The Relationship between Particulate Chemistry and Air Masses in Southern Indiana

The particulate characteristics of the surface layer of the atmosphere over a region of southwest Indiana were determined for forty-two 24-hour periods between September 1985 and April 1986. The water-soluble sulfate, chloride and sodium content of particles classified into mass median diameters (MMD) of 7, 3.3, 2, 1.1 μm and less than 1.1 μm, was related to different air masses. Atmospheric concentrations of chloride and sodium and the S/Cl and Na/Cl ratios in particles with MMD greater than or equal to 3.3 μm were used to differentiate between maritime and continental air masses. Maritime, compared to continental, air masses had higher concentrations of sulfate in all particle sizes. Both synoptic situations had high concentrations of sulfate-bearing particles with MMD < 1.1 μm and to a lesser degree with MMD 7 μm. It was concluded that the MMD > 3.3 μm particle chloride and sodium were primarily due to sea-salt particles and that the MMD < 1.1 μm and some of the MMD 7 μm sulfate particles in greater concentrations in the maritime air mass air were probably largely due to anthropogenic sources to the south of Indiana.