Using surgical specimens from patients with lung tumor, alveolar apertures and alveolar sizes were quantitatively assessed using scanning electron microscopy. Compared with smoking habits, increased apertures, defined as alveolar destruction were observed in patients smoking more than 35 years, whereas alveolar size was increased in patients, with a 15-year smoking history. Experimental studies with exposure to NO2, O3 and H2SO4 mist showed that exposure of NO2 and H2SO4 could induce epithelial injury such as disappearance of cilia in the central airways.