| Summary: | The source apportionment of fine particulate matters, especially PM<sub>2.5</sub>, has drawn great attention worldwide. Since rare earth elements (REEs) and Nd isotopes can serve as source tracers, in this study, the characteristics and provenance implications of REEs and Nd isotopes in PM<sub>2.5</sub> of four seasons in Xiamen city, China, were investigated. The range of the ratios of ΣREE to PM<sub>2.5</sub> was 1.04 × 10<sup>−5</sup> to 8.06 × 10<sup>−4</sup>, and the mean concentration of REEs in PM<sub>2.5</sub> were in the order of spring > autumn > winter > summer. According to the geoaccumulation index (<i>I</i><sub>geo</sub>), spring was the season in which anthropogenic sources had the greatest impact on the REEs in PM<sub>2.5</sub>. The chondrite-normalized REE distribution patterns exhibited light rare earth elements (LREEs, including La, Ce, Pr, Nd, Pm, Sm and Eu) enrichment and a flat heavy rare earth elements (HREEs, including Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) pattern. Significant negative Eu anomalies and no significant Ce anomalies were observed in the PM<sub>2.5</sub>. The results of La-Ce-Sm ternary plots indicated that the REEs in the PM<sub>2.5</sub> might be related to both natural and anthropogenic sources. Combined with the Nd isotope, the <sup>143</sup>Nd/<sup>144</sup>Nd versus Ce/Ce* plot further illustrated that the REEs in the PM<sub>2.5</sub> seemed to mostly originate from multiple potential sources, in which vehicle exhaust emissions, coal burning and cement dust made a great contribution to REEs in PM<sub>2.5</sub>.
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