George M. Russwurm

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.

CO 2 Laser Absorption Coefficients for Determining Ambient Levels of O 3 , NH 3 , and C 2 H 4

A carbon dioxide laser source was used to determine absorption coefficients for dilute absorber-air mixtures at wavelengths corresponding to several vibration-rotation lines in each branch of the 00 degrees 1-02 degrees 0 band at 9.4 microm and the 00 degrees 1-10 degrees 0 band at 10.4 microm. For all samples the total pressure was 1 atm and the temperature was 300 K; the concentrations ranged from 10 ppm (parts per million by volume) to 357 ppm for NH(3) and C(2)H(4), and from 10 ppm to 80 ppm for O(3). The absorption coefficients are tabulated, and the use of selected laser lines in monitoring ambient concentrations is discussed.

Composition and origin of summertime air pollutants at Deep Creek Lake, Maryland

Abstrset-A 1 month intensive summe~me field study conducted in rural western Maryland resulted in a ~mprehensive set of fine particle, gaseous and met~rolo~~l data. Sulfur in the assumed form of Arnold sulfate accounted for 67% of the average tine particle mass and had a very high correlation with fine particIe mass (r=O.99). Other measured species, including carbon and nitrate, made only minor contributions to the fine mass. Peak sulfate concentrations, averaged over 6-h intervals, exceeded 50 pg mm3. Nitric acid concentrations showed strong daytime maxima and on a 24 h basis were about four times those of fine particle nitrate. Sulfur in the gas phase (SO,) constituted more than half of the total sulfur, indicating that the sampling site was being influenced by local sources. Fine particle selenium was well corretated with fine partide sulfur (r=O.70}. The ratio of fine particle suifur to selenium was 2800, characteristic of a rural site downwind of coal-burning areas. Mixed-layer back trajectories were used to id~t~y possible source regions for the measured parameters. Wind f~quency-noes con~nt~tio~ of parameters associated with coal-burning (S, Se, SO, and mass) were highest for back trajectories arriving at Reep Creek Lake from the west-northwest. Use of Rahn and Lowenthal regional signatures showed an overwhelming dominance by the Lower Midwest region, and a surprisingly weak impact by the Upper Midwest region, at the site.

Long-path FTIR Measurements of Volatile Organic Compounds in an Industrial Setting

A long-path Fourier transform spectrometer was used to make measurements of volatile organic compounds in an industrial complex in New Castle, Delaware as part of the Superfund Innovative Technology Evaluation (SITE) program. These data are compared to data taken with a whole-air canister technique. To provide an effective comparison the canisters were transported along the path for a 32-min period. For each FTIR spectrum, 256 interferograms were co-added over a 4-mln period. Eight individual spectra were then co-added to obtain the comparison data.

Long-path laser monitor of carbon monoxide: system improvements

A system for measurement of long-path absorption of carbon monoxide has been redesigned for improved performance. The diode laser source is frequency stabilized by automatically correcting the laser current and is limited to a single-wavelength output by a tunable étalon. As a result, sensitivity variations of the system to CO are limited to +/-0.7%, and system response is linear with respect to CO concentrations.

A method for reducing and evaluating blanks in Tenax air sampling cartridges

Abstract Clean sorbent cartridges are essential in ambient air sampling to avoid false analytical results. This paper describes a procedure for the construction and cleaning of a Tenax cartridge. A definition is formulated to describe a clean cartridge quantitatively.

Helmholtz resonator enhancement of photoacoustic signals.

A Helmholtz resonator attached to a nonresonant photoacoustic cell enhances the responsivity to trace gas absorption by as much as a factor of 15.3. A simple system model based on a lumped parameter approach predicts the experimentally determined resonance frequency f(0) within 6% for all five resonator volumes tried and gives a pressure amplitude response at resonance proportional to f(0)(-5/2), which is the approximate experimental dependence. Optimization of response based on the model shows a pressure amplitude dependence on a(1/2), the square root of the radius of the cylindrical tube connecting the cell and the resonator.

laser-based, long path monitoring of ambient gases — analysis of two systems

New long path absorption techniques for measurement of ambient O3 and CO have recently been demonstrated using a CO2 laser and a semiconductor diode laser, respectively. For the CO2 laser system the use of closely spaced wavelengths minimizes system drift and simplifies the determination of ambient O3 concentrations. For the diode laser system, multimoding of commercially available diodes can cause a nonlinear response and frequency detuning can occur unless a proper feedback network is provided. Area monitoring, monitoring along boundaries in regional air pollution studies and model validation are potential applications.

Effects of a nonlinear response of the Fourier-transform infrared open-path instrument on the measurements of some atmospheric gases

The response of a Fourier-transform infrared (FTIR) instrument to changes in absorbance is inherently nonlinear for a number of reasons. One is that the interferogram acquired by the FTIR is truncated and then apodized before further processing of the data is accomplished. A commonly used apodization function in open-path FTIR research is triangular apodization, and all the research presented here has been done with that function. We calculated a set of absorption spectra by using the HITRAN database, covering ranges in both concentration and temperature for water, ammonia, and methane. Plots of these data reveal nonlinear results. The commonly used analysis technique, classical least squares, assumes that the response is linear. We describe some of the effects of this nonlinearity and present ways to address these effects.

Design of a sampling cartridge for the collection of organic vapors

Abstract A sampling cartridge using the sorbent Tenax-GC has been designed, manufactured, and tested. This new sampling cartridge minimizes field handling of the cartridge and, thus, reduces the opportunity for inadvertent contamination. The design incorporates the standard glass sampling tube into a special container that seals the sorbent tube from external contamination during shipping, handling, and storage; does not contaminate the sample; is durable, reusable, and easily installed into an appropriately outfitted sampler; and confines the sample stream to two tandem, sorbent tubes. The design, manufacturing procedure, and preliminary test results are given here.