Degradation rates of CFC-11, CFC-12 and CFC-113 in anoxic shallow aquifers of Araihazar, Bangladesh

Chlorofluorocarbons CFC-11 (CCl(3)F), CFC-12 (CCl(2)F(2)), and CFC-113 (CCl(2)F-CClF(2)) are used in hydrology as transient tracers under the assumption of conservative behavior in the unsaturated and saturated soil zones. However, laboratory and field studies have shown that these compounds are not stable under anaerobic conditions. To determine the degradation rates of CFCs in a tropical environment, atmospheric air, unsaturated zone soil gas, and anoxic groundwater samples were collected in Araihazar upazila, Bangladesh. Observed CFC concentrations in both soil gas and groundwater were significantly below those expected from atmospheric levels. The CFC deficits in the unsaturated zone can be explained by gas exchange with groundwater undersaturated in CFCs. The CFC deficits observed in (3)H/(3)He dated groundwater were used to estimate degradation rates in the saturated zone. The results show that CFCs are degraded to the point where practically no (<5%) CFC-11, CFC-12, or CFC-113 remains in groundwater with (3)H/(3)He ages above 10 yr. In groundwater sampled at our site CFC-11 and CFC-12 appear to degrade at similar rates with estimated degradation rates ranging from approximately 0.25 yr(-1) to approximately 6 yr(-1). Degradation rates increased as a function of reducing conditions. This indicates that CFC dating of groundwater in regions of humid tropical climate has to be carried out with great caution.     

Decline in the concentrations of chlorofluorocarbons (CFC-11, CFC-12 and CFC-113) in an urban area of Beijing,China

During this study 352 whole air samples were collected in an urban area of Beijing between January 2005 and March 2007. The temporal variation of the concentrations of chlorofluorocarbons (CFCs: CFC-11, CFC-12, and CFC-113) in air in the Beijing urban atmosphere is presented and discussed. The weighted mean monthly values of these concentrations have been compared with the data from the north hemisphere. It has been concluded that, in the observed period of time, the mean enhancement of CFCs was relatively small, with increase of 10–15%, with respect to the global background. Change rate in concentrations of CFCs is −1.39, −1.04, and −0.16 pptv/month for CFC-11, CFC-12, and CFC-113, respectively. The tendency of the CFC concentration of the three compounds toward background values is observed to fall and indicates that limitation of emission of CFCs is taking effect, under the Montreal Protocol.     

Transport of hydrocarbons from an emplaced fuel source experiment in the vadose zone at Airbase Vaerløse, Denmark

An emplaced hydrocarbon source field experiment was conducted in the relatively homogeneous sandy geology of the vadose zone at Airbase Vaerl?se, Denmark. The source (10.2 l of NAPL) consisted of 13 hydrocarbons (n-, iso- and cyclo-alkanes and aromates) and CFC-113 as a tracer. Monitoring in the 107 soil gas probes placed out to 20 m from the centre of the source showed spreading of all the compounds in the pore air and all compounds were measured in the pore air within a few hours after source emplacement. Seven of the fourteen compounds were depleted from the source within the 1 year of monitoring. The organic vapours in the pore air migrated radially from the source. The CFC-113 concentrations seemed to be higher in the deeper soil gas probes compared with the hydrocarbons, indicating a high loss of CFC-113 to the atmosphere and the lack of degradation of CFC-113. For the first days after source emplacement, the transport of CFC-113, hexane and toluene was successfully simulated using a radial gas-phase diffusion model for the unsaturated zone. Groundwater pollution caused by the vadose zone hydrocarbon vapours was only detected in the upper 30 cm of the underlying groundwater and only during the first 3 months of the experiment. Only the most water-soluble compounds were detected in the groundwater and concentrations decreased sharply with depth (approximately one order of magnitude within 10 cm depth) to non-detect at 30 cm depth. The groundwater table varied more than 1 m within the measurement period. However that did not influence the direction of the groundwater flow. Approximately 7 months after source emplacement the groundwater table rose more than 1 m within 1 month. That did not cause additional pollution of the groundwater.     

