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1.
Formaldehyde (CH 2O) emissions from particleboard underlayment have been measured in 0.17 and 0.2 m 3 chambers at separate laboratories to test the comparability of small scale environmental chamber measurements under different ventilation and product loading conditions. Absolute CH 2O calibration was established through intermethod comparison of different monitoring techniques against a CH 2O generation apparatus. Interlaboratory precision was enhanced via co-calibration of each laboratory’s CH 2O colorimetric analyzer against the same blank and bi-level generation source at the beginning and end of the study. The results show excellent intermethod and interlaboratory agreement in both the CH 2O calibration and particleboard emissions testing. The CH 2O emission rates of the test specimens demonstrate a Fick’s Law dependence on CH 2O vapor concentration. Measured CH 2O concentrations are described by a single-compartment, single emitter model, and are inversely proportional to the ratio [N/L (m/h)] of the air exchange rate [ N(h -1)] and product loading [L(m -1)]. Comparison tests at varying N and L, but uniform N/L were performed; similar CH2O concentrations were measured for N and L levels selected from an indoor compartment model, and for fivefold larger N and L values, which are more convenient for small-scale chamber testing. 相似文献
2.
To investigate the impacts of major factors on carbon loss via gaseous emissions, carbon dioxide (CO 2) and methane (CH 4) emissions from the ground of open dairy lots were tested by a scale model experiment at various air temperatures (15, 25, and 35 °C), surface velocities (0.4, 0.7, 1.0, and 1.2 m sec ?1), and floor types (unpaved soil floor and brick-paved floor) in controlled laboratory conditions using the wind tunnel method. Generally, CO 2 and CH 4 emissions were significantly enhanced with the increase of air temperature and velocity ( P < 0.05). Floor type had different effects on the CO 2 and CH 4 emissions, which were also affected by air temperature and soil characteristics of the floor. Although different patterns were observed on CH 4 emission from the soil and brick floors at different air temperature-velocity combinations, statistical analysis showed no significant difference in CH 4 emissions from different floors ( P > 0.05). For CO 2, similar emissions were found from the soil and brick floors at 15 and 25 °C, whereas higher rates were detected from the brick floor at 35 °C ( P < 0.05). Results showed that CH 4 emission from the scale model was exponentially related to CO 2 flux, which might be helpful in CH 4 emission estimation from manure management. Implications: Gaseous emissions from the open lots are largely dependent on outdoor climate, floor systems, and management practices, which are quite different from those indoors. This study assessed the effects of floor types and air velocities on CO 2 and CH 4 emissions from the open dairy lots at various temperatures by a wind tunnel. It provided some valuable information for decision-making and further studies on gaseous emissions from open lots. 相似文献
3.
Abstract The persistence of two insecticidally active compounds from the neem tree, azadirachtin A and B, was determined at two different temperatures (15 and 25°C) in the laboratory after application of the commercial neem insecticide, Margosan‐O, to a sandy loam soil. The influence of microbial activity on degradation was also examined by comparing autoclaved and non‐autoclaved soils also at 15 and 25°C. Temperature influenced degradation rates. The DT 50 (time required for 50% disappearance of the initial concentration) for azadirachtin A was 43.9 and 19.8 d for non‐autoclaved soil kept at 15 and 25°C, respectively. The DT 50 for azadirachtin B was 59.2 and 20.8 d for non‐autoclaved soil kept at 15 and 25°C, respectively. Microbial activity was also responsible for faster degradation because DT 50 ’s for autoclaved soil were much longer than for non‐autoclaved soils. DT 50 ‘s for azadirachtin A in autoclaved soil were 91.2 (15°C) and 31.5 d (25°C). DT50 ’s for azadirachtin B in autoclaved soil were 115.5 (15°C) and 42.3 d (25°C). Two degradation products of azadirachtin were detected, but were not identified. Higher levels of the two degradation products were detected in non‐autoclaved soil. 相似文献
4.
