Kinetic studies of O3 reactions with 3-bromopropene and 3-iodopropene in the temperature range 288–328 K

The kinetics of the reactions of O₃ with 3-bromopropene and 3-iodopropene has been studied over the temperature range of 288–328 K at atmospheric pressure. The results obtained for the room temperature rate constants are (1.88 ± 0.22) × 10^?18 and (3.52 ± 0.43) × 10^?18 cm³ molecule^?1 s^?1, and the proposed Arrhenius expressions are k = (3.47 ± 1.28) × 10^?15 exp[(?2233 ± 110)/T] and k = (8.17 ± 2.12) × 10^?14 exp[(?2991 ± 80)/T] cm³ molecule^?1 s^?1 for 3-bromopropene and 3-iodopropene, respectively. The atmospheric chemical lifetimes of these two compounds with O₃ were also estimated from these values.     

Heterogeneous reactions of ozone with pyrene, 1-hydroxypyrene and 1-nitropyrene adsorbed on particles

This work deals with the kinetic study of the reactions of ozone with pyrene, 1-hydroxypyrene and 1-nitropyrene, adsorbed on model particles. Experiments were performed at room temperature and atmospheric pressure, using a quasi-static flow reactor in the absence of light. Compounds were extracted from particles using pressurized fluid extraction (PFE) and concentration measurements were performed using gas chromatography/mass spectrometry (GC/MS). The pseudo-first order rate constants were obtained from the fit of the experimental decay of particulate polycyclic compound concentrations versus reaction time. Experiments were performed at three different O₃ concentrations from which second order rate constants were calculated. The following rate constant values were obtained at 293 K: k(O₃ + Pyrene) = (3.2 ± 0.7) × 10^?16 cm³ molecule^?1 s^?1; k(O₃ + 1OHP) = (7.7 ± 1.4) ×10 ^?16 cm³ molecule^?1 s^?1; and k(O₃ + 1NP) = (2.2 ± 0.5) × 10^?17 cm³ molecule^?1 s^?1, for pyrene, 1-hydroxypyrene and 1-nitropyrene adsorbed on silica particles. The variation in the rate constants demonstrates the strong influence of the substituent (OH or NO₂) on the heterogeneous reactivity of pyrene. The pyrene particulate concentration was also varied in order to check how this parameter may influence the experiments. Finally, oxidation products were investigated for all reactions and some were detected and identified for the first time for ozone heterogeneous reaction with pyrene adsorbed on particles.     

Rate constant for the reaction of ozone with diethyl sulfide

The rate constant for the reaction of diethyl sulfide (DES; C₂H₅SC₂H₅) with ozone was determined for the first time, which was (2.77±0.27)×10⁻¹⁹ cm³ molecule⁻¹ s⁻¹ under a room temperature of (289±1) K. Experiments were conducted under supposedly pseudo-first-order decay conditions, keeping [DES]₀>50[O₃]₀, but having different combinations of [DES]₀ and [O₃]₀. Cyclohexane was added into the reactor to eliminate the effect of OH radicals. The wall decay of ozone and the role of cyclohexane were also discussed in the present work.     

Gas-phase chemistry of benzyl alcohol: Reaction rate constants and products with OH radical and ozone

A bimolecular rate constant, k_{OH+Benzyl alcohol}, of (28 ± 7) × 10^?12 cm³ molecule^?1 s^?1 was measured using the relative rate technique for the reaction of the hydroxyl radical (OH) with benzyl alcohol, at (297 ± 3) K and 1 atm total pressure. Additionally, an upper limit of the bimolecular rate constant, k_{O3+Benzyl alcohol}, of approximately 6 × 10^?19 cm³ molecule^?1 s^?1 was determined by monitoring the decrease in benzyl alcohol concentration over time in an excess of ozone (O₃). To more clearly define part of benzyl alcohol's indoor environment degradation mechanism, the products of the benzyl alcohol + OH were also investigated. The derivatizing agents O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) and N,O-bis(trimethylsilyl) trifluoroacetamide (BSTFA) were used to positively identify benzaldehyde, glyoxal and 4-oxopentanal as benzyl alcohol/OH reaction products. The elucidation of other reaction products was facilitated by mass spectrometry of the derivatized reaction products coupled with plausible benzyl alcohol/OH reaction mechanisms based on previously published volatile organic compound/OH gas-phase reaction mechanisms.     

