A theoretical and experimental study of atmospheric reactions of amines and their degradation products

Amine-based CO2 capture has been proposed as a way of mitigating climate change. In this work, the fundamental processes governing the atmospheric gas phase chemistry of amines released from CO2 capture have been studiedusing computational and experimental methods. The reactions of amines, amides and imines with OH radicals have been studied with computational methods. The reactions are all characterized by strongly bound pre-reaction complexes and submerged barriers to hydrogen abstraction. Rate coefficients calculated from statistical rate theory show negative temperature dependencies and are in good agreement with experimental results where available. It has been suggested that the climate effect of amine based CO2 capture may be counteracted by the formation of N2O as a minor product in the photo-oxidation of methylamine. Calculations in this work unambiguously show that N2O is not a product in the photo-oxidation of methylamine. The reaction rate coefficients for the OH radical reactions of N-methylformamide and N,N-dimethylformamide have been measured as a function of temperature and pressure by using the flash photolysis laser-induced fluorescence technique. The reactions are significantly slower than the corresponding amine reactions and show a negative temperature dependence. The study further reveals that the amides have a higher potential for nitramine and nitrosamine formation and that they may therefore constitute a previously undisclosed health risk. Kinetic isotope effects for the OH radical reaction of HCN have been measured in a smog chamber through the use of FTIR spectroscopy. The measured values and calculated results confirm that the reaction, unlike the other reactions in this work, mainly occur through an addition channel. The present work has contributed significantly to our understanding of the atmospheric reactions of the intermediates in the atmospheric degradation of methyl amines

Characterization of two photon excited fragment spectroscopy (TPEFS) for HNO3 detection in gas-phase kinetic experiments

We have developed and tested two-photon excited fragment spectroscopy (TPEFS) for detecting HNO3 in pulsed laser photolysis kinetic experiments. Dispersed (220–330 nm) and time-dependent emission at (310 ± 5) nm following the 193 nm excitation of HNO3 in N2, air and He was recorded and analysed to characterise the OH(A2Σ) and NO(A2Σ+) electronic excited states involved. The limit of detection for HNO3 using TPEFS was ∼5 × 109 molecule cm−3 (at 60 torr N2 and 180 μs integration time). Detection of HNO3 using the emission at (310 ± 5 nm) was orders of magnitude more sensitive than detection of NO and NO2, especially in the presence of O2 which quenches NO(A2Σ+) more efficiently than OH(A2Σ). While H2O2 (and possibly HO2) could also be detected by 193 nm TPEFS, the relative sensitivity (compared to HNO3) was very low. The viability of real-time TPEFS detection of HNO3 using emission at (310 ± 5) nm was demonstrated by monitoring HNO3 formation in the reaction of OH + NO2 and deriving the rate coefficient, k2. The value of k2 obtained at 293 K and pressures of 50–200 torr is entirely consistent with that obtained by simultaneously measuring the OH decay and is in very good agreement with the most recent literature values

Atmospheric Chemistry of tert-butylamine and AMP

The atmospheric chemistry of (CH3)3CNH2 (tert-butylamine, tBA) and (CH3)2(CH2OH)CNH2 (2-amino-2-methyl-1-propanol, AMP) has been studied by quantum chemistry methods and in photo-oxidation experiments in the EUPHORE chamber in Valencia (Spain). Aerosol formation and composition has been quantified. Yields of nitramines and other products in the photo-oxidations have been determined and complete photo-oxidation schemes including branching between the major reaction routes have been obtained. Published by Elsevier Ltd

Floating Patches of HCN at the Surface of Their Aqueous Solutions - Can They Make "HCN World" Plausible?

The liquid/vapor interface of the aqueous solutions of HCN of different concentrations has been investigated using molecular dynamics simulation and intrinsic surface analysis. Although HCN is fully miscible with water, strong interfacial adsorption of HCN is observed at the surface of its aqueous solutions, and, at the liquid surface, the HCN molecules tend to be located even at the outer edge of the surface layer. It turns out that in dilute systems the HCN concentration can be about an order of magnitude larger in the surface layer than in the bulk liquid phase. Furthermore, HCN molecules show a strong lateral self-association behavior at the liquid surface, forming thus floating HCN patches at the surface of their aqueous solutions. Moreover, HCN molecules are staying, on average, an order of magnitude longer at the liquid surface than water molecules, and this behavior is more pronounced at smaller HCN concentrations. Because of this enhanced dynamical stability, the floating HCN patches can provide excellent spots for polymerization of HCN, which can be the key step in the prebiotic synthesis of partially water-soluble adenine. All of these findings make the hypothesis of "HCN world" more plausible

