Ambient pressure proton transfer mass spectrometry: detection of amines and ammonia

Nonagricultural emissions enhance dimethylamine and modulate urban atmospheric nucleation

Gas-phase dimethylamine (DMA) has recently been identified as one of the most important vapors to initiate new particle formation (NPF), even in China's polluted atmosphere. Nevertheless, there remains a fundamental need for understanding the atmospheric life cycle of DMA, particularly in urban areas. Here we pioneered large-scale mobile observations of the DMA concentrations within cities and across two pan-region transects of north-to-south (∼700 km) and west-to-east (∼2000 km) in China. Unexpectedly, DMA concentrations (mean ± 1σ) in South China with scattered croplands (0.018 ± 0.010 ppbv) were over three times higher than those in the north with contiguous croplands (0.005 ± 0.001 ppbv), suggesting that nonagricultural activities may be an important source of DMA. Particularly in non-rural regions, incidental pulsed industrial emissions led to some of the highest DMA concentration levels in the world (>2.3 ppbv). Besides, in highly urbanized areas of Shanghai, supported by direct source-emission measurements, the spatial pattern of DMA was generally correlated with population (R² = 0.31) due to associated residential emissions rather than vehicular emissions. Chemical transport simulations further show that in the most populated regions of Shanghai, residential DMA emissions can contribute for up to 78% of particle number concentrations. Shanghai is a case study for populous megacities, and the impacts of nonagricultural emissions on local DMA concentration and nucleation are likely similar for other major urban regions globally.

Recent Advances in Chemodosimeters Designed for Amines

The analysis of amines has long been a very important task in science, industry, and healthcare. To date, this task has been accomplished by using expensive and time-consuming methods. Colorimetric and fluorescent chemodosimeters enable the fast, accurate, and sensitive analysis of various species with inexpensive instruments or the naked eye. Accordingly, the studies on these probes have gained great momentum in the last 20 years. In this review, amine chemodosimeters developed in the last 10 years were investigated. The investigated chemodosimeters are metal-free structures based on small organic compounds. The strategies for the detection, differentiation, and quantification of amines were discussed by considering the reaction types.

Measurement of atmospheric nanoparticles: Bridging the gap between gas-phase molecules and larger particles

Atmospheric nanoparticles are crucial components contributing to fine particulate matter (PM_2.5), and therefore have significant effects on visibility, climate, and human health. Due to the unique role of atmospheric nanoparticles during the evolution process from gas-phase molecules to larger particles, a number of sophisticated experimental techniques have been developed and employed for online monitoring and characterization of the physical and chemical properties of atmospheric nanoparticles, helping us to better understand the formation and growth of new particles. In this paper, we firstly review these state-of-the-art techniques for investigating the formation and growth of atmospheric nanoparticles (e.g., the gas-phase precursor species, molecular clusters, physicochemical properties, and chemical composition). Secondly, we present findings from recent field studies on the formation and growth of atmospheric nanoparticles, utilizing several advanced techniques. Furthermore, perspectives are proposed for technique development and improvements in measuring atmospheric nanoparticles.

Experimental and Theoretical Study on the Enhancement of Alkanolamines on Sulfuric Acid Nucleation

Alkanolamines such as monoethanolamine (MEA), diethanolamine (DEA), and triethanolamine (TEA) are extensively used for CO₂ capture and consumer products. Despite their prevalence in industrial applications, the fate of alkanolamines in the atmosphere remains relatively unknown. One likely reaction pathway for these chemicals in the atmosphere is new particle formation with sulfuric acid. Here, we present the first experimental results showing the formation of sulfuric acid dimers enhanced by MEA, DEA, and TEA from the measurement of molecular clusters. This study examines the nucleation reactions of MEA, DEA, and TEA with sulfuric acid in a clean, laminar flow reactor. The chemical compositions and concentrations of the freshly nucleated clusters were analyzed using a custom-built atmospheric pressure chemical ionization long time-of-flight mass spectrometer known as the Pittsburgh Cluster CIMS. Quantum chemical calculations and kinetic modeling of sulfuric acid-MEA/DEA/TEA clusters were also performed to determine relative cluster stabilities between these sulfuric acid-base systems. Experimental results indicate that MEA, DEA, and TEA at the part per trillion by volume (pptv) concentrations can enhance sulfuric acid dimer formation rates but to a lesser extent than dimethylamine (DMA). Thus, MEA, DEA, and TEA will potentially play an important role in new particle formation in industrial cities where these alkanolamines are emitted.

