Chlorine initiated oxidation studies of hydrochlorofluorocarbons: Results for HCFC-123 (CF3CHCl2) and HCFC-141b (CFCl2CH3)

Oxidation reactions of the proposed CFC substitutes HCFC-123 (CF₃CHCl₂) and HCFC-141b (CFCl₂CH₃) have been studied in the laboratory using long-path Fourier transform infrared spectroscopy. The air oxidation of the HCFCs was initiated by the photolysis of Cl₂ forming Cl atoms that abstract H atoms from the HCFC. CF₃C(O)Cl was the only carbon containing compound observed in the infrared spectrum of the products of the HCFC-123/Cl₂ irradiations and its yield was approximately one. The product data are consistent with formation of CF₃C(O)Cl by Cl elimination of the intermediate halogenated alkoxy radical CF₃CCl₂O. The Cl-initiated oxidation of HCFC-141b led to the formation of CO and C(O)FCl. The product data are consistent with a 1 : 1 relationship between C(O)FCl formed and HCFC-141b reacted. Product data were compatible with both decomposition by cleavage of the C–C bond of the radical CFCl₂CH₂O leading to the prompt generation of C(O)FCl and reaction of the radical with O₂ forming the two carbon halogenated aldehyde CFCl₂CH(O), which in the presence of Cl was likely oxidized to C(O)FCl. An approximate method was developed in which the ratio was extracted from analysis of the time evolution of HCFC-141b, C(O)FCl, and CO. The data suggest that the contributions are comparable.     

Determination of rate constants for reactions of some hydrohaloalkanes with OH radicals and their atmospheric lifetimes

Rate constants have been measured for the gas-phase reactions of hydroxyl radical with partly halogenated alkanes using the discharge-flow-EPR technique over the temperature range 298–460 K. The following Arrhenius expressions have been derived (units 10^–13 cm³ molecule^–1 s^–1): (8.1 _–1.2 ^+1.5 ) exp{–(1516±53)/T} for CHF₂Cl (HCFC-22); (10.3 _–1.5 ^+1.8 ) exp{–(1588±52)/T} for CH₂FCF₃ (HFC-134a); (11.3 _–1.6 ^+2.1 ) exp{–(918±52)/T} for CHCl₂CF₂Cl (HCFC-122); (9.2 _–2.0 ^+2.5 ) exp{–(1281±85)/T} for CHFClCF₂Cl (HCFC-123a).The atmospheric lifetimes for the substances have been estimated to be 12.6, 12.9, 1.05, and 4.8 years, respectively, and the accuracy of the estimates is discussed.     

Tropospheric degradation products of CH2FCF3 (HFC-134a)

Chlorine atom-initiated photooxidations of CH₂FCF₃ (HFC-134a) in O₂-N₂ diluent were carried out to identify the products formed from the \(CF_3 CHF\dot O\) radical reactions and to determine the product yields as a function of temperature, pressure and O₂ concentration. CF₃C(O)F and HC(O)F were the major ‘first-generation’ products observed, along with smaller yields of C(O)F₂ and, as yet, undetermined yields of CF₃OOOCF₃ and CF₃OOC(O)F. The relative importance of the two major \(CF_3 CHF\dot O\) reaction pathways, is expressed by the rate constant ratio $$k_{O_2 } /k_d = 3.2 \times 10^{ - 25} e^{(3510 \pm 470)/T} cm^3 molecule^{ - 1}$$ The decomposition reaction leading to HC(O)F and ?F₃ radical products is predicted to be the dominant pathway at the Earth's surface while mainly CF₃C(O)F formation will occur at the tropopause.     

Temperature-dependence of ultraviolet absorption cross-sections of alternative chlorofluoroethanes

The absorption cross-sections of HCFC-123 (CF₃–CHCl₂), HCFC-141b (CH₃–CFCl₂) and HCFC-142b (CH₃–CF₂Cl) are measured between 170 and 250 nm for temperatures ranging from 295 to 210 K with uncertainties between 2 and 4%. They are compared with other available determinations. Temperature effects are discussed and parametrical formulae are proposed to compute the absorption cross-section for wavelengths and temperatures useful in atmospheric modelling calculations. Photodissociation coefficients are presented and their temperature-dependence is discussed.     

