Figure 4

Concentration ratios of benzo(e)pyrene/benzo(a)pyrene (BeP/BaP) and 9-fluorenone/fluorene (9-FLUO/FLUO), which are used to indicate atmospheric transport and oxidation.
Note: The chronologies older than 1850 were obtained by assuming the average accumulation rate of the upper layers because the 210Pb method can only produce reliable chronologies of 150–170 years. Consequently, the older dates have a high uncertainty.