Short-Term Respiratory Effects of Sulfuric Acid in Fog: A Laboratory Study of Healthy and Asthmatic Volunteers

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Abstract
To explore short-term respiratory health risks from acid-polluted fog, 22 normal and 22 asthmatic adult volunteers were exposed in an environmental control chamber to light fogs (∼0.1 g/m3 liquid water content, 10 μm median droplet diameter, 10°C) containing nominally 0, 500, 1000, and 2000 μg/m3 of sulfuric acid. Fog was produced by atomizing dilute acid solution Into purified air humidified to near 100 percent by steam injection. Exposures were administered in random order at 1-week intervals, lasted 1 h, and Included three 10-min periods of moderately heavy exercise. Responses were measured in terms of forced expiratory function, airway resistance, Irritant symptoms, and bronchial reactivity to methacholine aerosol. Sulfuric acid per se showed no more than a slight effect on pulmonary function, even at the highest concentration. Asthmatics experienced bronchoconstrlction, attributable to exercise, under all exposure conditions. Despite the lack of substantial function changes, modest statistically significant Increases in respiratory symptoms occurred with increasing acid concentrations. This unusual response pattern suggests that acid fog effects occur via a mechanism somewhat different from those which govern responses to Irritant gases like SO2 or O3. To the extent these results are relevant to ambient “acid fog” exposures, they predict that no pulmonary dysfunction, and only slight respiratory symptoms if any, are likely to occur.