the algorithm in vain attempts to adjust for the strong local emissions which are not represented in the a priori field. This is reflected in the poor reproduction of the K-Puszta time series when using the original inversion settings (Supporting Information, Table S2). We therefore increased the uncertainty of the grid cell containing the K-Puszta station by a factor of 10, allowing the inversion to reliably adjust for these local emissions. This modification has only very little influence on the estimated emission distribution more distant (>500 km) from the K-Puszta site, and it leads to a significant reduction in the overall posterior model-data mismatch (Supporting Information, Table S2).

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Figure 1. Atmospheric observations of the halocarbons CFC-12, CFC-11, Halon 1211, HCFC-141b, HCFC-142b, HCFC-22, HFC-125, HFC-134a, and HFC-152a at K-Puszta (red) and Monte Cimone (gray) between March and October 2009. For K-Puszta, only the daytime measurements are shown (12:00 to 18:00).

Uncertainty of Results. The standard deviations of the optimized emissions were calculated as38

σ post ¼ ðHT σ z
1 H þ σprior
1 Þ
1 Additionally, we repeated the inversion by independently setting the a priori emissions and/or uncertainties to 50%, 100%, or 200% of its original value. The solution space of these results is expected to capture the uncertainties associated with the choice of the a priori definitions, and we adopted the most conservative estimate from either the analytical solution or the sensitivity studies as our estimate of the emissions’ standard deviation. As expected, the results become most uncertain where the constraint on emissions is weakest, namely, in the East, Southeast, and Southwest (Supporting Information, Figure S1). The uncertainties are particularly large in the East, where the results for some compounds such as CFC-11 and CFC-12 show a significant dependency on the a priori definitions. On the other hand, little sensitivity on the a priori settings was found for those areas with the highest particle residence times (Austria, Germany, northern Italy, Ireland, Slovenia, and Switzerland), and our results are therefore most accurate there. Our estimates provide the mean emission pattern between April 2009 and October 2009. As emissions of long-lived halocarbons show only small seasonal variations of a maximum of 20%,39,40 our results are considered to be representative of the entire year. This is supported by the fact that, for the three continuous sites, the inversion results based on the entire 2009 data deviate by a maximum of 25% (3% on average) compared with those from the more limited time period used here.

’ RESULTS Figure 1 shows the K-Puszta observations of all nine halocarbons. For all compounds, the determined background values are within 10% of the background observed at Monte Cimone, 219

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Figure 2. A priori and a posteriori (optimized) emission fields for HFC-152a as determined without (left) and with (right) the K-Puszta data. Also shown are the respective inversion uncertainty reductions and the total calculated footprint residence times.

where a nearly identical instrument is installed, lending substantial credibility to our measurements. Except for the locally polluted HFC-125 and HFC-134a, the concentration variability at K-Puszta is comparable to those at the three other sites (Supporting Information, Table S2), reflecting the fairly remote character of this site and supporting the proposal that the K-Puszta station is well suited for allocating the sources of Central and Eastern European halocarbon emissions. Inversion Performance. As exemplarily shown for HFC-152a in the Supporting Information, Figure S2, the posterior modelpredicted concentrations follow the observations much better than the prior modeled concentrations. This is also reflected by the fact that, on average, the correlations of the optimized predicted concentrations with the observations are increased by Δr2 = 0.15 as compared to those of the a priori predictions (Supporting Information, Table S2). This is comparable to the results of similar studies10,20,21 and suggests a good inversion performance. The overall best agreement is found for Mace Head (average r2 = 0.59), followed by K-Puszta (r2 = 0.44), Monte Cimone (r2 = 0.36), and Jungfraujoch (r2 = 0.31). This reflects the fact that, for Mace Head, the distinct change between

advection of clean marine air and advection of polluted European air is reproduced well in the model, whereas the inversion performance becomes somewhat reduced at the other sites owing to the more complex emission pattern. The average reductions in the normalized root-mean-square error (NRMSE) range from 12% at Monte Cimone to 22% at K-Puszta, which is again comparable to those of other studies, and which indicates that all four measurement sites have a similar influence on the results. Emission Maps. The inversely determined emission field of HFC-152a is exemplarily shown in Figure 2, and the emission maps of all investigated compounds are provided in Figures S3
S5 of the Supporting Information. A summary of the results is presented in Table 1. To facilitate interpretation, we grouped the emissions into the eight geographical regions central west, central north, northwest, central south, southeast, northeast, east, and southwest (see Table 1 and Figure 3). Note that, for these regional estimates, an additional uncertainty arises from the fact that the emission attribution is difficult for grid boxes belonging to more than one region (for example, at the border of central west and southwest). This problem is determined by the grid 220