Atmospheric Sulfuric Acid Dimer Formation in a Polluted Environment

New particle formation (NPF) contributes significantly to atmospheric particle number concentrations and cloud condensation nuclei (CCN). In sulfur-rich environments, field measurements have shown that sulfuric acid dimer formation is likely the critical step in NPF. We investigated the dimer formation process based upon the measured sulfuric acid monomer and dimer concentrations, along with previously reported amine concentrations in a sulfur-rich atmosphere (Atlanta, USA). The average sulfuric acid concentration was in the range of 1.7 × 10⁷-1.4 × 10⁸ cm^-3 and the corresponding neutral dimer concentrations were 4.1 × 10⁵-5.0 × 10⁶ cm^-3 and 2.6 × 10⁵-2.7 × 10⁶ cm^-3 after sub-collision and collision ion-induced clustering (IIC) corrections, respectively. Two previously proposed acid-base mechanisms (namely AA and AB) were employed to respectively estimate the evaporation rates of the dimers and the acid-amine complexes. The results show evaporation rates of 0.1-1.3 s^-1 for the dimers based on the simultaneously measured average concentrations of the total amines, much higher than those (1.2-13.1 s^-1) for the acid-amine complexes. This indicates that the mechanism for dimer formation is likely AA through the formation of more volatile dimers in the initial step of the cluster formation.

Emissions of Ammonia and Other Nitrogen-Containing Volatile Organic Compounds from Motor Vehicles under Low-Speed Driving Conditions

Emissions of NH₃ and nine nitrogen-containing volatile organic compounds (NVOCs) (C_1-3-amines, C_1-3-amides, and C_1-3-imines) from motor vehicles powered by gasoline, diesel, and natural gas under low-speed driving conditions from roadside in situ measurements were characterized using a water-cluster chemical ionization mass spectrometer and trace gas monitors. The total emission strength of diesel trucks was the greatest followed by those of gasoline cars and natural gas cars. NH₃ emission per vehicle was found to be 2-3 orders of magnitude greater than that of all NVOCs, regardless of the type of vehicle. Although much lower than the emissions of amides or imines, emissions of amines were sufficient to produce atmospheric concentrations exceeding the threshold level for amines to enhance atmospheric nucleation by several orders of magnitude. Different engine emission reduction technologies (e.g., three-way catalytic converter vs selective catalytic reduction) can lead to different NH₃ and NVOC emission profiles. During the lifetime of a vehicle, its emission level was most likely to increase with its mileage. Source profiles of NH₃ and NVOC emissions from the three types of vehicles were also obtained from the measurements. These profiles can be a valuable contribution to the air pollution management system in terms of source apportionment, elucidating the emission contributions from a specific type of vehicle.

Microscopic Insights Into the Formation of Methanesulfonic Acid–Methylamine–Ammonia Particles Under Acid-Rich Conditions

Understanding the microscopic mechanisms of new particle formation under acid-rich conditions is of significance in atmospheric science. Using quantum chemistry calculations, we investigated the microscopic formation mechanism of methanesulfonic acid (MSA)–methylamine (MA)–ammonia (NH3) clusters. We focused on the binary (MSA)2n-(MA)n and ternary (MSA)3n-(MA)n-(NH3)n, (n = 1–4) systems which contain more acid than base molecules. We found that the lowest-energy isomers in each system possess considerable thermodynamic and dynamic stabilities. In studied cluster structures, all bases are protonated, and they form stable ion pairs with MSA, which contribute to the charge transfer and the stability of clusters. MA and NH3 have a synergistic effect on NPF under acid-rich conditions, and the role of NH3 becomes more remarkable as cluster size increases. The excess of MSA molecules does not only enhance the stability of clusters, but provides potential sites for further growth.

Protonated acetone ion chemical ionization time-of-flight mass spectrometry for real-time measurement of atmospheric ammonia

