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1.
Proc Natl Acad Sci U S A ; 117(21): 11321-11327, 2020 May 26.
Artigo em Inglês | MEDLINE | ID: mdl-32393627

RESUMO

The neonicotinoid nitenpyram (NPM) is a multifunctional nitroenamine [(R1N)(R2N)C=CHNO2] pesticide. As a nitroalkene, it is structurally similar to other emerging contaminants such as the pharmaceuticals ranitidine and nizatidine. Because ozone is a common atmospheric oxidant, such compounds may be oxidized on contact with air to form new products that have different toxicity compared to the parent compounds. Here we show that oxidation of thin solid films of NPM by gas-phase ozone produces unexpected products, the majority of which do not contain oxygen, despite the highly oxidizing reactant. A further surprising finding is the formation of gas-phase nitrous acid (HONO), a species known to be a major photolytic source of the highly reactive hydroxyl radical in air. The results of application of a kinetic multilayer model show that reaction was not restricted to the surface layers but, at sufficiently high ozone concentrations, occurred throughout the film. The rate constant derived for the O3-NPM reaction is 1 × 10-18 cm3⋅s-1, and the diffusion coefficient of ozone in the thin film is 9 × 10-10 cm2⋅s-1 These findings highlight the unique chemistry of multifunctional nitroenamines and demonstrate that known chemical mechanisms for individual moieties in such compounds cannot be extrapolated from simple alkenes. This is critical for guiding assessments of the environmental fates and impacts of pesticides and pharmaceuticals, and for providing guidance in designing better future alternatives.

2.
Environ Sci Process Impacts ; 22(1): 66-83, 2020 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-31670732

RESUMO

Secondary organic aerosol (SOA) particles are ubiquitous in air and understanding the mechanism by which they grow is critical for predicting their effects on visibility and climate. The uptake of three organic nitrates into semi-solid SOA particles formed by α-pinene ozonolysis either with or without an OH scavenger was investigated. Four types of experiments are presented here. In Series A, uptake of the selected organic nitrates (2-ethylhexyl nitrate (2EHN); ß-hydroxypropyl nitrate (HPN); ß-hydroxyhexyl nitrate (HHN)) into impacted SOA particles was interrogated by attenuated total reflectance (ATR)-FTIR. In this case, equilibrium was reached and partition coefficients (KSOA = [-ONO2]SOA/[-ONO2]air) were measured to be K2EHN = (3.2-11) × 104, KHPN = (4.4-5.4) × 105, and KHHN = (4.9-9.0) × 106. In Series B, SOA particles were exposed on-the-fly to gas phase organic nitrates for comparison to Series A, and uptake of organic nitrates was quantified by HR-ToF-AMS analysis, which yielded similar results. In Series C (AMS) and D (ATR-FTIR), each organic nitrate was incorporated into the SOA as the particles formed and grew. The incorporation of the RONO2 was much larger in Series C and D (during growth), exceeding equilibrium values determined in Series A and B (after growth). This suggests that enhanced uptake of organic nitrates during SOA formation and growth is due to a kinetically controlled "burying" mechanism, rather than equilibrium partitioning. This has important implications for understanding SOA formation and growth under conditions where the particles are semi-solid, which is central to accurately predicting properties for such SOA.


Assuntos
Aerossóis , Poluentes Atmosféricos , Ozônio , Aerossóis/química , Poluentes Atmosféricos/química , Clima , Monoterpenos , Viscosidade
3.
Rapid Commun Mass Spectrom ; 34(10): e8561, 2020 May 30.
Artigo em Inglês | MEDLINE | ID: mdl-31429122

