Size distributions and size-segregated chemical profiles of particulate matter in a traffic tunnel of East-Central China

Abstract

Size distributions for number and mass concentrations, size-segregated chemical compositions and chemical profiles of particulate matter (PM) were determined at two sampling sites (SP1 and SP2) in a traffic tunnel of East-Central China. Particle size distributions of number concentration presented single large peaks at 6–17 nm and inconspicuous peaks around 100 nm on each day, with peak phenomenon in line with rush hours. Particle mass distributions showed high concentrations with particle diameters in the last stage (6800–10000 nm). For size-segregated particles, PM mass concentration in 1.1–2.1 μm was found to be high, and particles smaller than 2.1 μm (PM2.1) accounted for 43% (SP1) and 37% (SP2) of particles smaller than 10 μm (PM10). PM in 3.3–4.7 μm size range was also high for SP2 (accounting for 15% of PM10). High organic carbon (OC), NH4+, K+, Cl−, NO3−, and SO42− concentration were observed in PM2.1, and Mg2+, Ca2+, and F− in size range of 2.1–10 μm was high. For fine particle (PM2.5) profiles, average mass concentrations of PM2.5 were 199 ± 63 and 247 ± 45 μg m−3 for SP1 and SP2. OC was the highest constituent, followed by SO42− and then NO3− for SP2, while SO42− and NO3− were higher than OC for SP1. OC and elemental carbon (EC) concentrations for SP2 were higher than those for SP1. Comparing to other tunnel studies, PM2.5 mass concentration at SP2 was similar to that of Shing Mun Tunnel, but 6 and 4 times higher than those of Loma Larga Tunnel and Chung-Liao Tunnel. OC proportion in this study was approximately 0.5, 0.2 and 1 times relative to those in other three tunnels, and EC was 0.1, 0.4 and 0.2 times relative to those in other tunnels, which depended on traffic fleet and vehicle types. The crustal elements in this tunnel showed higher content than those in other tunnels, illustrating the local differences.