Estimated emissions of chlorofluorocarbons, hydrochlorofluorocarbons,
and hydrofluorocarbons based on an interspecies correlation
method in the Pearl River Delta region, China
Jing Wua, Xuekun Fanga, Jonathan W. Martinb, Zihan Zhaia, Shenshen Sua, Xia Hua, Jiarui Hana, Sihua Lua,
Chen Wanga, Jianbo Zhanga, Jianxin Hua,⁎
aState Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing, China
bDivision of Analytical and Environmental Toxicology, Department of Laboratory Medicine and Pathology, University of Alberta, Edmonton, AB, Canada
H I G H L I G H T S
• The bank emissions of CFCs still exist.
• The concentrations and emissions of HCFCs and HFCs have significantly increased.
• The PRD region makes a great contribution to the China's halocarbon emissions.
a b s t r a c t a r t i c l ei n f o
Received 17 July 2013
Received in revised form 19 September 2013
Accepted 22 September 2013
Available online xxxx
Editor: Xuexi Tie
Although many studies have been conducted in recent years on the emissions of chlorofluorocarbons (CFCs),
hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs) at the large regional (such as East Asia)
and national scales, relatively few studies have been conducted for cities or metropolitan areas. In this study,
mixingratios of six halocarbons were analyzed, including trichlorofluoromethane (CFC-11,CCl3F),dichlorodiflu-
oromethane (CFC-12, CCl2F2), monochlorodifluoromethane (HCFC-22, CHClF2), 1,1-dichloro-1-fluoroethane
(HCFC-141b, CH3CCl2F), 1-dichloro-1,1-fluoroethane (HCFC-142b, CH3CClF2), and 1,1,1,2-tetrafluoroethane
(HFC-134a, CH2FCF3), and their emissions were estimated based on an interspecies correlation method using
HCFC-22 as the reference species. The results showed no significant change in the regional concentration
and emission of CFC in the past 10 years, suggesting that the continuous regional emission of CFC has had no
significant effect on the CFC regional concentration in the PRD region. Concentrations and emissions of HCFCs
and HFCs are significantly higher compared to previous research in the PRD region (P b 0.05). The largest
emission was for HCFC-22, most likely due to its substitution for CFC-12 in the industrial and commercial refrig-
eration subsector, and the rapid development of the room air-conditioner and extruded polystyrene subsectors.
The PRD's ODP-weighted emissions of the target HCFCs provided 9% (7–12%) of the national emissions for the
corresponding species. The PRD's GWP-weighted emissions of the target HCFCs and HFC-134a account for 10%
tant contributions to China's total emissions.
© 2013 Elsevier B.V. All rights reserved.
Chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs),
and hydrofluorocarbons (HFCs) are all man-made chemical substances
used in many industrial and commercial fields, such as refrigeration,
foam blowing, metered dose inhalers, and fire extinguishing, as well
as solvents (Metz et al., 2005). CFCs and HCFCs are of great concern
due to their high ozone depletion potential (ODP) (Montzka et al.,
2011). Moreover, CFCs, HCFCs, and HFCs are greenhouse gases, and
HFCs are included among the Kyoto Protocol (KP) targets (Solomon
et al., 2007). Therefore, studies estimating their emissions have become
treal Protocol (MP), CFCs have been phased out on a global scale
(Montzka et al., 2011). The phase-out of HCFCs was requested to
begin in 1996 by non-Article 5 parties (mainly developed countries),
butitwasnotuntil 2013 thatArticle5parties(mainlydevelopingcoun-
tries) were requested totakeaction (UNEP, 2009).Influencedbyphase-
Science of the Total Environment 470–471 (2014) 829–834
⁎ Corresponding author at: College of Environmental Sciences and Engineering, Peking
University, No.5 Yiheyuan Road, Beijing 100871, China. Tel.: +86 10 62756593; fax: +86
E-mail address: email@example.com (J. Hu).