Ultraviolet absorption cross-sections of chloro and chlorofluoro-methanes at stratospheric temperatures

Absorption cross-sections of nine halomethanes (CCl₄, CHCl₃, CH₂Cl₂, CH₃Cl, CFCl₃, CF₂Cl₂, CF₃Cl, CHFCl₂, and CHF₂Cl), measured between 174 and 250 nm for temperatures ranging from 225 to 295 K, are presented with uncertainties ranging from 2 to 4% and compared with previous determinations made for comparable temperature ranges.The largest temperature effect which takes place near the absorption threshold, decreases the absorption cross-section up to 50% for highly chlorinated methanes, but is negligible for molecules highly stabilized by hydrogen and/or fluorine. Extrapolated values for temperatures of aeronomical interest are presented, as well as parametrical formulas which give absorption cross-section values for given wavelength and temperature ranges.     

Ultraviolet absorption spectra of some Br-containing haloalkanes

The ultraviolet absorption cross sections were measured for CF₃Br, CF₂ClBr, CF₂Br-CF₂Br, CF₂Br₂, CHF₂Br, CHFBr-CF₃, CH₂Br-CF₃, CHClBr-CF₃ in the wavelength range 190–320 nm at 295 K. The photolysis is concluded to be the minor atmospheric sink for CHF₂Br, CHFBr-CF₃, CH₂Br-CF₃, CHClBr-CF₃.     

Reaction of OH Radicals with Acetone: Determination of the Branching Ratio for the Abstraction Pathway at 298 K and 1 Torr

We have determined the 2-oxo-propyl CH₃C(O)CH₂ (sometimes called 1-methylvinoxy or acetonyl) radical yield for the reaction of acetone with OH radical relative to the 2-oxo-propyl yields for the reactions of F- and Cl atoms with acetone using the Discharge Flow technique. The 2-oxo-propyl radical has been monitored by Laser Induced Fluorescence LIF at short reaction times in the systems: OH + acetone (R1), F + acetone (R2), and Cl + acetone (R3). From these measurements we have deduced the branching ratio for the 2-oxo-propyl radical formation in the title reaction to be in the range 0.8 R 1.     

The 1985 chlorine and fluorine inventories in the stratosphere based on ATMOS observations at 30° north latitude

The set of high-resolution infrared solar observations made with the Atmospheric Trace Molecule Spectroscopy (ATMOS)-Fourier transform spectrometer from onboard Spacelab 3 (30 April-1 May 1985) has been used to evaluate the total budgets of the odd chlorine and fluorine chemical families in the stratosphere. These budgets are based on volume mixing ratio profiles measured for HCl, HF, CH₃Cl, ClONO₂, CCl₄, CCl₂F₂, CCl₃F, CHClF₂, CF₄, COF₂, and SF₆ near 30° north latitude. When including realistic concentrations for species not measured by ATMOS, i.e., the source gases CH₃CCl₃ and C₂F₃Cl₃ below 25 km, and the reservoirs ClO, HOCl and COFCl between 15 and 40 km (five gases actually measured by other techniques), the 30° N zonal 1985 mean total mixing ratio of chlorine, Cl, was found to be equal to (2.58±0.10) ppbv (parts per billion by volume) throughout the stratosphere, with no significant decrease near the stratopause. The results for total fluorine indicate a slight, but steady, decrease of its volume mixing ratio with increasing altitude, around a mean stratospheric value of (1.15±0.12) ppbv. Both uncertainties correspond to one standard deviation. These mean springtime 1985 stratospheric budgets are commensurate with values reported for the tropospheric Cl and F concentrations in the early 1980s, when allowance is made for the growth rates of their source gases at the ground and the time required for tropospheric air to be transported into the stratosphere. The results are discussed with emphasis on conservation of fluorine and chlorine and the partitioning among source, sink, and reservoir gases throughout the stratosphere.     

