Effect of no2 and O3 exposure on O3 uptake in human lungs

Nitrogen Dioxide (NO₂) and ozone (O₃) are among the most biologically damaging photochemical oxidants found in urban smog. Both react quickly with mucus substrates in the lungs, oxidizing unsaturated fatty acids and proteins. It has been shown that during quiet breathing, O₃ is almost entirely absorbed in the conducting airways. The purpose of our work is to determine how pre-exposure to either NO2 or O₃ changes the dosimetry of inhaled O₃. Ten subjects (five male and five female) were exposed to air, 0.36 ppm O₃> and 0.75 ppm NO2 on three separate days using a personal exposure chamber designed in this laboratory. Prior to exposure, subjects inhaled 30 breaths containing a 3.0 ppm bolus of ozone mixed with air. The depth of bolus penetration (Vp) was varied to encompass the central conducting airways by changing the time of bolus injection into the breath stream. O₃ concentration at the lips was monitored throughout each breath to determine the fraction of O₃ absorbed (A) A second-order polynomial fit through the initial A-VP data provided a means of comparison with measurements taken during exposure. The time averaged fractional uptake was significantly lower during O₃ exposure relative to air exposure (AA0j < AA ) (p<0,01 ). The NO2 data suggested an opposite positive trend with respect to air(AANO > AAy, ). Although the change was not significant for the entire sample (p>0.10), it was significant for men (p<0.05). The opposite trend between NO₂ and O₃ exposure may occur because the NO₂ causes increased secretion of substrate that reacts only with O₃.