RESUMO

RATIONALE: Contaminants present in ambient air or in sampling lines can interfere with the target analysis through overlapping peaks or causing a high background. This study presents a positive outcome from the unexpected presence of N-methyl-2-pyrrolidone, released from a PALL HEPA filter, in the analysis of atmospherically relevant gas-phase amines using chemical ionization mass spectrometry. METHODS: Gas-phase measurements were performed using a triple quadrupole mass spectrometer equipped with a modified atmospheric pressure gas chromatography (APGC) source which allows sampling of the headspace above pure amine standards. Gas-phase N-methyl-2-pyrrolidone (NMP) emitted from a PALL HEPA filter located in the inlet stream served as the ionizing agent. RESULTS: This study demonstrates that some alkylamines efficiently form a [NMP + amine+H]+ cluster with NMP upon chemical ionization at atmospheric pressure. The extent of cluster formation depends largely on the proton affinity of the amine compared with that of NMP. Aromatic amines (aniline, pyridine) and diamines (putrescine) were shown not to form cluster ions with NMP. CONCLUSIONS: The use of NMP as an ionizing agent with stand-alone APGC provided high sensitivity for ammonia and the smaller amines. The main advantages, in addition to sensitivity, are direct sampling into the APGC source and avoiding uptake on sampling lines which can be a significant problem with ammonia and amines.

4.
J Agric Food Chem ; 67(6): 1638-1646, 2019 Feb 13.
Artigo em Inglês | MEDLINE | ID: mdl-30698961

RESUMO

Neonicotinoids (NN), first introduced in 1991, are found on environmental surfaces where they undergo photolytic degradation. Photolysis studies of thin films of NN were performed using two approaches: (1) transmission FTIR, in which solid films of NN and the gas-phase products were analyzed simultaneously, and (2) attenuated-total-reflectance FTIR combined with transmission FTIR, in which solid films of NN and the gas-phase products were probed in the same experiment but not at the same time. Photolysis quantum yields using broadband irradiation centered at 313 nm were (2.2 ± 0.9) × 10-3 for clothianidin (CLD), (3.9 ± 0.3) × 10-3 for thiamethoxam (TMX), and (3.3 ± 0.5) × 10-3 for dinotefuran (DNF), with all errors being ±1 s. At 254 nm, which was used to gain insight into the wavelength dependence, quantum yields were in the range of (0.8-20) × 10-3 for all NNs, including acetamiprid (ACM) and thiacloprid (TCD). Nitrous oxide (N2O), a potent greenhouse gas, was the only gas-phase product detected for the photolysis of nitroguanidines, with yields of ΔN2O/ΔNN > 0.5 in air at both 313 and 254 nm. The atmospheric lifetimes with respect to photolysis for CLD, TMX, and DNF, which absorb light in the actinic region, are estimated to be 15, 10, and 11 h, respectively, at a solar zenith angle of 35° and 12, 8, and 10 h at a solar zenith angle of 15°.


Assuntos
Inseticidas/química , Neonicotinoides/química , Óxido Nitroso/química , Fotólise/efeitos da radiação , Espectroscopia de Infravermelho com Transformada de Fourier , Luz Solar
5.
Phys Chem Chem Phys ; 20(34): 22249-22259, 2018 Aug 29.
Artigo em Inglês | MEDLINE | ID: mdl-30123899

RESUMO

The effect of water on the growth of dry nano-size acid-base particles is not yet known. In this paper, we investigate the uptake of water by nano-size particles composed of methanesulfonic acid (MSA) and methylamine (MA) using a combination of quantum chemical calculations and laboratory experiments. Calculations were performed on the (MSA-MA)4 cluster as the dry nanoparticle model, which forms a pseudo-cubic structure, to which twelve water molecules were added successively. Theoretical results show that the hydrated clusters (MSA-MA)4-(H2O)n, n = 1 to 12 are thermodynamically stable. In ab initio dynamic simulations, no loss of water or significant changes of structure are seen for at least 10 picoseconds. In all the clusters studied, most of the water molecules lie on the face of the (MSA-MA)4 initial dry unit, and water is found to be incorporated inside the initial unit for n ranging from five to twelve. Sizes of hydrated clusters exceed significantly that of the dry cluster only for n ≥ 6. These theoretical results suggest that dry MSA-MA clusters cannot dissociate in small quantities of water. Calculations of hydrated cluster distributions at steady state show that the cluster compositions studied, with up to 12 water molecules, encompass all the hydrated clusters under the experimental conditions (RH ∼ 19%, 300 K). Experiments performed in a glass flow reactor showed no changes in size or number concentration when particles formed from MSA-MA were subsequently exposed to water vapor, in contrast to increases in both size and number when water was present during particle formation. Thus, the results seem to imply for both experiment and theory that growth in size of a particle due to uptake of water requires the previous presence of some level of hydration. These results illustrate the importance for atmospheric models of understanding on a molecular basis the mechanisms of particle formation in air.