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Table 1. European Halocarbon Emissions (Mg/y) in 2009 CFC-11 (CCl3F)

CFC-12 (CCl2F2)

Halon 1211 (CBrClF2)

HCFC-141b (CH3CFCl2)

HCFC-142b (CH3CF2Cl)

(GWP = 4750)

(GWP = 10900)

(GWP = 1890)

(GWP = 725)

(GWP = 2310)

prior

post

prior

a

post

prior

post

prior

post

prior

post

central west 612 1025 (865
1180)

519 431 (263
598)

67 26 (15
38)

335

234 (140
329)

247

556 (460
647)

central north 685 697 (550
844)

581 388 (241
535)

75 39 (28
51)

369

184 (146
221)

265

154 (101
207)

northwest

506 336 (265
408)

429 177 (121
233)

55 58 (48
69)

272

122 (92
153)

200

44 (13
75)

central south 609 804 (641
966)

517 517 (334
699)

66 52 (39
66)

326

361 (223
506)

243

276 (233
320)

southeast

555 344 (106
583)

471 226 (32
420)

62 53 (25
108)

306

466 (273
671)

212

202 (149
255)

northeast

453 488 (345
631)

384 135 (30
240)

49 54 (40
69)

244

47 (20
89)

180

41 (22
60)

east southwest

420 165 (41
289) 426 323 (113
534)

356 108 (11
205) 362 195 (0
502)

50 50 (13
88) 46 35 (7
64)

250 198

184 (59
311) 290 (114
465)

184 168

86 (37
135) 59 (0
122)

total

4270 4180 (2930
5440) 3620 2180 (1030
3430) 470 370 (210
550)

prior

2300

1890 (1070
2740)

1700

HCFC-22 (CHClF2)

HFC-125 (CHF2CF3)

HFC-134a (CH2FCF3)

HFC-152a (CH3CHF2)

(GWP = 1810)

(GWP = 3500)

(GWP = 1430)

(GWP = 124)

post

prior

post

1180 562 (422
798)

prior

post

prior

1420 (1010
1820)

post

central west

2260 2720 (1950
3490)

central north

2420 1330 (762
1900)

northwest

1830 1080 (768
1380)

804 639 (546
805)

4240 2340 (1980
2700)

122

100 (77
122)

58.7

central south southeast

2230 2590 (1990
3470) 1910 1760 (1110
3140)

1140 862 (743
1210) 160 632 (372
948)

3060 3140 (2680
4240) 2840 3600 (2350
6140)

132 356

504 (406
546) 1160 (715
1570)

64.1 75.2

210

264 (219
308)

858 873 (727
1060)

7040 2480 (1850
3120)

717

186 (130
242)

5670 4030 (3420
4650)

412

412 (351
473)

population (million)

northeast

1640 746 (399
1030)

136 499 (398
675)

3350 2980 (2330
3640)

east

1520 734 (45
1970)

12 406 (216
596)

241 1210 (363
2540)

342 1110 (731
1710)

3030 2490 (1560
4250)

southwest total

1540 2480 (1350
3990)

0.4 53 (24
83) 355

15350 13440 (8390
20400) 5580 5580 (4150
7810) 29600 22300 (16500
31300) 2300

173 (71
274) 2850 (1990
3620)

71.6 102

55.9 40.2 39.9 508

a

Emissions are grouped as follows: central west (Belgium, France, and Luxembourg), central north (Denmark, Germany, and The Netherlands), northwest (Ireland and the United Kingdom), central south (Austria, Italy, and Switzerland), southeast (Albania, Bulgaria, parts of Greece, Hungary, Romania, and former Yugoslavia), northeast (Czech Republic, Poland, and Slovakia), east (Belarus, Latvia, Lithuania, Moldova, and the western part of the Ukraine), and southwest (Portugal and Spain).

