= 5,6,7 slightly stable, stable, and extremely stable. to those obtained for the AISI sampler; they indicate that high wind speeds rather than high thermal mixing result in the lower concentrations. An attempt was made to demonstrate the influence of a "heat island" effect by plotting stability classes for station maximum levels on a map. The expected order if there were no "heat island" effect would place maximum levels at the upper end of the scale (7) and minimum levels at the lower end (1). A consistent change from the expected pattern across the air pollution basin would be indicative of "heat island" effects. The results did not show a consistent pattern, possibly because of the overriding influences of wind speed and source strength-direction. Although not included in this report, these results are mentioned to prevent duplication of effort by others who may use these data. In addition to the high-volume air samplers, the National Air Sampling Network has operated sulfur dioxide samplers in some of the larger metropolitan areas. The results from St. Louis and some other cities for 1963 are given in Table 18. Of the 14 cities listed, four had arithmetic means above that for St. Louis, which was equal to that of two other cities. The St. Louis mean was somewhat below the average for the 14. The trend of sulfur dioxide concentrations in the St. Louis area since 1936 is given in Table 39. It is easy to see from these figures that the concentrations in 1963-64 and 1964-65 were considerably lower than in 1936-37. The major portion of this reduction occurred as a result of: 1. 2. 3. Required use of low volatile coal (lower in sulfur also) Change from coal to a fuel of lesser sulfur content (influenced by 1 and 2 and availability of gas at compe- HYDROGEN SULFIDE Hydrogen sulfide data were obtained at sites 505-740 and 510-742 (not a network site) during September, October, and November 1964. These results are given in Tables 40 and 41. Odor threshold levels reported for hydrogen sulfide vary from 10 to 100 parts per billion (ppb). Hydrogen sulfide is very obnoxious to humans. Under certain meteorological conditions, it causes significant damage to lead-base paints at a concentration of approximately 100 ppb. 7 19 19 The State of New York ambient air quality objective for hydrogen sulfide is 100 ppb for 1 hour, which is the same as the California standard. The U.S.S.R. has established a much lower standard of 5 ppb for 24 hours. The Terre Haute, Indiana report of June 1964 suggests a goal of 50 ppb for 1 hour. 21 20 The highest hydrogen sulfide measurement made during this Study was 62.5 ppb, a 2-hour average, which could but probably does not exceed the New York or California Table 39. SULFUR DIOXIDE TREND IN ST. LOUIS AREA SINCE 1936 Table 40. HYDROGEN SULFIDE DATA FROM SITE NO. 505-740 (ppb) Table 41. (Cont'd) HYDROGEN SULFIDE DATA FROM SITE NO. 510-742 (ppb) standards. It does exceed the Terre Haute suggested goal. On 7 days, concentrations of 10 ppb or greater were measured at site 510-742. The peak concentrations usually began in the late afternoon and continued through the night into the next morning. The wind was from the south-southeast or south during each episode. The highest average concentrations occurred between 2 and 4 a.m. at site 510-742, and between midnight and 2 a.m. at site 505-740. The occurrence of typical hydrogen-sulfidetype paint damage during the measurement period indicates that exposure was probably greater than measured; either in concentration or duration. VISIBILITY A summary of the visibility observations made from the project office (493713) is given in Table 42. These results for relative humidity of less than 70 percent show that visibility east across the river into the East St. Louis area was equal to or less than 3 miles during 58.7 percent of the observations during the fall, |