The heterogeneous interaction of limonene and toluene with Saharan dusts was investigated under dark conditions, pressure of 1 atm, and temperature 293 K. The mineral dust samples were collected from ...six different regions along the Sahara desert, extending from Tunisia to the western Atlantic coastal areas of Morocco, and experiments were carried out with the smallest sieved fractions, that is, inferior to 100 μm. N2 sorption measurements, granulometric analysis, and X-ray fluorescence and diffraction (XRF and XRD) measurements were conducted to determine the physicochemical properties of the particles. The chemical characterization showed that dust originating from mideastern Sahara has a significantly higher SiO2 content (∼82%) than dust collected from the western coastal regions where the SiO2 relative abundance was ∼50%. A novel experimental setup combining diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), selected-ion flow-tube mass spectrometry (SIFT–MS), and long path transmission Fourier transform infrared spectroscopy (FTIR) allowed us to follow both the adsorbed and gas phases. The kinetic adsorption/desorption measurements were performed using purified dry air as bath gas, exposing each dust surface to 10 ppm of the selective volatile organic compound (VOC). The adsorption of limonene was independent of the SiO2 content, given the experimental uncertainties, and the coverage measurements ranged between (10 and 18) × 1013 molecules cm–2. Experimental results suggest that other metal oxides that could possibly influence dust acidity may enhance the adsorption of limonene. On the contrary, in the case of toluene, the adsorption capacities of the Saharan samples increased with decreasing SiO2 content; however, the coverage measurements were significantly lower than those of limonene and ranged between (2 and 12) × 1013 molecules cm–2. Flushing the surface with purified dry air showed that VOC desorption is not a completely reversible process at room temperature. The reversibly adsorbed fraction and the rate coefficients of desorption, k des, depended inversely on the SiO2 relative abundance for both VOCs.
In the current study, the temperature dependence of the Cl atom rate coefficient with 2‐methyl‐3‐butene‐2‐ol (MBO) is re‐assessed. Relative rate kinetic measurements were performed inside THALAMOS ...(thermally regulated atmospheric simulation chamber) facility under atmospheric pressure (760 Torr) of zero air in the temperature range of 256–353 K. The rate coefficient of the title reaction was found to be independent of temperature with a value of kMBO = (3.20 ± 0.10) × 10−10 cm3 molecule–1 s–1, where the quoted error corresponds to 2σ standard error of the mean value and includes the overall uncertainty of the measurements. Besides the kinetic study we have also determined the yields of the major products formed, in the temperature range of 273–353 K. Acetone and chloroacetaldehyde were identified as primary oxidation products with almost identical yields, ranging between 60% and 80%. Formaldehyde and methyl vinyl ketone were also observed with yields below 10% and 0.5%, respectively. Our experimental results indicate that the dominant reaction pathway is the addition of Cl atoms to the terminal carbon atom of MBO.
Earlier studies suggest that SO2 gas reacts at the surface of mineral dust and forms sulfites or bisulfites, which are then converted to sulfates. In order to monitor and quantify the amounts of both ...sulfites and sulfates formed on the surface of mineral dusts of volcanic and desert origins an accurate and precise reversed-phase liquid chromatography method was developed and validated to extract, stabilize and individually analyze sulfites and sulfates initially present on the surface of dusts exposed to SO2. The method was developed on a 25 mm Restek Ultra Column C18, Particle size: 5 μm, I.D. 4.60 mm column which was dynamically coated with 1.0 mM cetylpyridinium chloride in 7% acetonitrile solution to produce a charged surface as recommended in the literature. Mobile phase used: 1 mM Potassium Hydrogen Phthalate at pH 6.5 at a flow rate of 1.0 ml/min with negative UV–Vis detection at 255 nm in 15 min. The method was validated for specificity, linearity and range, injection repeatability, stability, robustness, limit of detection and limit of quantitation, and sample preparation and extraction reproducibility. The method was adapted for straight sulfite and sulfate quantification: (i) of environmental samples, and (ii) natural samples additionally exposed to SO2 gas in a dedicated laboratory setup. The method was then successfully applied to quantify sulfites and sulfates on natural volcanic and a desert dust samples both collected in the environment and additionally exposed to SO2 gas in the laboratory. The method can be efficiently used to identify sulfites and sulfates on fresh volcanic ash following an eruption, on aeolian desert dust exposed to industrial pollutants, as well as for laboratory investigations of sulfite and sulfate formation on the surface of minerals and natural dusts of different origins.