resolution and is not related to the inversion algorithm, and no attempt was made here to adjust for these potential uncertainties. Chlorofluorocarbons. CFC-11 and CFC-12 have been extensively used as aerosol propellants, foam blowing agents, and refrigerants41 and have the highest background concentrations of all measured halocarbons. At all four measurement sites, the concentration fluctuations are less than 6%, and total emissions for the study area are estimated at 4.2 (2.9
5.4) Gg/y (CFC-11) and 2.2 (1.0
3.4) Gg/y (CFC-12). For both compounds, the highest emissions are obtained for central west, central north, and central south (Table 1 and Supporting Information, Figure S3). Halon 1211. The usage of Halon 1211 is nowadays restricted to a few specialized applications such as fire suppression in airplanes, and only small variations of less than 2% relative to the background are observed in the time series. As a consequence, only small emissions are determined, ranging between 26 (15
38) Mg/y in the central west and 54 (40
69) Mg/y in the northeast. The only site with some concentration variability is K-Puszta, where values occasionally rise above more than 20% of the observed background value (Figure 1). These events are mostly associated with air transport from the northeast, resulting in the highest emissions from these areas (Supporting Information, Figure S3). Hydrochlorofluorocarbons. HCFC-22 has been widely used as a refrigerant, a foam blowing agent, and a feedstock for polymer production.42 Our top-down estimate of European emissions

amounts to 13.4 (8.4
20.4) Gg/y. The inferred emissions are highest for the central west and central south (SI Figure 4), as was already found in a previous study for the years 2005 and 2006 using a very similar inversion method.10 However, our estimates for the central west and northwest are 30% (11
51%) and 49% (26
61%), respectively, lower than the values reported there, suggesting a considerable emission decrease within the past few years in these regions. HCFC-142b has been primarily employed as a foam blowing agent and as a replacement compound for CFC-12,14 and its total emissions are estimated at 1.4 (1.0
1.8) Gg/y, with a remarkably high fraction of 69% (55
82%) attributed to the central north, central south, and central west (Table 1). The total estimated emissions of HCFC-141b, which has been mainly used as a foam blowing agent in place of CFC-11,14 amount to 1.9 (1.1
2.7) Gg/y, with 60% (33
88%) of the emissions concentrated in Southern Europe. Hydrofluorocarbons. HFCs have become the halocarbon of choice over the past few years as they have no direct effect on stratospheric ozone depletion. This becomes apparent from the large concentration variability above the background observed for these compounds, in particular for HFC-125 and HFC-134a. Excluding the locally polluted emissions in the K-Puszta grid box, total European emissions are estimated at 22.3 (16.5
31.3) Gg/ y for HFC-134a and 5.6 (4.2
7.8) Gg/y for HFC-125, which is within 25% of the aggregated UNFCCC data (Table 1). 221

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individually on the basis of population data.33 All emissions are weighted by their GWPs, allowing for a direct comparison of the climatic influence of the investigated halocarbons. As shown in Figure 3, our estimated total emissions range between 177 (93
329) kg of CO2 equiv/y per capita for the east and 402 (277
640) kg of CO2 equiv/y per capita for the southwest. In all regions except the central west and central south, the HFCs have the largest share of total halocarbon emissions with an average contribution of 41% (31
52%), supporting the leading role of this compound class in the European halocarbon mix. This is especially true as the HFC fractions derived here are likely to provide a lower estimate given that some important HFCs, including HFC-23 and HFC-143a, are not considered in this study, while contributions of other HCFCs and CFCs can be assumed to be negligible.5,25 Aggregated HFC emissions range between 77 (63
99) kg of CO2 equiv/y per capita in the central west and 187 (1427
302) kg of CO2 equiv/y per capita in the southwest. Due to the comparatively low GWP of HFC-152a of 124, this compound accounts for only 0.2
5% of these emissions. Among the various regions, the derived posterior emissions typically agree within 60%—despite large differences in the a priori values. This result is conceivable given that HFC-125 and HFC-134a are nowadays employed in virtually all mobile and stationary air conditioners and a comparable usage of these systems can be expected for the study region. The relative contribution of CFC-11 and CFC-12 to total emissions varies largely across Europe, ranging from 23% (1.5
45%) in the southwest to 45% (36
55%) in the central west, with an average of 35% (27
43%). For both CFCs, an east to west emission gradient is derived, with more than twice as high emissions in the central west (134 (107
162) kg of CO2 equiv/y per capita) and central south (149 (116
182) kg of CO2 equiv/y per capita) compared to Eastern Europe, where emissions average 60 (29
91) kg of CO2 equiv/y per capita. This result suggests a less widespread former usage of CFCs in Eastern and Southeastern Europe, which is possibly attributable to a delayed technological development in these regions relative to Western Europe. Similar considerations also apply for the HCFCs, which make up between 13% (7
17%) in the northeast and 30% (23
37%) in the central west of the total CO2 equivalent halocarbon emissions. Following the pattern of HCFC-22—which dominates HCFC emissions by 85% (80
90%)—the per capita emissions are highest in Western and Southwestern Europe (90
120 kg of CO2 equiv/y per capita), while only moderate emissions of 28
55 kg of CO2 equiv/y per capita are found in the other regions. Results in an International Context. We estimate the total halocarbon emissions over the study region at 125 (106
150) Tg of CO2 equiv for the year 2009 (Table 2). Extrapolating the most recently reported global emission trends5 to 2009, this value corresponds to 6% (5
7%) of the estimated 2009 worldwide emissions of the same compounds (2140 Tg of CO2 equiv; see Table 2 and the Supporting Information, Table S3). However, the share of global emissions varies significantly between the individual species. For instance, our derived HFC-125 emissions of 19.5 (14.5
27.3) Tg of CO2 equiv are 23% (17
33%) of the extrapolated 2009 global emissions (83.3 Tg of CO2 equiv), implying that Europe plays a key role in the global budget of HFC-125. On the other hand, contributions of only 3
6% are determined for the CFCs and HCFCs, reflecting the successful replacement of these compounds in Europe (Tables 2 and S3).

