Fig. 3. Relation between distance to the center of Moscow and the recent mean concentrations of the sum of 21 polycyclic aromatic hydrocarbons (21PAHs) normalized to the concentration of soil organic carbon (SOC) (n = 3 for each of the forest and grassland sites, except n = 2 for the grassland samples collected at Nenashevo in 1996). Error bars represent standard errors. Different lowercase letters indicate significant differences of the means at p < 0.05 (Games Howell post hoc test).