High-frequency, in situ global observations of HCFC-22 (CHClF
The 2007 adjustment to the Montreal Protocol required the accelerated
phase-out of emissive uses of HCFCs with global production and consumption
capped in 2013 to mitigate their environmental impact as both ozone-depleting substances and important greenhouse gases. We find that this change
has coincided with a stabilisation, or moderate reduction, in global
emissions of the four HCFCs with aggregated global emissions in 2015 of
449
Hydrochlorofluorocarbons (HCFCs) were first used in the 1940s and, in the
1980s, adopted as alternatives to chlorofluorocarbons (CFCs) in some
refrigeration and air conditioning applications. Production and consumption
grew rapidly in developed countries until the mid-1990s (AFEAS, 2016).
However, because they are ozone-depleting substances (ODSs), HCFCs were
included in the 1992 Montreal Protocol amendment, with a view to eventual
phase-out of production and consumption. Subsequently the 2007 adjustments to
the Montreal Protocol required an accelerated phase-out of emissive uses of
HCFCs in both “non-Article 5” developed and “Article 5” developing
countries, with a 2004 cap on production and consumption for non-Article 5
countries and a 2013 global cap on production and consumption (UNEP, 2016a).
Historically, HCFC-22, -141b and -142b account for
A more rapid phase-out of the HCFCs should result in a marginally faster (0.1–0.2 %, 2015–2050; Harris et al., 2014) recovery of the depleted stratospheric ozone layer, with the additional benefit of mitigating climate change, since these compounds are also potent greenhouse gases (GHGs). The ozone depletion potential (ODP), global warming potential (GWP) and atmospheric lifetimes of these eight compounds are listed in Table 1.
Detailed studies of the rates of atmospheric accumulation of the HCFCs indicate periods of rapid growth, temporary slowing followed by accelerated growth (Oram et al., 1995; Simmonds et al., 1998; O'Doherty et al., 2004; Reimann et al., 2004; Derwent et al., 2007; Montzka et al., 2009; Miller et al., 2010; Saikawa et al., 2012; Fortems-Cheiney et al., 2013; Carpenter et al., 2014; Krummel et al., 2014; Rigby et al., 2014; Graziosi et al., 2015). More recently the global growth rates of HCFC-22 and HCFC-142b have slowed significantly and Montzka et al. (2015) reported that the 2007 adjustments to the Montreal Protocol had limited HCFC emissions significantly prior to the 2013 cap on global production, although the atmospheric growth rate of HCFC-141b had almost doubled between 2007 and 2012.
HFCs, which have been introduced as replacements for the HCFCs and CFCs, have grown rapidly in abundance since their introduction (Montzka et al., 1996, 2015; Oram et al., 1996; Reimann et al., 2004; O'Doherty et al., 2009, 2014; Rigby et al., 2014; Carpenter et al., 2014). As discussed by Velders et al. (2009, 2015) projected HFC emissions may make a large contribution to future climate forcing if they continue to be used in the transition away from ODSs.
In this study we focus on high-frequency atmospheric measurements (6–12 per
day) of HCFC-22, HCFC-141b, HCFC-142b and HCFC-124 and their main
replacements HFC-134a, HFC-125, HFC-143a, and HFC-32 from the five core
globally distributed Advanced Global Atmospheric Gases Experiment (AGAGE)
sites, listed in Table 2, with 10–20-year records (Prinn et al., 2000). We
have previously estimated global emissions of HFC-152a (CH
Steady-state atmospheric lifetimes (year), ozone depletion and global warming potentials (100-year time horizon) for the HCFCs and HFCs discussed in this study.
Overview of the core AGAGE sites used in this study, their coordinates and periods for which data are available.
For instrumental description see Sect. 2.2.
