Trace Elements and Polycyclic Aromatic Hydrocarbons Variation Along the Guang-Shen Expressway Before and After the 2016 Qingming Festival in Guangzhou

PM2.5 samples (particles with aerodynamic diameter < 2.5 μm) were collected along the Guang-Shen expressway around the Qingming Festival, one of the most congested periods in China, which started from April 2–4, in 2016. Twenty-five trace elements and 16 priority polycyclic aromatic hydrocarbons (PAHs) of the samples were analyzed. Their major sources at different periods were identified. The concentrations of PAHs distinctly increased with growing traffic flow 2 days before the Qingming Festival (March 31th and April 1st), decreased gradually on the first 2 days of the 3-day festival (April 2nd and 3rd) and rose again on the last day (April 4th). The proportion changing of higher molecular weight containing 5- and 6-ring PAHs (HMW PAHs) closely related to the traffic flow variation were consistent with the concentration variation of PAHs during the experimental period. Indicators of gasoline/diesel engines emission, i.e., Mo, Co, Mn, and Pb showed similar concentration variation with PAHs. The concentrations of trace elements, mainly derived from wear instead of combustion process, such as Cu, Zn, Ti, and Sb, raised significantly during the rainy days. Incremental lifetime cancer risk (ILCR) values were calculated to evaluate the health risk caused by PAH around the Qingming Festival. The ILCR values increased by 3–10 times 2 days before and on the last day of the festival comparing with other days, as a result of traffic related sources, including engine emission and wearing of tires. It concluded by recommending the necessity of traffic diversion to alleviate the health risk to drivers and nearby residents during important festivals.