Ammonia (NH₃) is ubiquitous in the atmosphere, it can affect the formation of secondary aerosols and particulate matter, and cause soil eutrophication through sedimentation. Currently, the use of radioactive primary reagent ion source and the humidity interference on the sensitivity and stability are the two major issues faced by chemical ionization mass spectrometer (CIMS) in the analysis of atmospheric ammonia. In this work, a vacuum ultraviolet (VUV) Kr lamp was used to replace the radioactive source, and acetone was ionized under atmospheric pressure to obtain protonated acetone reagent ions to ionize ammonia. The ionization source is designed as a separated three-zone structure, and even 90 vol.% high-humidity samples can still be directly analyzed with a sensitivity of sub-ppbv. A signal normalization processing method was designed, and with this new method, the quantitative relative standard deviation (RSD) of the instrument was decreased from 17.5% to 9.1%, and the coefficient of determination was increased from 0.8340 to 0.9856. The humidity correction parameters of the instrument were calculated from different humidity, and the ammonia concentrations obtained under different humidity were converted to its concentration under zero humidity condition with these correction parameters. The analytical time for a single sample is only 60 sec, and the limit of detection (LOD) was 8.59 pptv (signal-to-noise ratio S/N = 3). The ambient measurement made in Qingdao, China, in January 2021 with this newly designed CIMS, showed that the concentration of ammonia ranged from 1 to 130 ppbv.

A new method of simultaneous determination of atmospheric amines in gaseous and particulate phases by gas chromatography-mass spectrometry

As more attention is being paid to the characteristics of atmospheric amines, there is also an increasing demand for reliable detection technologies. Herein, a method was developed for simultaneous detection of atmospheric amines in both gaseous and particulate phases using gas chromatography-mass spectrometry (GC-MS). The amine samples were collected with and without phosphoric acid filters, followed by derivatization with benzenesulfonyl chloride under alkaline condition prior to GC-MS analysis. Furthermore, the method was optimized and validated for determining 14 standard amines. The detection limits ranged from 0.0408-0.421 µg/mL (for gaseous samples) and 0.163-1.69 µg/mL (for particulate samples), respectively. The obtained recoveries ranged from 68.8%-180% and the relative standard deviation was less than 30%, indicating high precision and good reliability of the method. Seven amines were simultaneously detected in gaseous and particulate samples in an industrial park using the developed method successfully. Methylamine, dimethylamine and diethylamine together accounted for 76.7% and 75.6% of particulate and gaseous samples, respectively. By comparing the measured and predicted values of gas-particle partition fractions, it was found that absorption process of aqueous phase played a more important role in the gas-partition of amines than physical adsorption. Moreover, the reaction between unprotonated amines and acid (aq.) in water phase likely promoted water absorption. Higher measured partition fraction of dibutylamine was likely due to the reaction with gaseous HCl. The developed method would help provide a deeper understanding of gas-particle partitioning as well as atmospheric evolution of amines.

Chemical composition of different size ultrafine particulate matter measured by nanoparticle chemical ionization mass spectrometer

New particle formation (NPF) is the primary source of nanoparticles and contributes a large number of concentrations of cloud condensation nuclei. In recent years, field campaigns and laboratory experiments have been conducted to promote cognition of the mechanism for NPF and its following growth processes. The chemical composition measurement of nanoparticles could help deepen understanding of the initial step of particulate matter formation. In this work, we developed a nanoparticle chemical ionization mass spectrometer to measure nanoparticles' chemical compositions during their initial growth stage. Meanwhile, a non-radioactive ion source was designed for aerosol charging and chemical ionization. Time of flight mass spectrometer coupled with integrated aerosol size selection and collection module would guarantee the picogram level detection limit and high-resolution ability to measure the matrix of ambient samples. The performance of this equipment was overall evaluated, including the transmission efficiency and collection efficiency of custom-built nano differential mobility analyzer, chemical ionization efficiency, and mass resolution of the mass spectrometer. The high sensitivity measurement of ammonium sulfate and methylammonium sulfate aerosols with diameters ranging from 10 to 25 nm could guarantee the application of this instrument in the ambient measurement.

Observations of Gas-Phase Alkylamines at a Coastal Site in the East Mediterranean Atmosphere

Atmospheric amines are ubiquitous compounds in the atmosphere, having both natural and anthropogenic origin. Recently, they have been identified as important contributors to new particle formation in the atmosphere, but observations of their atmospheric concentrations are scarce. In the present study we introduce the first systematic long-term observations of gas-phase amines measurements in the East Mediterranean atmosphere. Air samples were collected at the Finokalia monitoring station of the University of Crete during a 3.5-year period from January 2013 to July 2016, and analyzed after extraction using a high-performance liquid chromatography triple quadrupole mass spectrometer. The detected alkylamines were the sum of dimethylamine and ethylamine (DMA+EA), trimethylamine (TMA), diethylamine (DEA) and triethylamine (TEA). DMA+EA and TMA were the most abundant alkylamines, with concentrations spanning from the detection limit to 78.0 and 69.8 pptv, and average concentrations of 7.8 ± 12.1 and 7.5 ± 12.4 pptv, respectively. Amines showed pronounced seasonal variability with DMA+EA and TMA concentrations being higher in winter. Statistical analysis of the observations showed different sources for each of the studied amines, except for DMA+ΕA and DEA that appear to have common sources in the region. This analysis points to a marine source of TMA and animal husbandry in the area as a potential source of TEA. None of the alkylamines is correlated with other anthropogenic sources. Furthermore, no clear association was found between the seasonality of NPF events and alkylamines concentrations, while a clear correlation was detected between the seasonality of nucleation mode particle (dp < 25 nm) number concentrations and alkylamine concentrations, indicating that amines may contribute to nucleation mode particles’ production.