We combine these observations with a two-dimensional (12-box) atmospheric
chemical transport model whose circulations are based on meteorological
climatology, which has been adjusted in inverse modelling studies to provide
improved agreements with global distributions of reactive and stable trace
gases (Cunnold et al., 1983; Rigby et al., 2011). We then estimate global
emissions which we relate to the global phase-out and adoption schedules of
HCFCs and HFCs, respectively. We compare these estimated global emissions
with the quantities of HCFCs emitted based on consumption data (see
Supplement) compiled from national reports to the United Nations
Environment Programme (UNEP) for HCFCs and the United Nations Framework
Convention on Climate Change (UNFCCC) for HFCs and the
Emissions Database for Global Atmospheric Research (EDGAR v4.2;
We examine the evolution of the changing growth rates of the HCFCs with a view to determining whether the 2013 cap on their production and consumption has been reflected in an accelerated reduction in HCFC emissions. Furthermore, we examine the rapid growth rates of the HFCs and whether these reflect manufacturers of air conditioning and refrigeration equipment switching to HFC refrigerant blends with lower GWPs, as suggested by Montzka et al. (2015). For example HFC-143a with a high GWP (4800, 100-year) is a major component of refrigerant blends R-404A and R-507A. Lower-GWP blends such as R-407C and R-410A (with equal GWPs of 1923, 100-year) have been progressively introduced into existing and new refrigeration equipment (Lunt et al., 2015; Montzka et al., 2015). However, there are a significant number of other blends where there is no specific information on their usage and when they were introduced. In the Supplement we attempt to reconcile the quantities of individual HFCs released with the composition of the refrigerant blends.
HCFC-22 is used in commercial and domestic refrigeration, air conditioning, extruded polystyrene foams and as a feedstock in the manufacture of fluoropolymers. We also note the linkage between HCFC-22 and HFC-23, also a potent GHG, which is emitted during the production of HCFC-22 and has been demonstrated to be avoidable (Miller et al., 2010; Rigby et al., 2014). Therefore, further reductions in HCFC-22 production and consumption will benefit the efforts of the UNFCCC Clean Development Mechanism (CDM) to mitigate HFC-23 emissions by voluntary incineration.
HCFC-141b and HCFC-142b are primarily used as foam blowing agents; in addition, HCFC-141b is used as a solvent in electronics and precision cleaning applications; HCFC-142b is also used as an aerosol propellant and as a refrigerant. HCFC-124 has uses in specialised air conditioning equipment, refrigerant mixtures, and fire extinguishers and as a component of sterilant mixtures (Midgley and McCulloch, 1999).
HFC-134a has been used since the early 1990s in vehicle air conditioning systems and other refrigeration and air conditioning largely to replace CFC-12. Other uses include plastic foam blowing, as a cleaning solvent and as a propellant. HFC-125 and HFC-32 have been used as a 50 : 50 blend (R-410A) in residential air conditioning systems as well as in three-component blends with HFC-134a. HFC-125 has also found application as a fire suppressant agent. HFC-143a is predominantly a component of refrigerant blends used in commercial refrigeration and in some air conditioning applications (Ashford et al., 2004).
Although the HFCs make no contribution to the destruction of stratospheric ozone, as GHGs the HFC-143a, -125, -134a and -32 have global warming potentials (GWP 100-year horizon) of 4800, 3170, 1300, and 677, respectively (Myhre and Shindell, 2013). The HCFCs, in addition to their ozone depletion potentials (ODPs), listed in Table 1, are also GHGs with GWPs comparable to the HFCs. This combination of ozone depletion and climate forcing has provided the impetus for the accelerated phase-out of the HCFCs.
The data used here are compiled from in situ measurements at the five core AGAGE sites. Table 2 lists the coordinates and the time frame when the measurements of individual HCFCs and HFCs are available at each AGAGE site.
