Particle-size distribution of PAH in the air of a remote Norway spruce forest in northern Bavaria

The aim of the present study was to elucidate the distribution of particulate polycyclic aromatic hydrocarbons (PAH) in the air of a remote Norway spruce (Picea abies (L.) karst.) stand. The study encompassed a total of twenty different congeners. Particles in ambient air were alternatively collected by two different Berner cascade impactors at the field site in Northern Bavaria over a 14-weeks period from the end of April through to the end of July 1994 and subsequently analyzed for their PAH content. The concentrations of total suspended particulate matter (TSP) ranged from 9-31 mug m(-3), suggesting that the field site is an area with a low level of airborne particles. There was a negative relationship of total particle concentrations with the amount of canopy precipitation due to particle wash out at precipitation events. The distribution of the particle masses on the different size fractions with a maximum in the 1-mum range is typical for remote areas and indicates a medium-range transport. The aerosol-bound PAH load decreased from spring samples with 2-4 ng m(-3) to values <1 ng m(-3) in the summer samples. Concurrently, the proportion of low molecular weight congeners in the total PAH load declined. Frequently, the highest PAH concentrations (referring to the air) were found in the 0.1-3 mum size separates (accumulation mode). The results suggest that apart from PAH input to the soil with litter, dry and wet deposition of aerosol particles is an important pathway of PAH contamination of acid forest soils in the Fichtelgebirge mountain range.