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Semicontinuous monitoring of aerosol chemical composition has continually increased in demand because of the high spatial and temporal variability of atmospheric particles and the effects these aerosols have on human health and the environment. To address this demand, we describe the preliminary development of a semicontinuous aerosol composition analyzer consisting of a growth tube particle collector coupled to a microfluidic device for chemical analysis. The growth tube enlarges particles through water condensation in a laminar flow, permitting inertial collection into the microchip sample reservoir. Analysis is done by electrophoresis with conductivity detection. To avoid hydrodynamic interference from the sampling pressure, the microchip was operated isobarically by sealing the buffer reservoirs from the atmosphere and interconnecting all the reservoirs with air ducts. The collector samples at 1 L [min.sup.-1] and deposits particles into 30 [micro]L of solution. Sample accumulates with time, and sequential injections are performed as aerosol concentration increases. For extended analyses, a sample rinsing system flushes the sample collection reservoir periodically. For inorganic anions, temporal resolution of 1 min and estimated detection limits of 70-140 ng [m.sup.-3] min were obtained. The system was used to measure sulfate and nitrate, and results were compared to a particle-into-liquid-sampler running in parallel. Results indicate that the prototype growth tube-microchip system (termed aerosol chip electrophoresis, ACE) could provide a useful complement to existing aerosol monitoring technologies, especially when less expensive and/or rapid analyses are desired. 10.1021/ac901903m

The particle size distribution and composition of nano-second laser-generated aerosols from brass samples in atmospheric argon has been measured by low-pressure impaction and subsequent quantitative analysis of the aerosols by total reflection X-ray fluorescence. Ablation was performed applying a Nd:YAG laser at 1.06 [micro]m both without and with a prepulse plasma breakdown generated by a second Nd:YAG laser at 2-60 [micro]s prior to the ablation pulse. The beam of the prepulse laser had orthogonal direction to the ablation laser beam, and the breakdown was produced 2.5 mm above the ablation spot. Ultrafine aerosol particles (< 50 nm) were generated in the double-pulse experiment representing practically the total mass impacted, while in single-pulse ablation the proportion of large particles (> 0.1 [micro]m) was dominating. The predominance of ultrafine aerosols in the prepulse experiment indicates that particle formation from vapor-phase condensation is the major mechanism, while the appearance of large particles in single-pulse ablation points at fragmentary evaporation in the laser-produced plasma. It was also shown that the total mass impacted in double-pulse ablation increases almost linearly with the power of the prepulse laser. The better atomization and the larger sample mass ablated can be assumed to be the main reasons for the increase of the line intensities in double-pulse laser-induced breakdown spectrometry with orthogonal prepulses reported by several research groups.

A new approach for the carbon-specific determination of humic-like substances (HULIS) in atmospheric aerosols is presented. The method is based on a two-step isolation procedure of HULIS and the determination of HULIS carbon with a dissolved organic carbon analyzer. In the first step, a C18 solid-phase extraction is performed to separate HULIS from inorganic and hydrophilic organic sample constituents in aqueous sample solutions. The second isolation step is conducted on a strong anion exchanger to separate HULIS from remaining carbonaceous compounds. This ion chromatographic separation step including the subsequent on-line detection of HULIS carbon was performed fully automated to avoid the risk of sample contamination and to enhance the reproducibility of the method. With a 5-mL sample volume, a limit of detection of 1.0 mg C/L was obtained; this corresponds to an absolute amount of 5 [micro]g of HULIS carbon. The reproducibility of the method given as the relative standard deviation was 4.3% (n = 10). The method was applied for the determination of water-soluble HULIS in airborne particulate matter. PM10 concentrations at an urban site in Vienna, Austria, ranged from around 0.1 to 1.8 [micro]g of C/[m.sup.3] (n = 49); the fraction of water-soluble HULIS in OC was 12.1 [+ or -] 7.2% (n = 49).