Two similar measurement technologies have been used at AGAGE stations over
time, both based on gas chromatography coupled with mass spectrometry (GC-MS)
and cryogenic sample pre-concentration techniques. The earlier instrument,
referred to as the GC-MS-ADS, incorporated an adsorption–desorption system
(ADS) based on a Peltier-cooled microtrap maintained at
The GC-MS-Medusa system is currently deployed at all AGAGE sites used in this
study (Table 2). Typically for each measurement the analytes from 2 L
of air are collected on the sample traps, and after various steps of
fractionated distillation, purifications and transfers, desorbed onto a
single main capillary chromatography column (CP-PoraBOND Q,
0.32 mm ID
The on-site quaternary standards are compared weekly to tertiary standards from the central calibration facility at the Scripps Institution of Oceanography (SIO) in order to propagate the primary calibration scales and to characterise any potential long-term drift of the measured compounds in the quaternary standards. Importantly, all of the stations report HCFC and HFC measurements relative to the SIO (SIO-05, SIO-07 and SIO-14) and University of Bristol (UB-98) calibration scales.
The GC-MS-Medusa measurement precisions for the four HCFCs and four HFCs are determined as the precisions of replicate measurements of the quaternary standards over twice the time interval as for sample-standard comparisons (Miller et al., 2008). Accordingly, they are upper-limit estimates of the precisions of the sample-standard comparisons. Typical daily precisions for each compound vary with abundance and individual instrument performance over time. Typical ranges for each compound measured between 2004 and 2016 are 0.5–1.0 ppt for HCFC-22; 0.05–0.1 ppt for HCFC-141b; 0.05–0.1 ppt for HCFC-142b; 0.03–0.06 ppt for HCFC-124; 0.15–0.3 ppt for HFC-134a; 0.03–0.06 ppt for HFC-125; 0.07–0.15 ppt for HFC-143a; and 0.04–0.2 ppt for HFC-32.
The estimated accuracies of the calibration scales for the various HCFCs and
HFCs are reported below, and more detailed discussion of the measurement
techniques and calibration procedures are reported elsewhere (Miller et al.,
2008; O'Doherty et al., 2009; Mühle et al., 2010). As noted in the
preceding section, these AGAGE HCFC and HFC measurements are reported
relative to SIO and UB primary calibration scales: SIO-05 (HCFC-22, -141b,
-142b, and HFC-134a), UB98 (HCFC-124), SIO-07 (HFC-143a, and -32), and
SIO-14 (HFC-125). SIO calibration scales are defined by suites of standard
gases prepared by diluting gravimetrically prepared analyte mixtures in
N
The absolute accuracies of these primary standard scales are difficult to assess because they are vulnerable to systematic effects that are difficult to quantify or may not even be identified. This is why the use of traceable calibration scales that are tied to a maintained set of specific calibration mixtures is of paramount importance in the measurement of atmospheric composition change. Combining known uncertainties such as measurement and propagation errors and quoted reagent purities generally yields lower uncertainties than are supported by comparisons among independent calibration scales (Hall et al., 2014). Furthermore, some systematic uncertainties may be normally distributed, while others like reagent purity are skewed in only one direction. Estimates of absolute accuracy are nevertheless needed for interpretive modelling applications, and in this work they are liberally estimated at 2 % for HCFC-22, -141b, and -142b; 10 % for HCFC-124; 1.5 % for HFC-134a; and 3 % for HFC-125, -143a, and -32.
Baseline in situ monthly mean HCFC and HFC mole fractions were calculated by excluding values enhanced by local and regional pollution influences, as identified by the iterative AGAGE pollution identification algorithm (for details see Appendix in O'Doherty et al., 2001). Briefly, baseline measurements are assumed to have Gaussian distributions around the local baseline value, and an iterative process is used to filter out the points that do not conform to this distribution. A second-order polynomial is fitted to the subset of daily minima in any 121-day period to provide a first estimate of the baseline and seasonal cycle. After subtracting this polynomial from all the observations a standard deviation and median are calculated for the residual values over the 121-day period. Values exceeding three standard deviations above the baseline are thus identified as non-baseline (polluted) and removed from further consideration. The process is repeated iteratively to identify and remove additional non-baseline values until the new and previous calculated median values agree within 0.1 %.