6.
Environ Sci Technol ; 52(5): 2760-2767, 2018 03 06.
Artigo em Inglês | MEDLINE | ID: mdl-29345468

RESUMO

The environmental fates of nitenpyram (NPM), a widely used neonicotinoid insecticide, are not well-known. A thin solid film of NPM deposited on a germanium attenuated total reflectance (ATR) crystal was exposed to radiation from a low-pressure mercury lamp at 254 nm, or from broadband low pressure mercury photolysis lamps centered at 350 or 313 nm. The loss during photolysis was followed in time using FTIR. The photolysis quantum yields (ϕ), defined as the number of NPM molecules lost per photon absorbed, were determined to be (9.4 ± 1.5) × 10-4 at 350 nm, (1.0 ± 0.3) × 10-3 at 313 nm, and (1.2 ± 0.4) × 10-2 at 254 nm (±2σ). Imines, one with a carbonyl group, were detected as surface-bound products and gaseous N2O was generated in low (11%) yield. The UV-vis absorption spectra of NPM in water was different from that in acetonitrile, dichloromethane, and methanol, or in a thin solid film. The photolytic lifetime of solid NPM at a solar zenith angle at 35° is calculated to be 36 min, while that for NPM in water is 269 min, assuming that the quantum yield is the same as in the solid. Thus, there may be a significant sensitivity to the medium for photolytic degradation and the lifetime of NPM in the environment.


Assuntos
Luz Solar , Raios Ultravioleta , Neonicotinoides , Fotoquímica , Fotólise
7.
Phys Chem Chem Phys ; 19(47): 31949-31957, 2017 Dec 06.
Artigo em Inglês | MEDLINE | ID: mdl-29177355

RESUMO

Mechanisms of particle formation and growth in the atmosphere are of great interest due to their impacts on climate, health and visibility. However, the microscopic structures and related properties of the smallest nanoparticles are not known. In this paper we pursue computationally a microscopic description for the formation and growth of methanesulfonic acid (MSA) and methylamine (MA) particles under dry conditions. Energetic and dynamics simulations were used to assess the stabilities of proposed model structures for these particles. Density functional theory (DFT) and semi-empirical (PM3) calculations suggest that (MSA-MA)4 is a major intermediate in the growth process, with the dissociation energies, enthalpies and free energies indicating considerable stability for this cluster. Dynamics simulations show that this species is stable for at least 100 ps at temperatures up to 500 K, well above atmospheric temperatures. In order to reach experimentally detectable sizes (>1.4 nm), continuing growth is suggested to occur via clustering of (MSA-MA)4. The dimer (MSA-MA)4(MSA-MA)4 may be one of the smaller experimentally measured particles. Step by step addition of MSA to (MSA-MA)4, is also a likely potential growth mechanism when MSA is excess. In addition, an MSA-MA crystal is predicted to exist. These studies demonstrate that computations of particle structure and dynamics in the nano-size range can be useful for molecular level understanding of processes that grow clusters into detectable particles.