Rate constants for reactions of OH radicals with some Br-containing haloalkanes

Rate constants have been measured for the gas-phase reactions of hydroxyl radical with two halons and three of their proposed substitutes and also with CHClBr-CF₃ using the discharge-flow-EPR technique over the temperature range 298–460 K. The following Arrhenius expressions have been derived (units are 10^–13 cm³ molecule^–1 s^–1): (9.3 _–0.9 ^+1.0 ) exp{–(1326±33)/T} for CHF₂Br; (7.2 _–0.6 ^+0.7 ) exp{–(1111±32)/T} for CHFBrCF₃; (8.5 _–0.8 ^+0.9 ) exp{–(1113±35)/T} for CH₂BrCF₃; (12.8 _–1.2 ^+1.5 ) exp{–(995±38)/T} for CHClBrCF₃. The rate constants at 298 K have been estimated to be <2×10^–17 cm³ molecule^–1 s^–1 for CF₃Br and CF₂Br—CF₂Br. The atmospheric lifetimes due to hydroxyl attack have been estimated to be 5.5, 3.3, 2.8, and 1.2 years for CHF₂Br, CHFBr—CF₃, CH₂Br—CF₃ and CHClBr—CF₃, respectively.     

Effect of temperature on the methyl chloride production rate in a marine phytoplankton, <Emphasis Type="Italic">Phaeodactylum tricornutum</Emphasis>

Methyl halides such as methyl chloride (CH₃Cl) are known to be important carriers of halogen from the ocean to the atmosphere, and the halogens they release into the stratosphere by photolysis catalyze ozone depletion. Marine phytoplankton have been reported as a source of CH₃Cl, but the effects of environmental temperature on the CH₃Cl production by phytoplankton have not been investigated. In this study, we investigated the effects of temperature on the production of CH₃Cl in the culture of a marine diatom, Phaeodactylum tricornutum CCMP 630, incubated at 10, 15, 20, 25, and 30 °C. CH₃Cl concentrations in cultured samples were determined using purge and trap gas chromatograph–mass spectrometry. Phytoplankton growth was monitored by measuring the chlorophyll a concentrations. CH₃Cl production was observed for several weeks at four different temperatures ranging from 10 to 25 °C. The CH₃Cl production from P. tricornutum was increased with increasing temperature from 10 to 25 °C, and the maximum production rate for CH₃Cl was 0.21~0.26 μmol (g chlorophyll a)^?1 d^?1 at 25 °C, which was several times higher than that at 10 °C (~0.03 μmol (g chlorophyll a)^?1 d^?1). The Arrhenius equation was successfully used to characterize the effects of temperature on the production rates of CH₃Cl in the culture of P. tricornutum. Our results suggest that water temperature directly affects CH₃Cl production derived from P. tricornutum and that water temperature would be a significant factor for estimating the emissions of CH₃Cl from marine environments.     

中国三氟甲烷处置运行补贴政策效果评估

三氟甲烷（HFC-23）是我国排放量最大的氢氟碳化物（HFCs）,受到《联合国气候变化框架公约》和《关于消耗臭氧层物质的蒙特利尔议定书》的管控。2015年我国出台了HFC-23运行补贴政策,支持国内企业开展HFC-23的处置。通过对2014—2018年公开减排数据的汇总分析,发现运行补贴政策的实施有效地激励了企业的减排,受补贴企业HFC-23处置率达98%。2014—2018年累计减排HFC-23约5.20万t,折合6.08亿t CO₂-eq。此外,对照国际公约未来履约义务,建议在运行补贴政策结束后尽快出台明确针对全行业的管控政策,包括定量化减排目标和统一的企业自主监测标准。     

