Standard: API 27-30841


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The overall objective of this project was to determine whether exposure of humans to "worst case" ambient concentrations of sulfate-containing aerosols might cause measurable health effects. To accomplish this goal we:

1. Developed a high-capacity aerosol generator and an aerosol injection system for the Rancho environmental exposure chamber.

2. Implemented real-time mass concentration and particle size monitoring to keep a continuous check on the aerosol in the chamber.

3. Exposed human volunteers to ammonium sulfate, ammonium sulfate and sulfuric acid aerosols; measured pulmonary function and assessed clinical symptoms before and after exposure.

The major impetus for studying sulfates in this manner was epidemiological information which had suggested that ambient concentrations of particulate sulfates caused acute respiratory morbidity. (1,2) Some attempts to confirm this finding experimentally had not produced convincing evidence (3-8) that submicron-sized sulfate aerosols at concentrations less than 350μ g/m3 caused any acute changes. It was felt that the Rancho chamber, with its elaborate air purification and environmental control systems, coupled with an available aerosol generation facility, would provide an excellent vehicle for testing individual sulfate aerosols in an environment free of possible confounding impurities.

Most of the sulfates in the ambient aerosol are thought to be initially present in the acid form (H2SO4), but are rapidly neutralized by reaction with atmospheric ammonia (NH3) to form ammonium sulfate (NH4HSO4) and sulfates generally appears to be bimodal. Most of the sulfate mass appears to consist of submicron aerosol with diameters in the range if 0.1 to 0.5μm and a mass median aerodynamic diameter (MMAD) of about 0.4μm. (10) A minor fraction of the sulfate aerosol ass is associated with large particles of about 3μm MMAD. These large particles are thought to be sodium sulfate and they probably originate from reaction of SO2 with natural ocean salt spray aerosols. (11,12) Acidic sulfates may also react with basic metal oxides, usually present in ambient aerosols, to form relatively minor concentrations of metallic sulfate salts. It is conceivable that accumulation mode particles, in the range of 0.1 to 1um diameter, might contain small amounts of lead sulfate, vanadium sulfate, and zinc sulfate, as well as zinc ammonium sulfate. Larger particles, in the range of 1.0 to 10.0μm diameter, might contain ferric sulfate and ferric ammonium sulfate.

While there is some evidence that certain metallic sulfates, eg zinc ammonium sulfate and ferric sulfate (13,14) are highly irritant in animals, most of the sulfate mass consist of sulfuric acid and its ammonia neutralizstion products. It therefore seemed reasonable to begin our studies of particulate sulfur oxide human health effects with these latter sulfate compounds. An aerosol size distribution with a MMAD of 0.4um and a standard deviation between 2 and 3 was generated from aqueous solutions of pure sulfate compounds. The chamber atmospheric concentration was selected to simulate a "worst case" ambient exposure, based on the highest reported two-hour average sulfate ion concentrations measured in the Los Angeles area.

Organization: American Petroleum Institute
Document Number: api 27-30841
Publish Date: 1978-07-31
Page Count: 78
Available Languages: EN
DOD Adopted: NO
ANSI Approved: NO
Most Recent Revision: YES
Current Version: NO
Status: Inactive