Aerosol Sulfur Episodes in St. Louis, Missouri

Aerosol sulfur and volatilizable sulfuric acid were measured for 8 days in Aug 1979 in St. Louis, MO, by using a quasi-continuous, in situ particulate sulfur monitor. Two types of episodes were observed. The first, which occurred during the afternoons of Aug 4-8, was characterized by rapid increases in aerosol sulfur, sulfuric acid, and sulfur dioxide but no corresponding increases in light scattering. These were hypothesized to result from gas-phase oxidation of SO₂, in a point source plume with subsequent condensation onto preexisting particles or into new particles. The second type of episode occurred over several days and was characterized by a broad peak in both aerosol sulfur and light scattering, little or no volatilizable sulfuric acid, and essentially no relationship between the daily variations of sulfur dioxide and particulate sulfur. This episode was associated with the long-range transport of a polluted air mass.