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•Method developed for the quantification of sulfites and sulfates on mineral dust.•Extraction and stabilization of sulfites and sulfates from natural dust samples.•Selective quantifications of sulfites and sulfates using HPLC.•Application of the method to laboratory aged samples, as well as natural samples.
Polyaniline (PAni)-based sensors are a promising solution for ammonia (NH3) detection at the ppb level. However, the nature of the NH3–PAni interaction and underlying drivers remain unclear. This ...paper proposes to characterize the interaction between doped PAni (dPAni) sensing material and NH3 by using a Knudsen cell. First, to characterize the dPAni interface, the probe-gas method, i.e., titration of surface sites with a gas of specific properties, is deployed. The dPAni interface is found to be homogeneous with more than 96% of surface sites of acid nature or with hydroxyl functional groups. This result highlights that basic gases such as amines might act as interfering gases for NH3 detection by polyaniline-based sensors. Second, the adsorption isotherms of NH3 and trimethylamine (TMA) on dPAni are reported at ambient temperature conditions, 293 K. The uptake of NH3 and TMA on dPAni follows a Langmuir-type behavior. This approach allows for the first time to quantify the uptake of NH3 and TMA on gas-sensor materials and determine typical Langmuir adsorption parameters, i.e., the partitioning coefficient, K Lang, and the maximum surface coverage, N max. The corresponding values obtained for NH3 and TMA are K lang (NH3) = 19.7 × 10–15 cm3 molecules–1 N max (NH3) = 11.6 × 1014 molecules cm–2, K Lang (TMA) = 7.0 × 10–15 cm3 molecules–1 N max (TMA) = 5.0 × 1014 molecules cm–2. K Lang and N max values of NH3 are higher than those of TMA, suggesting that NH3 is more efficiently taken up than TMA on dPAni. The results of this work suggest that strong hydrogen bonding drives the performance of a polyaniline-based gas sensor for NH3 and amines. In conclusion, the Knudsen cell approach allows reconsidering the fundamentals of NH3 interactions with dPAni and provides new insights on drivers to enhance sensing properties.
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•Metal co-doping to improve the performance of TiO2 based photocatalysts.•Degradation kinetics of acetaldehyde under simulated indoor and outdoor conditions.•Metal co-doping leads to ...a synergetic effect of acetaldehyde uptake and degradation under UV light conditions.•Degradation of acetaldehyde on Mn-TiO2 in presence of visible light leads to nontoxic byproducts.
This study demonstrates the photocatalytic decomposition of an indoor air pollutant, acetaldehyde (CH3CHO), over 0.04 mol% metal-doped TiO2 (Mn-, Co- and Mn/Co-) nanoparticles activated by ultraviolet and visible irradiation. The photocatalytic activity, the photodegradation kinetics, and the final product analysis were examined using a Static Photochemical Reactor coupled with a FTIR spectrophotometer. CH3CHO undergoes efficient decomposition over all photocatalysts under UV irradiation in the presence of one atmosphere N2 or synthetic air (SA). Metal doping causes substantial influence to photocatalysis by altering the amount of electron/hole pairs generated and/or the electron/hole recombination rates. Simulating the experimental results with pseudo-first order kinetics the corresponding degradation rate coefficients were determined for each photocatalyst under UV irradiation and SA environment: kdUV(Mn-TiO2) = (1.9 ± 0.2)×10−1 h−1, kdUV(Co-TiO2) = (2.8 ± 0.3)×10−1 h−1, and kdUV(Mn/Co-TiO2) = (6.0 ± 0.7)×10−1 h−1. These degradation kinetics under UV light irradiation are significantly faster than undoped TiO2 revealing that the transition metal doping of TiO2 nanomaterials boosts the photocatalytic degradation of organic pollutants. Substantial decomposition of CH3CHO was achieved over Mn-TiO2 under visible light in oxygen presence kdVis(SA) = (0.44 ± 0.04)×10−1 h−1 while for other samples no visible light photocatalysis was observed. CO2, CO, and H2O were the main oxidation products, with CO2 yields almost 100% under UV excitation, and CO yields up to 20% under UV and <1% under visible excitation. Our experimental results suggest that Mn-TiO2 (0.04 mol%) nanoparticles may be considered as a potentially safe photocatalyst to remove acetaldehyde particularly from indoor atmospheric environments under visible irradiation, without yielding significant toxic by-products. Other possible atmospheric implications are also discussed in the paper.