A synchrotron radiation based aerosol time-of-flight mass spectrometer using tunable vacuum--ultraviolet (VUV) light is described for real-time analysis of organic compounds in ultrafine and large aerosol particles. Particles are sampled from atmospheric pressure and are focused through an aerodynamic lens assembly into the mass spectrometer. As the particles enter the source region, they impinge on a cartridge heater and are vaporized. The particle vapor expands back into the source region and is softly ionized with tunable, quasicontinuous VUV light generated with synchrotron radiation. The radiation can be tuned to an energy close to the ionization energy of the sample molecules, thus minimizing the complications resulting from ion fragmentation. Photoionization efficiency scans (photon scans) can be readily collected, which permit measurement of the molecule's ionization energy and fragmentation onsets. Four high molecular weight, low vapor pressure organic compounds of importance in atmospheric aerosols are analyzed and their ionization energies measured with uncertainties of [+ or -] 60 meV. These are oleic acid (8.68 eV), linoleic acid (8.52 eV), linolenic acid (8.49 eV), and cholesterol (8.69 eV).

Atmospheric aerosols consist of a complex heterogeneous mixture of particles. Single-particle analysis techniques are known to provide unique information on the size-resolved chemical composition of aerosols. A scanning electron microscope (SEM) combined with a thin-window energy-dispersive X-ray (EDX) detector enables the morphological and elemental analysis of single particles down to 0.1 [micro]m with a detection limit of 1-10 wt %, low-Z elements included. To obtain data statistically representative of the air masses sampled, a computer-controlled procedure can be implemented in order to run hundreds of single-particle analyses (typically 1000-2000) automatically in a relatively short period of time (generally 4-8 h, depending on the setup and on the particle loading). However, automated particle analysis by SEM--EDX raises two practical challenges: the accuracy of the particle recognition and the reliability of the quantitative analysis, especially for micrometer-sized particles with low atomic number contents. Since low-Z analysis is hampered by the use of traditional polycarbonate membranes, an alternate choice of substrate is a prerequisite. In this work, boron is being studied as a promising material for particle microanalysis. As EDX is generally said to probe a volume of approximately 1 [micro][m.sup.3], geometry effects arise from the finite size of microparticles. These particle geometry effects must be corrected by means of a robust concentration calculation procedure. Conventional quantitative methods developed for bulk samples generate elemental concentrations considerably in error when applied to microparticles. A new methodology for particle microanalysis, combining the use of boron as the substrate material and a reverse Monte Carlo quantitative program, was tested on standard particles ranging from 0.25 to 10 [micro]m. We demonstrate that the quantitative determination of low-Z elements in microparticles is achievable and that highly accurate results can be obtained using the automatic data processing described here compared to conventional methods.

A new type of aerosol collector employing a liquid at laboratory temperature for continuous sampling of atmospheric particles is described. The collector operates on the principle of a Venturi scrubber. Sampled air flows at high linear velocity through two Venturi nozzles 'atomizing' the liquid to form two jets of a polydisperse aerosol of fine droplets situated against each other. Counterflow jets of droplets collide, and within this process, the aerosol particles are captured into dispersed liquid. Under optimum conditions (air flow rate of 5 L/min and water flow rate of 2 mL/min), aerosol particles down to 0.3 [micro]m in diameter are quantitatively collected in the collector into deionized water while the collection efficiency of smaller particles decreases. There is very little loss of fine aerosol within the aerosol counterflow two-jets unit (ACTJU). Coupling of the aerosol collector with an annular diffusion denuder located upstream of the collector ensures an artifact-free sampling of atmospheric aerosols. Operation of the ACTJU in combination with on-line detection devices allows in situ automated analysis of water-soluble aerosol species (e.g., N[O.sub.2]- , N[O.sub.3]-) with high time resolution (as high as 1 s). Under the optimum conditions, the limit of detection for particulate nitrite and nitrate is 28 and 77 ng/[m.sup.3], respectively. The instrument is sufficiently rugged for its application at routine monitoring of aerosol composition in the real time.