Rapid and highly sensitive measurement of trimethylamine in seawater using dynamic purge-release and dopant-assisted atmospheric pressure photoionization mass spectrometry

Trimethylamine (TMA) is ubiquitous in the marine systems and may affect atmospheric chemistry as a precursor and strong stabilizer of atmospheric secondary aerosol, influencing cloud formation. Rapid and accurate measurement of the concentration of TMA in seawater is challenging due to their polarity, aqueous solubility, volatility and existence at low concentrations in marine environments. In this study, a dopant-assisted atmospheric pressure photoionization time-of-flight mass spectrometry (DA-APPI-TOFMS) coupled with a dynamic purge-release method was developed for rapid and sensitive analysis of TMA in seawater. A novel three-zones ionization source has been developed for improving the ionization efficiency of analyte molecules and minimizing the influence of high-humidity of the sample gas, which allowed direct analysis of high-humidity (RH> 90%) gas samples from microbubble purging process by the mass spectrometer. At atmospheric pressure, the three-zones ionization source allows the use of high-speed purge gas to quickly purge all organic amines dissolved in the water into the gas phase, ensuring quantitative accuracy. The limit of quantification (LOQ) for TMA down to 0.1 μg L^-1 was obtained in less than 2 min by consuming only 2 mL seawater sample. This method was applied for the determination of the concentrations of TMA in the coastal seawater to validate its practicability and reliability for analysis of trace amines in marine environments.

Novel ionization reagent for the measurement of gas-phase ammonia and amines using a stand-alone atmospheric pressure gas chromatography (APGC) source

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.

Simultaneous determination of nine atmospheric amines and six inorganic ions by non-suppressed ion chromatography using acetonitrile and 18-crown-6 as eluent additive

Atmospheric amines contribute to the nucleation and initial growth of new particles as well as secondary organic aerosol formation, influencing the radiative balance of the Earth's atmosphere. In this study, we develop an ion chromatography (IC) method for separating and quantifying the nine most abundant amines (methylaminium (MMAH⁺), dimethylaminium (DMAH⁺), trimethylaminium (TMAH⁺), ethylaminium (MEAH⁺), diethylaminium (DEAH⁺), propylaminium (MPAH⁺), butylaminium (MBAH⁺), ethanolaminium (MEOH⁺), and triethanolaminium (TEOH⁺)) from six common inorganic species in atmospheric aerosols. The retention times of the amines were altered by the addition of acetonitrile to the eluent because acetonitrile can reduce the adsorption of hydrophobic amines on the stationary phase. The developed method achieved the successful separation of DEAH⁺ and TMAH⁺ from inorganic cations, which often coelute with each other in established IC methods. The interference of K⁺ on the determination of MEAH⁺ was eliminated by the complexation of K⁺ with 18-crown-6, which prolonged the retention time of K⁺. Finally, 9 target amines and 6 common inorganic cations were separated, with a resolution Rs ≥ 1.2 for DEAH⁺ and MPAH⁺ and Rs > 1.5 for other species. The detection limits varied in the range of 0.34-1.48 ng for the 9 amines and 0.19-0.56 ng for the inorganic cations. The developed method was successfully applied for the determination of low molecular weight amines and inorganic cations in PM_2.5 collected from an urban site in Shanghai and an isolated coast of Chongming Island. Eight amines were detected in the urban samples, in which MMAH⁺ and DMAH⁺ dominated. The average amine concentration in the urban aerosols was 76.3 ± 38.4 ng m^-3, which is approximately 4-fold higher than those in the marine samples collected from the coast.