8.
Phys Chem Chem Phys ; 19(41): 28286-28301, 2017 Oct 25.
Artigo em Inglês | MEDLINE | ID: mdl-29028063

RESUMO

Atmospheric particles influence visibility, health and climate but the mechanisms of their formation from initial clusters and their growth to detectable particles remain largely unknown. Previous studies show that reactions of methanesulfonic acid (MSA) with ammonia and amines form particles, a process which is enhanced by water. We report here results from a combined experimental-theoretical investigation of the effect of oxalic acid (OxA) on particle formation and growth from the reaction of MSA with trimethylamine (TMA) in the absence and presence of water. The gas phase reactants were mixed in an aerosol flow reactor (1 atm, 294 K). Particle number concentrations and size distributions were measured as a function of reaction time from 0.8-12 s. The interaction of OxA with TMA with and without water does not lead to significant particle formation. When OxA is present during the reaction of MSA with TMA, there is little change (≤2 times more) in the particle number concentration but particles are larger compared to the base case of MSA with TMA alone. However, the presence of water with MSA and TMA overwhelms the effect of OxA so that OxA has no significant impact on particle number concentration or size. Results of these experiments suggest the MSA hydrate is important for particle formation and growth of the four component OxA-MSA-TMA-H2O system. These results are compared to earlier studies of the effect of OxA on the MSA-methylamine reaction and interpreted based on theoretically calculated properties of small clusters of the components.

9.
Phys Chem Chem Phys ; 19(38): 26296-26309, 2017 Oct 04.
Artigo em Inglês | MEDLINE | ID: mdl-28936531

RESUMO

While atmospheric particles affect health, visibility and climate, the details governing their formation and growth are poorly understood on a molecular level. A simple model system for understanding the interactions between the gas and particle phases is the reaction of bases with acids, both of which are common constituents of atmospheric particles. In the present study, uptake coefficients for the reactions of gas phase ammonia, methylamine, ethylamine, dimethylamine and trimethylamine with a series of solid dicarboxylic acids (diacids) were measured at 296 ± 1 K using a Knudsen cell interfaced to a quadrupole mass spectrometer. The uptake coefficients (γ) for a given amine follow an odd-even trend in carbon number of the diacid, and are larger for the odd carbon diacids. Values range from γ = 0.4 for ethylamine on malonic acid (C3) to less than ∼10-6 for ammonia and all amines on adipic (C6) and pimelic (C7) acids. Basicity or structure of the amines/ammonia alone do not explain the effect of the base on uptake. The crystal structures of the diacids also play a key role, which is especially evident for malonic acid (C3). Evaporation of aqueous mixtures of amines/ammonia with odd carbon diacids show the formation of ionic liquids (ILs) or in some cases, metastable ILs that revert back to a stable solid salt upon complete evaporation of water. The trends with amine and diacid structure provide insight into the mechanisms of uptake and molecular interactions that control it, including the formation of ionic liquid layers in some cases. The diversity in the kinetics and mechanisms involved in this relatively simple model system illustrate the challenges in accurately representing such processes in atmospheric models.

10.
Rapid Commun Mass Spectrom ; 31(19): 1659-1668, 2017 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-28782138

RESUMO

RATIONALE: Ambient ionization mass spectrometry methods are convenient, sensitive and require little sample preparation. However, they are susceptible to species present in air surrounding the mass spectrometer. This study identifies some challenges associated with the potential impacts of indoor air contaminants on ionization and analysis involving open-air methods. METHODS: Unexpected effects of volatile organic compounds (VOCs) from floor maintenance activities on ambient ionization mass spectrometry were studied using three different ambient ionization techniques. Extractive electrospray ionization (EESI), direct analysis in real time (DART) and ionization by piezoelectric direct discharge (PDD) plasma were demonstrated in this study to be affected by indoor air contaminants. Identification of contaminant vapors was verified by comparison with standards using EESI-MS/MS product ion scans. RESULTS: Emissions of diethylene glycol monoethyl ether and ethylene glycol monobutyl ether are identified from floor stripping and waxing solutions using three ambient ionization mass spectrometry techniques. These unexpected indoor air contaminants are capable of more than 75% ion suppression of target analytes due to their high volatility, proton affinity and solubility compared with the target analytes. The contaminant vapors are also shown to form adducts with one of the target analytes. CONCLUSIONS: The common practice in MS analysis of subtracting a background air spectrum may not be appropriate if the presence of ionizable air contaminants alters the spectrum in unexpected ways. For example, VOCs released into air from floor stripping and waxing are capable of causing ion suppression of target analytes.