Figure 3. Average per capita halocarbon emissions per region in 2009, weighted by their GWPs. Numbers below the bars indicate total aggregated emissions in kilograms of CO2 equivalents per capita and year.

However, our results suggest a different spatial distribution of these emissions compared to the UNFCCC data, with on one hand significantly higher (up to 10 times more) emissions attributed to some Eastern European countries such as Romania (for HFC-134a) and Poland (HFC-125), where none or only very low, but unrealistic emissions are reported. For the central west, on the other hand, our estimates are less than half of the respective inventories. HFC-152a has primarily been used as a foam blowing agent. Over the past few years, reported HFC-152a emissions markedly decreased, which potentially can be attributed to the industrial replacement of this compound by halocarbons with even lower GWPs.43 While our top-down estimate of European emissions of 2.9 (2.0
3.6) Gg/y is within 24% (0
57%) of the aggregated UNFCCC emissions, significant inconsistencies are found over the southeast and central south (Table 1). Our aggregated emissions over Western Europe are only 25% (19
33%) below the estimates for the years 2005 and 2006,10 not supporting the strong emission decrease of HFC-152a reported to the UNFCCC.

’ DISCUSSION Comparison with U.K. Met Office Estimates. Annual halocarbon emissions from the United Kingdom and Ireland (northwest) and Northwestern Europe (NW EU: central west, central north, and northwest) are routinely derived by the U.K. Met Office using a different inversion technique based on simulations with the numerical atmospheric-dispersion modeling environment (NAME) model and using Mace Head measurements only.25 As shown in Table 2, our estimates are on average 30% lower than the Met Office numbers. However, none of the obtained differences are statistically significant, and the uncertainty ranges expressed by the two methods overlap for all estimates except for CFC-12 in the northwest. Regional Emission Differences. To further assess regional differences in European halocarbon emissions, we calculated the per capita emissions for each of the eight geographical regions 222

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Table 2. Aggregated European Halocarbon Emissions (Tg of CO2 equiv/y) Compared with Those of Other Regions NW EUa 2009

United Kingdom and Ireland, 2009

Europe except Scandinavia, this study CFC-11 CFC-12 Halon 1211 HCFC-141b HCFC-142b HCFC-22 HFC-125 HFC-134a HFC-152a total a

Met Officeb

this study

Met Officeb

1.6

2.6

9.8

(1.3
1.9)

(1.9
3.3)

(8.0
11.6) (9.5
14.3)

11.9

1.9

3.5

10.9

(1.3
2.5)

(3.3
4.4)

(6.8
14.9) (10.9
21.8)

18.5 0.32

United States, global, global growth China, 2008c 2004
2006d

2008e

19.9

52.3

380

(13.9
25.8)

(42.8
71.3) (33.3
66.5)

2009, this study

52.3

23.7

66.5

(11.3
37.4)

(48.0
92.7) (0
174)

95.9

3.3 (1.6
4.9)

36.98

∼+2.2

12.0

85.47

∼+9.2

0.23

0.70

2.8

1.1

(0.17
0.30) (0.27
0.40)

(0.41
1.0)

(1.9
3.8)

(0.57
1.5)

0.089 (0.067
0.11)

0.12 (0.094
0.13)

0.4 (0.3
0.5)

1.4 (0.8
2.0)