Integrated experimental and theoretical approach to probe the synergistic effect of ammonia in methanesulfonic acid reactions with small alkylamines

While new particle formation events have been observed worldwide, our fundamental understanding of the precursors remains uncertain. It has been previously shown that small alkylamines and ammonia (NH3) are key actors in sub-3 nm particle formation through reactions with acids such as sulfuric acid (H2SO4) and methanesulfonic acid (CH3S(O)(O)OH, MSA), and that water also plays a role. Because NH3 and amines co-exist in air, we carried out combined experimental and theoretical studies examining the influence of the addition of NH3 on particle formation from the reactions of MSA with methylamine (MA) and trimethylamine (TMA). Experiments were performed in a 1 m flow reactor at 1 atm and 296 K. Measurements using an ultrafine condensation particle counter (CPC) and a scanning mobility particle sizer (SMPS) show that new particle formation was systematically enhanced upon simultaneous addition of NH3 to the MSA + amine binary system, with the magnitude depending on the amine investigated. For the MSA + TMA reaction system, the addition of NH3 at ppb concentrations produced a much greater effect (i.e. order of magnitude more particles) than the addition of ∼12 000 ppm water (corresponding to ∼45-50% relative humidity). The effect of NH3 on the MSA + MA system, which is already very efficient in forming particles on its own, was present but modest. Calculations of energies, partial charges and structures of small cluster models of the multi-component particles likewise suggest synergistic effects due to NH3 in the presence of MSA and amine. The local minimum structures and the interactions involved suggest mechanisms for this effect.

Optical Recognition of Ammonia and Amine Vapor Using "Turn-on" Fluorescent Chitosan Nanoparticles Imprinted on Cellulose Strips

A practical fluorescent test dipstick for an efficient recognition of ammonia and amines vapors was developed. The prepared testing strip was based on a composite of molecularly imprinted chitosan nanoparticles, supported on cellulose paper assay, with artificial fluorescent receptor sites for ammonia/amines recognition in aqueous and gaseous phases. A modified chitosan nanoparticles containing fluorescein molecules, were successfully prepared and employed on cellulose paper strip creating fluorescent cellulose (FL-Cell) to act as "turn-on" fluorescent sensor for sensing and determining ammonia and organic amine vapor. We employed chitosan nanoparticles that had fluorescein incorporated as the fluorescent probe molecule, with a readout limit achieved for aqueous ammonia as low as 280 ppm at room temperature and atmospheric pressure. The sensor responded linearly relying on the aqueous ammonia concentration in the range of 0.13-280 ppm. The chromogenic fluorescent cellulose platform response depended on the acid-base characteristic effects of the fluorescein probe. The protonated form of fluorescein molecules immobilized within the chitosan nanoparticles were in a nanoenvironment demonstrating only weak fluorescence. When binding to ammonia/amine vapor, the fluorescein active sites were deprotonated and exhibited higher "turned-on" fluorescence as a result of exposure to those alkaline species. The simple fabrication and abovementioned characteristics of such fluorescent chitosan nanoparticles are such that they should be applicable for monitoring of ammonia/amines in either aqueous or vapor states. We studied the distribution of the fluorescent chitosan onto paper sheets fabricated from bleached bagasse pulp and coated with two different thicknesses of a fluorescent nanochitosan and blank nanochitosan solutions. A thin fluorescent nanochitosan layer was created on the surface of cellulose strips using an applicator. Its distribution was assessed by scanning electron microscopic (SEM) and transmission electron microscopic (TEM) analysis as well as Fourier-transform infrared spectroscopic (FT-IR) measurements. The mechanical properties were also tested. The exploitation of this "turn-on" fluorescence sensor invented platform should be amenable to different situations where determination of ammonia/amine vapor or aqueous solution is required.

Experimental and computational studies of Criegee intermediate reactions with NH3 and CH3NH2

The significance of removal of atmospheric ammonia and amines by reaction with Criegee intermediates is assessed by kinetic studies.

Multicomponent new particle formation from sulfuric acid, ammonia, and biogenic vapors

A major fraction of atmospheric aerosol particles, which affect both air quality and climate, form from gaseous precursors in the atmosphere. Highly oxygenated organic molecules (HOMs), formed by oxidation of biogenic volatile organic compounds, are known to participate in particle formation and growth. However, it is not well understood how they interact with atmospheric pollutants, such as nitrogen oxides (NO _x ) and sulfur oxides (SO _x ) from fossil fuel combustion, as well as ammonia (NH₃) from livestock and fertilizers. Here, we show how NO _x suppresses particle formation, while HOMs, sulfuric acid, and NH₃ have a synergistic enhancing effect on particle formation. We postulate a novel mechanism, involving HOMs, sulfuric acid, and ammonia, which is able to closely reproduce observations of particle formation and growth in daytime boreal forest and similar environments. The findings elucidate the complex interactions between biogenic and anthropogenic vapors in the atmospheric aerosol system.

