Solvent separation and determination by ion chromatography of sulfuric acid, ammonium bisulfate, and ammonium sulfate in the atmosphere

The method of solvent separation and determination for sulfate aerosol {H2SO4, NH4HSO4, and (NH4) 2SO4} was investigated. The sulfate aerosol collected on a Teflon filter is extracted by two kinds of solvents (benzaldehyde and 2-propanol). Benzaldehyde is used for the separation of H2SO4 from NH4HSO4 and (NH4)2S04, and 2-propanol is used for the separation of NH4HSO4 from (NH4) 2SO4. The extraction efficiencies of H2SO4, NH4HSO4, and (NH4)2SO4 by benzaldehyde were 96%, 3.2%, and 1.7%, and by 2-propanol were 92%, 50%, and 4.8%, respectively. These results indicated that benzaldehyde could separate H2SO4 from NH4HSO4 and (NH4)2SO4. However, the separation of NH4HSO4 from (NH4)2SO4 by 2-propanol were not sufficient. After extraction by solvents, a sample solutions in benzaldehyde and 2-propanol were reextracted or diluted with distilled water for ion chromatographic analysis. In order to prevent the effect of solvents in sample solutions for ion chromatographic analysis, a pre-column that trapped only sulfate ion and removed solvents was installed in the sample injector. The analytical precision of this method for sulfate was within 2.5%. The detection limits of atmospheric sulfate by this method was 0.005 µg/m3 at 40 m3 air sample volume. Atmospheric sulfate were measured by using this method in Yokohama in September, October, and December, 1982. The concentrations of H2SO4 and total sulfate in the air were (0.03~0.1)µg/m3 and (0.6~3.2) µg/m3, respectively. The percentage of H2SO4 in total sulfate was (1.3~6.2) %. Therefore, it is considered that most of sulfate aerosol is in neutralized chemical form such as NH4HSO4 and (NH4)2SO4.