European sources of halocarbons and nitrous oxide: Update 1986

Semi-continuous measurements of CFCl₃, CF₂Cl₂, CCl₄, CH₃CCl₃ and N₂O were made at Adrigole, Ireland as part of the Atmospheric Lifetime Experiment (ALE). Clean, baseline air from the Atlantic Ocean was measured approximately 70% of the time; pollution events from Europe, for the remainder. The two final years of ALE data from Adrogole give a five-year record from July 1978 to June 1983. This paper extends previous work on the relative enhancements of trace gases during pollution episodes and presents (1) unambiguous identification of elevated levels of N₂O concurrent with halocarbon pollution events, (2) detection of trends in emission of CH₃CCl₃, (3) discovery of seasonal variations in emission of CF₂Cl₂, CCl₄ and CH₃CCl₃, (4) characterization of typical summer and winter pollution episodes, and (5) identification of weather patterns over Europe that are associated with high concentrations of CFCs at Adrigole. Some of these results assume that CFCl₃ represents a uniform, well buffered source from the continent. The latter two results are particularly useful in the testing and calibration of three-dimensional chemical transport models. Observed enhancements are marginally consistent with estimates of halocarbon use by the chemical industry. The source of nitrous oxide correlated with halocarbons is 0.8 Tg(N)/yr from Europe alone and represents approximately 10% of the global stratospheric loss.     

Scenarios of possible changes in atmospheric temperatures and ozone concentrations due to man's activities,estimated with a one-dimensional coupled photochemical climate model

A one-dimensional coupled climate and chemistry model has been developed to estimate past and possible future changes in atmospheric temperatures and chemical composition due to human activities. The model takes into account heat flux into the oceans and uses a new tropospheric temperature lapse rate formulation. As found in other studies, we estimate that the combined greenhouse effect of CH₄, O₃, CF₂Cl₂, CFCl₃ and N₂O in the future will be about as large as that of CO₂. Our model calculates an increase in average global surface temperatures by about 0.6°C since the start of the industrial era and predicts for A.D. 2050 a twice as large additional rise. Substantial depletions of ozone in the upper stratosphere by between 25% and 55% are calculated, depending on scenario. Accompanying temperature changes are between 15°C and 25°C. Bromine compounds are found to be important, if no rigid international regulations on CFC emissions are effective. Our model may, however, concivably underestimate possible effects of CFCl₃, CF₂Cl₂, C₂F₃Cl₃ and other CFC and organic bromine emissions on lower stratospheric ozone, because it can not simulate the rapid breakdown of ozone which is now being observed worldwide. An uncertainty study regarding the photochemistry of stratospheric ozone, especially in the region below about 25 km, is included. We propose a reaction, involving excited molecular oxygen formation from ozone photolysis, as a possible solution to the problem of ozone concentrations calculated to be too low above 45 km. We also estimate that tropospheric ozone concentrations have grown strongly in the northern hemisphere since pre-industrial times and that further large increases may take place, especially if global emissions of NO_x from fossil fuel and biomass burning were to continue to increase. Growing NO_x emissions from aircraft may play an important role in ozone concentrations in the upper troposphere and low stratosphere.     

The Henry's Law Constants of the Haloacetic Acids

Henry's law constants K_H (mol kg^-1 atm^-1) have been measured between 278.15 K and 308.15 K for the following organic acids: CH₂FCOOH (ln(K_H[298.15 K]) = 11.3 ± 0.2), CH₂ClCOOH (11.59 ± 0.14), CH₂BrCOOH (11.94 ± 0.21), CHF₂COOH (10.32 ± 0.10), CHCl₂COOH (11.69 ± 0.11), CHBr₂COOH (12.33 ± 0.29), CBr₃COOH (12.61 ± 0.21), and CClF₂COOH (10.11 ± 0.12). The variation of K_H with temperature was determined for all acids except CH₂FCOOH and CBr₃COOH, with _r H° for the dissolution reaction ranging from –85.2 ± 2.6 to –57.1 ± 2.5 kJ mol^-1, meaning that their solubility is generally more sensitive to temperature than is the case for the simple carboxylic acids. The Henry's law constants show consistent trends with halogen substitution and, together with their high solubility compared to the parent (acetic) acid (ln(K_H[298.15 K]) = 8.61), present a severe test of current predictive models based upon molecular structure. The solubility of haloacetic acids and strong dissociation at normal pH mean that they will partition almost entirely into cloud and fog in the atmosphere (0.05–1.0 g H₂O m^-3), but can reside in both phases for the liquid water contents typical of aerosols (10^-5-10^-4 g H₂O m^-3).     