15.
Faraday Discuss ; 200: 11-58, 2017 08 24.
Artigo em Inglês | MEDLINE | ID: mdl-28686249

RESUMO

The term "Anthropocene" was coined by Professor Paul Crutzen in 2000 to describe an unprecedented era in which anthropogenic activities are impacting planet Earth on a global scale. Greatly increased emissions into the atmosphere, reflecting the advent of the Industrial Revolution, have caused significant changes in both the lower and upper atmosphere. Atmospheric reactions of the anthropogenic emissions and of those with biogenic compounds have significant impacts on human health, visibility, climate and weather. Two activities that have had particularly large impacts on the troposphere are fossil fuel combustion and agriculture, both associated with a burgeoning population. Emissions are also changing due to alterations in land use. This paper describes some of the tropospheric chemistry associated with the Anthropocene, with emphasis on areas having large uncertainties. These include heterogeneous chemistry such as those of oxides of nitrogen and the neonicotinoid pesticides, reactions at liquid interfaces, organic oxidations and particle formation, the role of sulfur compounds in the Anthropocene and biogenic-anthropogenic interactions. A clear and quantitative understanding of the connections between emissions, reactions, deposition and atmospheric composition is central to developing appropriate cost-effective strategies for minimizing the impacts of anthropogenic activities. The evolving nature of emissions in the Anthropocene places atmospheric chemistry at the fulcrum of determining human health and welfare in the future.

16.
J Phys Chem A ; 121(12): 2377-2385, 2017 Mar 30.
Artigo em Inglês | MEDLINE | ID: mdl-28287734

RESUMO

Understanding the properties of atmospheric particles made of several components is a very challenging problem. In this paper, we perform quantum chemical calculations for small multicomponent clusters of atmospheric relevance that incorporate methanesulfonic acid (MSA), methylamine (MA), oxalic acid (OxA), and water (H2O). Potential correlations between theoretical predictions of proton transfer in the small clusters and findings of recent experiments on formation of particles of detectable sizes (>2 nm) from the same components are studied. It is proposed that proton transfer from the acid to the amine in the 1:1 clusters correlates with experiments on particle formation in systems, such as MSA-MA and MSA-MA-OxA. In the case of OxA + MA, which has been observed to give few particles, proton transfer does not occur for the 1:1 cluster but does for the 2:2 cluster. Adding H2O to OxA-MA promotes the occurrence of proton transfer, and corresponding particles are slightly enhanced. The partial charge on the MA component increases by adding OxA or H2O to MSA-MA, which is correlated with enhanced particle formation compared to MSA-MA alone. Ab initio molecular dynamics simulations show that proton transfer at room temperature (T = 298 K) and high temperature (T = 500 K) is little affected compared with the equilibrium structure (T = 0 K). These results suggest that small cluster calculations may be useful in predicting the formation of multicomponent particles in the atmosphere.

17.
Phys Chem Chem Phys ; 19(6): 4893, 2017 02 08.
Artigo em Inglês | MEDLINE | ID: mdl-28117464

RESUMO

Correction for 'New particle formation and growth from methanesulfonic acid, trimethylamine and water' by Haihan Chen et al., Phys. Chem. Chem. Phys., 2015, 17, 13699-13709.

