Figure 1

Ratio of vegetation deposition flux to traffic emission flux; depending on surface area of vegetation with differing leaf deposition velocity (V_d) in a street canyon of 100 m length with annual PM₁₀ concentration of 37 µg m⁻³, average emission factor 100 µg vehicle⁻¹ m⁻¹ for PM₁₀, traffic intensity of ~ 40,000 vehicles day⁻¹ (adapted from^56,58). The black dashed lines indicate the % PM₁₀ removal (~ 40%) by leaf deposition, with 8 silver birch trees (V_d = 4.6 cm s⁻¹, canopy diameter 8 m, total leaf surface area = 125 m²/tree).