10.9 (8.0
15.2)

0.10

0.15

1.7

1.5

3.3

20.8

(0.03
0.17)

(0.12
0.20)

(1.3
2.1)

(1.3
1.8)

(2.3
4.2)

(15.9
30.0) (5.5
21.3)

11.6

24.3

150

83.3

(15.2
36.9)

(115
197)

(38.0
125)

2.5

9.3

(1.4
2.5)

(2.2
3.1)

(6.3
12.3) (9.6
14.5)

2.2

2.8

7.3

11.6

29.5

10.9

(1.9
2.8)

(2.2
3.4)

(5.9
9.3)

(7.7
14.4)

(14.5
27.3)

(8.1
15.1)

3.3 (2.8
3.9)

4.2 (3.3
5.0)

12.7 18.6 (10.4
15.0) (14.3
24.3)

31.9 (23.6
44.7)

11.9 (8.9
15.7)

38.6 (17.2
55.8) 0.94

0.19

633.5 77

0.012

0.0095

0.09

0.4

0.67

(0.01
0.015)

(0.007
0.014)

(0.07
0.13) (0.15
0.21)

(0.2
0.5)

(0.50
0.92) (0.71
1.2)

11.4

16.1

52.3

125

327

287

(10.3
12.5)

(14.7
17.7)

(46.3
58.5) (64.7
82.8)

(106
150)

(286
385)

(177
380)

74.7


68 ∼
0.76

0.16 (0.13
0.19)

1.9

0

10.96

0.11 (0.09
0.13)

0.60 (0.52
0.70)

708.5

ratee

213.1 6.2

∼+25 6.3 +11.4 +0.37

2152

Northwestern Europe: central west, central north, and northwest. b Reference 25. c Reference 44. d Reference 19. e Reference 5.

This pattern is distinctly different from the most recent estimates from China for 2008,44 where the HCFCs were found to be the most important group with a share of 56% (45
70%) of the halocarbons investigated here, while the HFCs account for only 7.2% (5.9
8.9%) (Table 2). This can be attributed to the less rigid restriction of CFC and HCFC usage in China and hence a later transition toward the newer generation halocarbons. If Chinese emissions did not change significantly between 2008 and 2009, Chinese per capita emissions of the HCFCs are 2
4 times higher than our results for Europe, while emissions of HFC-125, HFC-134a, and HFC-152a are 4.6, 6.9, and 1.6 times lower, respectively (Supporting Information, Table S4). For the CFCs, the obtained per capita emissions are within 10% of our estimates for Europe. To compare our estimates with halocarbon emissions from the United States, we extrapolated recently reported U.S. emissions for the years 2004
200619 (Table 2) to 2009 by presuming the same relative change of individual halocarbon emissions as in Europe, yielding a total halocarbon emission rate of 265 (172
345) Tg of CO2 equiv (Supporting Information, Table S3). From that, total 2009 per capita halocarbon emissions in the United States are estimated at 851 (553
1110) kg of CO2 equiv/y (Supporting Information, Table S4). This is 3.5 (2.3
4.5) times higher than our mean estimate of 246 (144
370) kg of CO2 equiv/y per capita for Europe, suggesting a more abundant use of halocarbons in the United States compared to Europe. Benefits of Adding an Eastern European Site to the Inversion System. The results presented here provide new insights into halocarbon emissions in Europe down to the regional scale, with special attention to undersampled regions of Central and Eastern Europe. Our results point toward significant

regional differences in per capita halocarbon emissions—even for similarly developed areas. This suggests that large errors may arise from extrapolating estimated halocarbon emissions to areas where fluxes are unknown. Any additional measurement site can significantly increase the geographic extent and the quality of an inverse modeling system. For instance, when performing the inversion for HFC-152a without the K-Puszta data, the extension of the inversion domain is reduced by 13% and intriguingly high emissions of 372 (309
532) Mg/y are attributed to the now undersampled region of Poland and Eastern Europe (Figure 2). By adding the Hungarian observations, these emissions are reduced by 58% and the achieved uncertainty reductions in Eastern Europe become 50
80%, which is comparable to those of Central Europe. While the measurements at K-Puszta provide valuable information on the current fluxes, the studied time period is too short to investigate trends in Central and Eastern European halocarbon emissions. For this important task, continuous long-term measurements are required, ideally from a site located in a remote area in Hungary, Slovakia, or Southern Poland.