A thermal decomposition method that measures aerosol sulfur at the nanogram level directly from the collection substrate is described. A thermal decomposition apparatus was designed. A stainless steel strip was used as the aerosol collection substrate. A 0.1 mol/L Mn[Cl.sub.2] solution was added as the thermal decomposition catalyst. Currents were passed through the strip where aerosol particles had been deposited. In this way, the strip was heated at 780 [+ or -] 10 [degrees]C, and particulate sulfur was evaporated. A sulfur dioxide analyzer (SDA) with flame photometric detector (FPD) was used to detect gaseous sulfur. High sulfur recoveries from [(N[H.sub.4]).sub.2]S[O.sub.4] and other inorganic sulfates, such as N[H.sub.4]HS[O.sub.4], [K.sub.2]S[O.sub.4], MgS[O.sub.4], and Ca[SO.sub.4], were obtained. From the sulfur blank and the calibration, a lower limited detection of 0.2 ng of sulfur and the determination range of 3.3-167 ng of sulfur were estimated. The method is effective for measuring the sulfate size distributions of urban aerosols in a small sample air volume of 50-60 L. The method is applicable to measuring the sulfur in aqueous extracts of size-segregated urban aerosols collected by impactor and comparing the results with the sulfate data measured by ion chromatography.

Laser-scattering techniques are utilized for the first time to visualize the aerosol droplets in an inductively coupled plasma (ICP) torch from the nebulizer tip to the site of analytical measurements. The resulting images provide key information about the spatial distribution of the aerosol introduced by direct injection and conventional sample introduction devices: (1) a direct injection high-efficiency nebulizer (DIHEN); (2) a large-bore DIHEN; and (3) a MicroFlow PFA nebulizer with a PFA Scott-type spray chamber. Moreover, particle image velocimetry is used to study the in situ behavior of the aerosol before interaction with the plasma, while the individual surviving droplets are explored by particle tracking velocimetry. Directly introduced aerosols are highly scattered across the plasma torch as a result of their radial motion, indicating less than optimum sample consumption efficiency for the current direct injection devices. Further, the velocity distribution of the surviving droplets demonstrates the importance of the initial droplet velocities in complete desolvation of the aerosol for optimum analytical performance in ICP spectrometries. These new observations are critical in the design of the next-generation direct injection devices for lower sample consumption, higher sensitivity, lower noise levels, suppressed matrix effects, and developing smart spectrometers.

A pyrolysis-gas chromatography-ion mobility spectromemy (Py-GC--IMS) briefcase system has been shown to detect and classify deliberately released bioaerosols in outdoor field scenarios. The bioaerosols included Gram-positive and Gram-negative bacteria, MS-2 coliphage virus, and ovalbumin protein species. However, the origin and structural identities of the pyrolysate peaks in the GC--IMS data space, their microbiological information content, and taxonomic importance with respect to biodetection have not been determined. The present work interrogates the identities of the peaks by inserting a time-of-flight mass spectrometry system in parallel with the IMS detector through a Tee connection in the GC module. Biological substances producing ion mobility peaks from the pyrolysis of microorganisms were identified by their GC retention time, matching of their electron ionization mass spectra with authentic standards, and the National Institutes for Standards and Technology mass spectral database. Strong signals from 2-pyridinecarboxamide were identified in Bacillus samples including Bacillus anthracis, and its origin was traced to the cell wall peptidoglycan macromolecule. 3-Hydroxymyristic acid is a component of lipopolysaccharides in the cell walls of Gram-negative organisms. The Gram-negative Escherichia coli organism showed significant amounts of 3-hydroxymyristic acid derivatives and degradation products in Py-GC--MS analyses. Some of the fatty acid derivatives were observed in very low abundance in the ion mobility spectra, and the higher boiling lipid species were absent. Evidence is presented that the Py-GC--ambient temperature and pressure-IMS system generates and detects bacterial biochemical information that can serve as components of a biological classification scheme directly correlated to the Gram stain reaction in microorganism taxonomy.

We report a new method developed for the determination of stable carbon isotopic composition of homologous [alpha], [omega]-dicarboxylic acids and phthalic acid isolated from environmental samples such as atmospheric aerosols and snow. Dicarboxylic acids are derivatized with B[F.sub.3]/1-butanol to dibutyl esters, which are analyzed for the stable carbon isotopic composition using a capillary GC interfaced to on-line combustion isotope ratio mass spectrometer. The [delta][sup.13]C values for individual dicarboxylic acid are then calculated from [delta][sup.13]C of 1-butanol and butyl ester derivative using a mass balance equation. The accuracy of the [delta][sup.13]C measurement for [C.sub.2]-[C.sub.10] diacids is within 0.8 [per thousandth]. We report a few examples of the [delta][sup.13]C ratios of saturated [C.sub.2]-[C.sub.9] [alpha], [omega]-dicarboxylic acids, unsaturated (maleic, phthalic) diacids, and oxocarboxylic acids in the aerosol and snow samples.