18.
Environ Sci Technol ; 51(4): 2124-2130, 2017 02 21.
Artigo em Inglês | MEDLINE | ID: mdl-28117992

RESUMO

Atmospheric particles are notorious for their effects on human health and visibility and are known to influence climate. Though sulfuric acid and ammonia/amines are recognized as main contributors to new particle formation (NPF), models and observations have indicated that other species may be involved. It has been shown that nucleation from methanesulfonic acid (MSA) and amines, which is enhanced with added water, can also contribute to NPF. While organics are ubiquitous in air and likely to be involved in NPF by stabilizing small clusters for further growth, their effects on the MSA-amine system are not known. This work investigates the effect of oxalic acid (OxA) on NPF from the reaction of MSA and methylamine (MA) at 1 atm and 294 K in the presence and absence of water vapor using an aerosol flow reactor. OxA and MA do not efficiently form particles even in the presence of water, but NPF is enhanced when adding MSA to OxA-MA with and without water. The addition of OxA to MSA-MA mixtures yields a modest NPF enhancement, whereas the addition of OxA to MSA-MA-H2O has no effect. Possible reasons for these effects are discussed.


Assuntos
Ácido Oxálico , Água , Aerossóis , Amônia , Humanos , Metilaminas
19.
Phys Chem Chem Phys ; 19(6): 4827-4839, 2017 Feb 08.
Artigo em Inglês | MEDLINE | ID: mdl-28133655

RESUMO

Atmospheric particles adversely affect visibility, health, and climate, yet the kinetics and mechanisms of particle formation and growth are poorly understood. Multiphase reactions between amines and dicarboxylic acids (diacids) have been suggested to contribute. In this study, the reactions of n-butylamine (BA) with solid C3-C8 diacids were studied at 296 ± 1 K using a Knudsen cell interfaced to a quadrupole mass spectrometer. Uptake coefficients for amines on the diacids with known geometric surface areas were measured at initial amine concentrations from (3-50) × 1011 cm-3. Uptake coefficients ranged from 0.7 ± 0.1 (2σ) for malonic acid (C3) to <10-6 for suberic acid (C8), show an odd-even carbon number effect, and decrease with increasing chain length within each series. Butylaminium salts formed from evaporation of aqueous solutions of BA with C3, C5 and C7 diacids (as well as C8) were viscous liquids, suggesting that ionic liquids (ILs) form on the surface during the reactions of gas phase amine with the odd carbon diacids. Predictions from the kinetic multi-layer model of aerosol surface and bulk chemistry (KM-SUB) were quantitatively consistent with uptake occurring via dissolution of the underlying diacid into the IL layer and reaction with amine taken up from the gas phase. The butylaminium salts formed from the C4 and C6 diacids were solids, and their uptake coefficients were smaller. These experiments and kinetic modeling demonstrate the unexpected formation of ILs in a gas-solid reaction, and suggest that ILs should be considered under some circumstances in atmospheric processes.

20.
Environ Sci Technol ; 51(1): 243-252, 2017 01 03.
Artigo em Inglês | MEDLINE | ID: mdl-27935699

RESUMO

Previous studies have shown that methanesulfonic acid (MSA) reacts with amines and ammonia to form particles, which is expected to be particularly important in coastal and agricultural areas. We present the first systematic study of temperature dependence of particle formation from the reactions of MSA with trimethylamine (TMA), dimethylamine (DMA), methylamine (MA), and ammonia over the range of 21-28 °C and 0.4-5.9 s in a flow reactor under dry conditions and in the presence of 3 × 1017 cm-3 water vapor. Overall activation energies (Eoverall) for particle formation calculated from the dependence of rates of particle formation on temperature for all of these bases are negative. The negative Eoverall is interpreted in terms of reverse reactions that decompose intermediate clusters in competition with the forward reactions that grow the clusters into particles. The average values of Eoverall for the formation of detectable particles are: TMA, -(168 ± 19) kcal mol-1; DMA, -(134 ± 30) kcal mol-1; MA, -(68 ± 23) kcal mol-1; NH3, -(110 ± 16) kcal mol-1 (±1σ). The strong inverse dependence of particle formation with temperature suggests that particle formation may not decline proportionally with concentrations of MSA and amines if temperature also decreases, for example at higher altitudes or in winter.


Assuntos
Amônia , Temperatura , Aminas
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