0048-9697/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
Contents lists available at ScienceDirect
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journal homepage: www.elsevier.com/locate/scitotenv
out progress and market demand, significant differences were found
among countries for the emissions of CFCs, HCFCs, and HFCs (Li et al.,
2011). Studying the atmospheric mixing ratios (in units of parts per
trillion volume, pptv, in this paper) and emissions of these species in a
particular country or region can help totrack theimplementation effec-
tiveness of the MP and KP, and can provide basic information for multi-
scale environmental studies and policy making.
The interspecies correlation method has been widely used in recent
years, applying aircraft monitoring or high-frequency measurements at
remotesites to estimatetheemissionsof CFCs, HCFCs,and HFCs in large
et al., 2010; Li et al., 2011; Palmer et al., 2003; Yokouchi et al., 2005,
2006). However, the observational data from a remote background
site are not suitable for estimating emissions in smaller areas using
the interspecies correlation method because distinguishing the individ-
difficult. An improved method was to use the interspecies correlation
method, but based on local atmospheric data, as shown by Shao et al.
(2011), in estimating halocarbon emissions in the Pearl River Delta
(PRD) region in 2004.
The PRD region is one of the most densely populated and highly
developed metropolitan areas in China, and also features a large manu-
facturing industry (Streets et al., 2006). Its regional air quality has been
worsened by rapid urbanization and industrialization, and halocarbon
emissions in thisareaareof specialinternational interest. Observational
studies were widely carried out when CFCs were being phased out, as
the consumption of CFCs was allowed in China until 2010 (Chan and
Chu, 2007; Chan et al., 2006; Fang et al., 2012; Guo et al., 2009; Shao
et al., 2011; Zhang et al., 2006a,b, 2010). A great deal has changed in
the past few years, but recent halocarbon emissions have not been re-
ported yet for the PRD region. In this study, 192 whole air samples
were collected in the PRD region in November 2010, and the interspe-
cies correlation method was applied to estimate the emissions of six
difluoromethane (CFC-12, CCl2F2), monochlorodifluoromethane (HCFC-
22, CHClF2), 1,1-dichloro-1-fluoroethane (HCFC-141b, CH3CCl2F),
1-dichloro-1,1-fluoroethane (HCFC-142b, CH3CClF2), and 1,1,1,2-
tetrafluoroethane (HFC-134a, CH2FCF3). This latest study will help to
track the implementation effectiveness of the MP in this region.
2.1. Sampling and analysis
The PRD region is located in southern China and consists of nine
administrative areas in Guangdong Province, with an area of about
42,000 km2(Streets et al., 2006). In this region, we selected three
sampling sites, including one urban site in Guangzhou (23.130°N,
113.260°E) and two rural sites in Heshan (22.711°N, 113.548°E) and
Wanqingsha (22.711°N, 112.927°E), respectively (Fig. 1). All three
sites were on the top of a hill or on the roof of a high building to mini-
mize the influence of any proximate emission sources. In total, 192 air
samples were collected in 3.2-L electro-polished stainless-steel canis-
ters, which had been cleaned and evacuated by a canister cleaner
(3100A; Entech, Irvine, CA, USA) before shipment to the sampling
sites. The restricted grab sampler (39-RS-x; Entech), which has a 5-μm
Silonite-coated metal particulate filter, was placed on the inlet of the
canister to completely eliminate dust and particulate intrusion during
sampling. At each sampling site, one sample was collected at 09:00
(local time) and another at 13:00 (local time) on each day between
November 9 and 29, 2010. Moreover, on 3 of these days (November
collection of an additional five to seven samples at each site.