It is shown that a liquid (or an amorphous solid) is the thermodynamically stable phase, even in the absence of water as solvent, provided that a sufficiently high number of miscible components are present. It is experimentally demonstrated that the deliquescence relative humidity of aqueous solutions of dicarboxylic acids decreases with an increasing number of components present in the solution.

Study of the domain pattern evolution for the case of dendrimer molecules on mica, a materials system amenable to control of the competing interactions is reported. The domain patterns were fabricated by simple aerosol deposition of dilute solutions of dendrimer molecules in pentanol under ambient conditions followed by slow evaporation.

Airborne fungal spores contribute potentially to the organic carbon of the atmospheric aerosol, mainly in the 'coarse aerosol' size range 2.5-10 [micro] m aerodynamic equivalent diameter (aed). Here, we report about a procedure to determine the organic carbon content of fungal spores frequently observed in the atmosphere. Furthermore, we apply a new (carbon/individual) factor to quantify the amount of fungal-spores-derived organic carbon in aerosol collected at a mountain site in Austria. Spores of representatives of Cladosporium sp., Aspergillus sp., Penicillium sp., and Alternaria sp., the four predominant airborne genera, were analyzed for their carbon content using two different analytical procedures. The result was an average carbon content of 13 pg C/spore (RSD, 46%), or expressed as a carbon-per-volume ratio, 0.38 pg C/[micro] [m.sup.3] (RSD, 30%). These values are comparable to conversion factors for bacteria and some representatives of the zooplankton. Because biopolymers are suspected of interfering with elemental carbon determination by thermal methods, the amount of 'fungal carbon' that might be erroneously mistaken for soot carbon was determined using the 'two-step combustion' method of Cachier et al. (1) and termed as 'apparent elemental carbon' (AEC). This fraction amounted to up to 46% of the initial fungal carbon content. Although the aerosol samples were collected in March under wintry conditions, the organic carbon from fungal spores amounted to 2.9-5.4% of organic carbon in the 'coarse mode' size fraction.

Aerosol particles are studied in a smog chamber and sampled near Riverside, California using aerosol time-of-flight mass spectrometry (ATOFMS) to find an effective method that may determine the major compounds in these particles, and the primary sources of aliphatic amine pollution. Ion peaks are graphed, and used to investigate the concentration aliphatic amines in the samples and possible sources are discussed.

The effect of aerosols on clouds is estimated and charted worldwide for sources such as anthropogenic organic matter, natural organic matter, anthropogenic black carbon, and dust. The uncertainty of such measures is mathematically modeled and the likely result on climate changes is discussed.

The following study examines common ambient aerosols, including marine, urban and traffic influenced aerosols. Because studies show that indoor aerosols are derived primarily from outdoor sources, it is important to examine the effects of different ambient environments on indoor radon dose. Inhaled progeny of (super 222) RN (radon progeny) is the biggest source of irradiation of the human respiratory tract, and studies of underground miners of uranium and other minerals have given estimates of lung cancer risk from exposure to radon progeny.