Influence of temperature on the chemical removal of 3-methylbutanal,trans-2-methyl-2-butenal,and 3-methyl-2-butenal by OH radicals in the troposphere

Absolute rate coefficients for the gas-phase reactions of OH radical with 3-methylbutanal (k₁), trans-2-methyl-2-butenal (k₂), and 3-methyl-2-butenal (k₃) have been obtained with the pulsed laser photolysis/laser-induced fluorescence technique. Gas-phase concentration of aldehydes was measured by UV absorption spectroscopy at 185 nm. Experiments were performed over the temperature range of 263–353 K at total pressures of helium between 46.2 and 100 Torr. No pressure dependence of all k_i (i = 1–3) was observed at all temperatures. In contrast, a negative temperature dependence of k_i (i.e., k_i increases when temperature decreases) was observed in that T range. The resulting Arrhenius expressions (±2σ) are: k₁(T) = (5.8 ± 1.7)×10^?12 exp{(499 ± 94)/T} cm³ molecule^?1 s^?1, k₂(T)=(6.9 ± 0.9)×10^?12 exp{(526 ± 42)/T} cm³ molecule^?1 s^?1, k₃(T)=(5.6 ± 1.2)×10^?12 exp{(666 ± 54)/T} cm³ molecule^?1 s^?1.The tropospheric lifetimes derived from the above OH-reactivity trend are estimated to be higher for 3-methylbutanal than those for the unsaturated aldehydes. A comparison of the tropospheric removal of these aldehydes by OH radicals with other homogeneous degradation routes leads to the conclusion that this reaction can be the main homogeneous removal pathway. However, photolysis of these aldehydes in the actinic region (λ > 290 nm) could play an important role along the troposphere, particularly for 3-methyl-2-butenal. This process could compete with the OH reaction for 3-methylbutanal or be negligible for trans-2-methyl-2-butenal in the troposphere.     

Kinetic study of the OH reaction with some hydrochloroethers under simulated atmospheric conditions

Using the relative rate technique, rate constants for the gas-phase reactions of hydroxyl radicals with 2-chloroethyl methyl ether (k₁), 2-chloroethyl ethyl ether (k₂) and bis(2-chloroethyl) ether (k₃) have been measured. Experiments were carried out at (298 ± 2) K and atmospheric pressure using synthetic air as bath gas. Using n-pentane and n-heptane as reference compounds, the following rate constants were derived: k₁ = (5.2 ± 1.2) × 10^?12, k₂ = (8.3 ± 1.9) × 10^?12 and k₃ = (7.6 ± 1.9) × 10^?12, in units of cm³ molecule^?1 s^?1. This is the first experimental determination of k₂ and k₃ under atmospheric pressure. The rate constants obtained are compared with previous literature data and the observed trends in the relative rates of reaction of hydroxyl radicals with the ethers studied are discussed. The atmospheric implications of the results are considered in terms of lifetimes and fates of the hydrochloroethers studied.     

Environmental photochemical fate of pesticides ametryn and imidacloprid in surface water (Paranapanema River,São Paulo,Brazil)

In addition to direct photolysis studies, in this work the second-order reaction rate constants of pesticides imidacloprid (IMD) and ametryn (AMT) with hydroxyl radicals (HO^●), singlet oxygen (¹O₂), and triplet excited states of chromophoric dissolved organic matter (³CDOM^*) were determined by kinetic competition under sunlight. IMD and AMT exhibited low photolysis quantum yields: (1.23?±?0.07)?×?10^–2 and (7.99?±?1.61)?×?10^–3 mol Einstein^?1, respectively. In contrast, reactions with HO^● radicals and ³CDOM* dominate their degradation, with ¹O₂ exhibiting rates three to five orders of magnitude lower. The values of k_IMD,HO● and k_AMT,HO● were (3.51?±?0.06)?×?10⁹ and (4.97?±?0.37)?×?10⁹ L mol^?1 s^?1, respectively, while different rate constants were obtained using anthraquinone-2-sulfonate (AQ2S) or 4-carboxybenzophenone (CBBP) as CDOM proxies. For IMD this difference was significant, with k_IMD,3AQ2S*?=?(1.02?±?0.08)?×?10⁹ L mol^?1 s^?1 and k_IMD,3CBBP*?=?(3.17?±?0.14)?×?10⁸ L mol^?1 s^?1; on the contrary, the values found for AMT are close, k_AMT,3AQ2S*?=?(8.13?±?0.35)?×?10⁸ L mol^?1 s^?1 and k_AMT,3CBBP*?=?(7.75?±?0.80)?×?10⁸ L mol^?1 s^?1. Based on these results, mathematical simulations performed with the APEX model for typical levels of water constituents (NO₃^?, NO₂^?, CO₃^2?, TOC, pH) indicate that the half-lives of these pesticides should vary between 24.1 and 18.8 days in the waters of the Paranapanema River (São Paulo, Brazil), which can therefore be impacted by intensive agricultural activity in the region.

