Thomas G. Dzubay

Sampling and analysis of atmospheric sulfates and related species

Abstract Sampling and analytical methods to measure atmospheric concentrations of sulfur, sulfates and related species are compared for aerosols collected in New York City, Philadelphia, PA, South Charleston. WV, St. Louis, MO; Glendora. CA; and Portland, OR. Dichotomous samplers equipped with virtual impactors were used to separately collect fine ( 3.5μm) particles on membrane filters. Both size fractions were analyzed by energy-dispersive X-ray fluorescence spectroscopy to determine the total amounts of sulfur and other elements, and the samples were analyzed by an Ion Chromatograph and by the thorin spectrophotometeric method to determine sulfate. These analyses reveal that more than 70% of the sulfur occurs in the fine particle fraction for at least 90% of the samples. Sulfate typically accounts for about 40% of the mass of the fine particle fraction, and in some instances it accounts for more than 50%. For the fine particle fraction, the ratio of the sulfate and the sulfur mass concentrations is 2.96 ±0.15, which is in excellent agreement with the value of 3.00 for sulfate. To test for the existence of sulfite ions in the samples, a cold extraction procedure was developed, which minimizes the conversion of sulfite to sulfate. Analysis for sulfite using the Ion Chromatograph indicates that less than 2% of the sulfur collected in South Charleston, WV. and Philadelphia, PA, is in the form of sulfite. A procedure was developed to preserve the acidity of aerosols collected with an automated dichotomous sampler and was recently used to sample aerosols in Research Triangle Park. NC. Analysis of the samples for H+, NH42− and SO42− ions revealed that the sulfate concentrations were typically 10 to 14μg3 and that H+ ions accounted for 5 to 60% of the cations associated with sulfate. In addition the sum of NH4+ and H+ equalled the SO42− concentration expressed in nanoequivalents. In the network of stations that was part of the Regional Air Pollution Study (RAPS) the hi-volume sampler gave mass and sulfate concentrations that were consistently higher than values obtained for the automated dichotomous sampler. For samples collected at eight RAPS stations at St. Louis, MO. between September and December 1975, the ratio for sulfate determined for the two types of samplers was 1.32.

A composite receptor method applied to philadelphia aerosol

Particles were collected in dichotomous samplers at three sites in the Philadelphia area during summer, 1982, and analyzed by x-ray fluorescence, instrumental neutron activation, pyrolysis, and ion chromatography. An intermethod comparison showed that fine-fraction results agreed within measurement error for S, Ca, Mn, Fe, Zn and Sb. A composite of chemical mass balance, multiple linear regression, and stratification by wind direction was used to apportion mass into ten categories. Primary emissions from residual-oil combustion, catalytic crackers, an antimony roaster, and municipal incinerators contributed less than 10% of PM-10. The portions of average PM-10 attributed to crustal matter and vehicle exhaust were 17 + or - 2 and 6 + or - 2, respectively. That attributed to sulfate plus related water and ions was 50 to 55%. Wind-stratified data indicated that 80 + or - 20% of the sulfate was from a regional background. Multiple linear regression of S vs tracers Se and either V or Ni indicated that 72 + or - 8 and 16 + or - 5% could be attributed to coal- and residual oil-fired power plants, respectively.

Characterization of the aerosol in the Great Smoky Mountains

A six-day field study was conducted in the Great Smoky Mountains to measure the composition of the aerosol that pervades this region. Sampling was performed with three dichotomous samples, a mobile laboratory containing instruments to measure gaseous pollutants, and two gas chromatographs for measuring halocarbons. Sulfate and its associated cations represented 61% of the particle mass. The average ionic composition of the ammonia, hydrogen, and sulfate ions was equivalent to ammonium bisulfate. Of the total mass measured in the fine particles, elemental carbon accounted for 5% and organic carbon accounted for 10%. Crustal elements such as aluminum, calcium, iron, and silica were minor constituents of the fine-particle mass. During the period of the study the fine-particle aerosol in the Great Smoky Mountains was dominated by acid sulfates rather than by natural organic compounds. (2 graphs, 36 references, 8 tables)

Characterization of individual fly-ash particles emitted from coal- and oil-fired power plants

Abstract Individual particles from coal- and oil-fired power plants were analyzed by scanning electron microscope equipped with an energy dispersive X-ray spectrometer to investigate size, morphology, and composition. Samples were collected on filters by dichotomous sampler in the fine ( 95%) smooth, mineral spheres. No cenospheres (perforated hollow spheres) were detected, and almost 90% of the mass concentrations occurred in the coarse fraction. Sulfur as lared as a surface layer on the mineral core; the abundances of Fe and S were highly variable. The Al/Si ratio was fairly constant for most of the spheres but not for the relatively few Fe-rich or non-spherical coal fly ash particles. Over 90% of the mass of oil fly ash occurred in the fine fraction. The size distribution of chemical and morphological properties of individual oil fly ash particles was found to be trimodal. Oil fly ash particles smaller than 0.7 μ (geometric diameter) were non-spherical and relatively pure in sulfate, and 90% of such particles were smaller than 0.5 μm; V or Ni could be detected in 50% to 60% of such particles larger than 0.3 μm. Those particles in the 0.7–3 μm range of geometric diameters were predominantly spherical and of mineral composition, highly variable in Al, Si, P, Ca, Ti and Fe; 50–60% of them contained detectable amounts of V or Ni. Larger oil fly ash particles had a lacy morphology and consisted of carbonaceous material and sulfur.