There are several sources of information on production and emissions of HCFCs
and HFCs, none of which, on their own, provide a complete database of global
emissions. The more geographically comprehensive source of information for
HFC emissions is provided by the parties to the UNFCCC, but only includes
Annex 1 countries (developed countries). The 2014 database covers years 1990
to 2012 and emissions are reported in Table 2(II) s1 in the Common Reporting
Format (CRF) available at
Similar emission estimates are not available for HCFCs, but using HCFC consumption data published by the Montreal Protocol Secretariat of the United Nations Environment Programme (UNEP, 2016c) we calculate HCFC emissions as described in the Supplement.
Such bottom-up emission estimates of HFCs and HCFCs are based on industry production, imports, distribution and usage data for these compounds, reported to national governments and thence to UNEP and UNFCCC. We discuss these independent emission estimates because they are helpful as a priori data constraints on our model analysis and to compare them with our observation-based top-down estimates.
To estimate global-average mole
fractions and derive growth rates, a two-dimensional model of atmospheric
chemistry and transport was employed. The AGAGE 12-box model simulates trace
gas transport in four equal mass latitudinal sections (divisions at
30–90
Based on the output from the 12-box model, into which AGAGE observations had
been assimilated, Fig. 1 illustrates the global mean mole fractions for the
four HCFCs and the four HFCs (the model output was used for “gap-filling”
purposes). To compare AGAGE HCFCs results with the recent measurements
reported by NOAA (Montzka et al., 2015), we list NOAA 2012 global mean mole
fractions (pmol mol
Illustrates the global mean mole fractions for the four HCFCs and the four HFCs discussed here (the model output was used for “gap-filling” purposes). Shading in the figure reflects the uncertainty on the mole fractions derived in the inversion and includes a contribution from random and scale-related measurement errors and modelling uncertainties (further details are provided in Rigby et al., 2014). Note that for HCFC-124, HFC-143a and HFC-32 we only use GC-MS-Medusa data for these calculations; for all others we use combined GC-MS-ADS and GC-MS-Medusa data.
Although global mean mole fractions of HCFC-22, -141b, and -142b have
increased throughout the observation period reaching 234, 24.3 and
22.4 pmol mol
Average global mean mole fraction growth rates
(pmol mol
Global HCFC emissions (Gg yr
Global mean HCFC-22 reached a maximum rate of increase of
8.2 pmol mol
The HFCs all show increasing global mean mole fractions and growth rates over
the entire period of observations. The global mean mole fractions
(pmol mol
Montzka et al. (2015) reported 2012 HFC mean mole fractions
(pmol mol
Estimated global emissions flux (Gg yr
Global HFC emissions (Gg yr
AGAGE box-model-derived global emissions (based on atmospheric data) of HCFC-22
increased from 234
These two HCFCs have exhibited several fluctuations in emissions with maxima
around 2000 of 63
Global emissions of this less abundant HCFC had a maximum in 2003 of
7.3
The combined model-derived aggregated global emissions of these four HCFCs in
2015 were 449
In contrast to the HCFCs, estimates of HFC emissions fluxes shown in
Fig. 4a–d (see Supplement for actual values) have increased over the entire
observational record, reaching maxima in 2015 of
209
UNFCCC emission estimates (UNFCCC, 2016) which are compiled only from Annex 1 countries are consistently lower than our HFC emission estimates. This same discrepancy was noted in Lunt at al. (2015) due to the fact that many developing nations are not required to report HFC emissions and reporting methods for individual HFCs are subject to substantial inaccuracies. EDGAR v4.2 inventory emissions of HFC-143a post-2000 are substantially larger than our estimates, but the other three HFCs are in reasonable agreement (within the uncertainties of our estimates). Published HFC-134a emissions estimates by Velders et al. (2009) are in close agreement with the results from this work. For HFC-32 the Velders et al. (2009) results agree within the uncertainties of our estimates with the exception of the early period from 1995–2002. Post-2012, Velders et al. (2009) HFC-125 and HFC-143a projections begin to diverge substantially from our emission estimates.
