At 10 ppm, juvenile females had high levels of vacuolated epithelium in the proximal airways, as measured by morphometric approaches. Epithelial damage (V_s) is defined as volume of epithelium containing vacuolated cells, normalized to basal lamina surface area (μm³/μm²). Mass of vacuolated epithelium in the controls ranged from 0.00 to 0.13 μm³/μm². These measurements confirmed that proximal airways (A) have a greater volume of epithelial damage per basal lamina than distal airways (terminal bronchioles) (B) at 10 ppm. Statistics (n = 5): 2-way ANOVA (age, sex) with Tukey’s post hoc test (*p < .05).