Anaerobic transformations and bioremediation of chlorinated solvents

Chlorinated aliphatic compounds, notably the chlorinated solvents, are common contaminants in soil and groundwater at hazardous waste sites. While these compounds are often recalcitrant, under favorable conditions they can be transformed and degraded through microbially mediated processes. There is great interest in understanding the transformations that are observed at contaminated sites and in manipulating these systems to achieve remediation. An important class of transformations occurs in anaerobic environments. Many of the transformations are reductive, and many yield useful energy to specific anaerobic bacteria. They include reductive dechlorination, dehydrochlorination and dichloroelemination. Of these, reductive dechlorination is often a growth-supporting reaction, while the others may be abiological or catalyzed by biological molecules. The reactions may result in chlorinated products, but there are often reaction sequences leading to completely dechlorinated products. The behavior of carbon tetrachloride (CT), 1,1,2,2-tetrachloroethane (TeCA) and the chloroethenes, perchloroethylene (PCE) and trichloroethylene (TCE), illustrate the range of anaerobic transformations that are possible, as well as the limited transformation that often is seen in the environment. CT undergoes reductive and substitutive reactions that are catalyzed by biological molecules but do not support bacterial growth. The anaerobic degradation of TeCA, which is a major contaminant at a site near Tacoma, WA, USA, provides examples of each type of transformation, and the products formed are consistent with the chlorinated compounds that are found in groundwater extraction wells. A laboratory study, using anaerobic sludge that had been fed chlorinated compounds, a cell-free extract from the sludge, and killed controls, showed that TeCA was transformed to four products and that these were further transformed, suggesting that it might be possible to degrade TeCA to innocuous products. Reductive dechlorination of PCE and TCE has been studied in many laboratories. Studies with mixed anaerobic consortia and with several dehalogenating bacteria, including strain 195 (. Isolation of a bacterium that reductively dechlorinates tetrachloroethane to ethane. Science 276, 1568-1571) that transforms PCE to ethene, have demonstrated that reductive dechlorination supports growth of the novel bacteria that carry out the reactions. Hydrogen has been shown to be an electron donor for the bacterial dehalogenation reactions, and kinetic and thermodynamic considerations indicate that dehalogenators can compete in some, but not all, anaerobic environments, pointing to applications of in situ bioremediation and to its limitations. Selected field studies of anaerobic transformations help delineate the applications of this type of bioremediation.     

Decomposition of organohalogen compounds in municipal solid waste incineration plants. Part I: Chlorofluorocarbons

Disposal of chlorofluorocarbons in a municipal solid waste incinerator has been studied. Destruction of CFC-11 (trichloromonofluoromethane) and CFC-113 (trichlorotrifluoroethane) was found to be better than 99.9%. Neither emission limits for hydrogen chloride or hydrogen fluoride specified in the 17^th BImSchV are exceeded during CFC incineration nor could formation of toxic halogenated organic compounds like dibenzo-p-dioxins or dibenzofurans be observed.     

The use of CFC-12, CFC-11 and CH3CCl3 to trace terrestrial airborne pollutant transport by land–sea breezes

Time-series observations of the atmospheric concentrations of the halocarbons, trichlorofluorocarbon (CFC-11), dichlorofluorocarbon (CFC-12), 1,2-trichlorofluoroethane (CFC-113), methyl chloroform (CH₃CCl₃) and carbon tetrachloride (CCl₄) were conducted at a site in Lukang, in Central Taiwan between April and August 2004. Fluctuations in atmospheric concentrations of CFC-11, CFC-12 and CH₃CCl₃ were generally driven by diurnal land–sea breeze and anthropogenic activity in this area. Elevated levels of CFC-11, CFC-12, and CH₃CCl₃ frequently occurred when the air was stagnant and the prevailing seaward land breeze was dominant. Atmospheric concentrations of CFC-113 and CCl₄ were much less variable relative to CFC-11, CFC-12 and CH₃CCl₃ during the same period, indicating that emissions of these two species from anthropogenic activities were small. The time-series distributions of atmospheric levels of CFC-12, CFC-11, CH₃CCl₃ and CO were characterized as a diurnal cycle with an elevated level at night and a low level during the daytime for most of the observed periods. As CFC-12, CFC-11 and CH₃CCl₃ behave as traffic- and industry-derived airborne pollutants in the urban atmosphere, they provide as a useful tracer in the application for the study of terrestrial airborne pollutants transport across the coastal area driven by land–sea breezes in this area.     

