Characteristics of the nanoparticles in a road tunnel

Abstract

In a one-way road tunnel with a sidewalk for pedestrians (total length: 667 m, 2 lanes: 7 m width, sidewalk: 3.5 m width), size-fractionated particles that were suspended in the air were sampled and tested for the potential health risks to pedestrians. These particles were predominantly emitted from motorized traffic. Particles down to the nano-size range were collected using a PM0.07 sampler based on the "inertial filter" technology, which can be applied for the separation of nano-size particles. PM10 and fine particles less than 1 μm were simultaneously monitored online by a tapered element microbalance (TEOM), a condensation particle counter (CPC) and scanning mobility particle sizer (SMPS), and a video camera was used to monitor the amount of traffic and the wind velocity inside the tunnel. Concentrations of mass and polycyclic aromatic hydrocarbons (PAHs) in each size range of particles were discussed relative to the total traffic amount, the types of motorized vehicles, and the sampling duration, and then compared with other data that had been either simultaneously or separately obtained at different sampling locations outside the tunnel. The correlation was clear between PM0.1 and heavy traffic involving large diesel vehicles, such as buses and trucks. The mass concentrations and fractions of PAHs in the road tunnel became larger than at the mouth of the tunnel and the rural sampling site. PM emissions could be classified into fine particles smaller than 0.5 μm and coarse particles larger than 2.5 μm, which referred to exhaust and road dust, respectively. PM0.07 particles from vehicle exhaust might have contained a higher component of PAHs. © Taiwan Association for Aerosol Research.