This paper describes a laboratory project to assess the accuracy of emission and indoor air quality models to be used in predicting formaldehyde (HCHO) concentrations in residences due to pressed-wood products made with urea-formaldehyde bonding resins. The products tested were partlcleboard underlayment, hardwood- plywood paneling and medium-density fiberboard (mdf). The products were initially characterized in chambers by measuring their formaldehyde surface emission rates over a range of formaldehyde concentrations, air exchange rates and two combinations of temperature and relative humidity (23° C and 5 0% RH; 26°C and 60% RH). They were then installed in a two-room prototype house in three different combinations (underlayment flooring only; underlayment flooring and paneling; and underlayment flooring, paneling, and mdf). The equilibrium formaldehyde concentrations were monitored as a function of air exchange rate. Particleboard underlayment and mdf, but not paneling, behaved as the emission model predicted over a large concentration range, under both sets of temperature and relative humidity. Good agreement was also obtained between measured formaldehyde concentrations and those predicted by a mass-balance indoor air quality model. 相似文献
5.
Rate coefficients for the gas-phase reactions of Cl atoms with a series of unsaturated esters CH 2C(CH 3)C(O)OCH 3 (MMA), CH 2CHC(O)OCH 3 (MAC) and CH 2C(CH 3)C(O)O(CH 2) 3CH 3 (BMA) have been measured as a function of temperature by the relative technique in an environmental chamber with in situ FTIR detection of reactants. The rate coefficients obtained at 298 K in one atmosphere of nitrogen or synthetic air using propene, isobutene and 1,3-butadiene as reference hydrocarbons were (in units of 10 ?10 cm 3 molecule ?1 s ?1) as follows: k(Cl+MMA) = 2.82 ± 0.93, k(Cl+MAC) = 2.04 ± 0.54 and k(Cl+BMA) = 3.60 ± 0.87. The kinetic data obtained over the temperature range 287–313 K were used to derive the following Arrhenius expressions (in units of cm 3 molecule ?1 s ?1): k(Cl+MMA) = (13.9 ± 7.8) × 10 ?15 exp[(2904 ± 420)/ T], k(Cl+MAC) = (0.4 ± 0.2) × 10 ?15 exp[(3884 ± 879)/ T], k(Cl+BMA) = (0.98 ± 0.42) × 10 ?15 exp[(3779 ± 850)/ T]. All the rate coefficients display a slight negative temperature dependence which points to the importance of the reversibility of the addition mechanism for these reactions. This work constitutes the first kinetic and temperature dependence study of the reactions cited above.An analysis of the available rates of addition of Cl atoms and OH radicals to the double bond of alkenes and unsaturated and oxygenated volatile organic compounds (VOCs) at 298 K has shown that they can be related by the expression: log kOH = 1.09 log kCl ? 0.10. In addition, a correlation between the reactivity of unsaturated VOCs toward OH radicals and Cl atoms and the HOMO of the unsaturated VOC is presented. Tropospheric implications of the results are also discussed. 相似文献
6.
In the last few years, several works dealing with Fenton oxidation of ionic liquids (ILs) have proved the capability of this technology for their degradation, achieving complete ILs removal and non-toxic effluents. Nevertheless, very little is known about the kinetics of this process, crucial for its potential application. In this work, the effect of several operating conditions, including reaction temperature (50–90 °C), catalyst load (10–50 mg L ?1 Fe 3+), initial IL concentration (100–2000 mg L ?1), and hydrogen peroxide dose (10–200% of the stoichiometric amount for the complete IL mineralization) on 1-butyl-3-methylimidazolium chloride ([C 4mim]Cl) oxidation has been investigated. Under the optimum operating conditions ( T = 90 °C; [Fe 3+] 0 = 50 mg L ?1; [H 2O 2] 0 = 100% of the stoichiometric amount), the complete removal of [C 4mim]Cl (1000 mg L ?1) was achieved at 1.5-min reaction time. From the experimental results, a potential kinetic model capable to describe the removal of imidazolium-based ILs by Fenton oxidation has been developed. By fitting the proposed model to the experimental data, the orders of the reaction with respect to IL initial concentration, Fe 3+ amount and H 2O 2 dose were found to be close to 1, with an apparent activation energy of 43.3 kJ mol ?1. The model resulted in a reasonable fit within the wide range of operating conditions tested in this work. 相似文献
7.
