Dry deposition of atmospheric polycyclic aromatic hydrocarbons in three Plantago species

The concentrations of polycyclic aromatic hydrocarbons (PAHs) in the leaf w ax of three Plantago species were determined weekly for 3 weeks. The almost glabrous, free-standing leaves of Plantago major and the sparsely hairy Pl antago lanceolata leaves were more heavily contaminated with low molecular weight (MW) PAHs (MW < 228) than the densely hairy, partly overlapping Plan tago media leaves. This may be caused by the lower canopy roughness (higher aerodynamic resistance), the higher amount of leaf hairs (higher boundary resistance), and/or the higher leaf overlap (smaller accessible leaf area) of P. media. On the other hand, PAHs with MW greater than or equal to 252 t ended to show higher concentrations in P. media than in the other two speci es. This is likely caused by the dense layer of hairs on P. media leaves, w hich can efficiently intercept the largely particle-bound high MW PAHs. Whe n the PAH concentrations were normalized to projected leaf surface area, th e differences between P, media and the other two species became significant (p < 0.05) for the high MW PAHs, while the differences for the low MW PAHs decreased. Although the differences in PAH concentrations between species are relatively small (factor 2-5), this study clearly shows that plant arch itecture and leaf hairs influence the dry deposition of PAHs.