Sulfate aerosol generation and characterization for controlled human exposures

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Abstract
Carefully controlled human exposures to ammonium sulfate, ammonium bisulfate, and sulfuric acid aerosols were performed to provide valid data concerning effects of potentially harmful atmospheres at “worst case” ambient and possibly industrial levels. The aerosols were produced by a specially designed generator, based upon the Babington nebulization principle. Volunteer human subjects were exposed to nominal sulfate aerosol concentrations of 100 µg/m3 (mass median aerodynamic diameter [MMAD] of 0.3 µ. and a geometric standard deviation of approximately 2.9) at 31.1°C (88°F), 40% relative humidity, in a 62.3 m3 (2200 ft3) chamber. The chamber was continuously supplied with air at a flow rate of 14 m3/min (500 ft3/min) which was well mixed with the existing chamber air to assure that no concentration gradients existed within the subject exposure zone. Real-time monitoring of aerosol mass and size was performed by a computer-controlled electrical aerosol size analyzer/optical particle counter system. The total suspended paniculate concentration and MMAD within each two hour exposure study varied less than 10%, while the range of exposure concentrations generated during the course of the studies varied from 162 to 348 µg/m3. Particle mass concentrations and size distributions, as well as ammonium, sulfate, and hydrogen ion concentrations, were obtained by gravimetric and chemical analyses of total and cascade impactor filter samples. The data demonstrate the potential value of the total system for carefully controlled human exposures and the requirement for detailed characterization in undertaking any controlled exposure study.