Intensive beef production has increased during recent decades in Brazil and may substantially increase both methane (CH 4) and nitrous oxide (N 2O) emissions from manure management. However, the quantification of these gases and methods for extrapolating them are scarce in Brazil. A case study examines CH 4 and N 2O emissions from one typical beef cattle feedlot manure management continuum in Brazil and the applicability of Manure-DNDC model in predicting these emissions for better understand fluxes and mitigation options. Measurements track CH 4 and N 2O emissions from manure excreted in one housing floor holding 21 animals for 78 days, stockpiled for 73 days and field spread (360 kg N ha ?1). We found total emissions (CH 4 + N 2O) of 0.19 ± 0.10 kg CO 2eq per kg of animal live weight gain; mostly coming from field application (73%), followed housing (25%) and storage (2%). The Manure-DNDC simulations were generally within the statistical deviation ranges of the field data, differing in ?28% in total emission. Large uncertainties in measurements showed the model was more accurate estimating the magnitude of gases emissions than replicate results at daily basis. Modeled results suggested increasing the frequency of manure removal from housing, splitting the field application and adopting no-tillage system is the most efficient management for reducing emissions from manure (up to about 75%). Since this work consists in the first assessment under Brazilian conditions, more and continuous field measurements are required for decreasing uncertainties and improving model validations. However, this paper reports promising results and scientific perceptions for the design of further integrated work on farm-scale measurements and Manure-DNDC model development for Brazilian conditions. 相似文献
8.
Knowing the fraction of methane (CH 4) oxidized in landfill cover soils is an important step in estimating the total CH 4 emissions from any landfill. Predicting CH 4 oxidation in landfill cover soils is a difficult task because it is controlled by a number of biological and environmental factors. This study proposes an artificial neural network (ANN) approach using feedforward backpropagation to predict CH 4 oxidation in landfill cover soil in relation to air temperature, soil moisture content, oxygen (O 2) concentration at a depth of 10 cm in cover soil, and CH 4 concentration at the bottom of cover soil. The optimum ANN model giving the lowest mean square error (MSE) was configured from three layers, with 12 and 9 neurons at the first and the second hidden layers, respectively, log-sigmoid (logsig) transfer function at the hidden and output layers, and the Levenberg-Marquardt training algorithm. This study revealed that the ANN oxidation model can predict CH 4 oxidation with a MSE of 0.0082, a coefficient of determination ( R 2) between the measured and predicted outputs of up to 0.937, and a model efficiency ( E) of 0.8978. To conclude, further developments of the proposed ANN model are required to generalize and apply the model to other landfills with different cover soil properties. Implications: To date, no attempts have been made to predict the percent of CH4 oxidation within landfill cover soils using an ANN. This paper presents modeling of CH4 oxidation in landfill cover soil using ANN based on field measurements data under tropical climate conditions in Malaysia. The proposed ANN oxidation model can be used to predict the percentage of CH4 oxidation from other landfills with similar climate conditions, cover soil texture, and other properties. The predicted value of CH4 oxidation can be used in conjunction with the Intergovernmental Panel on Climate Change (IPCC) First Order Decay (FOD) model by landfill operators to accurately estimate total CH4 emission and how much it contributes to global warming. 相似文献
9.
Acrylate esters are α,β-unsaturated esters that contain vinyl groups directly attached to the carbonyl carbon. These compounds are widely used in the production of plastics and resins. Atmospheric degradation processes of these compounds are currently not well understood. The kinetics of the gas phase reactions of OH radicals with methyl 3-methylacrylate and methyl 3,3-dimethylacrylate were determined using the relative rate technique in a 50 L Pyrex photoreactor using in situ FTIR spectroscopy at room temperature (298?±?2 K) and atmospheric pressure (708?±?8 Torr) with air as the bath gas. Rate coefficients obtained were (in units cm 3 molecule ?1 s ?1): (3.27?±?0.33)?×?10 ?11 and (4.43?±?0.42)?×?10 ?11, for CH 3CH═CHC(O)OCH 3 and (CH 3) 2CH═CHC(O)OCH 3, respectively. The same technique was used to study the gas phase reactions of hexyl acrylate and ethyl hexyl acrylate with OH radicals and Cl atoms. In the experiments with Cl, N 2 and air were used as the bath gases. The following rate coefficients were obtained (in cm 3 molecule ?1 s ?1): k 3 (CH 2═CHC(O)O(CH 2) 5CH 3?+?Cl)?=?(3.31?±?0.31)?×?10 ?10, k 4(CH 2═CHC(O)OCH 2CH(CH 2CH 3)(CH 2) 3CH 3?+?Cl)?=?(3.46?±?0.31)?×?10 ?10, k 5(CH 2═CHC(O)O(CH 2) 5CH 3?+?OH)?=?(2.28?±?0.23)?×?10 ?11, and k 6(CH 2═CHC(O)OCH 2CH(CH 2CH 3)(CH 2) 3CH 3?+?OH)?=?(2.74?±?0.26)?×?10 ?11. The reactivity increased with the number of methyl substituents on the double bond and with the chain length of the alkyl group in –C(O)OR. Estimations of the atmospheric lifetimes clearly indicate that the dominant atmospheric loss process for these compounds is their daytime reaction with the hydroxyl radical. In coastal areas and in some polluted environments, Cl atom-initiated degradation of these compounds can be significant, if not dominant. Maximum Incremental Reactivity (MIR) index and global warming potential (GWP) were also calculated, and it was concluded that these compounds have significant MIR values, but they do not influence global warming. 相似文献
10.
