Abstract
Estimates of lung dose of submicron particles in the human respiratory system play an essential role in assessing health outcomes of aerosol exposure. The objectives of this study are to calculate the regional lung dose of traffic-generated particles by different metrics from exposure in outdoor and indoor environments and to identify main factors determining the lung dose. Particle number size distributions were collected in both indoor and outdoor environments in two unoccupied apartments from 22nd February to 30th April 2012 in Bologna, Italy. The whole lung doses of outdoor aerosols by number, surface area and mass at a traffic site were 1.0 × 1010 particles/h, 130 mm2/h and 1.9 μg/h, respectively. A majority of particles by number and surface area were found to deposit in the alveolar region (65%). The physical properties of particles such as shape, hygroscopicity and density play an important role in the calculation of surface area and mass dose due to shifting of the lung deposition curve. Particle number can predict well the regional dose by number, while PM2.5 and PM10 are good metrics for the prediction of surface area and mass dose. Good correlations between NOx and the surface areas and mass dose (r2 ~ 0.8) and number dose (r2 ~ 0.7) of submicron aerosols suggest that NOx may be a good indicator for predicting the health outcomes of traffic-generated aerosols. The doses of indoor sub-micrometre aerosols are less than those of outdoor aerosols by factors of 4.1 (for number), 2.7 (for surface area) and 2.1 (for mass). Due to traffic emissions, the lung dose of outdoor aerosols in the traffic area was much higher than that in the residential area by 5 times for number and surface area and 2 times for mass. A different exercise level (standing, walking, running and cycling) has only a slight influence on the whole lung deposition fraction of submicron aerosols but has a large effect on the dose due to differences in ventilation rate.
Highlights
Road traffic is well-known as a major source of aerosol in cities
Values expressed by surface area and mass were lower, and the deposited fractions (DFs) of submicron particles by surface area and mass in the whole lung were 0.32 ± 0.02 and 0.32 ± 0.02
Rissler et al (2012) experimentally determined the DFs of diesel aerosols in the human respiratory tract and reported the DFs by number in the whole lung were 0.47 and 0.65, while DFs were in the range of 0.27– 0.32 for surface area and mass
Summary
Road traffic is well-known as a major source of aerosol in cities. Recent source apportionment studies have found that road traffic accounts for 56.5 and 10.3% of particles by number and PM2.5 mass in an urban background area in London, UK, respectively (Vu et al 2016; Crilley et al 2017). Exposure to road traffic-generated aerosols is consistently associated with adverse health effects (Künzli et al 2000; Weinmayr et al 2015). Road traffic-generated aerosols and their health impacts have been of much concern in recent years. In order to determine the health outcomes of aerosol exposure, the majority of epidemiological studies have used the particle mass (PM2.5 or PM10) only as an indicator (Harrison et al 2010).
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