Apportioning light extinction coefficients to chemical species in atmospheric aerosol

Abstract A 1978 Denver aerosol data set has been analyzed by a variety of methods for determining light scattering and extinction coefficients per unit mass concentration for specific chemical species in fine particles (

Source apportionment methods applied to the determination of the origin of ambient aerosols that affect visibility in forested areas

An aerosol characterization, visibility, and receptor modeling study was conducted in the Shenandoah Valley, VA between 14 July and 15 August 1980. The objectives of this study were to: (1) determine the origin of the ambient particles, (2) determine the major chemical species contributing to the light extinction coefficient, (3) evaluate analytical methods to characterize aerosols and (4) provide data for comparison with chemical composition of aerosols collected in the Great Smoky Mountains and in the Abastumani Mountains of Georgian Soviet Socialist Republic. The average sulfate concentrations measured in fine particles (<2.5μm) at these three locations were: 12.0μgm−3 at Great Smoky Mountains; 13.6 μg m−3 at Shenandoah Valley, and 4.6 μg m−3 at Abastumani Mountains; the fractions of sulfate in the fine particle mass concentrations at each site were 0.50,0.50 and 0.38, respectively. For the two studies in the United States, the fine particle sulfate during sulfate maxima was mostly in the form of ammonium acid sulfate. Factor analysis of the fine aerosol composition measured in the Shenandoah Valley yielded a persistent factor containing large loadings on mass, SO2−4, S, NH+4, H+, Se and total nitrate (sum of particulate nitrate and nitric acid), which is characteristic of coal-fired sources. This factor analysis grouping along with additional emissions information suggests that coal-fired power plants are the principal source of sulfate and nitrate.

A two stage respirable aerosol sampler using nuclepore filters in series.

Abstract Respirable and nonrespirable particles are separately collected from the atmosphere in a size selective sampler consisting of two Nuclepore niters in series. The first filter has pore diameters of 12 μm and collects, to a close approximation, the nonrespirable fraction as defined by the ACGIH criteria. The second filter has pore diameters of 0.2 μm and collects the respirable fraction. Experimental measurements of the efficiency of the 12-μm filter are found to be in good agreement with theoretical predictions based on calculated particle trajectories in a flow field that satisfies the Navier-Stokes equations. Atmospheric samples were collected using both the techniques of series filtration and of virtual impaction. A mass and elemental analysis of the aerosol deposits using gravimetric and X-ray fluorescence techniques demonstrated that the results from the two types of sampler are comparable. Filter loading as great as 90 μg/cm2 was investigated and found to produce no change in filter performance as measured by the location of the 50% cutpoint.

General Motors Sulfate Dispersion Experiment: Summary of EPA Measurements

In October 1975, General Motors sponsored a study of sulfate exposures utilizing a fleet of catalyst equipped motor vehicles in controlled, simulated, highway driving conditions. This paper reports some EPA sponsored measurements. Sulfuric acid aerosol, in the Aitken nuclei mode, geometric mean diameter (GMD) of about 0.02 µm, is emitted in the exhaust of catalyst equipped vehicles. Measurement of sulfuric acid 20 m downwind of the roadway indicated a lack of complete neutralization by ammonia. When the wind was perpendicular to the roadway there was little coagulation of sulfuric acid into the accumulation mode, GMD of about 0.24 µm From measurement of the mass flow rate of aerosol sulfur from the simulated freeway, the aerosol sulfur emission rate per car was determined to be 3.5 ± 0.8 µg/m (5.6 ±1.3 mg/mile) corresponding to a 12 ± 3% conversion of fuel sulfur into emitted aerosol sulfur.

Interlaboratory comparison of Receptor Model results for Houston aerosol

Abstract In exercises for the Mathematical and Empirical Receptor Models Workshop (Quail Roost II), nine investigators independently applied receptor models to apportion ambient aerosol mass concentrations to components from emission sources in Houston, TX. The receptor model results were based upon ambient aerosol compositional data supplied to investigators that included mass, elemental and ionic species concentrations for consecutive 12-h sampling periods at the University of Houston between 10 and 19 September 1980. Some investigators performed additional analyses by X-ray powder diffraction, scanning electron microscopy with automated image analysis and X-ray energy spectroscopy and light microscopy. In most cases, the fine (0.2–2.5 μm) and coarse (2.5–15 μm) fractions were analyzed separately by the receptor models. The models tested include effective variance type chemical mass balance, weighted ridge regression, multiple linear regression, factor analysis and target transformation factor analysis. The number of source classes determined ranged from 4 (by multiple linear regression) to 23 (by light microscopy). Results are presented and compared in eight general emissions categories.

Fitting Multimodal Lognormal Size Distributions to Cascade Impactor Data

A procedure is described for fitting multimodal lognormal size distributions to cascade impactor data. The method was applied to published cascade impactor measurements for ammonium and nitrate that were previously analyzed by procedures that do not assume a functional form for the size distribution. An evaluation of the lognormal fitting procedure by Monte Carlo simulations demonstrated that unbiased parameters and reliable estimates of their uncertainties require correct specifications of measurement precision and impactor characteristics.