Effect of Oxygen Sputter Pressure on the Structural, Morphological and Optical Properties of ZnO Thin Films for Gas Sensing Application

ZnO thin films were prepared on glass substrates at low (5 × 10-4 mbar) and high (3 × 10-3 mbar) sputter pressure using dc reactive magnetron sputtering. The structural, morphological, compositional and optical properties of the thin films were investigated. XRD patterns of both films confirmed the polycrystalline nature of the films with hexagonal Wurtzite structure. SEM study indicates that the surface of the film formed at high sputter pressure was more uniform, compact and porous in nature. From the EDAX analysis, no other characteristic peaks of other impurities were observed and the formation of single phase of ZnO was confirmed. From the study of photoluminescence, three peaks were observed, one strong near band-edge emission at 390 nm followed by weak and broad visible emissions around 420-480 nm. Room temperature ammonia sensing characteristics of ZnO nanothin films formed at higher sputter pressure were studied for different ammonia vapour concentration levels. The response of the Ammonia sensor at room temperature (30 °C) operation was observed to be of high sensitivity with quick response and recovery times.

New particle formation in China: Current knowledge and further directions

New particle formation (NPF) studies have been conducted in China since 2004. Formation of new atmospheric aerosol particles has been observed to take place in diverse environments, even under the circumstances of high pre-existing particle loading, challenging the traditional and present understanding of the physicochemical nucleation mechanisms, which have been proposed based on the investigations in clean environments and under laboratory experimental conditions. This paper summarizes the present status and gaps in understanding NPF in China and discusses the main directions opening for future research.

Particle formation and growth from oxalic acid, methanesulfonic acid, trimethylamine and water: a combined experimental and theoretical study

A combined experimental-theoretical study on the effect of oxalic acid on particle formation and growth from the reaction of MSA with trimethylamine in the absence and presence of water.

Quantitative analysis of aliphatic amines in urban aerosols based on online derivatization and high performance liquid chromatography

A method combining online derivatization with high performance liquid chromatography/fluorescence detection was developed for the determination of seven aliphatic amines (ethanolamine, methylamine, ethylamine, propylamine, butylamine, pentylamine and hexylamine) in urban aerosols. The collected amines were online derivatized with o-phthalaldehyde to form highly fluorescent sulfonatoisoindole derivatives. The derivatives were completely separated in 13 min through gradient elution and detected by fluorescence detection at an excitation wavelength of 334 nm and an emission wavelength of 443 nm. Under the optimized conditions, the relative standard derivations (RSDs) of all detected amines were 0.02-2.03% and 1.04-1.52% for the retention time and peak area, respectively. Excellent linearity was achieved for each analyte, ranging from 5 μg L(-1) to 1000 μg L(-1) (R(2) > 0.99). The detection limits for all analytes were below 1.1 μg L(-1). The proposed method was used to analyze aliphatic amines in 35 samples of urban PM2.5 collected in Shanghai and was found to be suitable for the determination of particulate aliphatic amines at ng m(-3) levels in ambient air. Based on our measurements, ethanolamine and methylamine were the most abundant species on average in Shanghai during dry and wet seasons. The highest concentration was 15.3 ng m(-3) for ethanolamine and 13.2 ng m(-3) for methylamine.

Effect of dimethylamine on the gas phase sulfuric acid concentration measured by Chemical Ionization Mass Spectrometry

Sulfuric acid is widely recognized as a very important substance driving atmospheric aerosol nucleation. Based on quantum chemical calculations it has been suggested that the quantitative detection of gas phase sulfuric acid (H₂SO₄) by use of Chemical Ionization Mass Spectrometry (CIMS) could be biased in the presence of gas phase amines such as dimethylamine (DMA). An experiment (CLOUD7 campaign) was set up at the CLOUD (Cosmics Leaving OUtdoor Droplets) chamber to investigate the quantitative detection of H₂SO₄ in the presence of dimethylamine by CIMS at atmospherically relevant concentrations. For the first time in the CLOUD experiment, the monomer sulfuric acid concentration was measured by a CIMS and by two CI-APi-TOF (Chemical Ionization-Atmospheric Pressure interface-Time Of Flight) mass spectrometers. In addition, neutral sulfuric acid clusters were measured with the CI-APi-TOFs. The CLOUD7 measurements show that in the presence of dimethylamine (<5 to 70 pptv) the sulfuric acid monomer measured by the CIMS represents only a fraction of the total H₂SO₄, contained in the monomer and the clusters that is available for particle growth. Although it was found that the addition of dimethylamine dramatically changes the H₂SO₄ cluster distribution compared to binary (H₂SO₄-H₂O) conditions, the CIMS detection efficiency does not seem to depend substantially on whether an individual H₂SO₄ monomer is clustered with a DMA molecule. The experimental observations are supported by numerical simulations based on A Self-contained Atmospheric chemistry coDe coupled with a molecular process model (Sulfuric Acid Water NUCleation) operated in the kinetic limit.