The atmospheric reaction of a series of furan compounds (furan (F), 2-methylfuran (2-MF), 3-methylfuran (3-MF), 2,5-dimethylfuran (2,5-DMF), and 2,3,5-trimethylfuran (2,3,5-TMF)) with nitrate radical ...(NO3) has been investigated using the relative rate kinetic method in the CHamber for the Atmospheric Reactivity and the Metrology of the Environment (CHARME) simulation chamber at the laboratoire de Physico-Chimie de l’Atmosphere (LPCA) laboratory (Dunkerque, France). The experiments were performed at (294 ± 2) K atmospheric pressure and under dry conditions (relative humidity, RH < 2%) with proton transfer mass reaction–time of flight–mass spectrometer (PTR-ToF-MS) for the chemical analysis. The following rate coefficients (in units cm3 molecule–1 s–1) were determined: furan, k (F) = (1.51 ± 0.38) × 10–12, 2-methylfuran, k (2‑MF) = (1.91 ± 0.32) × 10–11, 3-methylfuran, k (3‑MF) = (1.49 ± 0.33) × 10–11, 2,5-dimethylfuran, k (2,5‑DMF) = (5.82 ± 1.21) × 10–11, and 2,3,5-trimethylfuran, k (2,3,5‑TMF) = (1.66 ± 0.69) × 10–10. The uncertainty on the measured rate coefficient (Δk FC) includes both the uncertainty on the measurement and that on the rate coefficient of the reference molecule. To our knowledge, this work represents the first determination for the rate coefficient of the 2,3,5-TMF reaction with NO3. This work shows that the reaction between furan and methylated furan compounds with nitrate radical (NO3) is the dominant removal pathway during the night with lifetimes between 0.5 and 55 min for the studied molecules.
Molecular hydrogen (H2) is now considered among the most prominent substitute for fossil fuels. The environmental impacts of a hydrogen economy have received more attention in the last years, but ...still, the knowledge is relatively poor. In this work, the reaction of H2 with NO3 radical (the dominant night-time detergent of the atmosphere) is studied for the first time using high-level composite G3B3 and modification of high accuracy extrapolated ab initio thermochemistry (mHEAT) methods in combination with statistical kinetics analysis using non-separable semi-classical transition state theory (SCTST). The reaction mechanism is characterized, and it is found to proceed as a direct H-abstraction process to yield HNO3 plus H atom. The reaction enthalpy is calculated to be 12.8 kJ mol−1, in excellent agreement with a benchmark active thermochemical tables (ATcT) value of 12.2 ± 0.3 kJ mol−1. The energy barrier of the title reaction was calculated to be 74.6 and 76.7 kJ mol−1 with G3B3 and mHEAT methods, respectively. The kinetics calculations with the non-separable SCTST theory give a modified-Arrhenius expression of k(T) = 10−15 × T0.7 × exp(−6120/T) (cm3 s−1) for T = 200–400 K and provide an upper limit value of 10−22 cm3 s−1 at 298 K for the reaction rate coefficient. Therefore, as compared to the main consumption pathway of H2 by OH radicals, the title reaction plays an unimportant role in H2 loss in the Earth’s atmosphere and is a negligible source of HNO3.
