Particle Mass Spectra Research Articles

Cluster analysis of single particle mass spectra measured at Flushing, NY

ART-2a and a density based cluster method, density based spatial clustering of application with noise (DBSCAN), have been used for classification of the single particle mass spectra measured at New York City. Using too large of a vigilance factor in ART-2a leads to many similar clusters with overlap, and thus a low vigilance factor was used in this study. The DBSCAN method can identify clusters with complex shapes and various sizes, and representative spectra are chosen to identify different particle types within each cluster. The cluster structure of the single particle mass spectra were examined by DBSCAN. Both methods found that the major clusters were sea salt and anthropogenic combustion emissions. The continua in sulfate, potassium and OC particles were found by DBSCAN and a large cluster was formed, while ART-2a broke it into several small clusters without finding this continuum. A detailed discussion of the cluster analysis results including representative mass spectra, size distributions and temporal behavior will be provided.

Single Particle Laser Ablation Time-of-Flight Mass Spectrometer: An Introduction to SPLAT

We present our single particle mass spectrometer we call SPLAT. SPLAT was designed to make possible the detection and characterization of particles down to 100 nm, generate reproducible single particle mass spectra, and collect data at a high rate. The final instrument presented here is capable of characterizing individual particles down to 50 nm at the rate of 20 particles per second. In SPLAT mass spectra are generated by a two-step process, thet uses a pulsed infrared laser to heat the particle and a time delayed pulsed UV laser to create ions. We describe a mode of operation that makes it possible to take advantage of the gas phase ionization of the semivolatile components of the particle, while also generating mass spectral signatures of the nonvolatile fraction, thereby proividing complete particle mass spectra. We present some sample results from two field deployments of SPLAT.

MALDI of Individual Biomolecule-Containing Airborne Particles in an Ion Trap Mass Spectrometer

Individual airborne biomolecule-containing particles were detected and characterized in near real-time by matrix-assisted laser desorption/ionization (MALDI) with an ion trap mass spectrometer. Biomolecule-containing particles were laboratory-generated and passed through a heated region containing a solution of matrix in equilibrium with the gas phase. Passage into a cooler region created a supersaturation, resulting in rapid deposition of the matrix vapor onto the biomolecule-containing particles, whereupon they were sampled into the inlet of our spectrometer. The coated particles were collimated and individually sized by light-scattering-based time-of-flight. When the sized particle reached the center of the ion trap, it was irradiated with a focused 266-nm laser, and the resulting ions were mass-analyzed. Mass spectra of leucine enkephalin, bradykinin, substance P, and polylysine-containing particles were determined with attomole sensitivity. Structural information of the peptides contained in an individual particle was obtained by tandem mass spectrometry. Analysis of the results yields insights into the aerosol laser ablation ionization process that suggests an optically limited mechanism for ion production that has interesting ramifications on the utility of aerosol-based MALDI as an analytical technique.

Determination of Single Particle Mass Spectral Signatures from Light-Duty Vehicle Emissions

