Understanding spatial patterns of traffic pollutant reduction by vegetated earth berms

• Herbaceous plants on earth berms accumulated total PM (74.6–646.9 mg m - ²) and TE (Fe, Cu, Zn, Cd, Pb, As: 4.6–2313.0 ppm) year-round. • PM deposition peaked in summer, up to 7-fold higher than in spring, especially on front-side plants. • Air PM 10 was highest near the road in winter, with back-side concentrations 32–86% lower than front-side. • Vegetated berms reduced the potential ecological risk (RI) of TE on the back-side by up to 42%. Air pollution, particularly involving particulate matter (PM) and trace elements (TE), poses significant health risks in urban areas. Road traffic is a major year-round PM source, and vegetated earth berms are commonly used as acoustic barriers, but their role in mitigating airborne pollutants is underexplored. This study quantified PM and TE accumulation by herbaceous plants on a highway berm across four seasons, sampling multiple height levels and sides. Two-way ANOVA showed that study site and season significantly influenced all PM fractions and categories, as well as most TE in plants. Plants on the back-side accumulated 18–66% less total PM than front-side. Total PM deposition peaked in summer (up to 7-fold higher than in spring), while PM 10 in air was highest near the road edge in winter (up to 1.3-fold higher), and back-side PM 10 was 32–86% lower than at corresponding front-side. TE concentrations (Fe, Cu, Zn, As) were highest near the road edge, with winter maxima; RI values were up to 42% lower on the back-side. PCA explained 72% of total variance, revealing strong correlations between air PM and deposited PM, highlighting site-specific accumulation patterns. Soil Fe, Cu, and Zn were elevated near the road, whereas Pb peaked at the top; pH and EC varied across sites and seasons. Overall, the berm reduced PM levels in air on the back-side by up to 71% relative to front-side. These findings demonstrate that herbaceous vegetation on earth berms can substantially reduce traffic-related air pollution in urban environments.