A review of hygroscopic growth factors of submicron aerosols from different sources and its implication for calculation of lung deposition efficiency of ambient aerosols

Abstract

Hygroscopic properties are an important parameter in determining the atmospheric behaviour of aerosols and their optical properties, influencing the direct and indirect effect of aerosols upon climate. As a result, particle hygroscopicity has received much attention with a rapid increase of publications in recent years. Likewise, hygroscopicity is an important characteristic influencing the deposition efficiency of particles in the human respiratory tract by affecting the particle size. The object of this study is to review the existing knowledge on the hygroscopic growth factor (G f ) of atmospheric submicron particles and its influence on the lung deposition calculation. The study briefly reviews first the G f values of particles generated from various sources, including nucleation, traffic emissions and biomass burning, discussing the spatial and temporal variations. It then summarises G f values of submicron particles and number fraction of each hygroscopic group measured in different ambient environments. These include marine, roadside, urban background and rural environments. The study concludes by estimating the lung deposition efficiency of ambient particles using a modified version of the International Commission on Radiological Protection (ICRP) model for hygroscopic particles. Furthermore, the effect of hygroscopicity on lung deposition efficiency of ambient particles has been estimated. The ICRP model seems to predict well the deposition efficiency (DE) values for small ambient particles in the extra-thoracic and tracheo-bronchial region, but not the alveolar region, where they are overestimated. However, for larger particles (D p >200 nm), the ICRP model underestimates the DE values, with the extra-thoracic region the most affected of the three. Hygroscopic atmospheric particles with a small diameter (D p <200 nm) showed a lower total lung deposition than hydrophobic particles of the same initial size due to their hygroscopic properties. On the other hand, larger hygroscopic particles (D p >200 nm) showed much higher lung deposition than hydrophobic particles.

Source Apportionment of the Lung Dose of Ambient Submicrometre Particulate Matter

“…Table 3 shows the regional lung deposition efficiencies (DE) of particles from different sources. These were estimated by apply a modified ICRP model (Vu et al, 2015) to the PMF factor profiles. In terms of particle number, particles released from nucleation (F3) and local traffic emission sources (F1) were found to have the highest deposition efficiencies in the total lung, with fractional efficiencies of 0.62 and 0.57, respectively, followed by aged traffic particles (F2, DE = 0.41).…”

“…To address this problem, we adjusted the ICRP curve for both hydrophobic and hygroscopic particles based on an assumption that particles generated from combustion sources (i.e., traffic emission or biomass burning) are nearly hydrophobic and inorganic/organic secondary aerosols are a mixture of less hygroscopic and more hygroscopic particles (Weingartner et al, 1997;Cruz and Pandis, 2000;Väkevä et al, 2002;Massling et al, 2005;Varutbangkul et al, 2006;Löndahl et al, 2009;Tritscher et al, 2011). The details of this method are given in Vu et al (2015). The regional and total lung deposition efficiencies of particles from different sources identified by PMF was estimated based on an application of the ICRP model to each source's particle size distribution as adjusted by its expected hygroscopicity.…”

“…This can be explained by a major contribution of secondary aerosol to particle volume. In addition, due to their more hygroscopic properties, their lung deposition efficiencies are much higher than those from hydrophobic particles with the same initial dry diameter (Vu et al, 2015). Accumulation mode particles account for 7.4%, 25.9%, 27.5% and 17.3% of total particle volume deposited in the ET, TB, AL and total lung, respectively.…”

Sources of sub-micrometre particles near a major international airport

“…Knibbs et al, 2011;Strak et al, 2012;Ostro et al, 2015;Lanzinger et al, 2016). At the current time, there is still limited knowledge of what specific characteris-tic or association of characteristics may dominate the particle toxicity and the consequent health outcomes (Atkinson et al, 2010;Strak et al, 2012;Vu et al, 2015a); nevertheless, it is well recognised that UFPs can reach the deepest regions of the lung (Salma et al, 2015) and may have orders of magnitude higher surface-area-to-mass ratios compared to larger particles. They offer more surface for the absorption of volatile and semi-volatile species (Kelly and Fussell, 2012;Strak et al, 2012).…”

Physical properties and lung deposition of particles emitted from five major indoor sources

“…Although the number of studies focusing on indoor aerosols has increased in recent years, the physical characterization database of indoor sources, particularly the hygroscopicity of indoor particles which is known to be an important determinant of lung deposition fraction of particles in the human respiratory tract, is still limited (Vu et al 2015a). The aim of this study was to investigate physical properties including size distribution, effective density and hygroscopicity of particles originating from five typical indoor sources.…”