Methoxy formation in the reaction of CH3O2 radicals with NO

Formation of methoxy (CH₃O) radicals in the reaction (1) CH₃O₂+NOCH₃O+NO₂ at 298 K has been observed directly using time resolved LIF. The branching ratio % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeqOXdyMaae% 4qaiaabIeadaWgaaWcbaGaae4maaqabaGccaqGpbGaaeiiaiaabIca% ieqacaWF9aGaa8hiaiaa-nbicaWFGaGaeuiLdqKaai4waiaaboeaca% qGibWaaSbaaSqaaiaabodaaeqaaOGaae4taiaac2facaWFVaGaeuiL% dqKaai4waiaaboeacaqGibWaaSbaaSqaaiaabodaaeqaaOGaae4tam% aaBaaaleaacaqGYaaabeaakiaac2facaqGPaaaaa!4E31!\[\phi {\rm{CH}}_{\rm{3}} {\rm{O (}} = -- \Delta [{\rm{CH}}_{\rm{3}} {\rm{O}}]/\Delta [{\rm{CH}}_{\rm{3}} {\rm{O}}_{\rm{2}} ]{\rm{)}}\] has been determined by quantitative cw-UV-laser absorption at 257 nm of CH₃O₂ and CH₃ONO, the product of the consecutive methoxy trapping reaction (2) % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaae4qaiaabI% eadaWgaaWcbaGaae4maaqabaGccaqGpbacbeGaa83kaiaa-bcaieaa% caGFobGaa43taiaa+bcacaGFOaGaa83kaiaa+1eacaGFPaGaa4hiai% abgkziUkaabccacaqGdbGaaeisamaaBaaaleaacaqGZaaabeaakiaa% b+eacaqGGaGaaeOtaiaab+eacaqGGaGaa4hkaiaa-TcacaGFnbGaa4% xkaiaa+5cacaGFGaGaa4hiaiabeA8aMnaaBaaajqwaacqaaiaaboea% caqGibWaaSbaaKazcaiabaGaae4maaqabaqcKfaGaiaab+eaaSqaba% aaaa!55AC!\[{\rm{CH}}_{\rm{3}} {\rm{O}} + NO ( + M) \to {\rm{ CH}}_{\rm{3}} {\rm{O NO }}( + M). \phi _{{\rm{CH}}_{\rm{3}} {\rm{O}}} \] is found to be (1.0±0.2). The rate constant k ₁ is (7±2) 10^-12 cm³/molecule · s in good agreement with previous results.     

Perverse incentives under the CDM: an evaluation of HFC-23 destruction projects

The clean development mechanism (CDM) under the Kyoto Protocol allows industrialized countries to use credits from greenhouse gas (GHG) abatement projects in developing countries. A key requirement of the CDM is that the emission reductions be real, measurable and additional. This article uses data from registered projects to evaluate the extent to which these objectives are met by projects that reduce hydrofluorocarbon-23 (HFC-23) emissions in the production of hydrochlorofluorocarbon-22 (HCFC-22). The data show that HCFC-22 plants produced significantly less HFC-23 during periods when no emission credits could be claimed compared with periods when HFC-23 destruction could be credited under the CDM. Moreover, the total amount of HCFC-22 produced appears to be determined mainly by CDM rules. This suggests that the claimed emission reductions may partly not be real and that the CDM provides perverse incentives to generate more HFC-23. The accelerated phase-out of HCFCs under the Montreal Protocol on Substances that Deplete the Ozone Layer could worsen this situation. To address these issues an ambitious emission benchmark for the baseline HFC-23 emissions is proposed.     