A variety of factors have been investigated with regard to the quantitation of chemical species within individual ambient aerosol particles analyzed by laser desorption time-of-flight mass spectrometry. Spectrum to spectrum differences in the interaction of the particle with the ionization laser beam, which affect the absolute peak areas in the mass spectra, can be minimized by using relative peak areas instead of absolute peak areas in each spectrum. Whereas absolute peak areas vary by an average of 59% for a given ion peak in single particle mass spectra of a monodisperse aerosol of particles formed from the same solution, relative peak areas in the same mass spectra vary only by an average of 16%. Relative sensitivity factors (RSF) relating the mass spectral ion intensity of NH(sub 4)(super +) and the alkali metal cations Li(super +), Na(super +), K(super +), Rb(super +), and Cs(super +) in single particle aerosol time-of-flight mass spectrometry to their bulk concentrations have been determined. The values for Li(super +)/Na(super +), K(super +)/Na(super +), Rb(super +)/Na(super +), Cs(super +)/ Na(super +), and NH(sub 4)(super +)/Na(super +) are found to be 0.14, 5.1, 6.0, 7.9, and 0.014, respectively. The higher response for heavier cations of the alkali metals is consistent with the periodic trends of both ionization potential and lattice energies of the species of interest. The response factor for sodium and potassium cations has been used to accurately determine the relative amounts of Na(super +) and K(super +) in sea-salt particles, by analyzing a sample of approximately 360 ambient sea-salt particles. The relative amounts of Na(super +) and K(super +) are found to be 97 and 3% in particles, respectively, whereas in seawater they are, on average, 98 and 2%.

The thermodynamics and the phase transition kinetics of aqueous NH4HSO4 solutions 0-60 wt% has been investigated using differential scanning calorimetry.

The focus of this study is the determination of the frequency-dependent optical constants from Fourier transform infrared spectra of liquid sulfuric acid and water aerosols. Results indicate the dependence of infrared complex refractive indices of sulfuric acid on temperatures and compositions.

A capacitance manometer has been utilized to determine equilibrium water partial pressures and salt solubilities in aqueous NH4HSO4 over low temperature ranges. Measured pressures above the H2SO4 solution are consistent with values calculated using the procedure of Clegg et al, while results for the NH4HSO4 solutions also agree with calculated equilibrium water partial pressures. Solids form in the NH4HSO4 solutions at temperatures 258.0(sub 6) plus or minus 0.1 K, 246.4(sub 7) plus or minus 0.1 K and 261.0(sub 1) plus or minus 0.1 K.

The first results are reported from a new single-particle two-color laser time-of-flight mass spectrometer, incorporating a combination of infrared (C[O.sub.2]) and UV (excimer) laser irradiation. This combination of lasers has the capability to effectively separate the desorption or evaporation step from the ionization step, thereby greatly improving the analytical capabilities of such an instrument. The results on liquid aerosols, such as aniline, show that prior evaporation of the aerosol particle with the IR laser increases the ion signal produced by the excimer laser by more than 2 orders of magnitude. In the case of nitrobenzene aerosols, the excimer laser alone produces no ions, while a very large signal is observed when the aerosol is first irradiated with the C[O.sub.2] laser. A simple model, based on the Coulomb explosion of the ionized aerosol, is used to estimate the number of ions generated by the excimer laser ([approximately][10.sup.5] ions). Experimental evidence based on the observed time delay of protonated aniline parent ions indicates that the laser irradiation of the liquid aerosol results in a stable neutral plasma which separates into positive and negative charges only after a 100-500-ns delay.

The differential scanning calorimetry was used to study the transition of emulsified binary HNO3/H2O and HNO3/H2SO4/H2O acid solutions from the liquid to the solid phase to determine the mechanism of ice formation from stratospheric aerosols. Results showed that binary solution droplets with less than 33 wt% HNO3 turn in to ice ar 37-65K, while those with higher concentrations form glasses instead of freezing. Results also indicated that the formation of ice particles from ternary aerosols at stratospheric temperatures require an ice saturation ratio of over 1.65.

A standard additions method for calibrating the response of laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) is assessed. Desolvated particles from an ultrasonic nebulizer and particles from an ablation cell are introduced simultaneously to a twin quadrupole ICPMS. Matrix-matched or pelletized solid standards are not required, and the solution standards are easily prepared. The transport of sample particles from the LA cell and of aerosol particles from the solution nebulizer must be measured. The relative accuracy for the analysis of steel reference materials is a few percent, which is comparable to that obtained with matched solid standards.