A cryogenic pre-concentration system (7100A; Entech) was
connected with a gas chromatography/mass spectroscopy (GC/MS) sys-
tem (Saturn 2100; Varian, Palo Alto, CA, USA) to analyze the six target
J. Wu et al. / Science of the Total Environment 470–471 (2014) 829–834
halocarbons. Details on the analytical method and the associated quality
control and assurance can be found in Fang et al. (2012). In brief, after
halocarbons were effectively separated on a GC-Gaspro capillary column
(60 m × 0.32 mm), analyzed by the ion trap mass spectrometer in SIM
mode, and quantified by a multipoint external standard curve covering
odically prepared by a dynamic dilution system (4600; Entech). Primary
standards were provided by TO-14A (Spectra Gases, Branchburg, NJ,
USA) and the National Institute of Metrology of China (NIMC, Beijing,
After dilution by a factor of 1000, calibration of the NIMC standard
gas in the four parallel canisters was performed by comparison against
the standard gas reported on the AGAGE network calibration scales
SIO-2005. The specific experimental process has been described in
detail by Wu et al. (2013). Results showed that small discrepancies
were observed for HCFC-141b (3.4–7.6%), HCFC-142b (0.2–3.8%), and
HFC-134a (−1.6% to 3.1%). However, the HCFC-22 mean concentration
for four canisters was found to be 118.0% of that in the standard gas
reported on SIO-2005. Therefore, HCFC-22 concentrations of ambient
samples in this study were adjusted by dividing by a factor of 118.0%.
The correlation coefficients for the standard curves changed from
0.995 to 1.000. The measurement precision was 3% for CFCs and 6% for
HCFCs andHFC-134a.All target halocarbonsin all samples werepresent
deviationsof thetargethalocarbon mixingratios, includingbackground
data in the Northern Hemisphere (NH) provided by NOAA/ESRL (2012)
are shown in Table 1.
2.2. Emission estimation
The emission of targeted halocarbons was estimated using an inter-
species correlation method based on the idea that the enhancement
ratio of the reference species and the target species reflects the ratio of
their emission strength. This method has been widely used to estimate
the emissions of halocarbons. The observational dataset used in this
study was collected over a short enough period (within 21 days)
when nosignificantchanges could be observedforthebackgroundcon-
centration of halocarbons. In addition, emissions were calculated based
the corresponding background concentration has been subtracted
(Shao et al., 2011). Therefore, we adopted the mixing ratios rather
than the enhanced mixing ratios, without subtracting the correspond-
ing background concentrations. In this study, HCFC-22 was selected as
the reference species because of its significant statistical correlation
with other species and its high enhanced atmospheric mean mixing
ratios above background level (Fig. 2). Emission of HCFC-22 was calcu-
lated based on production and consumption data using the bottom-up
approach; see details in Supporting Information 1. HCFC-22 is used for
three subsectors in the PRD region, namely, room air-conditioners, ex-
trudedpolystyrene(XPS)foam, and industrial and commercialrefriger-
ation. The results showed that the estimated emissions from these
subsectors are 9.0, 0.3, and 1.4 Gg/year, respectively. The total HCFC-
22 emission is 10.7 (±2.8) Gg/year (2.8 Gg/year is the uncertainties of
PRD's HCFC-22 emission, see details in Supporting Information 1). The
emissions of the target halocarbons were calculated according to the
Ex¼ EHCFC‐22? X=HCFC‐22
ð Þ ? Mx=MHCFC‐22
where Eandσ areemissionand uncertainty, respectively,X is thetarget
compound, and X/HCFC-22 is the molar ratio of the target species to
HCFC-22. So the molecular mass of X and HCFC-22 (MXand MHCFC-22)
should be considered. The slope of the regression curve was calculated
using an orthogonal distance regression (ODR), which calculates the
least-residual distance between the observational data and the regres-
sion line (Barnes et al., 2003). Results of the fit are shown in Table 2
and Fig. 3, and compared to two previous studies in the PRD region.
Note that our observational data were collected in autumn only,
which might have introduced uncertainty. Kim et al. (2010) pointed
pling distribution for most halocarbons because these species are emit-
ted from industrial and commercial sources, which are expected to be
fairly constant throughout the year. Therefore, interspecies ratios do
duce that the uncertainty introduced by the single sampling season
should not be significant.