ABSTRACT
The kinetics of the reactions of propane, n‐pentane, and n‐heptane with OH radicals has been studied using a low‐pressure flow tube reactor (P = 1 Torr) coupled with a quadrupole mass ...spectrometer. The rate constants of the title reactions were determined under pseudo–first‐order conditions, monitoring the kinetics of OH radical consumption in excess of the alkanes. A newly developed high‐temperature flow reactor was validated by the study of the OH + propane reaction, where the reaction rate constant, k1 = 5.1 × 10−17T1.85exp(–160/T) cm3 molecule−1 s−1 (uncertainty of 20%), measured in a wide temperature range, 230–898 K, was found to be in excellent agreement with previous studies and current recommendations. The experimental data for the rate constants of the reactions of OH with n‐pentane and n‐heptane can be represented as three parameter expressions (in cm3 molecule−1 s−1, uncertainty of 20%): k2 = 5.8 × 10−18T2.2exp(260/T) at T= 248–900 K and k3 = 2.7 × 10−16T1.7exp(138/T) at T= 248–896 K, respectively. A combination of the present data with those from previous studies leads to the following expressions: k1 = 2.64 × 10−17T1.93exp(–114/T), k2 = 9.0 × 10−17T1.8 exp(120/T), and k3 = 3.75 × 10−16 T1.65 exp(101/T) cm3 molecule−1 s−1, which can be recommended for k1, k2, and k3 (with uncertainty of 20%) in the temperature ranges 190–1300, 240–1300, and 220–1300 K, respectively.
ABSTRACT
Reactions of F2 molecules exhibit unusual features, manifesting in high reactivity of F2 with respect to some closed‐shell molecules and low reactivity toward chemically active species, such ...as halogen and oxygen atoms. The existing data base on the reactions of F2 being rather sparse, kinetic and mechanistic studies (preferably over a wide temperature range) are needed to better understand the nature of the specific reactivity of fluorine molecule. In the present work, reactions of F2 with Br atoms and Br2 have been studied for the first time in an extended temperature range using a discharge flow reactor combined with an electron impact ionization mass spectrometer. The rate constant of the reaction F2 + Br → F +BrF (1) was determined either from kinetics of the reaction product, BrF, formation or from the kinetics of Br consumption in excess of F2: k1 = (4.66 ± 0.93) × 10−11 exp(−(4584 ± 86)/T) cm3 molecule−1 s−1 at T = 300–940 K. The rate constant of the reaction F2 + Br2 → products (2), k2 = (9.23 ± 2.68) × 10−11 exp(−(8373 ± 194)/T) cm3 molecule−1 s−1, was determined in the temperature range 500–958 K by monitoring both reaction product (FBr) formation and F2 consumption kinetics in excess of Br2. The results of the experimental measurements of the yield of FBr (1.02 ± 0.07 at T = 960 K) combined with thermochemical calculations indicate that F+Br2F forming channel of reaction (2) is probably the dominant one, at least, at highest temperature of the study.
The adsorption of isopropanol on Gobi dust was investigated in the temperature (T) and relative humidity (RH) ranges of 273–348 K and <0.01–70%, respectively, using zero air as bath gas. The kinetic ...measurements were performed using a novel experimental setup combining Fourier-Transform InfraRed spectroscopy (FTIR) and selected-ion flow-tube mass spectrometry (SIFT-MS) for gas-phase monitoring. The initial uptake coefficient, γ0, of isopropanol was measured as a function of several parameters (concentration, temperature, relative humidity, dust mass). γ0 was found independent of temperature while it was inversely dependent on relative humidity according to the empirical expression: γ0 = 5.37 × 10–7/(0.77+RH0.6). Furthermore, the adsorption isotherms of isopropanol were determined and the results were simulated with the Langmuir adsorption model to obtain the partitioning constant, K Lin, as a function of temperature and relative humidity according to the expressions: K Lin = (1.1 ± 0.3) × 10–2 exp (1764 ± 132)/T and K Lin = 15.75/(3.21+RH1.77). Beside the kinetics, a detailed product study was conducted under UV irradiation conditions (350–420 nm) in a photochemical reactor. Acetone, formaldehyde, acetic acid, acetaldehyde, carbon dioxide, and water were identified as gas-phase products. Besides, the surface products were extracted and analyzed employing HPLC; Hydroxyacetone, formaldehyde, acetaldehyde, acetone, and methylglyoxal were identified as surface products while the formation of several other compounds were observed but were not identified. Moreover, the photoactivation of the surface was verified employing diffuse reflectance infrared fourier transform spectroscopy (DRIFTs).
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