A new approach is reported for determining the composition of multicomponent organic aerosols using FT-IR spectroscopy. In this study, laboratory-generated aerosol particles are thermally evaporated and the resulting ...
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A new approach is reported for determining the composition of multicomponent organic aerosols using FT-IR spectroscopy. In this study, laboratory-generated aerosol particles are thermally evaporated and the resulting vapor is immediately analyzed using FT-IR spectroscopy. The composition of the aerosol is determined by fitting the vapor spectrum to a linear combination of reference spectra of the individual components. Application of the method to the detection of polycyclic aromatic hydrocarbons, changes in aerosol composition, and analysis of diesel fuel is demonstrated.
A device capable of continuously sampling and mass analyzing aerosols in the 1-10 nm diameter size range (masses up to 1 MDa) at part per billion (ppb, 10(10) cm(-3)) concentrations is described. Small aliquots of an ...
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A device capable of continuously sampling and mass analyzing aerosols in the 1-10 nm diameter size range (masses up to 1 MDa) at part per billion (ppb, 10(10) cm(-3)) concentrations is described. Small aliquots of an aerosol flowing at atmospheric pressure are sampled into a time-of-flight mass spectrometer (TOFMS) via a pulsed molecular beam valve at 10-50 Hz. The aerosol molecular beam is singly and nondestructively ionized with light from an ultraviolet excimer laser and accelerated across a 20 kV electrostatic field. Ionized particle packers are separated in mass during a free flight and re-accelerated across an additional 30 kV into a stainless steel conversion dynode plate. Signals from ejected electrons and negative ion fragments resulting from the particle-dynode collisions are amplified in a dual microchannel plate detector, digitized, and stored in a fast transient recorder. Sampling of He flow streams bearing benzene, fullerenes, as well as Na, Mg, and CsI particles (nanocrystals) is demonstrated. In addition, the gas-phase reaction between a pre-formed Na nanocrystal and alkane thiols is monitored in real-time. (C) 1998 Elsevier Science Ltd. All rights reserved.
Light-absorbing organic aerosols, referred to as brown carbon (BrC), play a vital role in the global climate and air quality. Due to the complexity of BrC chromophores, the identified absorbing substances in the ambie...
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Light-absorbing organic aerosols, referred to as brown carbon (BrC), play a vital role in the global climate and air quality. Due to the complexity of BrC chromophores, the identified absorbing substances in the ambient atmosphere are very limited. However, without comprehensive knowledge of the complex absorbing compounds in BrC, our understanding of its sources, formation, and evolution mechanisms remains superficial, leading to great uncertainty in climatic and atmospheric models. To address this gap, we developed a constrained non-negative matrix factorization (NMF) model to resolve the individual ultraviolet-visible spectrum for each substance in dissolved organic aerosols, with the power of ultrahigh-performance liquid chromatography-diode array detector-ultrahigh-resolution mass spectrometry (UHPLC-DAD-UHRMS). The resolved spectra were validated by selected standard substances and validation samples. Approximately 40,000 light-absorbing substances were recognized at the MS1 level. It turns out that BrC is composed of a vast number of substances rather than a few prominent chromophores in the urban atmosphere. Previous understanding of the absorbing feature of BrC based on a few identified compounds could be biased. Weak-absorbing substances missed previously play an important role in BrC absorption when they are integrated due to their overwhelming number. This model brings the property exploration of complex dissolved organic mixtures to a molecular level, laying a foundation for identifying potentially significant compositions and obtaining a comprehensive chemical picture.
In addition to the well-known gaseous emissions many combustion processes also produce particulate emissions. While particles are significant as an air pollutant, they also serve as indicators for the state of a combu...
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In addition to the well-known gaseous emissions many combustion processes also produce particulate emissions. While particles are significant as an air pollutant, they also serve as indicators for the state of a combustion process, for example with result to completeness. Suitable measurements can be used to monitor, optimize and even control combustion processes. This article contains a short review of mechanisms leading to particle formation in combustion processes and some of the fundamental properties. The basic principles of several methods for the measurement of combustion particles are summarized. Two relatively new measurement methods are introduced. One involves measuring the combustion induced electrical charge on the particles. This is straghtfoward and gives information about the particle concentration and the mode of combustion (e.g. open flame, smoldering fire). The second method is based on the photoelectric effect, i.e. the emission of electrons from the particles upon irradiation with u.v. light, and gives information on the polyaromatic hydrocarbon (PAH) content of the particles.