In this study, 28 light-duty gasoline vehicles (LDV) were operated on a chassis dynamometer at the California Air Resources Board Haagen-Smit Facility in El Monte, CA. The mass spectra of individual particles emitted from these vehicles were measured using aerosol time-of-flight mass spectrometry (ATOFMS). A primary goal of this study involves determining representative size-resolved single particle mass spectral signatures that can be used in future ambient particulate matter source apportionment studies. Different cycles were used to simulate urban driving conditions including the federal testing procedure (FTP), unified cycle (UC), and the correction cycle (CC). The vehicles were selected to span a range of catalytic converter (three-way, oxidation, and no catalysts) and engine technologies (vehicles models from 1953 to 2003). Exhaust particles were sampled directly from a dilution and residence chamber system using particle sizing instruments and an ATOFMS equipped with an aerodynamic lens (UF-ATOFMS) analyzing particles between 50 and 300 nm. On the basis of chemical composition, 10 unique chemical types describe the majority of the particles with distinct size and temporal characteristics. In the ultrafine size range (between 50 and 100 nm), three elemental carbon (EC) particle types dominated, all showing distinct EC signatures combined with Ca, phosphate, sulfate, and a lower abundance of organic carbon (OC). The relative fraction of EC particle types decreased as particle size increased with OC particles becoming more prevalent above 100 nm. Depending on the vehicle and cycle, several distinct OC particle types produced distinct ion patterns, including substituted aromatic compounds and polycyclic aromatic hydrocarbons (PAH), coupled with other chemical species including ammonium, EC, nitrate, sulfate, phosphate, V, and Ca. The most likely source of the Ca and phosphate in the particles is attributed to the lubricating oil. Significant variability was observed in the chemical composition of particles emitted within the different car categories as well as for the same car operating under different driving conditions. Two-minute temporal resolution measurements provide information on the chemical classes as they evolved during the FTP cycle. The first two minutes of the cold start produced more than 5 times the number of particles than any other portion of the cycle, with one class of ultrafine particles (EC coupled with Ca, OC, and phosphate) preferentially produced. By number, the three EC with Ca classes (which also contained OC, phosphate, and sulfate) were the most abundant classes produced by the nonsmoking vehicles. The smoker category produced the highest number of particles, with the dominant classes being OC comprised of substituted monoaromatic compounds and PAHs, coupled with Ca and phosphate, thus suggesting used lubricating oil was associated with many of these particles. These studies show, by number, EC particles dominate gasoline emissions in the ultrafine size range particularlyforthe lowest emitting newer vehicles, suggesting the EC signature alone cannot be used as a unique tracer for diesels. This represents the first report of high time- and size-resolved chemical composition data showing the mixing state of nonrefractory elements in particles such as EC for vehicle emissions during dynamometer source testing.

Sol–gel transition in a coagulating mixture

The time evolution of a coagulating mixture in which binary coagulation governs the temporal changes to the particle mass and composition spectra is studied under the assumption that the coagulation kernel is proportional to the product of masses of the first and the second components in the coalescing particles. This model is shown to reveal the sol–gel transition, i.e., the formation of a cluster with mass comparable to the total mass of the whole system. This letter reports on the exact solution of this model. The evolution equation for the generating functional defining all properties of coagulating systems is solved exactly for this particular kernel. The single-particle mass spectrum is analysed in the thermodynamic limit and it is demonstrated how the gel appears in this mixed system.

Exact kinetics of the sol-gel transition

The formation of a gel in a disperse system wherein binary coagulation alone governs the temporal changes of particle mass spectra is studied under the assumption that the coagulation kernel is proportional to the product of masses of coalescing particles. This model is known to reveal the sol-gel transition, i.e., the formation of one giant cluster with the mass comparable to the total mass of the whole system. This paper reports on the exact solution of this model for a finite total mass of the coagulating system. The evolution equation for the generating functional defining all properties of coagulating systems is solved exactly for this particular kernel. The final output is the exact expression for the single-particle mass spectrum as a function of time. The analysis of the spectrum in the thermodynamic limit shows that after a critical time a giant single particle (the gel) appears. Although the concentration of this giant gel particle is zero in the thermodynamic limit, it actively interacts with smaller particles "eating" them and thus growing in mass. Special attention is given to the transition point, where the gel is appearing. It is demonstrated that the sol-gel transition reminds the second-order phase transition. The time dependencies of the gel mass, the number concentration, and the second moment of the particle mass spectrum are found.

Speciation of size‐resolved individual ultrafine particles in Pittsburgh, Pennsylvania

Approximately 236,000 single particle mass spectra were collected throughout the duration of the Pittsburgh Supersite experiment using the third‐generation rapid single particle mass spectrometer (RSMS‐3). The instrument was operated semicontinuously for 306 days, sampling particles with aerodynamic diameters in the range of 30–1100 nm and collecting both positive and negative ion spectra, particle size, and time of detection for each particle measured. The entire data set has been fully processed and analyzed. Spectra have been clustered into 20 distinct particle classes on the basis of the distribution of their positive ion mass peaks. Negative ion spectra were classified independently within each positive ion class. Frequency of occurrence versus particle size, month of the year, and wind direction has also been calculated for the full data set, as well as within each class. Results indicate a rich array of multicomponent ultrafine particles composed primarily of carbon and ammonium nitrate. Approximately 54% of all the particles measured fell into the carbonaceous ammonium nitrate (CAN) class. These particles were observed in all size bins and from most wind directions for the entirety of this study. Ubiquitous sources throughout the area, including vehicular emissions and secondary organic aerosol formation, are considered to be responsible for a larger fraction of these particles. In terms of particle number, metal containing aerosol dominated the remainder of the particle classes identified. These particles were rich in K+, Na+, Fe+, and Pb+ and to a lesser extent, Ga+ and Zn+. They tended to be smaller in size and were highly correlated with specific wind directions, facilitating the isolation of specific sources.