A new approach to the measurement of the size distribution of atmospheric particles as a function of chemical reactivity is demonstrated. In this method, particles are collected on an atomically flat mica substrate and imaged using atomic force microscopy. The particle size distribution is obtained from analysis of the image. The sample is then repeatedly exposed to a reactive gas such as ozone or oxygen atoms and reimaged. The dimensions of organic and graphitic (soot) particles are found to shrink at different rates due to formation of volatile products, while inorganic particles remain unchanged. Using this approach, it is possible to classify particles as organic, graphitic, or inorganic and to obtain the size distribution for each chemical class.

Research was conducted to examine the concept of directional energy transfer between different dye aggregates and monomer thionine by confining them in a reverse micellar environment. Varying amounts of monomer, dimer and higher order aggregates were obtained in dilute dye solutions by controlling the ratio of (dye)/(aerosol-OT). Results suggest the possibility of using H-type dye aggregates as antenna molecules to harvest light energy.

Monolayer films of some fatty acids, such as lauric and stearic, inhibit the hydroscopic growth rate of sulfuric acid aerosol. Such result can be attributed to the films' obstructive effect on the permeation of water vapor. The original film coating thickness was found to influence greatly the retardation effects of organic films.

The behavior urban aerosol particles is shown to be more complex than the Whitby trimodal aerosol paradigm and whose behavior in the atmosphere is primarily driven by the behavior of the primary aerosol, especially its accumulation properties. This is due to the action of the high-temperature combustion components of urban aerosols and the aerosol scavenging property of the secondary sulfate nuclei, which dictates hygroscopic growth and cloud processing.

A study was conducted to determine frequency-dependent complex refractive index from the aerosol infrared extinction spectra of nitric acid dihydrate particles. The aerosols were prepared in a laminar aerosol flow cell. The aerosol composition was changed by adjusting the composition of the vapor entering the cell by MKS mass flow controller. Results indicated that the aerosol spectra utilized to determine the refractive indices correlated with other aerosol studies.

The composition of aerosol droplets produced by ultrasound from aqueous solutions containing various concentrations of Triton X-100 and D-glucose was measured to determine whether the droplets would be enriched with surface-active solutes. The concentration of the surfactant in the droplets was significantly higher that that in atomized solution. The enrichment with the surfactant increases as the surfactant concentration in the atomized solution decreases.

The kinetics of uptake of HOBr, HNO3, O3 and NO2 by deliquescent NaCl aerosols at 75% relative humidity and room temperature were investigated. The results of aerosol kinetics flow tube analysis showed that for HOBr, the uptake coefficient is larger than 0.2 for highly acidid sea-salt aerosols. For HNO3, the uptake coefficient on unbuffered NaCl aerosols is greater than 0.2. Both NO2 and O3 showed low reactivity on PH neutral aerosols.

Direct Fourier transform infrared spectroscopy allowed the separation by polarity and identification of aerosol collected during the Smoky Mountain Aerosol and Visibility Study at Look Rock, TN. Results also revealed that the submicron organic aerosol was predominantly polar. The concentrations, composition and size distribution of the Smokey Mountain aerosol is governed by secondary formation processes.

Model results revealed that growth of hygroscopic aerosols near water surfaces enhances their dry deposition to water surfaces. Particles of (NH4)2SO4 greater than 0.1 micronm in diameter did not grow to their equilibrium size before depositing to a hypothetical water surface. Equilibrium models have overpredicted the effects of hygroscopic growth on deposition velocities by as much as a factor of 5.

The heterogeneous reactions of nitryl halides with aqueous salt solutions as a model substrate for atmospheric sea salt aerosol were investigated. The reaction of Br2 with nitrite solution was found to be a convenient approach to the synthesis of BrNO2. The heterogeneous reactions result in the formation and loss of BrNO2 on salt solutions. The temperature-dependent lifetime of BrNO2 in a quartz cell was measured and the activation energy for the unimolecular decay at atmospheric pressure was obtained.

Research was conducted to examine the deliquescence behavior of multicomponent aerosols. The experiment was carried out by measuring the particle size or weight growth at controlled relative humidities. Results suggest that as the ambient relative humidity reaches the deliquescence point of the system, the chemical composition of the particle surface shifts gradually with increasing relative humidity until the particle changes completely to an aqueous droplet.

