Bush, Michele L., Patrick T. Asplund, Kristen A. Miles, Abdellaziz Ben-Jebria, and James S. Ultman. Longitudinal distribution of O₃ absorption in the lung: gender differences and intersubject variability. J. Appl. Physiol. 81(4): 1651-1657, 1996.Because the National Ambient Air Quality Standard for ozone (O₃) is intended to protect the most sensitive individuals in the general population, it is necessary to identify sources of intersubject variation in the exposure-dose-response cascade. We hypothesize that differences in lung anatomy can modulate exposure-dose relationships between individuals, and this results in differences between their responsiveness to O₃ at a fixed exposure condition. During quiet breathing, the conducting airways remove the majority of inhaled O₃, so the volume of this region should have an important impact on O₃ dose distribution. Employing the bolus inhalation method, we measured the distribution of O₃ absorption with respect to penetration volume (V_P), and using the Fowler single-breath N₂ washout method, we determined the dead space volume (VD) in the lungs of 10 men and 10 women at a fixed respiratory flow of 250 ml/s. On average, the women absorbed O₃ at smaller V_P than the men, and the women had smaller VD than the men. When expressed in terms of V_P/ VD, the absorption distribution of the men and women was indistinguishable. Moreover, an interpretation of the O₃ distribution in terms of an intrinsic mass transfer parameter (Ka) indicated that differences between the O₃ dosimetry in all subjects, whether men or women, could be explained by a unique correlation with anatomic dead space: Ka (in s¹) = 610 VD^1.05 (in ml). Application of this result to measurements of O₃ exposure response indicated that previously reported gender differences may be due to a failure in properly accounting for tissue surface within the conducting airways.