A study of the gas-phase reaction of carbonyl fluoride with water

Ab initio molecular orbital calculations are carried out to determine the mechanism and energetics of the homogeneous reaction of carbonyl fluoride, CF₂O, with water, H₂O. The reaction is found to proceed through two chemically activated intermediates: CF₂(OH)₂ and FC(O)OH. These intermediates in the CF₂O+H₂O reaction are suggested to be transient. The CF₂(OH)₂ dissociates to form FC(O)OH and HF, and the FC(O)OH subsequently dissociates to form CO₂ and HF. The net reaction is CF₂O+H₂O 2HF+CO₂     

Emission estimates of methyl chloride from industrial sources in China based on high frequency atmospheric observations

Methyl Chloride (CH₃Cl) is a chlorine-containing trace gas in the atmosphere contributing significantly to stratospheric ozone depletion (Carpenter et al. 2014). In the global CH₃Cl budget, the atmospheric CH₃Cl emissions is predominantly maintained by natural sources, of which magnitudes have been relatively well-constrained. However, significant uncertainties still remain in the CH₃Cl emission strengths from anthropogenic sources. High-frequency and high-precision in situ measurements of atmospheric CH₃Cl concentrations obtained since 2008 at Gosan station (a remote background site in the East Asia) reveal significant pollution events superimposed on the seasonally varying regional background levels. Back trajectory statistics showed that air masses corresponding to the observed CH₃Cl enhancement largely originated from regions of intensive industrial activities in China. Based on an inter-species correlation method, estimates of CH₃Cl emissions from manufacturing industries including coal combustion, use of feedstocks, or process agents in chemical production for China (2008–2012) are 297 ± 71 Gg yr.^?1 in 2008 to 480 ± 99 Gg yr.^?1 in 2009, followed by a gradual decrease of about 25% between 2009 and 2012 (398 ± 92 Gg yr.^?1 for 2010; 286 ± 68 Gg yr.^?1 for 2011; 358 ± 92 Gg yr.^?1 for 2012). The annual average of industrial CH₃Cl emissions for 2008–2012 (363 ± 85 Gg yr.^?1) in China is comparable to the known total global anthropogenic CH₃Cl emissions accounting only for coal combustion and indoor biofuel use. This may suggest that unless emissions from the chemical industry are accounted for, global anthropogenic emissions of CH₃Cl have been substantially underestimated. In particular, since industrial production and use of CH₃Cl have not been regulated under the Montreal Protocol (MP) or its successor amendments, continuous monitoring of Chinese CH₃Cl outflow is important to properly evaluate its anthropogenic emissions.     

Numerical integration errors in calculated tropospheric photodissociation rate coefficients

Tropospheric photodissociation rate coefficients (J values) were calculated for NO₂, O₃, HNO₂, CH₂O, and CH₃CHO using high spectral resolution (0.1 mm wavelength increments), and compared to the J values obtained with numerically degraded resolution (=1, 2, 4, 6, 8, and 10 nm, and several commonly used nonuniform grids). Depending on the molecule, substantial errors can be introduced by the larger increments. Thus for =10 nm, errors are less than 1% for NO₂, less than 2% for HNO₂, +6.5% to -16% for CH₂O, -6.9% to +24% for CH₃CHO, and -24% to +110% for O₃. The errors for CH₂O arise from the fine structure of its absorption spectrum, and are prevalently negative (underestimate of J). The errors for O₃, and to a lesser extent for CH₃CHO, arise mainly from under-resolving the overlap of the molecular action spectrum and the tropospheric actinic flux in the wavelength region of stratospheric ozone attenuation. The sign of those errors depends on whether the actinic flux is averaged onto the grid before or after the radiative transfer calculation. In all cases studied, grids with 2 nm produced errors no larger than 5%.