     

Kinetics of the gas-phase reactions of NO3 radicals with ethyl acrylate,n-butyl acrylate,methyl methacrylate and ethyl methacrylate

The relative rate method has been used to determine the rate constants for the gas-phase reactions of NO₃ radicals with a series of acrylate esters: ethyl acrylate (k₁), n-butyl acrylate (k₂), methyl methacrylate (k₃) and ethyl methacrylate (k₄) at 298 ± 1 K and 760 Torr. The obtained rate constants are k₁ = (1.8 ± 0.25) × 10^?16 cm³ molecule^?1 s^?1, k₂ = (2.1 ± 0.33) × 10^?16 cm³ molecule^?1 s^?1, k₃ = (3.6 ± 1.2) × 10^?15 cm³ molecule^?1 s^?1, k₄ = (4.9 ± 1.7) × 10^?15 cm³ molecule^?1 s^?1. The experimental rate constants are in good agreement with theoretical rate constants calculated by an algorithm of the correlation between the rate constants and the orbital energies for the reactions of unsaturated VOCs with NO₃ radicals. In addition, the atmospheric lifetimes of the compound against NO₃ attack are estimated and the results show that NO₃ reactions contribute little to the atmospheric losses of acrylate esters except in polluted regions.     

Kinetics of the gas-phase reactions of alkylnaphthalenes with O3, N2O5 and OH radicals at 298 ± 2 K

Rate constants for the gas-phase reactions of the OH radical with 1-methylnaphthalene and of N₂O₅ with 1- and 2-methylnaphthalene and 2,3-dimethylnaphthalene have been determined at 298 ± 2 K by use of relative rate techniques. The rate constants determined were: for the reaction of OH radicals with 1-methylnaphthalene, (5.30 ± 0.48) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹; for the reaction of N₂O₅ with 1-methylnaphthalene, 2-methylnaphthalene and 2,3-dimethylnaphthalene, (3.3 ± 0.7) × 10⁻¹⁷, (4.2 ± 0.9) × 10⁻¹⁷ and (5.7 ± 1.9) × 10⁻¹⁷ cm³ molecule⁻¹ s⁻¹, respectively. In addition, an upper limit to the rate constant of 1.3 × 10⁻¹⁹ cm³ molecule⁻¹ s⁻¹ was measured for the reaction of O₃ with 1-methylnaphthalene at 298 ± 2 K. These data, when combined with data from previous literature, allow the atmospheric gas-phase removal processes of these alkylnaphthalenes to be quantified.     

Night-time tropospheric chemistry of the unsaturated alcohols (Z)-pent-2-en-1-ol and pent-1-en-3-ol: Kinetic studies of reactions of NO3 and N2O5 with stress-induced plant emissions

The night-time tropospheric chemistry of two stress-induced volatile organic compounds (VOCs), (Z)-pent-2-en-1-ol and pent-1-en-3-ol, has been studied at room temperature. Rate coefficients for reactions of the nitrate radical (NO₃) with these pentenols were measured using the discharge-flow technique. Because of the relatively low volatility of these compounds, we employed off-axis continuous-wave cavity-enhanced absorption spectroscopy for detection of NO₃ in order to be able to work in pseudo first-order conditions with the pentenols in large excess over NO₃. The rate coefficients were determined to be (1.53±0.23)×10⁻¹³ and (1.39±0.19)×10⁻¹⁴ cm³ molecule⁻¹ s⁻¹ for reactions of NO₃ with (Z)-pent-2-en-1-ol and pent-1-en-3-ol. An attempt to study the kinetics of these reactions with a relative-rate technique, using N₂O₅ as source of NO₃ resulted in significantly higher apparent rate coefficients. Performing relative-rate experiments in known excesses of NO₂ allowed us to determine the rate coefficients for the N₂O₅ reactions to be (5.0±2.8)×10⁻¹⁹ cm³ molecule⁻¹ s⁻¹ for (Z)-pent-2-en-1-ol, and (9.1±5.8)×10⁻¹⁹ cm³ molecule⁻¹ s⁻¹ for pent-1-en-3-ol. We show that these relatively slow reactions can indeed interfere with rate determinations in conventional relative-rate experiments.     