The concentration of tin in atmospheric aerosols has been measured at land and ship based sites in the northern and southern hemispheres. Tin concentrations in the northern hemisphere are up to three orders of magnitu...
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The concentration of tin in atmospheric aerosols has been measured at land and ship based sites in the northern and southern hemispheres. Tin concentrations in the northern hemisphere are up to three orders of magnitude greater than those in the southern hemisphere, indicating the importance of anthropogenic inputs to the atmospheric tin cycle. In aerosols sampled in Tallahassee, Florida [USA], tin is correlated with soot carbon in air masses originating in the central U.S., but is not correlated with locally produced soot carbon. Rainwaters collected in Tallahassee, Florida have been analyzed for dissolved tin and major ions. Factor analysis of the results indicates a continental and pollution source for tin. The dissolved fraction of tin in rain represents only a minor component of the deposition flux of tin. Rates of deposition of atmospheric tin are consistent with estimated fluxes of tin to the atmosphere.
Flammable aerosols have created many fire and explosion hazards in the process industry, but the flammability of aerosols has not been fully understood. The minimum ignition energy has been widely used as an indicator...
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Flammable aerosols have created many fire and explosion hazards in the process industry, but the flammability of aerosols has not been fully understood. The minimum ignition energy has been widely used as an indicator for flammability of combustible mixtures, but the amount of experimental data on the minimum ignition energy of aerosols is very limited. In this work, the minimum ignition energy of tetralin aerosols is predicted using an integrated model. The model applies the flame front propagation theory in aerosol systems to the growth of the flame kernel, which was created during the spark discharge in the ignition process. The aerosol minimum ignition energy was defined as the minimum level of energy in the initial flame kernel to maintain the kernel temperature above the minimum ignition temperature of 1073 K specific for tetralin aerosols during the kernel growth. The minimum ignition energy obtained in the model is influenced by the fuel-air equivalence ratio and the size of the aerosol droplets. For tetralin aerosols of 40 mu m diameter, E-min decreases significantly from 0.32 mJ to 4.3 x 10 e(-3) mJ when the equivalence ratio rises from 0.57 to 1.0. For tetralin aerosols of 0.57 equivalence ratio, E-min increases from as 0.09 mJ to 0.32 nil when the droplet diameter rises from 10 mu m to 60 mu m. The trends are in agreement with previous experimental observations. The method used in current work has the potential to prediction of the minimum ignition energy of aerosol. (C) 2011 Elsevier Ltd. All rights reserved.
Fourier transform infrared (FTIR) transmission spectrometry has been used to determine ammonium and sulfate in ambient aerosol particles collected on Teflon filters. Integrated absorbance as well as maximum absorbance...
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Fourier transform infrared (FTIR) transmission spectrometry has been used to determine ammonium and sulfate in ambient aerosol particles collected on Teflon filters. Integrated absorbance as well as maximum absorbance values for ammonium and sulfate are linearly related to X-ray fluorescence measurements of total sulfur. Apparent detection limits of 1.4 μg m −3 for sulfate and 0.5 μg m −3 for ammonium (for sample volumes of 21.6 m 3 ) were estimated for samples from Topeka, Kansas; Portage, Wisconsin; Steubenville, Ohio; and Charlottesville, Virginia. The apparent detection limits were essentially independent of sample loading over the range of 0–20 μg m −3 of total sulfur. The FTIR transmission measurements of these samples are very precise e.g. repetitive measurements vary ± 0.2% and blank variability is 0.13 μg m −3 and 0.20 μg m −3 in terms of sulfate and ammonium, respectively. Contributions to analytical uncertainty include 5–8% uncertainties in X-ray fluorescence measurements for total sulfur and the influence of unspecified site-dependent sample characteristics. The method offers the significant advantages of nondestructive analysis, no sample preparation, molecular speciation and rapid analysis.
A technique is described for generation of concentrated respirable aerosols and their administration to canine lungs. The functional characteristics of the system were delineated using aqueous solutions of disodium fl...