The herbicide 2,4-D [2,4-(dichlorophenoxy) acetic acid] is a widely used broadleaf control agent in cereal production systems. Although 2,4-D soil-residual activity (half-lives) are typicaly less than 10 days, this herbicide also has as a short-term leaching potential due to its relatively weak retention by soil constituents. Herbicide residual effects and leaching are influenced by environmental variables such as soil moisture and temperature. The objective of this study was to determine impacts of these environmental variables on the magnitude and extent of 2,4-D mineralization in a cultivated undulating Manitoba prairie landscape. Microcosm incubation experiments were utilized to assess 2,4-D half-lives and total mineralization using a 4 × 4 × 3 × 2 factorial design (with soil temperature at 4 levels: 5, 10, 20 and 40°C; soil moisture at 4 levels: 60, 85, 110, 135 % of field capacity; slope position at 3 levels: upper-, mid- and lower-slopes; and soil depth at 2 levels: 0–5 cm and 5–15 cm). Half-lives (t 1/2) varied from 3 days to 51 days with the total 2,4-D mineralization (M T ) ranging from 5.8 to 50.9 %. The four-way interaction (temperature × moisture × slope × depth) significantly ( p< 0.001) influenced both t 1/2 and M T. Second-order polynomial equations best described the relations of temperature with t 1/2 and M T as was expected from a biological system. However, the interaction and variability of t 1/2 and M T among different temperatures, soil moistures, slope positions, and soil depth combinations indicates that the complex nature of these interacting factors should be considered when applying 2,4-D in agricultural fields and in utilizing these parameters in pesticide fate models. 相似文献
11.
Rates of CO 2 production in the reaction CO + OH and CO + OH + halocarbon have been used to determine rate constants for some OH + halocarbon reactions at 29.5°C relative to that of k(CO + OH) = 2.69 × 10 ?13 cm 3 molecule ?1 sec ?1. The following rate constants were obtained: k(OH + CH 3Cl) = 3.1 ± 0.8, k(OH + CH 2Cl 2) = 2.7 ± 1.0, k(OH + C 2H 5Cl) = 44.0 ± 25, k(OH + CICH 2CH 2CI) = 6.5, (<29) and k(OH + CH 3CCl 3) = 2.1 (<5.7) cm 3 molecule ?1 sec ?1 × 10 ?14. The k values, CH 2Cl 2 excepted, are in substantial agreement with determinations made in nonoxygen environments. The present results for CH 2Cl 2 are almost certainly in error due to difficulties with the competitive approach used. 相似文献
12.
Acetaldehyde (CH 3CHO) and acetone (CH 3C(O)CH 3) concentrations in ambient air, in snowpack air, and bulk snow were determined at Alert, Nunavut, Canada, as a part of the Polar Sunrise Experiment (PSE): ALERT 2000. During the period of continuous sunlight, vertical profiles of ambient and snowpack air exhibited large concentration gradients through the top ∼10 cm of the snowpack, implying a flux of carbonyl compounds from the surface to the atmosphere. From vertical profile and eddy diffusivity measurements made simultaneously on 22 April, acetaldehyde and acetone fluxes of 4.2(±2.1)×10 8 and 6.2(±4.2)×10 8 molecules cm −2 s −1 were derived, respectively. For this day, the sources and sinks of CH 3CHO from gas phase chemistry were estimated. The result showed that the snowpack flux of CH 3CHO to the atmosphere was as large as the calculated CH 3CHO loss rate from known atmospheric gas phase reactions, and at least 40 times larger (in the surface layer) than the volumetric rate of acetaldehyde produced from the assumed main atmospheric gas phase reaction, i.e. reaction of ethane with hydroxyl radicals. In addition, acetaldehyde bulk snow phase measurements showed that acetaldehyde was produced in or on the snow phase, likely from a photochemical origin. The time series for the observed CH 3C(O)CH 3, ozone (O 3), and propane during PSE 1995, PSE 1998, and ALERT 2000 showed a consistent anti-correlation between acetone and O 3 and between acetone and propane. However, our data and model simulations showed that the acetone increase during ozone depletion events cannot be explained by gas phase chemistry involving propane oxidation. These results suggest that the snowpack is a significant source of acetaldehyde and acetone to the Arctic boundary layer. 相似文献
14.
