Thermal Characterization of Aminium Nitrate Nanoparticles

Atmospheric Chemistry of 2-Amino-2-methyl-1-propanol: A Theoretical and Experimental Study of the OH-Initiated Degradation under Simulated Atmospheric Conditions

The OH-initiated degradation of 2-amino-2-methyl-1-propanol [CH₃C(NH₂)(CH₃)CH₂OH, AMP] was investigated in a large atmospheric simulation chamber, employing time-resolved online high-resolution proton-transfer reaction-time-of-flight mass spectrometry (PTR-ToF-MS) and chemical analysis of aerosol online PTR-ToF-MS (CHARON-PTR-ToF-MS) instrumentation, and by theoretical calculations based on M06-2X/aug-cc-pVTZ quantum chemistry results and master equation modeling of the pivotal reaction steps. The quantum chemistry calculations reproduce the experimental rate coefficient of the AMP + OH reaction, aligning k(T) = 5.2 × 10^–12 × exp (505/T) cm³ molecule^–1 s^–1 to the experimental value k_exp,300K = 2.8 × 10^–11 cm³ molecule^–1 s^–1. The theoretical calculations predict that the AMP + OH reaction proceeds via hydrogen abstraction from the −CH₃ groups (5–10%), −CH₂– group, (>70%) and −NH₂ group (5–20%), whereas hydrogen abstraction from the −OH group can be disregarded under atmospheric conditions. A detailed mechanism for atmospheric AMP degradation was obtained as part of the theoretical study. The photo-oxidation experiments show 2-amino-2-methylpropanal [CH₃C(NH₂)(CH₃)CHO] as the major gas-phase product and propan-2-imine [(CH₃)₂C=NH], 2-iminopropanol [(CH₃)(CH₂OH)C=NH], acetamide [CH₃C(O)NH₂], formaldehyde (CH₂O), and nitramine 2-methyl-2-(nitroamino)-1-propanol [AMPNO₂, CH₃C(CH₃)(NHNO₂)CH₂OH] as minor primary products; there is no experimental evidence of nitrosamine formation. The branching in the initial H abstraction by OH radicals was derived in analyses of the temporal gas-phase product profiles to be B_CH3/B_CH2/B_NH2 = 6:70:24. Secondary photo-oxidation products and products resulting from particle and surface processing of the primary gas-phase products were also observed and quantified. All the photo-oxidation experiments were accompanied by extensive particle formation that was initiated by the reaction of AMP with nitric acid and that mainly consisted of this salt. Minor amounts of the gas-phase photo-oxidation products, including AMPNO₂, were detected in the particles by CHARON-PTR-ToF-MS and GC×GC-NCD. Volatility measurements of laboratory-generated AMP nitrate nanoparticles gave Δ_vapH = 80 ± 16 kJ mol^–1 and an estimated vapor pressure of (1.3 ± 0.3) × 10^–5 Pa at 298 K. The atmospheric chemistry of AMP is evaluated and a validated chemistry model for implementation in dispersion models is presented.

Theoretical and Experimental Study on the Reaction of tert-Butylamine with OH Radicals in the Atmosphere

The OH-initiated atmospheric degradation of tert-butylamine (tBA), (CH₃)₃CNH₂, was investigated in a detailed quantum chemistry study and in laboratory experiments at the European Photoreactor (EUPHORE) in Spain. The reaction was found to mainly proceed via hydrogen abstraction from the amino group, which in the presence of nitrogen oxides (NO _x), generates tert-butylnitramine, (CH₃)₃CNHNO₂, and acetone as the main reaction products. Acetone is formed via the reaction of tert-butylnitrosamine, (CH₃)₃CNHNO, and/or its isomer tert-butylhydroxydiazene, (CH₃)₃CN═NOH, with OH radicals, which yield nitrous oxide (N₂O) and the (CH₃)₃Ċ radical. The latter is converted to acetone and formaldehyde. Minor predicted and observed reaction products include formaldehyde, 2-methylpropene, acetamide and propan-2-imine. The reaction in the EUPHORE chamber was accompanied by strong particle formation which was induced by an acid-base reaction between photochemically formed nitric acid and the reagent amine. The tert-butylaminium nitrate salt was found to be of low volatility, with a vapor pressure of 5.1 × 10^-6 Pa at 298 K. The rate of reaction between tert-butylamine and OH radicals was measured to be 8.4 (±1.7) × 10^-12 cm³ molecule^-1 s^-1 at 305 ± 2 K and 1015 ± 1 hPa.

Thermal Stability of Particle-Phase Monoethanolamine Salts

The use of monoethanolamine (MEA, 2-hydroxyethanamine) for scrubbing of carbon dioxide from combustion flue gases may become the dominant technology for carbon capture in the near future. The widespread implementation of this technology will result in elevated emissions of MEA to the environment that may increase the loading and modify the properties of atmospheric aerosols. We have utilized experimental measurements together with aerosol microphysics calculations to derive thermodynamic properties of several MEA salts, potentially the dominant forms of MEA in atmospheric particles. The stability of the salts was found to depend strongly on the chemical nature of the acid counterpart. The saturation vapor pressures and vaporization enthalpies obtained in this study can be used to evaluate the role of MEA in the aerosol and haze formation, helping to assess impacts of the MEA-based carbon capture technology on air quality and climate change.