Speciation of Nitrogen-Bearing Species Using Negative and Positive Secondary Ion Spectra with Nano Secondary Ion Mass Spectrometry

In this study, we demonstrate that Nano Secondary Ion Mass Spectrometry (NanoSIMS) can be used to differentiate different nitrogen-containing species commonly observed in atmospheric aerosol particles with micrometer or submicrometer spatial resolution, on the basis of the relative intensity of secondary ion signals, both in negative and positive secondary ion mode, without the need to chemically or physically separate the samples. Compounds tested include nitrate, nitrite, ammonium salts, urea, amino acids, sugars, organic acids, amides, triazine, imidazole, protein, and biological tissue. We show that NO2(-) secondary ions are unique to the decomposition of nitrate and nitrite salts, whereas NH4(+) secondary ions are unique to samples containing ammonium ions, with low signal intensities observed from amino groups but none from biological tissue. CN(-) signals are obtained from all nitrogen-bearing compounds, but relative signal intensities are the highest for organic nitrogen-containing compounds. We demonstrate that quantitative determination of the elemental fractions of carbon, oxygen, and nitrate in nanometer-sized aerosol samples using normalized secondary ion intensities is possible. We further demonstrate that stable isotope ratios measured on in-house standards of unknown isotopic composition using the (12)C(15)N(-)/(12)C(14)N(-) ratio (all nitrogen-containing species), the (15)N(16)O2(-)/(14)N(16)O2(-) ratio (nitrate and nitrite species), and the (15)NH4(+)/(14)NH4(+) ratio (ammonium salts, amino acids, and urea) are stable and sufficiently precise for nitrogen isotope analysis.

Characterization of the nucleation precursor (H2SO4–(CH3)2NH) complex: intra-cluster interactions and atmospheric relevance

Amines have been proposed to participate in the nucleation process, but the electron density analysis and the determination of a temperature dependence of the clusters are still lacking.

Humidity independent mass spectrometry for gas phase chemical analysis via ambient proton transfer reaction

In this work, a humidity independent mass spectrometric method was developed for rapid analysis of gas phase chemicals. This method is based upon ambient proton transfer reaction between gas phase chemicals and charged water droplets, in a reaction chamber with nearly saturate humidity under atmospheric pressure. The humidity independent nature enables direct and rapid analysis of raw gas phase samples, avoiding time- and sample-consuming sample pretreatments in conventional mass spectrometry methods to control sample humidity. Acetone, benzene, toluene, ethylbenzene and meta-xylene were used to evaluate the analytical performance of present method. The limits of detection for benzene, toluene, ethylbenzene and meta-xylene are in the range of ∼0.1 to ∼0.3 ppbV; that of benzene is well below the present European Union permissible exposure limit for benzene vapor (5 μg m(-3), ∼1.44 ppbV), with linear ranges of approximately two orders of magnitude. The majority of the homemade device contains a stainless steel tube as reaction chamber and an ultrasonic humidifier as the source of charged water droplets, which makes this cheap device easy to assemble and facile to operate. In addition, potential application of this method was illustrated by the real time identification of raw gas phase chemicals released from plants at different physiological stages.

On the properties and atmospheric implication of amine-hydrated clusters

Amines have been recognized as important precursor species in the formation of new atmospheric particles.

Neutral molecular cluster formation of sulfuric acid-dimethylamine observed in real time under atmospheric conditions

For atmospheric sulfuric acid (SA) concentrations the presence of dimethylamine (DMA) at mixing ratios of several parts per trillion by volume can explain observed boundary layer new particle formation rates. However, the concentration and molecular composition of the neutral (uncharged) clusters have not been reported so far due to the lack of suitable instrumentation. Here we report on experiments from the Cosmics Leaving Outdoor Droplets chamber at the European Organization for Nuclear Research revealing the formation of neutral particles containing up to 14 SA and 16 DMA molecules, corresponding to a mobility diameter of about 2 nm, under atmospherically relevant conditions. These measurements bridge the gap between the molecular and particle perspectives of nucleation, revealing the fundamental processes involved in particle formation and growth. The neutral clusters are found to form at or close to the kinetic limit where particle formation is limited only by the collision rate of SA molecules. Even though the neutral particles are stable against evaporation from the SA dimer onward, the formation rates of particles at 1.7-nm size, which contain about 10 SA molecules, are up to 4 orders of magnitude smaller compared with those of the dimer due to coagulation and wall loss of particles before they reach 1.7 nm in diameter. This demonstrates that neither the atmospheric particle formation rate nor its dependence on SA can simply be interpreted in terms of cluster evaporation or the molecular composition of a critical nucleus.