Introduction In this study, we provide strategies for detecting and quantifying the structural isomers of polyfluorinated di- and tri-alkyl
surfactants (PFAS) by mass spectrometry (MS). We specifically investigate polyfluorinated dialkylated phosphate ester surfactants
( x:2/ y:2 diPAPS, (F(CF 2)
x
CH 2CH 2O-P(O)(O) −-OCH 2CH 2(CF 2)
y
F)) and their thioether analogues ( x:2/ y:2 S-diPAPS, F(CF 2)
x
CH 2CH 2SCH 2-C[CH 2O) 2P(O)(O) −]-CH 2SCH 2CH 2(CF 2)
y
F), which are used for industrial applications, such as oil- and water-repellent coatings on paper and board. DiPAPS have
been found in human blood and are metabolised to the persistent perfluoroalkyl carboxylic acids (PFCA) in rats. 相似文献
15.
Ultrasonic probe sonication (UPS) and microwave-assisted extraction (MAE) were used for rapid single extraction of Cd, Cr, Cu, Ni, Pb, and Zn from soils polluted by former mining activities (Mónica Mine, Bustarviejo, NW Madrid, Spain), using 0.01 mol L ?1 calcium chloride (CaCl 2), 0.43 mol L ?1 acetic acid (CH 3COOH), and 0.05 mol L ?1 ethylenediaminetetraacetic acid (EDTA) at pH 7 as extracting agents. The optimum extraction conditions by UPS consisted of an extraction time of 2 min for both CaCl 2 and EDTA extractions and 15 min for CH 3COOH extraction, at 30% ultrasound (US) amplitude, whereas in the case of MAE, they consisted of 5 min at 50 °C for both CaCl 2 and EDTA extractions and 15 min at 120 °C for CH 3COOH extraction. Extractable concentrations were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). The proposed methods were compared with a reduced version of the corresponding single extraction procedures proposed by the Standards, Measurements and Testing Programme (SM&T). The results obtained showed a great variability on extraction percentages, depending on the metal, the total concentration level and the soil sample, reaching high values in some areas. However, the correlation analysis showed that total concentration is the most relevant factor for element extractability in these soil samples. From the results obtained, the application of the accelerated extraction procedures, such as MAE and UPS, could be considered a useful approach to evaluate rapidly the extractability of the metals studied. 相似文献
16.
Methane biofiltration (MBF) is a novel low-cost technique for reducing low volume point source emissions of methane (CH 4). MBF uses a granular medium, such as soil or compost, to support the growth of methanotrophic bacteria responsible for converting CH 4 to carbon dioxide (CO 2) and water (H 2O). A field research program was undertaken to evaluate the potential to treat low volume point source engineered CH 4 emissions using an MBF at a natural gas monitoring station. A new comprehensive three-dimensional numerical model was developed incorporating advection-diffusive flow of gas, biological reactions and heat and moisture flow. The one-dimensional version of this model was used as a guiding tool for designing and operating the MBF. The long-term monitoring results of the field MBF are also presented. The field MBF operated with no control of precipitation, evaporation, and temperature, provided more than 80% of CH 4 oxidation throughout spring, summer, and fall seasons. The numerical model was able to predict the CH 4 oxidation behavior of the field MBF with high accuracy. The numerical model simulations are presented for estimating CH 4 oxidation efficiencies under various operating conditions, including different filter bed depths and CH 4 flux rates. The field observations as well as numerical model simulations indicated that the long-term performance of MBFs is strongly dependent on environmental factors, such as ambient temperature and precipitation. 相似文献
17.
