Sensitive Method for Measurement of Atmospheric Hydrogen Sulfide David F. S. Natusch,’ Homer B. Klonis, Herman D. Axelrod,2 Ronald J . Teck, and James P. Lodge, Jr. National Center for Atmospheric Research, Boulder, Colo. 80302 A method is described for measuring trace levels of atmospheric hydrogen sulfide as low as 5 parts per trillion (ppt, 10-12). H2Sis extracted from air by reacting with a AgN03 impregnated filter. The collected Ag2Sis then dissolved with NaCN solution and analyzed fluorimetrically using very dilute fluorescein mercuric acetate. The conditions required for quantitative collection, recovery, and analysis of H2S by this method are described and suitable prefilters are recommended. The method has proved to be both simple and reliable, and its use in field sampling indicates H2S levels of the order of 50 ppt in essentially “unpolluted” air in Colorado, U.S.A. The same procedure can also be used for pollution measurements where concentrations are several orders of magnitude higher.
ALTHOUGH A LARGE NUMBER of analytical methods for the determination of atmospheric H2S have been published, none are completely suitable for measuring atmospheric background levels, which have been estimated to be below 1 part per billion (ppb, 10-9). Bamesberger and Adams ( I ) modified the well known methylene blue method (2) for determining HzS by stabilizing the Cd(OH)? trapping solution with an antioxidant, but this did not completely prevent loss of the collected sulfide and the method was sensitive only to 0.8 ppb. Similarly, the spectrophotometric method of Humphrey, Hinze, and Jenkines (3) does not possess sufficient sensitivity for determining background levels of H?Sin the atmosphere. Finally, Stevens et al. (4) developed a gas chromatographic-flame photometric detector method which can measure as low as 3 ppb HzS, but this instrument requires support gases and is not practical for making measurements in remote areas. To date, the most sensitive published method for the determination of H2S is that of Axelrod et al. (5) who trapped the gas in an alkaline aqueous solution and estimated the resulting S2- by a fluorimetric technique. While the sensitivity of this method is adequate for background determinations, the collected S2- is unstable (6) and necessitates that analysis follow soon after sampling. Paper impregnated with Pb(II), Hg(II), and Ag(1) salts has been used extensively to trap H2S. Sensenbaugh and He)~ paper tapes, but this meon (7) used P ~ ( O A Cimpregnated system could be used only at low flow rates (