Relative kinetic measurements of rate coefficients for the gas-phase reactions of Cl atoms and OH radicals with a series of methyl alkyl esters

Relative kinetic studies have been performed on the reactions of Cl atoms with a series of methyl alkyl esters in a 405-liter borosilicate glass chamber at (298 ± 3) K and one atmosphere of synthetic air using in situ FTIR spectroscopy to monitor the reactants. Rate coefficients (in units of cm³ molecule^?1 s^?1) were determined for the following compounds: methyl acetate (2.48 ± 0.58) × 10^?12; methyl propanoate (1.68 ± 0.36) × 10^?11; methyl butanoate (4.77 ± 0.87) × 10^?11; methyl pentanoate (7.84 ± 1.15) × 10^?11; methyl hexanoate (1.09 ± 0.31) × 10^?10; methyl heptanoate (1.56 ± 0.37) × 10^?10; methyl cyclohexane carboxylate (3.32 ± 0.76) × 10^?10; methyl-2-methyl butanoate (9.41 ± 1.39) × 10^?11.In addition rate coefficients (in units of 10^?11 cm³ molecule^?1 s^?1) have been obtained for the reactions of OH radicals with the following compounds: methyl butanoate (3.55 ± 0.71), methyl pentanoate (5.41 ± 1.08), and methyl-2-methyl butanoate (4.08 ± 0.82).Using the kinetic rate data tropospheric lifetimes for the methyl alkyl esters with respect to their reactions with OH, and Cl have been estimated for typical ambient air concentrations of these oxidants.     

Atmospheric chemistry of 1-methyl-2-pyrrolidinone

Rate constants for the atmospheric reactions of 1-methyl-2-pyrrolidinone with OH radicals, NO₃ radicals and O₃ have been measured at 296±2 K and atmospheric pressure of air, and the products of the OH radical and NO₃ radical reactions investigated. Using relative rate techniques, rate constants for the gas-phase reactions of OH and NO₃ radicals with 1-methyl-2-pyrrolidinone of (2.15±0.36)×10^-11 cm³ molecule^-1 s^-1 and (1.26±0.40)×10^-13 cm³ molecule^-1 s^-1, respectively, were measured, where the indicated errors include the estimated overall uncertainties in the rate constants for the reference compounds. An upper limit to the rate constant for the O₃ reaction of <1×10^-19 cm³ molecule^-1 s^-1 was also determined. These kinetic data lead to a calculated tropospheric lifetime of 1-methyl-2-pyrrolidinone of a few hours, with both the daytime OH radical reaction and the nighttime NO₃ radical reaction being important loss processes. Products of the OH radical and NO₃ radical reactions were analyzed by gas chromatography with flame ionization detection and combined gas chromatography–mass spectrometry. N-methylsuccinimide and (tentatively) 1-formyl-2-pyrrolidinone were identified as products of both of these reactions. The measured formation yields of N-methylsuccinimide and 1-formyl-2-pyrrolidinone were 44±12% and 41±12%, respectively, from the OH radical reaction and 59±16% and ∼4%, respectively, from the NO₃ radical reaction. Reaction mechanisms consistent with formation of these products are presented.     

Temperature-dependent rate coefficients for the reactions of Cl atoms with methyl methacrylate,methyl acrylate and butyl methacrylate at atmospheric pressure

Rate coefficients for the gas-phase reactions of Cl atoms with a series of unsaturated esters CH₂C(CH₃)C(O)OCH₃ (MMA), CH₂CHC(O)OCH₃ (MAC) and CH₂C(CH₃)C(O)O(CH₂)₃CH₃ (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 cm³ 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 cm³ 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 k_OH = 1.09 log k_Cl ? 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.     

