[Pollution Characteristics of Heavy Metals in PM_2.5 Near Highway]

In this study, we evaluate the pollution characteristics of heavy metals in particulate matter with diameters less than 2.5 μm (PM_2.5) near highways. Three rounds of cluster sampling of PM_2.5 were conducted on three highways, Changzhang, Changtong, and Wenhou, in peri-urban areas near Nanchang from March to August 2018. The sampling sites included service areas, toll stations, tunnels, and areas near the highway. The concentrations of six heavy metals including Cu, Zn, Pb, Cd, Cr, and Ni in PM_2.5 were analyzed using inductively coupled plasma mass spectrometry (ICP-MS). The pollution and distribution of heavy metals in PM_2.5 near the highway were analyzed, and that pollution characteristics and the level of possible ecological jeopardy were assessed by using the Geoaccumulation Index and Potential Risk Index methods. No significant difference was observed in PM_2.5 or in heavy metals in PM_2.5 along highways with different traffic flow, but they differed significantly in among highway settings in the following order:super-long tunnels > long tunnels and area near the highway > service areas and toll stations. The heavy metal concentration in highways decreased in the following order:Zn (3.8 μg·m^-3) > Pb (10.2×10^-2 μg·m^-3) > Cr (6.8×10^-2 μg·m^-3) > Cu (3.5×10^-2 μg·m^-3) > Ni (1.5×10^-2 μg·m^-3) > Cd (0.1×10^-2 μg·m^-3). In accordance with the influence of temperature and precipitation, PM_2.5 and heavy metals in PM_2.5 showed significant variations among the monitoring months. The PM_2.5 concentration had a significant negative correlation with atmospheric temperature. We observed that PM_2.5 concentration was significantly lower from May to August than from March to April. The Zn concentration in PM_2.5 was more significant from May to August than from March to April. Pearson analysis showed a significant positive correlation between Zn in PM_2.5 with atmospheric temperature because elevated temperatures could aggravate wear and tear and metallic corrosion, which then prompts the emission of Zn. According to the Geoaccumulation Index and Potential Ecological Jeopardy Index, the level of pollution associated with heavy metals of PM_2.5 manifested in the following order:Zn and Cd > Pb > Cu > Ni and Cr. The pollution and degree of jeopardy associated with Zn and Cd were the most severe in the assessment criteria; therefore, the pollution by these elements and the sources of traffic should be noted in air pollution control plans. Super long tunnels, long tunnels, and areas near highways showed greater levels of pollution and higher potential ecological jeopardy than service areas and toll stations. The degree of pollution in densely populated service areas and toll stations was consistent across partially urban areas.