Effect Of Sahara Dust Events On The Deposited Fraction Of Atmospheric Aerosol In The Respiratory Tract

Deposition of inhaled atmospheric aerosol particles in the respiratory tract is related to both the physical properties of the particles and the anatomical and physiological characteristics of respiration. Mass size distribution of aerosol particles is an important factor in predicting the deposition fraction of the inhaled particles in various regions of the respiratory tract. Aerodynamic particle size correlates directly with regional deposition in the lungs and the upper respiratory tract. Sahara dust transport is a major source of airborne particulate matter (APM) in the greater Athens metropolitan area. Exceedances of the limit of the PM10 mass concentration due to Sahara dust transport events are often reported. The presence of such high concentrations of mineral dust raises concerns about the impact on human health. In this study the deposited fraction of APM in the human respiratory tract was examined in the case of Sahara and Non-Sahara dust transport events. Mass size distributions of atmospheric aerosol were obtained by means of a low pressure Berner cascade impactor. The measurement campaign took place at the GAW-DEM suburban background monitoring station (Spring 2010), located at the grounds of NCSR "Demokritos". The Berner impactor consists of 11 stages onto which the particles are deposited according to their aerodynamic diameter and its cut-off diameters ranged between 26 nm and 13 mu m. In order to calculate exposure to APM and deposition in the respiratory tract, the Multiple Path Particle Dosimetry model (ARA.inc, CIIT, RIVM) was applied. The MPPD model allows PM deposition fractions of the inhaled aerosol mass to be calculated for given human respiratory tract regions, under different exposure conditions and airway morphometry. For the studied moderate Sahara dust events an average increase of the order of 10 mu g/m(3) was observed in the PM10 mass concentration. According to the mass size distribution a significant increase was observed for coarse particles (7 mu g/m(3)) and fine particles (3 mu g/m(3)), as well. The results obtained from the dosimetry model showed that the contribution of Saharan dust to the deposited mass of coarse particles in the upper respiratory tract concentration was 63%, compared to the received amounts at background conditions. However, coarse particles can be normally cleared from the upper part of the respiratory system. On the other hand, the contribution of Saharan dust to the deposited mass of coarse particles in tracheabronchial and pulmonary region was 32%. The results obtained from MPPD model were also compared to the results obtained by means of a 1D, mechanistic, respiratory deposition model, based on the Eulerian approach (1D-Eul).