Determination of the Size Distribution of Polydisperse Nanoparticles with Single-Particle Mass Spectrometry: The Role of Ion Kinetic Energy

We develop a method to determine size and size distribution (30–150 nm) of polydisperse nanoparticles using a laser ablation/ ionization time-of-flight single-particle mass spectrometer that extends the work first described by Reents and Ge. We found a composition independent “power law” dependence between the total peak area and original particle volume that enables one to determine particle volume directly from a particles mass spectrum. This power-law relationship suggests that some ions ablated and ionized from a particle are selectively lost during transport from the laser ablation/ionization region to the detector. A numerical calculation of ion trajectories shows that ion loss is highly dependent on the initial kinetic energy of ions. We show that the size-dependent energetic ions formed by the laser-particle interaction lead to power-law relationship between the cube root of peak area and particle diameter. The results demonstrate that particle size distributions measured with the mass spectromete...

Heterogeneous Reactions of Glyoxal on Particulate Matter: Identification of Acetals and Sulfate Esters

Reactive uptake of glyoxal onto particulate matter has been studied in laboratory experiments in a 2 m3 Teflon reaction chamber. Inorganic seed particles of different composition were utilized, including (NH4)2SO4, (NH4)2SO4/ H2SO4, NaNO3, and simulated sea salt, while the relative humidity and acid concentration were varied. The organic composition of the growing particles was measured in situ with an aerosol mass spectrometer, providing particle mass spectra as a means of product identification. Aerosol physical characteristics were also measured with a differential mobility analyzer and condensation nucleus counter. Regardless of seed composition, particle growth was rapid and continuous over the course of several hours. Identification of several mass fragments greater than the glyoxal monomer suggested that heterogeneous reactionsto form glyoxal adducts of lowvolatility had occurred. Temporal analysis of the mass fragments was consistent with a proposed acid-catalyzed mechanism whereby glyoxal is first hydrated, followed by self-reaction to form cyclic acetal structures. Increased relative humidity slowed the formation of higher order oligomers, also consistent with the proposed mechanism. The relative contribution of various oligomers to the overall organic composition was strongly dependent on the relative humidity and hence the particulate water concentration. A mild acid catalysis was also observed upon increasing the acidity of the seed particles. Specific mass fragments were found that could only arise from sulfate esters and were not present on the non-sulfur-containing seed particles. This first evidence of the formation of organic sulfates in particles is presented together with a proposed mechanism and molecular structure. These results suggest that the formation of these products of glyoxal uptake can contribute significantly to secondary organic aerosol.

Exact particle mass spectrum in a gelling system

This letter reports on the exact particle mass spectrum in a coagulating system with the coagulation kernel proportional to the product of masses of two coalescing particles. This model is known to reveal the sol–gel transition, i.e., formation of a cluster with the mass comparable to the total mass of the whole system. The single-particle mass spectrum is analyzed in the thermodynamic limit and it is demonstrated explicitly how the gel appears in the system.

Stardust encounters comet 81P/Wild 2

Stardust successfully encountered comet 81P/Wild 2 on 2 January 2004 at a distance of 236.4 ± 1 km. All encounter investigations acquired valuable new and surprising findings. The time‐of‐flight spectrometer registered 29 spectra during flyby and measured the first negative ion mass spectra of cometary particles. The dust detectors recorded particles over a broad mass range, 10−11 to 10−4 g. Unexpectedly, the dust distribution along Stardust's flight path was far from uniform, but instead occurred in short “bursts,” suggesting in‐flight breakup of fragments ejected from the nucleus. High‐resolution, stunning images of the Wild 2 surface show a diverse and complex variety of landforms not seen from comets 1P/Halley and 19P/Borrelly or icy satellites of the outer solar system. Longer‐exposure images reveal large numbers of jets projected nearly around the entire perimeter of the nucleus, many of which appear to be highly collimated. A triaxial ellipsoidal fit of the Wild 2 nucleus images yields the principal nucleus radii of 1.65 × 2.00 × 2.75 km (± 0.05 km). The orientations and source locations on the nucleus surface of 20 highly collimated and partially overlapping jets have been traced. There is every indication that the expected samples were successfully collected from the Wild 2 coma and are poised for a return to Earth on 15 January 2006.