Characteristics of chlorofluorocarbons (CFCs) emitted from a municipal waste treatment facility

The emission concentrations of several chlorofluorocarbons (CFCs) were measured from a municipal waste treatment facility (located in Seoul, Republic of Korea) to investigate the emission characteristics of CFCs in the urban environment. To this end, a total of five CFCs (CFC-10, CFC-11, CFC-20, CFC-30, and CFC-113) were analyzed by the thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) method. The results of this study indicate that the formation of CFC-11 (8.21 ± 1.68 ppb in spring) and CFC-20 (3.92 ± 3.93 ppb in spring) proceeded very actively within the facility. Moreover, CFC-113 was also found in relatively high concentrations (3.34 ± 1.31 ppb in spring) in the treatment facility. Unlike other CFCs, CFC-10 was observed mainly at ambient (and reference) locations and one point inside the treatment facility. In conclusion, emissions of some important CFCs are a prominent process, as they were measured either frequently or abundantly both in winter and spring. It is further indicated that certain CFCs (like CFC-11 and CFC-30) are subject to highly significant seasonal variations.     

Analysis of 3-year observations of CFC-11, CFC-12 and CFC-113 from a semi-rural site in China

In-situ measurements of atmospheric chlorofluorocarbons (CFCs) can be used to the assess their global and regional emissions and to check for compliance with phase-out schedules under Montreal protocol and its amendments. The atmospheric mixing ratios of CFC-11 (CCl₃F), CFC-12 (CCl₂F₂) and CFC-113 (CCl₂F–CClF₂) have been measured by an automated in-situ GC-ECDs system at the regional Chinese Global Atmosphere Watch (GAW) station Shangdianzi (SDZ), from November 2006 to October 2009. The time series for these three principal CFCs showed large episodic events and background conditions occurred for approximately 30% (CFC-11), 52% (CFC-12) and 56% (CFC-113) of the measurements. The mean background mixing ratios for CFC-11, CFC-12 and CFC-113 were 244.8 ppt (parts per trillion, 10^?12, molar) 539.6 ppt and 76.8 ppt, respectively, for 2006–2009. The enhanced CFC mixing ratios compared to AGAGE sites such as Trinidad Head (THD), US and Mace Head (MHD), Ireland suggest regional influences even during background conditions at SDZ, which is much closer to highly-populated areas. Between 2006 and 2009 background CFCs exhibited downward trends at rates of ?2.0 ppt yr^?1 for CFC-11, ?2.5 ppt yr^?1 for CFC-12 and ?0.7 ppt yr^?1 for CFC-113. De-trended 3-year average background seasonal cycles displayed small fluctuations with peak-to-trough amplitudes of 1.0 ± 0.02 ppt (0.4%) for background CFC-11, 1.3 ± 2.1 ppt (0.3%) for CFC-12 and 0.2 ± 0.4 ppt (0.3%) for CFC-113. On the other hand, during pollution periods these CFCs showed much larger seasonal cycles of 11.2 ± 10.7 ppt (5%) for CFC-11, 7.5 ± 6.5 ppt (2%) for CFC-12 and 1.0 ± 1.2 ppt (1.2%) for CFC-113, with apparent winter minima and early summer maxima. This enhancement was attributed to prevailing wind directions from urban regions in summer and to enhanced anthropogenic sources during the warm season. In general, horizontal winds from northeast showed negative contribution to atmospheric CFCs loading, whereas South Western advection (urban sector: Beijing) had positive contributions.     

The kinetics of reductive dehalogenation of a set of halogenated aliphatic hydrocarbons in anaerobic sediment slurries

Disappearance rate constants are reported for the reductive transformation of 17 halogenated aliphatic hydrocarbons in anaerobic sediment-water samples. Statistical experimental design in combination with multivariate chemical characterization of their chemical properties was used to select the compounds. Degradation followed pseudo first-order kinetics through at least two half-lives for 15 of the 17 compounds. Of all the compounds investigated, 1,2,3-trichloropropane and dichloromethane were unique in that they were dehalogenated according to zero-order kinetics. Reductive dehalogenation was the sole transformation reaction taking place.     

