Spatial variability and health assessment of particle number concentration at different exposure locations near urban traffic arterial: A case study in Xi'an, China

Urban traffic arteries are considered as hot-spots of pollution of particle number concentration (PNC), but the knowledge of spatial variability and exposure levels of PNC with different particle sizes emitted by vehicles is yet less reported. In this paper, PNC in the size range from 6 to 10,000 nm were measured using the Electrical Low -Pressure Impactor Plus (ELPI+) at four sites near high-density traffic in Xi'an, including one traffic, one roadside, and two urban background. The results showed that PNC was highest at the distance closest to the traffic sources, and decreased exponentially with distance. Vehicle exhaust was the primary source of ambient ultrafine particle (UFP), contributing 60.03% and 54.48% of the number concentration of UFP in the clean and haze weathers, respectively. The average PNCs measured at the traffic site were 2.24 and 3.17 times greater than those at the roadside and urban background sites, respectively. Coarse mode particle concentrations exhibited a higher level at the roadside site due to the secondary dust generated by vehicles. An interesting phenomenon that an inverted U-shaped relationship between measured UFP levels and traffic flows was found when the flow was higher than 6000 veh h-1. Strong spatial inhomogeneity for UFP along the urban road, whereas particles larger than 100 nm in diameter tend to similar concentration distributions. The mean respiratory deposition dose (RDD) at four locations was (7.14 +/- 1.12) x 105 particles h-1, with the highest (14.61 +/- 2.29) x 1010 particles h-1 at the traffic site. Retired people had a higher exposure of UFP compared to children and adults. This improved understanding of the impact of vehicle emissions on the distribution of PNC near-road.

Automated summary

Urban traffic arteries are hot-spots of particle number concentration (PNC) pollution, especially for ultrafine particles (UFP). In this study, PNC measurements of different particle sizes were conducted at four sites in Xi'an. The results revealed that PNC was highest closest to the traffic sources, and vehicle exhaust was the primary source of UFP. The PNC at the traffic site was significantly higher compared to the roadside and urban background sites. Interestingly, there was an inverted U-shaped relationship between measured UFP levels and traffic flows.