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A technique is described for generation of concentrated respirable aerosols and their administration to canine lungs. The functional characteristics of the system were delineated using aqueous solutions of disodium fluorescein (DF). The aerosol was generated by delivering pressurized air and disodium fluorescein solution to a Turbotac jet nebulizer. The particles were dried with a sheath of warm air and concentrated using a seven orifice virtual impactor. The input aerosol particles were concentrated up to eight times, resulting in output aerosol concentration of about 10 mg m-3 at a flow rate of 20 1 min-1. The particles had predictable mass median aerodynamic diameters between 4 and 7 mum, and geometric standard deviations between 1.7 and 2.0. To conduct inhalation studies on beagle dogs, the aerosol generation and concentration system was pressurized to 18 cm of water. In these experiments the test aerosol consisted of a mixture of disodium fluorescein with technetium-99m tagged to iron oxide colloid, controlled delivery of the aerosol to the dogs was achieved by sequencing low resistance solenoid valves using a logic control box. The animals were anesthetized and endotracheally intubated. The aerosols were carried in the ventilating air stream. The duration of exposure was 3 min. Gamma scintigraphy confirmed deposition of the aerosol in the lower lungs as demonstrated by a total lung retention between 70 and 75% after 24 h. This methodology is applicable for use with solutions and/or colloidal suspensions and can be adapted for continuous aerosol generation and delivery.
Calcium species in mineral aerosols collected simultaneously in Aksu (near the Taklimakan Desert), Qingdao (eastern China), and Tsukuba (Japan) during dust and nondust periods were determined using Ca K-edge X-ray abs...
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Calcium species in mineral aerosols collected simultaneously in Aksu (near the Taklimakan Desert), Qingdao (eastern China), and Tsukuba (Japan) during dust and nondust periods were determined using Ca K-edge X-ray absorption near-edge structure ONES). From the fitting of XANES spectra, it was found that (i) calcite and gypsum were the main Ca species in the aerosol samples, and (ii) the gypsum fraction versus total Ca minerals [Gyp]/[Ca2+], increased progressively in the order Aksu < Qingdao < Tsukuba. Surface-sensitive XANES in the conversion electron yield mode (CEY) showed that the gypsum is formed selectively at the surface of mineral aerosols for all the samples except for that taken in Aksu during the dust period. The decrease of the [Gypp]/[Ca2+], ratio with an increase in particle size showed that the neutralization effect proceeds from the particle surface. For the Aksu sample in the dust period, however, (i) the [Gyp]/[Ca2+], ratios obtained by XANES measured in the fluorescence (FL, regarded as bulk analysis) and CEY modes were similar and (ii) size dependence was not found, showing that neutralization is not important for the sample because of the large supply of mineral aerosol with little neutralization effect in Aksu. It was also found that the pH of the aerosol and the ratio of (NH4)(2)SO4 to gypsum were positively and negatively correlated with the Ca (or calcite) content, respectively. The speciation of Ca by XANES revealed the neutralization processes of acidic sulfur species by calcite during the long-range transport of mineral aerosols.
To better understand the key kinetic mechanisms controlling heterogeneous oxidation in organic aerosols, submicron particles composed of an alkene and a saturated carboxylic acid are exposed to ozone in a variable-tem...
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To better understand the key kinetic mechanisms controlling heterogeneous oxidation in organic aerosols, submicron particles composed of an alkene and a saturated carboxylic acid are exposed to ozone in a variable-temperature flow tube reactor. Effective uptake coefficients (gamma eff) are obtained from the multiphase reaction kinetics, which are quantified by Vacuum Ultraviolet Photoionization Aerosol Mass Spectrometry. For aerosols composed of only of alkenes, gamma eff doubles (from 6 x 10-4 to 1.2 x 10-3) when the temperature is decreased from 293 to 263 K. Alternatively, for an alkene particle doped with a carboxylic acid, an efficient scavenger of stabilized Criegee Intermediates (sCI), gamma eff is observed to be weakly temperature dependent. A kinetic model, benchmarked to literature data, explains these results as arising from the temperature dependent competition between unimolecular pathways of sCI that promote radical chain cycling and those bimolecular pathways that form stable chain termination products (i.e., alpha-acyloxyalkyl hydroperoxides). The implication of these results for the kinetics of aerosol aging at low temperatures is discussed.
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