Generation and characterization of sulfate aerosols for laboratory studies

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Abstract
Sulfate aerosols, major air pollutants, including Na2SO4, (NH4)2SO4, NH4HSO4, MnSO4.cntdot.H2O, ZnSO4.cntdot.7H2O, Al2(SO4)3.cntdot.18H2O, Fe2(SO4)3.cntdot.xH2O, (NH4)2SO4.cntdot.ZnSO4.cntdot.6H2O and H2SO4 were generated and characterized with respect to size distribution, mass concentration, chemical component and crystal structure of the aerosols. The aerosols were generated utilizing an ultrasonic nebulizer whose performance characteristics were also investigated. The aerosol generation system was stable, showing no change in size distribution and total mass concentration (.+-. 5%) of the output aerosol during 6 h continuous operation. For solutions of same concentration of each salt, size distributions of the aerosols were similar without regard to the salt used. Distributions were log-normal with geometric SD (GSD) of 1.4-1.6. The mass median aerodynamic diameters (MMAD) averaged over all the sulfate aerosols used were in the size range of 0.3 .mu.m for 0.01% solution and 2.29 .mu.m for 10% solution, and could be expressed as MMAD = 1.18 S0.30 where S was the solution concentration by percent mass. Chemical analysis including ion analysis and X-ray diffraction studies showed that the aerosols used were hygroscopically stable under the environment < 40% RH [relative humidity] except for H2SO4 and that the aerosol particles were in the same crystal forms as those of the reagent salt used for the aerosol generation.

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