Generation of Nuclei-Mode Sulfuric Acid Aerosols for Health Effects Studies

Abstract

Numerous health effects studies with particulate sulfates have been performed with aerosols whose size ranges correspond to the accumulation mode aerosol (∼0.1 to 1,0 µm) or larger. However, particles produced by nucleation phenomena such as sulfuric acid aerosol from catalytic converters¹ or homogeneous gas phase reactions² produce a somewhat short-lived but finer aerosol in the nuclei-mode size range (∼0.01 to 0.1 µm). Such particles may have different deposition characteristics in the lung than those previously studied, particularly in consideration of the hygroscopic nature of H₂SO₄. Recent experiments with nuclei-mode H₂SO₄ aerosol indicate that growth under near saturation conditions (∼100% relative humidity) is limited to about a factor of two in geometric dimension.³ Theoretical deposition curves for humans based upon nonhygroscopic particles suggest pulmonary deposition efficiencies for nuclei-mode aerosol may be as great as ∼50-60%, even if the particles grow by a factor of two in size in the respiratory tract.⁴ Although ambient levels of nuclei-mode sulfates are an order of magnitude less than the levels at which deleterious health effects from exposure studies have been documented, additional studies with such particles are desirable because of possible differences in respiratory tract deposition site and efficiency.¹