Assessment of pedestrian exposure and deposition of PM10, PM2.5 and ultrafine particles at an urban roadside: A case study of Xi'an, China

Assessment of pedestrian exposure and lung deposition is critical to better understanding the health risks resulting from exposure to ambient particles, and to develop site-specific risk control countermeasures. In this study, real-time mobile-monitoring campaigns of three different PM size fractions (PM10, PM2.5 and UFP) were performed during morning and evening peak hours in two seasons (summer and winter), along road sections with differing characteristics (commercial and residential) in Xi'an, China. The Multiple-Path Particle Dosimetry model (MPPD) was utilized to quantify the total and regional depositions for both adults and teens of different genders. Observed PM10, PM2.5 and UFP concentrations showed pronounced regional, seasonal, and diurnal variabilities. The total deposition dose was higher in males than in females for all particle-size fractions in both age groups, except for UFPs in the teen group, the total deposition dose was higher in females. As for regional depositions, these were observed to be highest in the head region, compared with the tracheobronchial and pulmonary regions, regardless of a participant's age or gender. PM10 and PM2.5 showed the highest depositions in the head region for all age groups (PM10: 90%; PM2.5: 67%), while UFP was highly deposited in the pulmonary region (66%). The dominant percentage of UFP deposition in the pulmonary regions strengthens the need to incorporate UFP into the current air-quality index.