Improving ozone modeling in complex terrain at a fine grid resolution – Part II: Influence of schemes in MM5 on daily maximum 8-h ozone concentrations and RRFs (Relative Reduction Factors) for SIPs in the non-attainment areas

Part II presents a comprehensive evaluation of CMAQ for August of 2002 on twenty-one sensitivity simulations (detailed in Part I) in MM5 to investigate the model performance for O₃ SIPs (State Implementation Plans) in the complex terrain. CMAQ performance was quite consistent with the results of MM5, meaning that accurate meteorological fields predicted in MM5 as an input resulted in good model performance of CMAQ. In this study, PBL scheme plays a more important role than its land surface models (LSMs) for the model performance of CMAQ. Our results have shown that the outputs of CMAQ on eighteen sensitivity simulations using two different nudging coefficients for winds (2.5 and 4.5 × 10^?4 s^?1, respectively) tend to under predict daily maximum 8-h ozone concentrations at valley areas except the TKE PBL sensitivity simulations (ETA M-Y PBL scheme with Noah LSMs and 5-layer soil model and Gayno-Seaman PBL) using 6.0 × 10^?4 s^?1 with positive MB (Mean Bias). At mountain areas, none of the sensitivity simulations has presented over predictions for 8-h O₃, due to relatively poor meteorological model performance. When comparing 12-km and 4-km grid resolutions for the PX simulation in CMAQ statistics analysis, the CMAQ results at 12-km grid resolution consistently show under predictions of 8-h O₃ at both of valley and mountain areas and particularly, it shows relatively poor model performance with a 15.1% of NMB (Normalized Mean Bias). Based on our sensitivity simulations, the TKE PBL sensitivity simulations using a maximum value (6 × 10^?4) among other sensitivity simulations yielded better model performance of CMAQ at all areas in the complex terrain. As a result, the sensitivity of RRFs to the PBL scheme may be considerably significant with about 1–3 ppb in difference in determining whether the attainment test is passed or failed. Furthermore, we found that the result of CMAQ model performance depending on meteorological variations is affected on estimating RRFs for attainment demonstration, indicating that it is necessary to improve model performance. Overall, G_c (Gayo-Seaman PBL scheme) using the coefficient for winds, 6 × 10^?4 s^?1, sensitivity simulation predicts daily maximum 8-h ozone concentration closer to observations during a typical summer period from May to September and provides generally low future design values (DVFs) at valley and mountain areas compared to other simulations.     

Carbon monoxide photoproduction from rice and maize leaves

We investigated CO photoproduction from intact leaves of rice (Oryza sativa L.) and maize (Zea mays L.) by laboratory experiments. CO photoproduction showed positive correlation with light intensity and was positively dependent on oxygen concentration. The average CO photoproduction was 2.6±0.3×10¹⁰ molecules cm⁻² s⁻¹ from rice leaves and 2.2±0.1×10¹⁰ molecules cm⁻² s⁻¹ from maize leaves (n=5) at a radiation intensity of 49 mW cm⁻². CO photoproduction from senescent rice leaves was 9 times greater (25.7±1.5×10¹⁰ molecules cm⁻² s⁻¹, n=2) at the same radiation intensity than from live leaves, and responded slowly to changes in oxygen concentration and light intensity. CO photoproduction showed no correlation with CO₂ concentration or humidity. This indicates that CO photoproduction in leaves is not directly controlled by carbon metabolism or stomatal conductance. The lack of dependence on stomatal conductance leads to the conclusion that the diffusion of CO from inside the leaves to the atmosphere is not a controlling factor for CO photoproduction from rice and maize leaves.     

Atmospheric degradation of fluoroesters (FESs): Gas-phase reactivity study towards OH radicals at 298 K

Using the relative technique, rate coefficients have been measured for the gas phase reactions of hydroxyl radicals with four fluoroacetates, methyl trifluoroacetate (CF₃COOCH₃), ethyl trifluoroacetate (CF₃COOCH₂CH₃), methyl difluoroacetate (CF₂HCOOCH₃) and 2,2,2-trifluoroethyl trifluoroacetate (CF₃COOCH₂CF₃). Experiments were carried out at 296±2 K and atmospheric pressure (∼750 Torr) using nitrogen or synthetic air as bath gases. The following rate coefficients were derived for the reaction of OH radicals (in units of cm³ mol⁻¹ s⁻¹) with CF₃COOCH₃, k=(4.97±1.04)×10⁻¹⁴, CF₃COOCH₂CH₃, k=(2.64±0.59)×10⁻¹³, CF₂HCOOCH₃, k=(1.48±0.34)×10⁻¹³ and CF₃COOCH₂CF₃, (1.05±0.23)×10⁻¹³. The rate constants obtained are compared with previous literature data of other volatile organic compounds to establish reactivity trends. Atmospheric implications are discussed in terms of lifetimes and fates of the fluoroacetates in the troposphere.     