3. Results and discussion
3.1. Continued bank emissions of CFCs
icantly higher than the corresponding NH background levels (P b 0.05),
on the interspecies correlation method, the emissions of CFC-11 and
CFC-12 are estimated to be 0.9 (±0.4) and 1.6 (±0.5) Gg/year, respec-
tively (Table 2). Although China phased out the production and con-
sumption of CFCs in 2007, the residual blowing agent CFC-11 in
enclosed foam will be emitted steadily throughout its life cycle
(15 years). Similarly, the residual refrigerant CFC-12 in refrigeration
equipment, including automobile air-conditioners, refrigerators, and
freezers, will also be slowly emitted during operation and servicing
(Wan et al., 2009). Furthermore, CFCs can also be used for metered
Themeanandrelative standarddeviation(RSD)ofthe targethalocarbonmixing ratiosinthePRDregioninthis studyandpreviousstudies,togetherwiththe datameasuredin46 Chinese
cities in 2010 and the corresponding background data in the Northern hemisphere (NH) provided by NOAA/ESRL (in pptv).
Common namePRD for Nov 2010
in this study
PRD in Aug
(Guo et al., 2009)
46 Chinese cities
in Oct/Nov 2010
(Fang et al., 2012)
data in Aug
data In Oct–Nov
MeanRSD (%)MeanRSD (%)MeanRSDMeanRSD (%)MeanRSD (%)MeanRSD (%)Mean RSD (%)
aThe NOAA/ESRL data were the calculated averages of the monthly mean mixing ratios and the monthly RSDs during the sampling period, which were accessed at
ftp://ftp.cmdl.noaa.gov/hats. The monthly RSDs of HCFC-141b and HFC-134a were not provided on this Web site.
J. Wu et al. / Science of the Total Environment 470–471 (2014) 829–834
dose inhalers, an exempt usage that could bring about additional emis-
sions (SEPA, 2012).
The enhanced atmospheric mean mixing ratios above background
level can be used to examine the emission strengths of a species to
some extent. The mean enhanced mixing ratios of CFC-11 and CFC-12
in the PRD region in this study and previous studies were calculated
based on their observational data and corresponding NH background
data from Table 1. Results show that the mean enhanced atmospheric
mixing ratios of CFC-11 and CFC-12 observed in this study (26 pptv
and 59 pptv for CFC-11 and CFC-12, respectively) are comparable to
those in previous reports (see Table S1 in the Supporting Information),
changed significantly in recent years. Furthermore, all CFC data ob-
served in this study were also converted to the enhanced mixing ratios
by subtracting the corresponding NH background data (241 pptv and
531 pptv for CFC-11 and CFC-12, respectively), and a one-sample t-test
data calculated from previous studies (see Table S1 in the Supporting
Information). Results also show that the enhanced atmospheric mixing
ratios of CFC-11 and CFC-12 observed in this study are comparable to
those in previous reports (P b 0.05), further suggesting that the CFC
concentration change in the PRD region was insignificant. Our 2010 es-
timates of CFC emissions (see Table 2) are also close to the previous
two studies in 2001–2002 and in 2004 (Guo et al., 2009; Shao et al.,
2011). One could deduce that the continuous regional CFC emission in
the PRD region had no significant effect on the regional CFC concentra-
tion. Note that the emission magnitudes estimated by the interspecies
correlation method often depend on different sampling strategies
(suchassamplingtime, sampling sites, andsamplingfrequency), choice
of reference species (e.g., CO andHCFC-22), and calculation methods for
the slope of the regression curve and slope uncertainties (such as the
ODR method and Williamson–York method). Therefore, the differences
among the different estimated results could be very easily masked by
3.2. Fast-increasing emissions of HCFCs and HFC-134a
wasestimated to be 10.7 ± 2.8 Gg/year, which is much higher than the
emissions of other target halocarbons estimated by the interspecies
correlation method (see Table 2). Moreover, the mean mixing ratio of
HCFC-22 was shown to be 530 ± 156 pptv (Table 1), with a much
higher enhanced atmospheric concentration than other species (see
Table S1). Our inventory estimates indicated that the major emission
source of HCFC-22 is from room air-conditioners, accounting for 84%
of the PRD's HCFC-22 emission. The balance of HCFC-22 emissions was
14% from the industrial and commercial refrigeration subsector, and
2% from the XPS foam subsector. This was the only estimated emission
of HCFC-22 in the PRD region in 2010, and verifyingour results is there-
fore quite difficult. Based on the Chinese emissions estimated by Wan
et al. (2009), the HCFC-22 annual emission was calculated to make up
10% (8–13%) of the national HCFC-22 emissions, which is similar to
the PRD contribution to the gross domestic product (GDP; 9.4%).
