Sampling and analysis of atmospheric sulfates and related species

• Published in: Atmospheric environment 1978, Vol.12 (1), p.55-68
• Main Authors: Stevens, Robert K., Dzubay, Thoms G., Russwurm, George, Rickel, Dwight
• Format: Article
• Language: English
• ISSN: 0004-6981; 1352-2310
• DOI: 10.1016/0004-6981(78)90188-9

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 +, NH 4 2− and SO 4 2− ions revealed that the sulfate concentrations were typically 10 to 14μg 3̄ and that H + ions accounted for 5 to 60% of the cations associated with sulfate. In addition the sum of NH 4 + and H + equalled the SO 4 2− 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.