Patches of dung and urine are major contributors to the feedlot gas emissions. This study investigated the impacts of dung deposition frequency (partly reflecting animal stocking density of a feedlot), dairy feedlot floor conditions (old floor indicated with the presence of consolidated manure pad [CMP] vs. new floor with the absence of consolidated manure pad [CMPn]), and application of dicyandiamide (DCD) and hydroquinone (HQ) on nitrous oxide (N 2O) and methane (CH 4) emissions from patches in the laboratory, and the integrative impacts were expressed in terms of global warming potential (CO 2-equivalent). Dung deposition frequency, feedlot floor condition, and application of inhibitors showed inverse impacts on N 2O and CH 4 emissions from patches. Greenhouse gas (GHG) emissions from the dung, urine, and dung+urine patches on the CMP feedlot surface were approximately 7.48, 87.35, and 7.10 times those on the CMPn feedlot surface ( P < 0.05). Meanwhile, GHG emissions from CMP and CMPn feedlot surfaces under high deposition frequency condition were approximately 10 and 1.7 times those under low-frequency condition. Moreover, application of HQ slightly reduced the GHG emission from urine patches, by 14.9% ( P > 0.05), while applying DCD or DCD+HQ significantly reduced the GHG, by 60.3% and 65.0%, respectively ( P < 0.05). Overall, it is necessary to include feedlot management such as animal stocking density and feedlot floor condition to the process of determining emission factors for feedlots. In the future, field measurements to quantitatively evaluate the relative contribution of nitrification and denitrification to the N 2O emissions of feedlot surfaces are highly required for effective N 2O control. Implications: This study shows that feedlot CH4 and N2O emissions inversely respond to the dicyandiamide (DCD) application. Applying DCD significantly reduces GHG emissions of feedlot urine patches. Feedlot floor condition and stocking density strongly impact feedlot GHG emissions. Including feedlot floor condition and stocking density in the feedlot EF determining process is necessary. 相似文献
19.
Background, aim, and scope The adverse environmental impacts of chlorinated hydrocarbons on the Earth’s ozone layer have focused attention on the effort
to replace these compounds by nonchlorinated substitutes with environmental acceptability. Hydrofluoroethers (HFEs) and fluorinated
alcohols are currently being introduced in many applications for this purpose. Nevertheless, the presence of a great number
of C–F bonds drives to atmospheric long-lived compounds with infrared absorption features. Thus, it is necessary to improve
our knowledge about lifetimes and global warming potentials (GWP) for these compounds in order to get a complete evaluation
of their environmental impact. Tropospheric degradation is expected to be initiated mainly by OH reactions in the gas phase.
Nevertheless, Cl atoms reaction may also be important since rate constants are generally larger than those of OH. In the present
work, we report the results obtained in the study of the reactions of Cl radicals with HFE-7000 (CF 3CF 2CF 2OCH 3) (1) and its isomer CF 3CF 2CF 2CH 2OH (2).
Materials and methods Kinetic rate coefficients with Cl atoms have been measured using the discharge flow tube–mass spectrometric technique at 1 Torr
of total pressure. The reactions of these chlorofluorocarbons (CFCs) substitutes have been studied under pseudo-first-order
kinetic conditions in excess of the fluorinated compounds over Cl atoms. The temperature ranges were 266–333 and 298–353 K
for reactions of HFE-7000 and CF 3CF 2CF 2CH 2OH, respectively.
Results The measured room temperature rate constants were k(Cl+CF 3CF 2CF 2OCH 3) = (1.24 ± 0.28) × 10 −13 cm 3 molecule −1 s −1and k(Cl+CF 3CF 2CF 2CH 2OH) = (8.35 ± 1.63) × 10 −13 cm 3 molecule −1 s −1 (errors are 2 σ + 10% to cover systematic errors). The Arrhenius expression for reaction 1 was k
1(266–333 K) = (6.1 ± 3.8) × 10 −13exp[−(445 ± 186)/ T] cm 3 molecule −1 s −1 and k
2(298–353 K) = (1.9 ± 0.7) × 10 −12exp[−(244 ± 125)/ T] cm 3 molecule −1 s −1 (errors are 2 σ). The reactions are reported to proceed through the abstraction of an H atom to form HCl and the corresponding halo-alkyl
radical. At 298 K and 1 Torr, yields on HCl of 0.95 ± 0.38 and 0.97 ± 0.16 (errors are 2 σ) were obtained for CF 3CF 2CF 2OCH 3 and CF 3CF 2CF 2CH 2OH, respectively.