HCFC-22 is mainly used in room air-conditioners, and the GDP is an
indirect index to reflect the regional purchasing power of room air-
conditioners. Therefore, the similarity in the percentage of HCFC-22
emission and GDP could verify the reliability of our estimates to some
extent. In comparison, our observational data and emission estimates
were both significantly higher than those for 2001–2002 and 2004
(P b 0.05) (Guo et al., 2009; Shao et al., 2011), in agreement with the
rapidly increasing emissions in China (Wan et al., 2009) and in good
agreement with the findings of Zhang et al. (2010). The increased
HCFC-22 emission partly derives from its effective substitution for
CFC-12 in the industrial and commercial refrigeration subsector, and
Fig. 2. Interspecies Pearson correlation coefficient (r) in the PRD region during the
sampling period. Red background denotes that correlation is significant at the 0.01 level
plot shows the mean of enhanced concentrations above NH background concentration for
is referred to the web version of this article.)
The Pearson correlation coefficient (r) and regression slope (X/HCFC-22) between HCFC-22 and other halocarbons, and emissionsof all target halocarbons from the PRD estimated inthis
study, together with the previously reported values for PRD and Chinese emissions (Gg/year). The ranges of emissions were the estimated uncertainties, calculated by using Eq. (2).
Common namePRD for 2010, in this study PRD in 2001–2002
(Guo et al., 2009)
PRD in 2004
(Shao et al., 2011)
China in 2010
(Wan et al., 2009)
a*Correlation is significant at the 0.05 level (2-tailed), **Correlation is significant at the 0.01 level (2-tailed).
bHCFC-22 emission in this study was calculated by a bottom-up method, so no r and ΔX/ΔHCFC-22 are available for HCFC-22.
142b emission. We assumed that the annual growth rate of HCFC-142b emission was the same as that of HCFC-141b (14.9%) derived from Wan et al. (2009).
dEmission of HFC-134a was calculated under the combined scenario for the mobile air-conditioners (MACs) sector (Wan et al., 2009). HFC-134a is mainly used in the MACs sector in
J. Wu et al. / Science of the Total Environment 470–471 (2014) 829–834
also results from the rapid development of the other two subsectors
The mean mixing ratios of HCFC-141b and HCFC-142b were 96 ±
38 pptv and 39 ± 13 pptv, respectively. These values are both signif-
icantly higher than the corresponding NH background values (see
Table 1). Based on the interspecies correlation method, our 2010
PRD emission estimates for HCFC-141b and HCFC-142b were 1.2 ±
0.4 Gg/year and 0.6 ± 0.1 Gg/year, respectively (see Table 2). Our esti-
mated result for HCFC-141b substantially exceeds that for 2001–2002
(Guoet al., 2009), and the increasingtrendis consistentwith the results
of Wan et al. (2009).
HFC-134a is mainly used as a refrigerant in the automobile air-
conditioner sector in China as a substitute for CFC-12 (Hu et al., 2009).
The mean mixing ratio of HFC-134a in the PRD region was 90 ±
29 pptv, significantly higher than the corresponding NH background
values (see Table 1). Based on the interspecies correlation method, our
estimates for the PRD region showed that 1.3 ± 0.2 Gg/year of HFC-
134a was emitted in 2010 (see Table 2). This is the first study on HFC-
tive substitution for CFC-12.
