Distribution of PAHs in pine (Pinus thunbergii) needles and soils correlates with their gas-particle partitioning

Pine (Pinus thunbergii) needles and surface soils were simultaneously sampled at 35 sites across Liaoning province, China, to investigate the distribution of polycyclic aromatic hydrocarbons (PAHs) in the two media. We hypothesized that the distribution of PAHs in soils and pine needles was related to the subcooled liquid vapor pressure (p°L) and the gas-particle partition coefficient (K P), since soils accumulate PAHs mainly through dry/wet deposition of particles and pine needles sequester PAHs mainly from the gas phase, and the same physicochemical properties (e.g., p°L) determine the characteristics of PAHs deposition to soils and to needles. To verify the hypothesis, a soil−pine needle quotient (Q SP) was defined, which is a dimensionless ratio of PAH concentrations in soils and pine needles. A significant relationship between logQ SP and logp°L was observed (r = 0.94), and the variation of the regression parameters of logQ SP∼logp°L and logK P∼logp°L relationships was similar. An adjusted soil−pine needle quotient (Q′SP) was defined by deducting the contributions of particle PAHs to pine needles and the vapor PAHs to soils. LogQ′SP correlated with logp°L and logarithm of the particle to gas ratio (logC P/C A) more evidently than logQ SP. In addition, Q SP (and Q′SP) could be used to characterize the removal factors of PAHs during atmospheric transport. All the observations proved that Q SP (and Q′SP) carry the information of gas-particle partitioning and correlate with p°L.