Absolute and relative-rate measurement of the rate coefficient for reaction of perfluoro ethyl vinyl ether (C₂F₅OCF=CF₂) with OH

The rate coefficient (k1) for the reaction of OH radicals with perfluoro ethyl vinyl ether (PEVE, C2F5OCF[double bond, length as m-dash]CF2) has been measured as a function of temperature (T = 207–300 K) using the technique of pulsed laser photolysis with detection of OH by laser-induced fluorescence (PLP-LIF) at pressures of 50 or 100 Torr N2 bath gas. In addition, the rate coefficient was measured at 298 K and in one atmosphere of air by the relative-rate technique with loss of PEVE and reference reactant monitored in situ by IR absorption spectroscopy. The rate coefficient has a negative temperature dependence which can be parameterized as: k1(T) = 6.0 × 10−13 exp[(480 ± 38/T)] cm3 molecule−1 s−1 and a room temperature value of k1 (298 K) = (3.0 ± 0.3) × 10−12 cm3 molecule−1 s−1. Highly accurate rate coefficients from the PLP-LIF experiments were achieved by optical on-line measurements of PEVE and by performing the measurements at two different apparatuses. The large rate coefficient and the temperature dependence indicate that the reaction proceeds via OH addition to the C[double bond, length as m-dash]C double bond, the high pressure limit already being reached at 50 Torr N2. Based on the rate coefficient and average OH levels, the atmospheric lifetime of PEVE was estimated to be a few days

Kinetics of the OH + NO₂ reaction: rate coefficients (217-333 K, 16-1200 mbar) and fall-off parameters for N₂ and O₂ bath gases

The radical terminating, termolecular reaction between OH and NO2 exerts great influence on the NOy∕NOx ratio and O3 formation in the atmosphere. Evaluation panels (IUPAC and NASA) recommend rate coefficients for this reaction that disagree by as much as a factor of 1.6 at low temperature and pressure. In this work, the title reaction was studied by pulsed laser photolysis and laser-induced fluorescence over the pressure range 16–1200 mbar and temperature range 217–333 K in N2 bath gas, with experiments at 295 K (67–333 mbar) for O2. In situ measurement of NO2 using two optical absorption set-ups enabled generation of highly precise, accurate rate coefficients in the fall-off pressure range, appropriate for atmospheric conditions. We found, in agreement with previous work, that O2 bath gas has a lower collision efficiency than N2 with a relative collision efficiency to N2 of 0.74. Using the Troe-type formulation for termolecular reactions we present a new set of parameters with k0(N2) = 2.6×10−30  cm6 molecule−2 s−1, k0(O2) = 2.0×10−30 cm6 molecule−2 s−1, m=3.6, k∞=6.3×10−11 cm3 molecule−1 s−1, and Fc=0.39 and compare our results to previous studies in N2 and O2 bath gases

Development of the Palpation Domain for Muscle and Skin in the Global Body Examination

Objectives: To develop new scales within palpation of muscle and skin domains based on 16 items from the Global Physiotherapy Examination and 46 items from the Comprehensive Body Examination [CBE], and to investigate how well these new scales would discriminate between healthy individuals and different groups of patients, when compared with the original methods. Methods: Two physiotherapists independently examined 132 persons [34 healthy, 32 with localized pain, 32 with widespread pain, and 34 with psychoses]. Muscle and skin domains were studied separately. The numbers of items were reduced by omitting items with too high a correlation and by exploratory factor analysis [EFA]. Internal consistency was examined with Cronbach’s α. Discriminative validity was examined using the Mann–Whitney U-test and the area under the curve. Results: Only items from the left body half was included in the EFA, as very high correlation [mean r = 0.90] was found in the 23 bilateral palpation pairs in CBE. The initial 62 items were reduced to 11 for palpation of muscle and 5 for palpation of skin. Cronbach’s α was 0.88 for the subscales for Muscle and Skin. The new Palpation domain in the Global Body Examination showed excellent discriminative ability between healthy persons and the different patient groups [P < 0.001; area under the curve 0.81–0.94]. Patients with localized pain had significantly less muscular and skin aberration than patients with widespread pain. Conclusions: A new Global Body Examination Palpation domain with acceptable psychometric properties was developed. It had fewer items than the Global Physiotherapy Examination and CBE, but with almost the same discriminating ability