Modelling particle diffusion patterns inside urban road tunnels in Dalian, China, employing annual field measurement

Abstract

Urban road tunnels have been increasingly constructed to ease traffic congestion and the significant accumulation of particulate matter, posing a potential human health threat. A field measurement over one year in the Lianhuashan, Jiaojinshan, and Shimenshan urban tunnels in Dalian, China was conducted to evaluate particulate pollution levels. A semi-parametric particle diffusion model was then conceived and applied, with the aim of describing the influence of traffic flow, air flow induced by both natural winds and vehicle movements, and other factors, on particle mass concentrations in tunnels. The model was then verified and modified using the measured data. The results showed that PM2.5 mass concentrations in the Lianhuashan and Jiaojinshan tunnels were 29.8 ± 13.8 μg/m3 and 38.7 ± 9.9 μg/m3, respectively, which did not exceed the applicable 24 h averaged World Health Organization (WHO) standard (75 μg/m3). The PM2.5 mass concentrations in the Shimenshan tunnel were 77.2 ± 17.4 μg/m3, slightly exceeding the standard. PM2.5 mass concentrations in the Jiaojinshan and Shimenshan tunnels demonstrated quite clear seasonal patterns, with 36% and 10% higher particle concentrations in winter, respectively, compared with other seasons. The ratios for PM10, PM2.5, and PM1.0 mass concentration to PM0.3 mass concentration were approximately 5, 4, and 3, respectively. A 10 s update frequency for particle mass concentration measurements seemed optimal for model performance. Overall, the results from this study provide fundamental information for predicting particle exposure levels in tunnels and provide useful guidance for the design and operation of their ventilation systems.