Flow Reynolds number creates a slight impact on the deposition of aerosol in bends with turbulent flow. Aerosol penetration yielded changes not more than 5% when Reynolds number was allowed to set between 3200 and 19800. A correlation model that is effective for Stokes numbers ranging from 0.07 to 1.2, for bend angles ranging from 45 to 180 degrees, and for curvature ratios ranging from 2 to 10 was formulated to forecast aerosol penetration.

Studies reveal that the reaction of terbuthylazine (TBA) with OH radicals results to the abiotic degradation of TBA in the environment. A loss path not initiated by OH radicals was observed aside from the OH reaction. Acetyl-TBA, in addition to the des-alkylation product desethyl-TBA, were found to be the main products of the OH radical reaction.

Absorptive partitioning will tend to dominate the gas/particle (G/P) partitioning of semivolatile organic compunds sorbing to urban particulate matter that contains a high concentration of secondary carbon. This observation was noted in a study of G/P partitioning of n-alkanes and polynuclear aromatic hydrocarbons sorbing to liquid dioctyl phthalate, solid ammonium sulfate, and secondary organic aerosol.

The relative content of unburned-fuel (FHC) hydrocarbon appear to decrease from near combustion source to remote samples suggesting that FHC originally belong to the exchangeable fraction of combustion aerosol hydrocarbons. Results indicated that polycyclic aromatic hydrocarbons (PHC) and FHC show a decoupled affinity to soot. PHC are produced entirely in small particles while FHC are distributed onto all sizes.

A multi-photon ionization based fast conductance (MPIFC) technique was applied to detect combustion byproduct aerosols. These PAH-polluted aerosols were on-line sampled by means of renewable water microdroplets. The environmental cases considered here have involved such common air contaminants as motor car exhaust gas and cigarette smoke. The possibility of obtaining useful calibration curves has been addressed. Two droplet contamination regimes were clearly observed. These have been argued to be associated with either a volume uniform (i.e., a bulk type) or a surface-favored contamination. The latter regime is possible whenever the increasing droplet contamination extends beyond the solubility saturation of the PAH compounds. Detection limits as low as 1 pg were obtained for pyrene-contaminated renewable microdroplets.

Aerosol time-of-flight mass spectrometry (ATOFMS) allows for simultaneous determination of the aerodynamic particle size and chemical composition of individual particles in real time. Polydisperse particles originating from July 4, 1995, fireworks displays were monitored using ATOFMS over a 4-day period. Fireworks particles were identified by ion combinations in the single-particle mass spectra of potassium, aluminum, magnesium, barium, and lead and grouped into chemically specific categories. The relative number of ambient fireworks particles peaked on the morning of July 5, 1995, with representative particles being detected as late as July 19, 1995. The mass spectra of the detected particles are indicative of the original chemical composition of typical fireworks mixtures. This study demonstrates the ability of ATOFMS to serve as a real-time monitor of aerosols in the atmosphere, capable of detecting and tracking aerosol particles of a specific size and chemical composition from a particular source over time.

A research in organic aerosol photochemistry studied the products formed from the photodegradation of benz[a]anthracene in the presence of 9,10-anthraquinone, 9-xanthone and vanillin. Irradiation of these substances were done in toluene, benzene and benzene-d6 medium and analyzed using GCMS, FTIR and NMR. Results showed a high concentration of 7,12-benz[a]anthracenedione among the 13 tentatively identified products of benz[a]anthracene photodegradation.

Aerosol matrix-assisted laser desorption/ionization (MALDI) has been combined with a reflectron time-of-flight mass spectrometer for improved mass resolution. A methanol solution of matrix and analyte was sprayed directly into a reflectron time-of-flight mass spectrometer, and the aerosol particles were irradiated and ionized with a frequency-tripled Nd:YAG laser at 355 nm. Mass resolution of over 300 was observed for the peptides bradykinin, angiotensin II, and gramicidin D and for vitamin [B.sub.12]. This represents a resolution enhancement of approximately 10-fold over that previously reported for aerosol MALDI with a linear time-of-flight instrument.

