Evaluating particulate matter and heavy metal accumulation, and air pollution tolerance in roadside woody plants, Cheongju City, South Korea

Urban air pollution has risen because of increased traffic and industrial processes in rapidly expanding cities. Particulate matter (PM), a type of air pollution composed of a mixture of microscopic solid particles or liquid droplets, is among the most common pollutants. Plants, with their ability to absorb various contaminants, can help reduce air pollution. This study examined PM and heavy metals (HMs) accumulation in seven woody plant species that are commonly planted on South Korean city roadsides. The plant's air pollution tolerance index (APTI) was calculated using the leaf biochemical parameters (pH of leaf extract, relative water content, total chlorophyll, and ascorbic acid) to assess how the plants responded to air pollutants. Pinus densiflora was the most effective at accumulating PM on the leaf surface and wax layer, implying that it could be an ideal species to improve urban air quality. Furthermore, a strong positive correlation was found between the amount of epicuticular wax in leaves, ascorbic acid, and total PM buildup. Among the HMs, Al, Fe, and Zn were detected in the highest amount in all chosen plant species. While Zn is known to be associated with traffic emissions due to tire wear and brake dust, the elevated levels of Al and Fe lkely reflect contributions form both vehicular activity and resuspended soil particles near roadsides. Taxus cuspidata exhibited the highest APTI (8.91) and was classified as “tolerant,” and Zelkova serrata showed the lowest APTI (4.27) and was classified as “sensitive.” This study suggests that selecting plant species with high PM and HMs accumulation potential and high APTI scores may contribute to improving urban air quality when strategically incorporated into landscape planning.