Quantifying Olfactory and Alveolar Deposition of Ultrafine Particles Using Multiscale Modeling: Implications for...

Area of Science:

• Environmental Health
• Atmospheric Science
• Toxicology

Background:

• Current atmospheric particle exposure metrics (e.g., PM2.5 mass) underestimate health risks by neglecting particle surface area and direct brain pathways.
• Ultrafine particles (UFPs), though low in mass, significantly contribute to deposited surface area in the lungs and olfactory region.

Purpose of the Study:

• To quantify particle deposition using lung-deposited surface area (LDSA) and olfactory deposition, considering hygroscopic growth.
• To evaluate the role of UFPs and particle size in deposition and potential brain translocation.
• To investigate disparities in particle deposition doses across populations and sources.

Main Methods:

• Multiscale atmospheric modeling (continental to street level) validated with NO2, PM mass, composition, and size-resolved particle data.
• Calculation of lung-deposited surface area (LDSA) and olfactory deposition, incorporating particle hygroscopic growth.
• Source apportionment and population-specific dose estimations.

Main Results:

• UFPs constitute over one-third of alveolar deposition in urban areas; particles <400 nm dominate lung deposition despite low PM2.5 mass contribution.
• A persistent decoupling exists between PM2.5 mass and deposited surface area across various settings and populations.
• Children experience ~3-fold higher alveolar doses than adults; residential wood heating impacts winter deposition, while traffic influences particle number and olfactory deposition.

Conclusions:

• Particle surface area, particularly from UFPs, is a critical metric for assessing respiratory and direct brain exposure, surpassing mass-based measures.
• Olfactory deposition of UFPs may be a dominant pathway for brain particle delivery, exceeding blood-borne translocation.
• Source-specific and population-specific analyses are crucial for understanding and mitigating particle-related health risks, especially for vulnerable groups like children.