Ambient Particulate Matter Size Distributions Drive Regional and Global Variability in Particle Deposition in the Respiratory Tract

Abstract

Human exposure to airborne particulate matter (PM) increases the risk of negative health outcomes; however, substantial uncertainty remains in quantifying these exposure‐response relationships. In particular, relating increased risk of mortality to exposure to PM with diameters smaller than 2.5 μm (PM2.5) neglects variability in the underlying size distribution of PM2.5 exposure and size‐resolved deposition in human airways. In this study, we combine a size‐resolved respiratory particle‐deposition model with a global size‐resolved aerosol model to estimate the variability in particle deposition along the respiratory tract due to variability in ambient PM size distributions. We find that the ratio of deposited PM mass in the tracheobronchial and alveolar regions per unit ambient PM2.5 exposure (deposition ratio and DRTB + AV) varies by 20–30% between populated regions due to variability in ambient PM size distributions. Furthermore, DRTB + AV can vary by as high as a factor of 4 between the fossil‐fuel‐dominated region of the Eastern United States and the desert‐dust‐dominated region of North Africa. When considering individual PM species, such as sulfate or organic matter, we still find variability in the DRTB + AV on the order of 30% due to regional variability in the size distribution. Finally, the spatial distribution of DRTB + AV based on number or surface area is substantially different than the DRTB + AV based on mass. These results suggest that regional variability in ambient aerosol size distributions drive variability in PM deposition in the body, which may lead to variability in the health response from exposure to PM2.5.

Urban Aerosol Size Distributions: A Global Perspective

“…EA, for all respiratory tract regions. This is consistent with the findings of Kodros et al (2018), which reported high aerosol mass deposited concentrations in the human respiratory tract for India and Eastern China. Cities in NAAN and EU are associated with E / !$ lower in magnitude compared to the other geographical regions.…”

“…However, the full extent of the mass RTDDRs for LA and WA in the coarse mode cannot be reliably characterized due to the lack of mass PSD observations in the two regions. As shown in Kodros et al (2018), desert regions of WA and AF are associated with very high deposited mass concentrations in the human respiratory tract.…”

“…Hygroscopic growth of the inhaled aerosol can shift the size-resolved deposition fractions, and in turn, the estimated Löndahl et al, 2007). An inhaled dose study by Kodros et al (2018) found that the deposited mass concentration of aerosols in urban areas are lower than those in rural areas due to the higher hydrophobic content of urban aerosols. As aerosols are transported from an urban to rural area, the hydrophobic content becomes hydrophilic under atmospheric ageing, and the SO2 converts to particle-phase sulfate.…”

“…It has been observed that residential biomass burning, possibly for cooking and heating, can contribute to high particle number concentrations of accumulation mode particles in the evening in New Delhi, India (Mönkkönen et al, 2005). A recent study using the GEOS-Chem-TOMAS model identified significant aerosol emissions from biomass burning in India and Indonesia from residential, agricultural, and wildfire sources (Kodros et al, 2018). Direct burning has been reported to be a common technique to eliminate agricultural residuals in both China and India (Bi et al, 2019).…”

“…NOx, SO2, and VOCs) in polluted areas can aid particle growth to larger sizes. It has been reported that the concentrations of condensable vapors are higher in urban areas in China and India compared to those in NAAN and EU due to heavier air pollution in the former (Gao et al, 2009;Huang et al, 2014;Kodros et al, 2018;Kulmala et al, 2005;Misra et al, 2014; https://doi.org/10.5194/acp-2020-92 Preprint. Discussion started: 24 March 2020 c Author(s) 2020.…”