Enhanced durability of carbon nanotube grafted hierarchical ceramic microfiber-reinforced epoxy composites

As carbon nanotube (CNT) infused hybrid composites are increasingly identified as next-generation aerospace materials, it is vital to evaluate their long-term structural performance under aging environments. In this work, the durability of hierarchical, aligned CNT grafted aluminoborosilicate microfiber-epoxy composites (CNT composites) are compared against baseline aluminoborosilicate composites (baseline composites), before and after immersion in water at 25 °C (hydro) and 60 °C (hydrothermal), for extended durations (90 d and 180 d). The addition of CNTs is found to reduce water diffusivities by approximately 1.5 times. The mechanical properties (bending strength and modulus) and the damage sensing capabilities (DC conductivity) of CNT composites remain intact regardless of exposure conditions. The baseline composites show significant loss of strength (44 %) after only 15 d of hydrothermal aging. This loss of mechanical strength is attributed to fiber-polymer interfacial debonding caused by accumulation of water at high temperatures. In situ acoustic and DC electrical measurements of hydrothermally aged CNT composites identify extensive stress-relieving micro-cracking and crack deflections that are absent in the aged baseline composites. These observations are supported by SEM images of the failed composite cross-sections that highlight secondary matrix toughening mechanisms in the form of CNT pullouts and fractures which enhance the service life of composites and maintain their properties under accelerated aging environments.

Single Usage of a Kitchen Degreaser Can Alter Indoor Aerosol Composition for Days

To the best of our knowledge, this study represents the first observation of multiday persistence of an indoor aerosol transformation linked to a kitchen degreaser containing monoethanol amine (MEA). MEA remaining on the cleaned surfaces and on a wiping paper towel in a trash can was able to transform ammonium sulfate and ammonium nitrate into (MEA)₂SO₄ and (MEA)NO₃. This influence persisted for at least 60 h despite a high average ventilation rate. The influence was observed using both offline (filters, impactors, and ion chromatography analysis) and online (compact time-of-flight aerosol mass spectrometer) techniques. Substitution of ammonia in ammonium salts was observed not only in aerosol but also in particles deposited on a filter before the release of MEA. The similar influence of other amines is expected based on literature data. This influence represents a new pathway for MEA exposure of people in an indoor environment. The stabilizing effect on indoor nitrate also causes higher indoor exposure to fine nitrates.

Transition-Metal-Doped p-Type ZnO Nanoparticle-Based Sensory Array for Instant Discrimination of Explosive Vapors

The development of portable, real-time, and cheap platforms to monitor ultratrace levels of explosives is of great urgence and importance due to the threat of terrorism attacks and the need for homeland security. However, most of the previous chemiresistor sensors for explosive detection are suffering from limited responses and long response time. Here, a transition-metal-doping method is presented to remarkably promote the quantity of the surface defect states and to significantly reduce the charge transfer distance by creating a local charge reservoir layer. Thus, the sensor response is greatly enhanced and the response time is remarkably shortened. The resulting sensory array can not only detect military explosives, such as, TNT, DNT, PNT, PA, and RDX with high response, but also can fully distinguish some of the improvised explosive vapors, such as AN and urea, due to the huge response reaching to 100%. Furthermore, this sensory array can discriminate ppb-level TNT and ppt-level RDX from structurally similar and high-concentration interfering aromatic gases in less than 12 s. Through comparison with the previously reported chemiresistor or Schottky sensors for explosive detection, the present transition-metal-doping method resulting ZnO sensor stands out and undoubtedly challenges the best.

Multiphase chemistry of atmospheric amines

Heterogeneous reactions of amines have been recently shown to play an important role in the formation and transformation of atmospheric aerosols. This perspective summarizes the latest laboratory progress in the multiphase chemistry of amines. Particular emphasis is given to the contributions of amines to new particle formation, growth of submicron particles, and alteration in the physiochemical properties of pre-existing particles, including hygroscopicity, thermostability, density, phase, and optical properties, from exposure to gaseous amines. The atmospheric implications of the multiphase reactions of amines, including the potential impact on direct and indirect climate forcing of aerosols, and future research directions are discussed.

Physiochemical properties of alkylaminium sulfates: hygroscopicity, thermostability, and density

Although heterogeneous interaction of amines has been recently shown to play an important role in the formation and growth of atmospheric aerosols, little information is available on the physicochemical properties of aminium sulfates. In this study, the hygroscopicity, thermostability, and density of alkylaminium sulfates (AASs) have been measured by an integrated aerosol analytical system including a tandem differential mobility analyzer and an aerosol particle mass analyzer. AAS aerosols exhibit monotonic size growth at increasing RH without a well-defined deliquescence point. Mixing of ammonium sulfate (AS) with AASs lowers the deliquescence point corresponding to AS. Particles with AASs show comparable or higher thermostability than that of AS. The density of AASs is determined to be 1.2-1.5 g cm(-3), and an empirical model is developed to predict the density of AASs on the basis of the mole ratio of alkyl carbons to total sulfate. Our results reveal that the heterogeneous uptake of amines on sulfate particles may considerably alter the aerosol properties. In particular, the displacement reaction of alkylamines with ammonium sulfate aerosols leads to a transition from the crystalline to an amorphorous phase and an improved water uptake, considerably enhancing their direct and indirect climate forcing.