Enhanced reductive dechlorination of DDT in an anaerobic system of dissimilatory iron-reducing bacteria and iron oxide

The transformation of DDT was studied in an anaerobic system of dissimilatory iron-reducing bacteria (Shewanella decolorationis S12) and iron oxide (α-FeOOH). The results showed that S. decolorationis could reduce DDT into DDD, and DDT transformation rate was accelerated by the presence of α-FeOOH. DDD was observed as the primary transformation product, which was demonstrated to be transformed in the abiotic system of Fe²⁺ + α-FeOOH and the system of DIRB + α-FeOOH. The intermediates of DDMS and DBP were detected after 9 months, likely suggesting that reductive dechlorination was the main dechlorination pathway of DDT in the iron-reducing system. The enhanced reductive dechlorination of DDT was mainly due to biogenic Fe(II) sorbed on the surface of α-FeOOH, which can serve as a mediator for the transformation of DDT. This study demonstrated the important role of DIRB and iron oxide on DDT and DDD transformation under anaerobic iron-reducing environments.     

Characteristics of chlorofluorocarbons (CFCs) emitted from a municipal waste treatment facility

The emission concentrations of several chlorofluorocarbons (CFCs) were measured from a municipal waste treatment facility (located in Seoul, Republic of Korea) to investigate the emission characteristics of CFCs in the urban environment. To this end, a total of five CFCs (CFC-10, CFC-11, CFC-20, CFC-30, and CFC-113) were analyzed by the thermal desorption–gas chromatography–mass spectrometry (TD–GC–MS) method. The results of this study indicate that the formation of CFC-11 (8.21 ± 1.68 ppb in spring) and CFC-20 (3.92 ± 3.93 ppb in spring) proceeded very actively within the facility. Moreover, CFC-113 was also found in relatively high concentrations (3.34 ± 1.31 ppb in spring) in the treatment facility. Unlike other CFCs, CFC-10 was observed mainly at ambient (and reference) locations and one point inside the treatment facility. In conclusion, emissions of some important CFCs are a prominent process, as they were measured either frequently or abundantly both in winter and spring. It is further indicated that certain CFCs (like CFC-11 and CFC-30) are subject to highly significant seasonal variations.     

Fate of Terpene Compounds in Activated Sludge Wastewater Treatment Systems

ABSTRACT

Terpene-based cleaners are being widely used in industrial cleaning formulations because of their ability to replace suspected ozone-depleting chemicals such as 1,1,1-trichloroethane and 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113). Substitution of chlorinated solvents with ter-pene-based cleaners, however, is expected to result in increased discharges to wastewater from industrial operations. A pilot-scale study was conducted at the U.S. Environmental Protection Agency's (EPA) Test & Evaluation Facility in Cincinnati, OH, to quantify the fate of specific terpene compounds in the activated sludge wastewater treatment process. Biodegradation rates of terpenes were estimated from the difference between the influent terpene mass flow rates and the amounts volatilized to air, partitioned to waste sludge, and passed through the treatment process unchanged. Any chemical transformation of the terpene compounds studied was attributed to biodegradation.

Analytical methods were developed to determine ter-pene concentrations in aqueous and gaseous media. The fate of two common terpene compounds (d-limonene and terpinolene) were evaluated in three identical pilot-scale systems: (1) a system with a high target spike range (2–10 mg/L), (2) a system with a low target spike range (0.5–2 mg/L), and (3) a control system (no spike).

The study showed that the primary removal mechanism for the terpene compounds in the activated sludge process is biodegradation. Typically, greater than 90% of the mass of terpenes entering the aeration basin of the activated sludge process biodegrades to other compounds; volatilization from the reaction basin accounts for less than 10%, while loss to waste activated sludge and the secondary clarifier effluent accounts for less than 1%.     

Continuous-flow column study of reductive dehalogenation of PCE upon bioaugmentation with the Evanite enrichment culture

A continuous-flow anaerobic column experiment was conducted to evaluate the reductive dechlorination of tetrachloroethene (PCE) in Hanford aquifer material after bioaugmentation with the Evanite (EV) culture. An influent PCE concentration of 0.09 mM was transformed to vinyl chloride (VC) and ethene (ETH) within a hydraulic residence time of 1.3 days. The experimental breakthrough curves were described by the one-dimensional two-site-nonequilibrium transport model. PCE dechlorination was observed after bioaugmentation and after the lactate concentration was increased from 0.35 to 0.67 mM. At the onset of reductive dehalogenation, cis-dichloroethene (c-DCE) concentrations in the column effluent exceeded the influent PCE concentration indicating enhanced PCE desorption and transformation. When the lactate concentration was increased to 1.34 mM, c-DCE reduction to vinyl chloride (VC) and ethene (ETH) occurred. Spatial rates of PCE and VC transformation were determined in batch-incubated microcosms constructed with aquifer samples obtained from the column. PCE transformation rates were highest in the first 5 cm from the column inlet and decreased towards the column effluent. Dehalococcoides cell numbers dropped from approximately 73.5% of the total Bacterial population in the original inocula, to about 0.5% to 4% throughout the column. The results were consistent with estimates of electron donor utilization, with 4% going towards dehalogenation reactions.     

