CHEMICAL-STATES OF SULFATE AT SHENANDOAH-NATIONAL-PARK DURING SUMMER-1991

Despite the importance of the chemical states of sulfate in understand ing of particle growth, acidic impacts, and visibility, relatively few data are available during the intense summer sulfate haze periods cha racteristic of the eastern US. In order to establish the precise anion associated with sulfates, measurements were made of the chemical stat e of sulfates by size and time during September 1991, as part of a lar ger Shenandoah NP aerosol study. Inertial impactors were prepared with Teflon substrates to allow operation of existing IMPROVE analytical p rotocols on highly size resolved fine aerosol samples with a time reso lution of 4 h, Sept. 5 through 19, 1991. The results show that the fin est aerosols, below 0.34 mu m aerodynamic diameter, are predominantly ammonium sulfate during the entire period. Intermediate size particles in the 0.34 to 1.15 mu m range varied from almost pure ammonium sulfa te to almost pure sulfuric acid. Larger particles, 1.15 to 2.5 mu m, c ould not be chemically resolved due to the presence of excess hydrogen from organic matter. Due to the high humidity and hygroscopic nature of these species, the aerosols contained considerable water, enhancing their impact upon visibility.