Discussion The obtained kinetic rate constants are related to the previous data in the literature, showing a good agreement taking into
account the error limits. Comparing the obtained results at room temperature, k
1 and k
2, HFE-7000 is significantly less reactive than its isomer C 3F 7CH 2OH. A similar behavior has been reported for the reactions of other fluorinated alcohols and their isomeric fluorinated ethers
with Cl atoms. Literature data, together with the results reported in this work, show that, for both fluorinated ethers and
alcohols, the kinetic rate constant may be considered as not dependent on the number of –CF 2– in the perfluorinated chain. This result may be useful since it is possible to obtain the required physicochemical properties
for a given application by changing the number of –CF 2– without changes in the atmospheric reactivity. Furthermore, lifetimes estimations for these CFCs substitutes are calculated
and discussed. The average estimated Cl lifetimes are 256 and 38 years for HFE-7000 and C 3H 7CH 2OH, respectively.
Conclusions The studied CFCs’ substitutes are relatively short-lived and OH reaction constitutes their main reactive sink. The average
contribution of Cl reactions to global lifetime is about 2% in both cases. Nevertheless, under local conditions as in the
marine boundary layer, τ
Cl values as low as 2.5 and 0.4 years for HFE-7000 and C 3H 7CH 2OH, respectively, are expected, showing that the contribution of Cl to the atmospheric degradation of these CFCs substitutes
under such conditions may constitute a relevant sink. In the case of CF 3CF 2CF 2OCH 3, significant activation energy has been measured, thus the use of kinetic rate coefficient only at room temperature would
result in underestimations of lifetimes and GWPs.
Recommendations and perspectives The results obtained in this work may be helpful within the database used in the modeling studies of coastal areas. The knowledge
of the atmospheric behavior and the structure–reactivity relationship discussed in this work may also contribute to the development
of new environmentally acceptable chemicals. New volatile materials susceptible of emission to the troposphere should be subject
to the study of their reactions with OH and Cl in the range of temperature of the troposphere. The knowledge of the temperature
dependence of the kinetic rate constants, as it is now reported for the case of reactions 1 and 2, will allow more accurate
lifetimes and related magnitudes like GWPs. Nevertheless, a better knowledge of the vertical Cl tropospheric distribution
is still required. 相似文献
20.
In coastal Antarctica, freezing and thawing influence many physical, chemical and biological processes for ice-free tundra ecosystems, including the production of greenhouse gases (GHGs). In this study, penguin guanos and ornithogenic soil cores were collected from four penguin colonies and one seal colony in coastal Antarctica, and experimentally subjected to three freezing–thawing cycles (FTCs) under ambient air and under N 2. We investigated the effects of FTCs on the emissions of three GHGs including nitrous oxide (N 2O), carbon dioxide (CO 2) and methane (CH 4). The GHG emission rates were extremely low in frozen penguin guanos or ornithogenic soils. However, there was a fast increase in the emission rates of three GHGs following thawing. During FTCs, cumulative N 2O emissions from ornithogenic soils were greatly higher than those from penguin guanos under ambient air or under N 2. The highest N 2O cumulative emission of 138.24 μg N 2O–N kg ?1 was observed from seal colony soils. Cumulative CO 2 and CH 4 emissions from penguin guanos were one to three orders of magnitude higher than those from ornithogenic soils. The highest cumulative CO 2 (433.0 mgCO 2–C kg ?1) and CH 4 (2.9 mgCH 4–C kg ?1) emissions occurred in emperor penguin guanos. Penguin guano was a stronger emitter for CH 4 and CO 2 while ornithogenic soil was a stronger emitter for N 2O during FTCs. CO 2 and CH 4 fluxes had a correlation with total organic carbon (TOC) and soil/guano moisture (M c) in penguin guanos and ornithogenic soils. The specific CO 2–C production rate (CO 2–C/TOC) indicated that the bioavailability of TOC was markedly larger in penguin guanos than in ornithogenic soils during FTCs. This study showed that FTC-released organic C and N from sea animal excreta may play a significant role in FTC-related GHG emissions, which may account for a large proportion of annual fluxes from tundra ecosystems in coastal Antarctica. 相似文献
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