Deposition and resorption of organic aerosol constituents in the respiratory tract as calculated from particle size distribution data

Data on the particle size distributions of organic aerosol constituents were used as input for a study, designed to calculate the fractions of the particulate concentrations of these compounds, deposited into the respiratory tract. The known relation between the deposition probability and the particle size as described by the ICRP‐model was used. The organic constituents were from the classes of the aliphatic hydrocarbons, carboxylic acids, polycyclic and aza‐heterocyclic aromatic hydrocarbons. Aerosol samples were obtained by Hi‐Vol cascade impactor sampling at suburban, rural and sea shore background stations as well as in an industrial emission site (coke oven).

Our approach uses the measured concentrations, being average values within each impactor particle size interval, as well as the integrated average deposition probabilities. This procedure was validated experimentally for eight model distributions from the literature, for which an infinitesimal calculation of the deposited fractions was possible.

Dilution reduces total particulate concentrations in the remote areas and predominantly determines the total deposited pollutant concentrations. Of these, pulmonary and nasopharyngeal deposition are most significant and, as a first approximation, correspond largely to the relative importance of the accumulation and dispersion modes of the sampled aerosol. A particle size distribution shift toward larger particles within the accumulation mode occurs upon ageing of the aerosol and reduces the pulmonary deposited fraction of the measured compounds in the background sites, compared to the one in the suburb. The total deposited fraction, however, increases. The contributions of biogenic higher odd n‐alkanes and, to a lesser extent, of even carboxylic acids to the dispersion mode of the aerosol result in an increased nasopharyngeal deposition at the background sites mainly during summer.

Since little information on the bio‐availability of organic aerosol constituents is available in the literature, the fractions of the particulate pollutant concentrations, resorbed in the tissues from the deposited material, were calculated, assuming an average efficiency of 70% for pulmonary and of 10% for nasopharyngeal and tracheobronchial resorption. A nearly constant total resorbed fraction of 20±2% resulted, independent of the sampling station or the season chosen, in contrast with the total deposited fractions, for which significant differences were observed. The predominant pulmonary resorption as well as compensating effects of the nasopharyngeal resorption level out the relatively small differences in particle size distributions observed. Based on these data, a first estimate in nanogram of the daily intake by inhalation of the organic pollutants studied can be formulated as four times the particulate pollutant concentration, expressed in ngm^‐3.