Size-Resolved Respiratory-Tract Deposition of Fine and Ultrafine Hydrophobic and Hygroscopic Aerosol Particles During Rest and Exercise

Abstract

Airborne ultrafine particles (diameter <100 nm) are ubiquitous in the environment and have been associated with adverse health effects. The respiratory-tract deposition of these particles is fundamentally influenced by their hygroscopicity: their ability to grow by condensation of water in the humid respiratory system. Ambient particles are typically hygroscopic, to varying degrees. This article investigates the influence of hygroscopicity, exercise level, gender, and intersubject variability on size-dependent deposition of fine and ultrafine particles during spontaneous breathing. Using a novel and well-characterized setup, respiratory-tract deposition in the range 12-320 nm has been measured for 29 healthy adults (20 men, 9 women). Each subject completed four sessions: rest and light exercise on an ergometer bicycle while inhaling both hydrophobic (diethylhexylsebacate) and hygroscopic (NaCl) particles. The deposited fraction (DF) based on dry diameters was two to four times higher for the hydrophobic ultrafine particles than for the hygroscopic. The DF of hygroscopic ultrafine particles could be estimated by calculating their equilibrium size at 99.5% relative humidity. The differences in average DF due to exercise level and gender were essentially less than 0.03. However, the minute ventilation increased fourfold during exercise and was 18-46% higher for the men than for the women. Consequently the deposited dose of particles was fourfold higher during exercise and considerably increased for the male subjects. Some individuals consistently had a high DF in all four sessions. As an example, the results show that an average person exposed to 100-nm hydrophobic particles during exercise will receive a 16 times higher dose than a relaxed person exposed to an equal amount of hygroscopic (NaCl) particles.

A Set-up for Respiratory Tract Deposition Efficiency Measurements (15-5000 nm) and First Results for a Group of Children and Adults

“…The data showed that some subjects may have DFs that are more than twice as high as for others. This observation has also been reported in other studies (Löndahl et al, 2007).…”

“…There are no previous experimental studies that cover the full size range of 15-5000 nm, and very few that cover particles on both sides of the minima in the deposition curve. For particles below the minima, where diffusion is the dominating deposition mechanism, there is good agreement between the DFs here reported and those found in previous studies on healthy subjects, during spontaneous breathing of hydrophobic particles (Heyder et al, 1982;Bennett et al, 1996;Daigle et al, 2003;Chalupa et al, 2004;Wiebert et al, 2006a, b;Löndahl et al, 2007;Löndahl et al, 2012;Rissler et al, 2012), as shown in Fig. 3(b).…”

“…However, most individual variation was neither explained by age nor by gender, but by breathing pattern and lung intrinsic properties (investigated in more detail in a separate study : Rissler et al [2017]). The results showed that some individuals within the group did receive doses twice as high as those of others when exposed to the same particle levels, as was also observed in the study by Löndahl et al (2007). This can be part of the explanation as to why some individuals seem to be more susceptible to air pollution than others.…”

“…For example, we used the assumption that the particles were hydrophobic and spherical in the calculations. Particle hygroscopicity is known to alter the particle size in the lungs, and thus alter DF (Morrow, 1986;Löndahl et al, 2007). For particles < 400 nm, particle shape has no effect on DF if one is referring to the number of particles as a function of equivalent mobility particle diameters , as measured by the SMPS.…”

Size-Resolved Respiratory Tract Deposition of Sub-Micrometer Aerosol Particles in a Residential Area with Wintertime Wood Combustion

“…The literature data for dry hydrophobic particles has been taken from the Multiple Part Particle Deposition (MPPD) model (version 1.0, Chemical Industry Institute of Toxicology, Research Triangle Park, NC), with inspiratory fraction of 0.5, particle density of 1000 kg/m 3 , nasal breathing, tidal volume of 0.625l, and a breathing frequency of 12 breaths per minute. The reason for choosing this model is that the respiratory deposition of sub-200 nm particle diameter resembles that of the deposition previously measured with the RESPI instrument of hydrophobic particles during spontaneous breathing (Löndahl et al, 2007). For instance the MPPD model fits better with these empirical data than the ICRP model (ICRP, 1995), which is also frequently used.…”