Determination of Room Temperature OH Rate Constants for Acetylene,Ethylene Dichloride,Ethylene Dibromide,p-Dichlorobenzene and Carbon Disulfide

A relative rate procedure was used to measure hydroxyl rate constants at room temperature in the presence of oxygen. The photolysis of methyl nitrite in the presence of nitric oxide was used to generate OH radicals. The rate of loss of the test compounds was measured relative to that of ethane (k_OH = 2.74 × 10^-13 cm³ molec^-1 s^-1). The rates obtained at 297 ± 2 K are: acetylene = (7.8 ± 1.6) × 10^-13 cm³ molec^-1 s^-1,1,2-dichloroethane (2.8 ± Q.6) × 10^-13 cm³ molec^-1 s^-1, 1,2-dibromoethane (2.4 ± 0.5) × 10^-13 cm³ molec^-1 s^-1, p-dichlorobenzene (4.3 ± 0.9) × 10^-13 cm³ molec^-1 s^-1 and carbon disulfide (29 ± 6) × 10^-13 cm³ molec^-1 s^-1. Under a proposed EPA rule, this OH rate determination procedure could be used to determine if a given volatile organic will be subject to control for reduction of photochemical ozone.     

Measurements of nitrogen oxides from Hudson Bay: Implications for NOx release from snow and ice covered surfaces

Measurements of NO and NO₂ were made at a surface site (55.28 °N, 77.77 °W) near Kuujjuarapik, Canada during February and March 2008. NO_x mixing ratios ranged from near zero to 350 pptv with emission from snow believed to be the dominant source. The amount of NO_x was observed to be dependent on the terrain over which the airmass has passed before reaching the measurement site. The 24 h average NO_x emission rates necessary to reproduce observations were calculated using a zero-dimensional box model giving rates ranging from 6.9 × 10⁸ molecule cm^?2 s^?1 to 1.2 × 10⁹ molecule cm^?2 s^?1 for trajectories over land and from 3.8 × 10⁸ molecule cm^?2 s^?1 to 6.6 × 10⁸ molecule cm^?2 s^?1 for trajectories over sea ice. These emissions are higher than those suggested by previous studies and indicate the importance of lower latitude snowpack emissions. The difference in emission rate for the two types of snow cover shows the importance of snow depth and underlying surface type for the emission potential of snow-covered areas.     

Cross-sections and quantum yields for the atmospheric photolysis of the potent greenhouse gas nitrogen trifluoride

Although NF₃, a trace gas of purely anthropogenic origin with a large global warming potential is accumulating in the Earth's atmosphere, little photochemical data exists from which to calculate its atmospheric removal rate. In this study, photodissociation quantum yields, Φ₁, were derived following 193.3 nm laser photolysis of NF₃, and quantitative conversion of the F-atom photoproducts to OH, which was detected by laser induced fluorescence. Values of Φ₁(P, T) = (1.03 ± 0.05) were determined at pressures between 28 and 100 mBar of He or N₂ and at either room temperature or 255 K. Absorption cross-sections, σ, obtained between 184 and 226 nm were combined with the values of Φ₁(P, T) to confirm a long (≈700 year) photolysis lifetime for NF₃. No evidence for reaction of OH with NF₃ was found, indicating that this process makes little or no contribution to NF₃ removal from the atmosphere. These results underpin recent calculations of an NF₃ atmospheric lifetime τ ≈ 550 years, largely controlled by photolysis in the stratosphere. In the course of this work the rate coefficient k₂(298 K) = (1.3 ± 0.2) × 10^?11 cm³ molecule^?1 s^?1 was obtained for the reaction F + H₂O.     

Kinetics and equilibrium properties of the biosorption of Cu2+ by algae

The purpose of this study was to examine the kinetics and equilibrium properties of freshwater algae with Cu²⁺. This was a model system to explore using algae as biosensors for water quality. Methods included making luminescence measurements (fluorescence) and copper ion-selective electrode (CuISE) measurements vs. time to obtain kinetic data. Results were analyzed using a pseudo-first-order model to calculate the rate constants of Cu²⁺ uptake by algae: k _p(Cu?Calgae)?=?0.0025?±?0.0006?s^?1 by CuISE and k _p(Cu?Calgae)?=?0.0034?±?0.0011?s^?1 by luminescence. The binding constant of Cu?Calgae, K _Cu?Calgae, was 1.62?±?0.07?×?10⁷?M^?1. Fluorescence results analyzed using the Stern?CVolmer relationship indicate that algae have two types of binding sites of which only one appears to affect quenching. The fluorescence-based method was found to be able to detect the reaction of algae with Cu²⁺ quickly and at a detection limit of 0.1?mg?L^?1.