VEGETATION-ATMOSPHERE PARTITIONING OF POLYCYCLIC AROMATIC-HYDROCARBONS

The partitioning of polycyclic aromatic hydrocarbons (PAH) between vegetation and the atmosphere was studied throughout the growing season and under natural conditions. A vegetation-atmosphere partition coefficient (K(v)) was derived by analogy to partition coefficients for gas-particle partitioning and fish-water partitioning. K(v) is temperature dependent, and from this functional relationship we calculated PAH-vegetation binding energies. These energies were highly correlated with heats of vaporization. The PAH-vegetation partitioning process is primarily dependent upon the atmospheric gas-phase PAH concentration and ambient temperature. At low ambient temperatures (spring and fall) gas-phase PAH partition into vegetation, and at high ambient temperatures (summer), some PAH volatilize and return to the atmosphere. This study provides further evidence that atmospheric semivolatile organic compounds undergo an annual partitioning cycle with the surface of the earth.