From Sol to Gel Exactly

The time evolution of a disperse system wherein the binary coagulation alone governs the temporal changes of particle mass spectra is studied under the assumption that the coagulation kernel is proportional to the product of masses of the coalescing particles. This model is known to reveal the sol-gel transition, i.e., the formation of a cluster with mass comparable to the total mass of the whole system. This Letter reports on the exact solution of this model. The single-particle mass spectrum is analyzed in the thermodynamic limit and it is demonstrated explicitly how the gel appears in the system.

Real-time observation of metastable polymeric species formed from precursor soot

Micrometer-sized precursor soot particles were formed by pyrolysis of pure atmospheric-pressure acetylene in a flow tube reactor. Real-time analysis of both the gas and particle phases of the reactor effluent was performed with an ion trap-based aerosol mass spectrometer. Off-line analyses were also performed on the filter-collected reactor effluent. The real-time particle mass spectra revealed the presence of a polymeric mass distribution starting near 1000 Da and continuing to greater than 1750 Da. The spacing between the polymer peaks is approximately 70 Da. Comparison of real-time and off-line analyses reveals the metastable nature of the polymer-like high mass species.

Long-range sources of Toronto particulate matter (PM2.5) identified by Aerosol Laser Ablation Mass Spectrometry (LAMS)

Abstract An aerosol laser ablation mass spectrometer (LAMS) was operated continuously in downtown Toronto for a period of 11 months. The mass spectra of individual particles were classified according to their chemical composition using neural net-based adaptive resonance theory (ART-2a). The types of particles thereby identified were used as the basis for classifying particles from a 10-day sampling period within the 11-month sampling study. The particles within a class were further segregated by size, and the number of particles analyzed per hour was calculated for each of the resulting composition and sized based classes. ART-2a was used to combine these classes into groups based on similarity in their temporal trends. Two unusual sources were thereby identified: forest fire particles and intercontinental dust. The forest fire particles primarily exhibited potassium and potassium sulphate, while the intercontinental dust exhibited crustal metals, like titanium, aluminum, and iron. Back trajectory analysis of the air masses that transported these particles to Toronto revealed their origins as Northern Canada and Africa. From the chemical composition and size of the particles, a forest fire episode in Western Canada was identified during the 11-month sampling study on 1 June 2002. Other episodes of particles originating from Africa were not observed. These findings demonstrated the use of temporal variations in single particle chemistry to identify sources.

Biomass‐burning particle measurements: Characteristic composition and chemical processing

The NOAA Lockheed Orion WP‐3D aircraft intercepted a forest fire plume over Utah on 19 May 2002 during the Intercontinental Transport and Chemical Transformation (ITCT) mission. Large enhancements in acetonitrile (CH3CN), carbon monoxide (CO) and particle number were measured during the fire plume interception. In the 100 s plume crossing, the Particle Analysis by Laser Mass Spectrometry (PALMS) instrument acquired 202 positive mass spectra from ionizing single particles in the 0.2–5 μm size range. These particles contained carbon, potassium, organics, and ammonium ions. No pure soot particles were sampled directly from the plume. By characterizing these particle mass spectra, a qualitative biomass‐burning particle signature was developed that was then used to identify biomass‐burning particles throughout ITCT. The analysis was extended to identify biomass‐burning particles in four other missions, without the benefit of gas‐phase biomass‐burning tracers. During ITCT, approximately 33% of the particles sampled in the North American troposphere and 37% of the particles transported from Asia, not influenced by North American sources, were identified as biomass‐burning particles. During the WB‐57 Aerosol Mission (WAM), Atmospheric Chemistry of Combustion Emissions near the Tropopause (ACCENT) and ACCENT 2000 missions, 7% of stratospheric particles were identified as biomass‐burning particles. During the Cirrus Regional Study of Tropical Anvils and Cirrus Layers – Florida Area Cirrus Experiment (CRYSTAL‐FACE) this percentage increased to 52% because the regional stratosphere was strongly affected by an active fire season.