The combined AGAGE model-derived aggregated emissions from atmospheric
observations of these four HFCs in 2015 were 327
In Fig. 5, we plot individual HCFCs and HFCs in terms of CO
HCFC-141b and HCFC-142b exhibit declines in CO
Figure 6 shows the trends in CO
Each of these projections suggests a growth in HCFC emissions during this
period, whereas our observation-derived HCFC estimates show a decline. Over
this 5-year period, the accumulated difference between the top-down and
projected emissions is
Individual HCFC and HFC carbon dioxide equivalent (CO
Global emissions of HCFCs and HFCs in 2015 and a comparison of the cumulative emissions and the percentage change in emissions over two 5-year periods (2006–2010 and 2011–2015).
Aggregated HCFC and HFC emissions as CO
In Table 3, we compare the cumulative emissions of the four HCFCs and the
four HFCs over two 5-year periods, 2006–2010 and 2011–2015. From the
percentage change in emissions between the two periods we note that HCFC-141b
emissions have increased by 18 % and HCFC-22 by 1.7 %. In comparison
HCFC-142b and -124 emissions have decreased by 23 and 30 %, respectively.
Aggregating the four HCFCs we observe that there is an equal contribution of
3.9 Gt CO
Conversely, global emissions of the HFCs have grown continuously throughout
the period of observations with substantial increases between the two 5-year
periods. The largest increases in relative terms were observed for HFC-32
(143 %) and HFC-125 (92 %) with smaller increases for HFC-143a
(37 %) and HFC-134a (28 %). In terms of the aggregated HFC emissions
we see a 43 % increase representing a rise from 1.95 to
2.87 Gt CO
It is also apparent that emissions of HCFC-22 represent
Even though global production and consumption of HCFCs in Article 5 countries
was capped in 2013, these developing countries have substantially increased
their usage of HCFCs (Montzka et al., 2009) and are not required to phase-out
potentially emissive consumption fully until 2040. As noted in Fig. 2, the
HCFCs show decreasing rates of growth with HCFC-142b declining by
Although there has been a shift in developed countries (non-Article 5) from HCFCs to HFCs (Lunt et al., 2015; Montzka et al., 2015) the consumption of both HCFCs and HFCs in Article 5 countries has substantially increased, most notably in China (Wan et al., 2009; Li et al., 2011, 2014; Fang et al., 2012, 2016; Yao et al., 2012; Zhang and Wang, 2014; Su et al., 2015; Velders et al., 2015). There has been a trend in recent years to move to refrigerant blends with lower GWPs, and in Japan in 2014 residential air conditioners were switched to using HFC-32 (UNEP, 2016c).
HFC-134a, -125, -143a and -32 are the principal components of all alternative substitutes for HCFCs. In the Supplement we examine the composition of the main refrigerant blends to determine whether there is evidence for a significant use of single-component refrigerants. In general, we find that the atmospheric mole fractions of HFC-32, -125, and -143a are consistent with their release predominantly from blends.
This study confirms that the Montreal Protocol and its amendments have been
effective in slowing the atmospheric accumulation of the HCFCs. If there had
been no change in the emissions growth rate post-2010, we find that, based on
a linear projection of emissions pre-2010, there would have been an
additional 0.67
We calculate that the aggregated cumulative emissions of HCFC-22, -141b, -142b, and -124 during the most recent 5-year period (2011–2015) are only slightly larger than in the previous 5 years (2006–2010). This modest increase has most likely been driven by the emissions of HCFC-22 and -141b in Article 5 countries, offsetting the emission declines in non-Article 5 countries, suggesting that cumulative HCFCs emissions have recently stabilised. As shown in Fig. 2, the HCFC-22 growth rate has steadily declined since the introduction of the 2007 adjustment to the Montreal Protocol, yet global emissions have tended to remain approximately constant with only a modest decline in emissions post-2007 (see Fig. 5). Since we are only 2 years beyond the 2013 cap on emissive uses of HCFCs for non-Article 5 countries, it is probably too early for our current observations through 2015 to show an accelerating phase-out for all HCFCs, although HCFC-142b and -124 have both recently undergone substantial declines in global emissions.
