Lack of bronchoconstrictor response to sulfuric acid aerosols and fogs

Sulfuric acid (H2SO4) is the most common acid air pollutant in the United States and is thought to have adverse respiratory effects. Sulfuric acid exists in polluted air as a dissolved solute in both small (haze) and large (fog) particles. Previous work in our laboratory has failed to demonstrate bronchoconstriction after near ambient, large-particle H2SO4 exposure in subjects with asthma. However, other investigators have found slight but significant changes in lung function following inhalation of small-particle or small-particle, low-relative-humidity (RH) H2SO4 aerosols, leading us to hypothesize that particle size and/or RH may be important variables in acid aerosol exposure. We initially studied the effects of resting inhalation of large-particle (volume median diameter, VMD, approximately equal to 6 microns) and small-particle (VMD approximately equal to 0.4 microns) aerosols with an H2SO4 concentration of 3 mg/m3 through a mouthpiece and found no effect on specific airway resistance (SRaw) or symptom scores. In a second mouthpiece study designed to compare high-RH (100%), large-particle (VMD approximately equal to 6 microns) and low-RH (less than 10%), small-particle (VMD approximately equal to 0.3 microns) aerosols with an H2SO4 concentration of 3 mg/m3, we again found no effect of either aerosol. We then examined the effects of small-particle aerosols inhaled in dry air during moderate exercise. Although breathing low-RH air during exercise provoked increases in SRaw in almost all subjects, this could not be attributed to H2SO4 since low-RH saline aerosol produced a similar result.(ABSTRACT TRUNCATED AT 250 WORDS)