Acid fog and hospital visits for asthma: an epidemiological study

The aim of this study was to elucidate the adverse respiratory effects of naturally occurring acid fog. In total, 102 adult asthmatic patients (44 nonatopic and 58 atopic) were studied for a 2 yr period (January 1992 to December 1993) in Kushiro, a city with only a small industrial area, located in the northern-most island in Japan. Fog occurred on 378 out of 731 days, and the acidity of the fog ranged from pH 3.32 to 6.91 (mean pH 4.95). The association between hospital visits for asthma and meteorological factors or air pollutants was investigated. In nonatopic patients, fog, high ozone and water vapour pressure, low day-to-day temperature differences, low concentrations of atmospheric NO and NO2 contributed significantly (p