Although global emissions of HFCs have increased throughout the course of
this study, Montzka et al. (2015) suggested that there may have been a shift
to lower GWP refrigerant blends which can account for the observed emissions.
It is also noteworthy that the two HFCs with the largest percentage changes
in emissions in recent years are HFC-125 and -32 (see Table 3), which
implies a trend towards blends containing these two refrigerants. However, we
are unable to confirm the extent to which other lower-GWP blends (e.g.,
R-410A) have been substituted for R-404A and R-507A with the possibility that
there has simply been a switch from one blend to another with similar GWPs.
In terms of CO
With regard to HFC emissions it is important to acknowledge that attempting to quantify the release of individual HFCs to the atmosphere is complicated by the continuous introduction of new blends, many of which contain hydrocarbons and lower GWP refrigerants and their substitution into older existing refrigeration equipment. This problem is further compounded by the lack of information on the actual usage of the various blends in commercial and residential refrigeration, coupled with the difficulty of quantifying emission magnitudes from the many banks and immediate release as solvents and in foam blowing applications. Nevertheless, the atmospheric mole fractions observed are consistent with emissions of HFCs in refrigerant blends, rather than substantial emissions from single component refrigerants.
We find that the increase in HFC emissions from 2010 to 2015 has been more
rapid than the linear projection of growth, shown in Fig. 6, would imply.
This may provide some insight into the relative phase-in of HFCs and
phase-out of HCFCs. Compared to this linear trend, the cumulative excess of
HFCs emissions during this period is 0.12
Finally we note that national regulations to limit HFC use are already in place in the European Union, Japan and the USA, and recently there has been an agreement to amend the Montreal Protocol to further restrict HFC use beginning in 2019 (28th meeting of the Parties to the Montreal Protocol, Kigali, Rwanda, October 2016). By including HFCs, which do not deplete ozone, into the Montreal Protocol, this has the benefit of regulating production and consumption rather than emissions as by the Kyoto Protocol.
The entire ALE/GAGE/AGAGE database comprising every
calibrated measurement including pollution events is archived on the Carbon
Dioxide Information and Analysis Center (CDIAC) at the US Department of
Energy, Oak Ridge National Laboratory (
The authors declare that they have no conflict of interest.
We specifically acknowledge the cooperation and efforts of the station operators (G. Spain, Mace Head, Ireland; R. Dickau, Trinidad Head, California; P. Sealy, Ragged Point, Barbados; NOAA officer-in-charge, Cape Matatula, American Samoa; S. Cleland, Cape Grim, Tasmania) at the core AGAGE stations and all other station managers and staff. The operation of the AGAGE stations was supported by the National Aeronautics and Space Administration (NASA, USA) (grants NAG5-12669, NNX07AE89G, NNX11AF17G and NNX16AC98G to MIT; grants NAG5-4023, NNX07AE87G, NNX07AF09G, NNX11AF15G and NNX11AF16G to SIO), the Department of the Energy and Climate Change (DECC, UK) (contract GA0201 to the University of Bristol), the National Oceanic and Atmospheric Administration (NOAA, USA) (contract RA133R09CN0062 in addition to the operations of the American Samoa station), the Commonwealth Scientific and Industrial Research Organisation (CSIRO, Australia), and the Bureau of Meteorology (Australia) and Refrigerant Reclaim Australia. M. Rigby is supported by a NERC Advanced Fellowship NE/I021365/1. We finally thank S. Montzka, G. Velders and B. Xiang for supplying actual datasets from their publications. Edited by: R. Holzinger Reviewed by: two anonymous referees