Infrared studies of the reaction of methanesulfonic acid with trimethylamine on surfaces

Organosulfur compounds generated from a variety of biological as well as anthropogenic sources are oxidized in air to form sulfuric acid and methanesulfonic acid (MSA). Both of these acids formed initially in the gas phase react with ammonia and amines in air to form and grow new particles, which is important for visibility, human health and climate. A competing sink is deposition on surfaces in the boundary layer. However, relatively little is known about reactions after they deposit on surfaces. We report here diffuse reflectance infrared Fourier transform spectrometry (DRIFTS) studies of the reaction of MSA with trimethylamine (TMA) on a silicon powder at atmospheric pressure in synthetic air and at room temperature, either in the absence or in the presence of water vapor. In both cases, DRIFTS spectra of the product surface species are essentially the same as the transmission spectrum obtained for trimethylaminium methanesulfonate, indicating the formation of the salt on the surface with a lower limit to the reaction probability of γ > 10(-6). To the best of our knowledge, this is the first infrared study to demonstrate this chemistry from the heterogeneous reaction of MSA with an amine on a surface. This heterogeneous chemistry appears to be sufficiently fast that it could impact measurements of gas-phase amines through reactions with surface-adsorbed acids on sampling lines and inlets. It could also represent an additional sink for amines in the boundary layer, especially at night when the gas-phase reactions of amines with OH radical and ozone are minimized.

Molecular understanding of sulphuric acid-amine particle nucleation in the atmosphere

Nucleation of aerosol particles from trace atmospheric vapours is thought to provide up to half of global cloud condensation nuclei. Aerosols can cause a net cooling of climate by scattering sunlight and by leading to smaller but more numerous cloud droplets, which makes clouds brighter and extends their lifetimes. Atmospheric aerosols derived from human activities are thought to have compensated for a large fraction of the warming caused by greenhouse gases. However, despite its importance for climate, atmospheric nucleation is poorly understood. Recently, it has been shown that sulphuric acid and ammonia cannot explain particle formation rates observed in the lower atmosphere. It is thought that amines may enhance nucleation, but until now there has been no direct evidence for amine ternary nucleation under atmospheric conditions. Here we use the CLOUD (Cosmics Leaving OUtdoor Droplets) chamber at CERN and find that dimethylamine above three parts per trillion by volume can enhance particle formation rates more than 1,000-fold compared with ammonia, sufficient to account for the particle formation rates observed in the atmosphere. Molecular analysis of the clusters reveals that the faster nucleation is explained by a base-stabilization mechanism involving acid-amine pairs, which strongly decrease evaporation. The ion-induced contribution is generally small, reflecting the high stability of sulphuric acid-dimethylamine clusters and indicating that galactic cosmic rays exert only a small influence on their formation, except at low overall formation rates. Our experimental measurements are well reproduced by a dynamical model based on quantum chemical calculations of binding energies of molecular clusters, without any fitted parameters. These results show that, in regions of the atmosphere near amine sources, both amines and sulphur dioxide should be considered when assessing the impact of anthropogenic activities on particle formation.

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.

Supramolecular complexation for environmental control

Supramolecular complexes offer a new and efficient way for the monitoring and removal of many substances emanating from technical processes, fertilization, plant and animal protection, or e.g. chemotherapy. Such pollutants range from toxic or radioactive metal ions and anions to chemical side products, herbicides, pesticides to drugs including steroids, and include degradation products from natural sources. The applications involve usually fast and reversible complex formation, due to prevailing non-covalent interactions. This is of importance for sensing as well as for separation techniques, where the often expensive host compounds can then be reused almost indefinitely. Immobilization of host compounds, e.g. on exchange resins or on membranes, and their implementation in smart new materials hold particular promise. The review illustrates how the design of suitable host compounds in combination with modern sensing and separation methods can contribute to solve some of the biggest problems facing chemistry, which arise from the everyday increasing pollution of the environment.