Rapid anaerobic degradation of toxaphene in sewage sludge

We studied the degradation of technical toxaphene in anaerobic sewage sludge from a municipal waste water treatment plant. Chlorobornanes, chlorocamphenes and related compounds were rapidly degraded, with degradation rates in the order of decachloro>nonachloro>octochloro>heptachloro approximately = hexachloro compounds. The half-lives of individual congeners ranged from <1 day to several days. We also studied the degradation of technical toxaphene in previously sterilized sludge (control), and found it was slower than in the anaerobic sludge. The chlorobornanes that degraded most rapidly in the non-sterilized anaerobic sludge were those with gem chloro substitution on the 6-member carbon-ring, including the toxic congeners, Toxicant A and B. Non-gem chloro substituted congeners, like the biologically persistent P26 and P50, also degraded, but less rapidly. Toxaphene degradation in sewage sludge proceeded primarily via reductive dechlorination, leading to HxSed, HpSed, TC2 and other persistent metabolites. Enantioselective determinations indicated little, if any, enantioselectivity in the formation and/or degradation of these compounds. The isomer and enantiomer profiles of the hexa-, hepta-, and octachlorobornanes are similar to those observed in sediment from the Baltic Sea, suggesting that technical toxaphene is the source of these compounds and that its composition was changed via similar anaerobic degradation pathways.     

Microbial transformation and degradation of polychlorinated biphenyls

This paper reviews the potential of microorganisms to transform polychlorinated biphenyls (PCBs). In anaerobic environments, higher chlorinated biphenyls can undergo reductive dehalogenation. Meta- and para-chlorines in PCB congeners are more susceptible to dechlorination than ortho-chlorines. Anaerobes catalyzing PCB dechlorination have not been isolated in pure culture but there is strong evidence from enrichment cultures that some Dehalococcoides spp. and other microorganisms within the Chloroflexi phylum can grow by linking the oxidation of H(2) to the reductive dechlorination of PCBs. Lower chlorinated biphenyls can be co-metabolized aerobically. Some aerobes can also grow by utilizing PCB congeners containing only one or two chlorines as sole carbon/energy source. An example is the growth of Burkholderia cepacia by transformation of 4-chlorobiphenyl to chlorobenzoates. The latter compounds are susceptible to aerobic mineralization. Higher chlorinated biphenyls therefore are potentially fully biodegradable in a sequence of reductive dechlorination followed by aerobic mineralization of the lower chlorinated products.     

Biodegradation pathways of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) by Clostridium acetobutylicum cell-free extract

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), a military high explosive, is becoming an increasingly important pollutant in the US. The cleanup of RDX-contaminated soil and groundwater has been a serious challenge due to its recalcitrance in the environment. This study was conducted to determine the biodegradation kinetics of RDX by crude cell extract of Clostridium acetobutylicum (ATCC 824), and to examine whether this bacterium will carry out reductive transformation pathways similar to the transformation of 2,4,6-trinitrotoluene (TNT), 2,4- and 2,6-dinitrotoluenes (DNTs) we have reported previously. Batch studies on the anaerobic transformation of RDX were conducted in serum bottles with U-ring-14C-RDX. RDX and its transformation products were quantified by HPLC and qualified by LC/ MS interfaced to two soft ionization techniques--an atmospheric pressure ionization and an electron spray ionization (API-ES). Results demonstrated that C. acetobutylicum is capable of transforming RDX with H2 as the electron donor. The transformation followed a zero-order kinetics and the rates increased with increasing H2. RDX was transformed into several polar intermediates that could not be separated by reverse-phase HPLC and its molecular ions were unstable under the condition of commonly used electron impact detector. Using a polar and water immiscible solvent (ethyl acetate) and the softer MS ionization techniques, mass spectroscopy detected the presence of several RDX derivatives including mononitroso-, monohydroxylamino-, mononitrosomonohydroxylamino-, monoamino-, diamino-, and triamino-compounds. The presence of hydroxylamino compounds is analogous to the transformation of TNT and DNTs we elucidated previously.     