Toward understanding the ionization of biomarkers from micrometer particles by bio-aerosol mass spectrometry

The appearance of informative signals in the mass spectra of laser-ablated bio-aerosol particles depends on the effective ionization probabilities (EIP) of individual components during the laser ionization process. This study investigates how bio-aerosol chemical composition governs the EIP values of specific components and the overall features of the spectra from the bio-aerosol mass spectrometry (BAMS). EIP values were determined for a series of amino acid, dipicolinic acid, and peptide aerosol particles to determine what chemical features aid in ionization. The spectra of individual amino acids and dipicolinic acid, as well as mixtures, were examined for extent of fragmentation and the presence of molecular ion dimers, which are indicative of ionization conditions. Standard mixtures yielded information with respect to the significance of secondary ion plume reactions on observed spectra. A greater understanding of how these parameters affect EIP and spectra characteristics of bio-aerosols will aid in the intelligent selection of viable future biomarkers for the identification of bio-terrorism agents.

Field evaporation of tungsten in the presence of adsorbed water

The field evaporation of tungsten at T=300 and 600 K in the presence of water vapor in the residual atmosphere was studied using a static mass spectrometer with a moderate resolution (M/ΔM=200). The room-temperature mass spectrum of field-evaporated particles displayed only the peaks of triply charged ions; an increase in the temperature to 600 K added the peaks of doubly charged ions of approximately the same intensity. The presence of adsorbed water reduced the evaporating field strength by a factor of 2-2.5. At 300 K, an increase in the water content in the residual atmosphere markedly enhanced the field etching. No singly or quadruply charged tungsten ions were observed. The results are indicative of the activation mechanism of field evaporation at the temperatures studied and show evidence of a substantial decrease in the magnitude of evaporating field caused by the presence of water.

NEW STRING AMPLITUDES FROM OLD FERMAT (HYPER)SURFACES

The bosonic string theory evolved as an attempt to find a multidimensional analogue of Euler's beta function to describe the multiparticle Veneziano amplitudes. Such an analogue had in fact been known in mathematics at least in 1922. Its mathematical meaning was studied subsequently from different angles by mathematicians such as Selberg, Weil and Deligne among others. The mathematical interpretation of multidimensional beta function that was developed subsequently is markedly different from that described in physics literature. This paper aims to bridge the gap between the mathematical and physical treatments of such beta functions thus providing new topological, algebro-geometric, number-theoretic and combinatorial treatments of the multiparticle Veneziano and Veneziano-like amplitudes. As a result, the entirely new physical meaning of these amplitudes is emerging: they are periods connected with differential forms living on Fermat (hyper)surfaces. Such surfaces are considered as complex projective varieties of Hodge type. Obtained results allow to interpret the particle mass spectrum in terms of the Hodge spectrum of underlying Fermat (hyper)surface. The computational formalism although resembles that used in mirror symmetry calculations employs many additional results from topology, number theory, theory of singularities, etc. It allows to obtain the correlation functions in particle physics and conformal field theories using the same type of the Picard–Fuchs equations.

Toward understanding the ionization of biomarkers from micrometer particles by bio-aerosol mass spectrometry

The appearance of informative signals in the mass spectra of laser-ablated bio-aerosol particles depends on the effective ionization probabilities (EIP) of individual components during the laser ionization process. This study investigates how bio-aerosol chemical composition governs the EIP values of specific components and the overall features of the spectra from the bio-aerosol mass spectrometry (BAMS). EIP values were determined for a series of amino acid, dipicolinic acid, and peptide aerosol particles to determine what chemical features aid in ionization. The spectra of individual amino acids and dipicolinic acid, as well as mixtures, were examined for extent of fragmentation and the presence of molecular ion dimers, which are indicative of ionization conditions. Standard mixtures yielded information with respect to the significance of secondary ion plume reactions on observed spectra. A greater understanding of how these parameters affect EIP and spectra characteristics of bio-aerosols will aid in the intelligent selection of viable future biomarkers for the identification of bio-terrorism agents.

Horizontal variability 1–2 km below the tropical tropopause

Two long meridional flights of the WB57F high‐altitude aircraft 1–2 km below the tropical tropopause are examined for ozone and total water variability in the context of a large suite of tracers having lifetimes ranging from 10−2 to 103 years, together with mass spectra of individual aerosol particles. It is concluded that local correlations are predominant; contributing processes to the maintenance of the composition are marine convection, continental convection, in situ chemical production, biomass burning, downward transport from the stratosphere and recirculation.