0278-6826=01=$12.00 C.00 Growth and Deposition of Hygroscopic Particulate Matter

Transport and fate of inhaled particulate matter in the human lungs is calculated for realisticphysicochemical conditions by a new dosimetrymodel. The model solves a variant of the general dynamic equation for the size evolution of respirable particleswithin the hu-man tracheobronchial airways, starting at the tracheal entrance. We focus on ambient anthropogenic aerosols, which are of concern in inhalation toxicology because of their potential irritant and toxic effects on humans. The aerosols considered are polydisperse with respect to size and heterodisperse with respect to thermodynamic state and chemical composition, having initially bimodal lognormal size distribution that evolves with time as a result of condensation– evaporation and deposition processes. The architecture of the hu-man lung is described by Weibel’s symmetric bronchial tree. Simulations reveal that, due to the rapid growth of submicron-sizedparticles, increased number andmass fractions of the particle population can be found in the intermediate size range 0.1<Á< 1 m. Since deposition by diffusion decreases with size increase, ne nonhygroscopic particles are less persistent in the inspired air than hygroscopic particles of comparable initial size distribution. In contrast, the enhanced deposition of hygroscopic particles, ini-tially from the intermediate size range, increases their fraction in the biological dose delivered to the airways. The combined effect of growth and deposition tends to (i) decrease the size nonuniformity of persistent particles in the airways and form an aerosol that is characterizedby smaller variance; and (ii) alter the deposition pro- le along the airways. The modulated local dose consists of excess intermediate-sized particles, some of which may carry toxic com-ponents causing a systemic response or inducing localized lesions that can affect observed health effects