The behaviors and fate of polycyclic aromatic hydrocarbons (PAHs) in a coking wastewater treatment plant

The occurrence, behaviors and fate of 18 PAHs were investigated in a coking wastewater treatment plant in Songshan coking plant, located in Shaoguan, Guangdong Province of China. It was found that the target compounds occurred widely in raw coking wastewater, treated effluent, sludge and gas samples. In raw coking wastewater, high molecular weight (MW) PAHs were the dominant compounds, while 3-6 ring PAHs predominated in the final effluent. The dominant compounds in gas samples were phenathrene, fluoranthene and pyrene, while they were fluoranthene, pyrene, chrysene and benzo[k]fluoranthene for sludge. The process achieved over 97% removal for all the PAHs, 47-92% of eliminations of these target compounds in liquid phase were achieved in biological stage. Different behaviors of PAHs were observed in the primary tank, anaerobic tank, aerobic tank, hydrolytic tank and coagulation tank units, while heavier and lower ones were mainly removed in anaerobic tank and aerobic tanks, respectively. Regarding the fate of PAHs, calculated fractions of mass losses for low MW PAHs due to transformation and adsorption to sludge accounted for 15-50% and 24-49%, respectively, while the rest was less than 1%. For high MW PAHs, the mass losses were mainly due to adsorption to sludge and separation with tar (contributing 56-76% and 22-39%, respectively), and the removal through transformation was less.     

Rapid reductive destruction of hazardous organic compounds by nanoscale Fe0

Fe0-mediated reductive destruction of hazardous organic compounds such as chlorinated organic compounds (COCs) and nitroaromatic compounds (NACs) in the aqueous phase is one of the latest innovative technologies. In this paper, rapid reductive degradation of COCs and NACs by synthesized nanoscale Fe0 in anaerobic batch systems was presented. The nanoscale Fe0, characterized by high specific surface area and high reactivity, rapidly transformed trichloroethylene (TCE), chloroform (CF), nitrobenzene (NB), nitrotoluene (NT), dinitrobenzene (DNB) and dinitrotoluene (DNT) under ambient conditions, which results in complete disappearance of the parent compounds from the aqueous phase within a few minutes. GC analysis reported that the main products of the dechlorination of TCE and CF were ethane and methane as well as that most of the nitro groups in NACs were reductively transformed to amine groups. These results suggest that the rapid reductive destruction by nanoscale Fe0 is potentially a viable in situ or aboveground treatment of groundwater contaminated with hazardous organic compounds including COCs and NACs.     

Vertical distributions of non-methane hydrocarbons and halocarbons in the lower troposphere over northeast China

Vertical distributions of air pollutants are crucial for understanding the key processes of atmospheric transport and for evaluating chemical transport models. In this paper, we present measurements of non-methane hydrocarbons (NMHCs) and halocarbons obtained from an intensive aircraft study over northeast (NE) China in summer 2007. Most compounds exhibited a typical negative profile of decreasing mixing ratios with increasing altitude, although the gradients differed with different species. Three regional plumes with enhanced VOC mixing ratios were discerned and characterized. An aged plume transported from the northern part of the densely populated North China Plain (NCP; i.e. Beijing–Tianjin area) showed relatively higher levels of HCFC-22, 1,2-dichloroethane (1,2-DCE) and toluene. In comparison, the plume originating from Korea had higher abundances of CFC-12, tetrachloroethene (C₂Cl₄) and methyl chloride (CH₃Cl), while regional air masses from NE China contained more abundant light alkanes. By comparing these results with the earlier PEM-West B (1994) and TRACE-P (2001) aircraft measurements, continuing declining trends were derived for methyl chloroform (CH₃CCl₃), tetrachloromethane (CCl₄) and C₂Cl₄ over the greater China–northwestern Pacific region, indicating the accomplishment of China in reducing these compounds under the Montreal protocol. However, the study also provided evidence for the continuing emissions of several halocarbons in China in 2007, such as CFCs (mainly from materials in stock) and HCFCs.