Abstract
To determine the size distribution and source identification of PM-bound heavy metals in roadside environments, four different particle size (<0.2 μm, 0.2–0.5 μm, 0.5–1.0 μm and 1.0–2.5 μm) samples were collected and analyzed from four different types of roads during the summer of 2015 in Tianjin. The results showed that the concentrations of PM-bound heavy metal from the roadside environment sampling sites were 597 ± 251 ng/m3 (BD), 546 ± 316 ng/m3 (FK), 518 ± 310 ng/m3 (JY) and 640 ± 237 ng/m3 (WH). There were differences in the concentrations of the heavy metal elements in the four different particle size fractions. The concentrations of Cu, Zn, Cd, Sn and Pb were the highest in the larger particle size fraction (0.5–2.5 μm). Cd, Cu, Zn and Pb were the elements that indicated emissions from tire wear and brake pad wear. The concentrations of Cr, Co and Ni were the highest in the smallest particle size fraction (<0.5 μm), indicating that motor vehicle exhaust was their main source. The correlation analysis results showed that there are differences in the concentration, distribution and correlation of different PM-bound heavy metals in different particle size fractions. The PCA results show that the accumulative interpretation variances of PM0.2, PM0.2–0.5, PM0.5–1.0 and PM1.0–2.5 reached 80.29%, 79.56%, 79.57% and 71.42%, respectively. Vehicle exhaust was the primary source of PM-bound heavy metal collected from the roadside sampling sites, while brake pad wear and tire wear were the second most common sources of the heavy metal.
Highlights
Accepted: 31 August 2021Serious air pollution and smog are frequently observed in the Beijing-Tianjin-Hebei region
The total concentrations of these 10 heavy metal elements in the PM2.5 samples collected from the Baidi Road (BD), Fukang Road (FK), Jianyang Road (JY) and Waihuan Road (WH) sites were 597 ± 251 ng/m3, 546 ± 316 ng/m3, 518 ± 310 ng/m3 and 640 ± 237 ng/m3, respectively
The higher concentrations of Zn, Pb, Cu and Sb found in the samples collected from the secondary road (BD) may be caused by the longer congestion time, which indicated that the secondary roadside environment was more susceptible to pollution from motor vehicle emissions
Summary
Accepted: 31 August 2021Serious air pollution and smog are frequently observed in the Beijing-Tianjin-Hebei region. According to the latest source apportionment results released by the Ministry of Ecology and Environment (MEE), traffic emissions, industrial manufacturing, coal combustion and dust are the main sources of particulate matter (PM) in the ambient air of most cities in China. Among these sources, traffic has become the primary source of air pollution in Beijing, Guangzhou and Shenzhen. The contribution of traffic emissions to urban atmospheric environmental particulate matter is 45% in Beijing, 29.2% in Shanghai, 16.3% in Guangzhou and 20% in Tianjin [1]. This study focuses on the emission characteristics of PM-bound heavy metals in the road environment, which have been significantly contributed to by traffic emissions in city
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