’ ASSOCIATED CONTENT

bS

Supporting Information. Detailed description of the procedure to determine the a priori emissions of the CFCs, HCFCs, and Halon 1211 (Table S1), measurement statistics and inversion performance (Table S2), estimates of Chinese, U.S., and global emissions for 2009 (Table S3), corresponding per capita emissions (Table S4), total footprint calculated by FLEXPART (Figure S1), comparison of the observations of HFC152a against the respective modeled a priori and a posteriori

223

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concentrations (Figure S2), and emission maps of all investigated halocarbons (Figures S3
S5). This material is available free of charge via the Internet at http://pubs.acs.org/ .

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’ AUTHOR INFORMATION Corresponding Author

*Phone: +41 58 765 42 59; fax: +41 58 765 11 22; e-mail: [email protected].

’ ACKNOWLEDGMENT The measurements at Jungfraujoch are part of the Swiss National Air Pollution Monitoring Network (NABEL) and the HALCLIM project and are supported by the Swiss Federal Office for the Environment (FOEN). We also thank the Physics Department, National University of Ireland, Galway, for making the research facilities at Mace Head available. The operation of the Mace Head station was supported by the Department of Energy and Climate Change (DECC, United Kingdom) (Contracts GA01081 and GA01103 to the University of Bristol). This work was funded by the Swiss National Science Foundation (Projects 200021-117753, 200020-125092/1, and 200021-120238). ’ REFERENCES (1) Intergovernmental Panel on Climate Change/Technology and Economic Assessment Panel (IPCC/TEAP). IPCC/TEAP Special Report on Safeguarding the Ozone Layer and the Global Climate System: Issues Related to Hydrofluorocarbons and Perfluorocarbons; Cambridge University Press: Cambridge, U.K., and New York, 2005. (2) Intergovernmental Panel on Climate Change (IPCC). IPCC Fourth Assessment Report: Climate Change 2007 (AR4): The Physical Science Basis, Summary for Policymakers; Cambridge University Press: Cambridge, U.K., and New York, 2007. (3) World Meteorological Organization (WMO). Scientific Assessment in Ozone Depletion 2010; Global Ozone Research and Monitoring Project—Report No. 52; World Meteorological Organization (WMO): Geneva, Switzerland, 2011. (4) United Nations Framework Convention on Climate Change (UNFCCC). Kyoto Protocol to the United Nations Framework Convention on Climate Change; United Nations: New York, 1998. (5) Montzka, S. A.; Reimann, S.; Engel, A.; Kr€uger, K.; O’Doherty, S.; Sturges, W. T.; Blake, D.; Dorf, M.; Fraser, P.; Froidevaux, L.; Jucks, K.; Kreher, K.; Kurylo, M. J.; Mellouki, A.; Miller, J.; Nielsen, O.-J.; Orkin, V. L.; Prinn, R. G.; Rhew, R.; Santee, M. L.; Stohl, A.; Verdonik, D. Ozone-depleting substances (ODSs) and related chemicals. Scientific Assessment of Ozone Depletion: 2010; World Meteorological Organization: Geneva, Zurich, Switzerland, 2011; Chapter 1. (6) Cunnold, D. M.; Fraser, P. J.; Weiss, R. F.; Prinn, R. G.; Simmonds, P.G.; Miller, B. R.; Alyea, F. N.; Crawford, A. J. Global trends and annual releases of CCl3F and CCl2F2 estimated from ALE/ GAGE and other measurements from July 1978 to June 1991. J. Geophys. Res., [Atmos.] 1994, 99 (D1), 1107–1126. (7) Prinn, R. G.; Weiss, R. F.; Fraser, P. J.; Simmonds, P. G.; Cunnold, D. M.; Alyea, F. N.; O’Doherty, S.; Salameh, P.; Miller, B. R.; Huang, J.; Wang, R. H. J.; Hartley, D. E.; Harth, C.; Steele, L. P.; Sturrock, G.; Midgley, P. M.; McCulloch, A. A history of chemically and radiatively important gases in air deduced from ALE/GAGE/ AGAGE. J. Geophys. Res., [Atmos.] 2000, 105 (D14), 17751–17792. (8) Hurst, D. F.; Lin, J. C.; Romashkin, P. A.; Daube, B. C.; Gerbig, C.; Matross, D. M.; Wofsy, S. C.; Hall, B. D.; Elkins, J. W. Continuing global significance of emissions of Montreal Protocol-restricted halocarbons in the USA and Canada. J. Geophys. Res., [Atmos.] 2006, 111, D15302. 224

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