A direct current (dc) glow discharge mass spectrometer has been used to analyze atmospheric particulate matter. The sample preparation used is simple and time-saving. The air is sucked by a pump through a single-orifice impactor stage, in which the aerosols are impacted on a metal support, forming a central spot. This metal plate is directly used as a cathode in a dc glow discharge mass spectrometer. Evaluation of the sample loading and of the discharge parameters allowed us to optimize the signal intensity and to minimize its decrease, the latter being a consequence of its consumption by continuous sputtering in the discharge. The available aerosol analysis time could be prolonged to more than 3 h, a time span necessary to perform a multielement analysis using a magnetic sector instrument and long integration times. A NIST reference aerosol was measured to evaluate the quantitative analysis potential. The internal reproducibility was better than 10% RSD, and the limits of detection were estimated to be in the low ppm or sub ppm region. Even without the use of any standards or correction factors, glow discharge mass spectrometry could offer good semiquantitative results, based only on the use of an internal standard.

New aerosol sampling and polycyclic aromatic hydrocarbon (PAH) analysis techniques were used to develop an enhanced method for measuring PAH associated with size-segregated atmospheric aerosols. A micro-orifice impactor was used to collect aerosols from Boston and rural Massachusetts. Gas chromatography and mass spectrometry were used to identify and quantify PAH with molecular weights between 178-302. PAH were distributed among aerosol size fractions based on molecular weight in urban samples, while low and high molecular weight PAH were associated with both fine and coarse aerosols in rural samples.

The recent innovations and use of mass spectrometry for on-line, real-time analysis of single aerosol particles are discussed. The role of aerosol particles in air pollution and the properties of ideal aerosol analyzers are also discussed. The application of mass spectrometry for aerosol analysis, the latest instruments and techniques for laboratory and field studies are also presented.

An integrated sampling and supercritical fluid extraction (SFE) cell has been designed for whole-sample analysis of organic compounds on tropospheric aerosol particles. The low-volume, polymer-free, temperature-controlled extraction cell has been interfaced with a sampling manifold for aerosol collection in the field. After sample collection, the entire SFE cell was removed, transferred, and coupled to a gas chromatograph; after on-line extraction, the cryogenically focused sample was separated and the volatile compounds were detected with either a mass spectrometer or a flame ionization detector. A 20-min extraction at 450 atm and 90 [degrees] C with pure supercritical C[O.sub.2] is sufficient for quantitative extraction of most volatile compounds in aerosol samples. A comparison between SFE and thermal desorption, the traditional whole-sample technique for analyses of this type, was performed using ambient aerosol samples, as well as samples containing known amounts of standard analytes.

We have recently developed an aerosol-liquid introduction interface for matrix-assisted laser desorption ionization (MALDI) mass spectrometry. In this study, we examine the effect of matrix-to-analyte ratio and analyte concentration on analyte ion yield. These studies were performed using bradykinin, gramicidin S, bovine insulin, and myoglobin as analytes and [Alpha]-cyano-4-hydroxycinnamic acid and 4-nitroaniline as matrices. The optimum matrix-to-analyte molar ratio for aerosol MALDI was determined to be 10-100:1, which is lower than that typically used for conventional surface MALDI (10010 000:1). The ion yield was found to be a nonlinear function of analyte concentration. Possible explanations for these observations are discussed.

A radial diffusion model was developed to simulate the mass transfer of semivolatile organics in and out of combustion aerosols. Results indicate that mass transfer significantly depends on ambient temperatures and humidities and that time to sorption equilibrium is a function of particle size and vapor pressure of sorbing compounds. Results also suggest that the polycyclic aromatic hydrocarbon diffusion coefficient in diesel particles at 25 degrees celsius is of the order 10(super -15) cm2/s and the surface mass transfer coefficient for deuterated pyrene is of the order of 10(super -10) cm/s.

The influence of organic aerosol elements on the photodegradation rate of six polycyclic aromatic hydrocarbons (PAH) is investigated. Specifically, a photochemical reactor is employed to analyze the decay of PAHs in methoxyphenols and hexadecane solutions. The former is abundant in wood smoke whereas the latter is commonly found in automobile exhaust. The six are benz(a)anthracene, chrysene, benzo(a)pyrene, benzo(e)pyrene, benzo(b)fluoranthene and benzo(k)fluoranthene.