3.3. PRD's important contribution to China
Based on the Chinese emissions estimated by Wan et al. (2009), the
fraction of our estimated PRD emissions to national emissions was
calculated (see Table 2). Overall, the PRD emission of individual species
species, which is similar to the PRD contribution to the GDP (9.4%) and
population (4.2%), except for CFC-12. The PRD's CFC-12 emission was
a much larger fraction of the national emission, accounting for 71%
(52–91%), in line with the significantly higher concentration of CFC-12
observed in the PRD region than in 46 Chinese cities (Fang et al.,
2012). Wu et al. (2013) also observed higher CFC-12 concentration in
Guangzhou than in the other three Chinese cities. CFC-12 is mainly
used as a refrigerant for automobile air-conditioners, refrigerators, and
freezers, together with industrial and commercial refrigeration (Wan
et al., 2009). Ten years ago, when China started to phase out the
production and consumption of CFCs, the PRD region had already be-
come the manufacturing center of southern China. Its industries manu-
facture a wide variety of goods, including room air-conditioners,
refrigerators, and automobiles (Streets et al., 2006), which results in
the larger bank emission of CFC-12 in the PRD region compared with
other Chinese cities. The larger local emission is also likely due to the
higher demand for refrigeration products in the PRD region, resulting
from the higher average annual temperatures there (China Statistics
Press, 2012). Moreover, note that the fraction of CFC-12 was calculated
based on the Chinese emission estimated by Wan et al. (2009) using a
bottom-up method, which is the only available value in 2010. In com-
parison, we found that Wan et al.'s (2009) CFC-12 estimates are always
lower than other studies using top-down calculation methods in the
their 2008 estimate (3.869 Gg/year) is less than that of the other two
studies (Kim et al., 2010; Li et al., 2011), and their 2009 estimate
(3.060 Gg/year) is also lower than the estimate (7.2 ± 1.2 Gg/year) of
Fang et al. (2012). Thus, Wan et al.'s (2009) 2010 estimate may be
underestimated. That is, the actual fraction of CFC-12 may be
overestimated to some extent.
By summing the emissions of each target species multiplied by their
correspondingODPvalues or global warmingpotential (GWP, 100-year
time horizon) values (Solomon et al., 2007; see Table S2 in the
Supporting Information), the total ODP-weighted or GWP-weighted
emissions of all target halocarbons in the PRD region were calculated
to be 3.3 (2.3–4.5) Gg/year and 45.2 (33.1–58.9) Tg/year, respectively.
The PRD's ODP-weighted or GWP-weighted emissions of the target
HCFCs accounted for 9% (7–12%) and 10% (7–12%) of the national emis-
sions for the corresponding species, respectively. The GWP-weighted
emission of HFC-134a in the PRD region accounts for 8% (7–9%) of the
national HFC-134a emission. These results suggest that the PRD region
makes an important contribution to the halocarbon emissions in China.
Fig. 3. Relationship between HCFC-22 and other species in the data set. Regression lines are indicated by the solid lines. Statistical outliers were removed prior to performing the regressions.
J. Wu et al. / Science of the Total Environment 470–471 (2014) 829–834
were estimated using an interspecies correlation method. The results
show that CFC bank emissions still exist: 0.9 (±0.4) for CFC-11 and 1.6
(±0.5) Gg/year for CFC-12. This may derive from the remaining storage
in products or certain exempt usages. Also, in comparison, the deduction
was made that the continuous CFC regional emission has no significant
effect on the CFC regional concentration in the PRD region.
sions of their main substitutes, HCFCs and HFCs, in the PRD region have
increased significantly. The HCFC-22 annual emission is largest among
the target species (10.7 ± 2.8 Gg/year), making up 10% (8–13%) of
the national HCFC-22 emissions. This was followed by emissions of
HFC-134a and HCFC-141b, which accounted for 8% (7–9%) and 8%
The PRD regional emission of HCFC-142b is smallest and makes up the
smallest fraction of 5% (4–6%) of the national HCFC-142b emission.
The calculated result shows that the total ODP-weighted or GWP-
weighted emissions of all target halocarbons in the PRD region were
3.3 (2.3–4.5) Gg/year and 45.2 (33.1–58.9) Tg/year, respectively. The
halocarbon emissions from the PRD region contribute significantly to
the total emissions in China.
Conflict of interest
tion and there has been no significant financial support for this work
that could have influenced its outcome.
This work was supported by the National Natural Science Founda-
tion of China (Grant No. 41275156). We also thank all persons involved
in sampling at the three sampling sites in the PRD region.
Appendix A. Supplementary data
Supplementary data to this article can be found online at http://dx.
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