Observations of particle formation and growth in a mountainous forest region in central Europe

Held A, Nowak A, Birmili W, Wiedensohler A, Forkel R, Klemm O

Abstract

In the summers of 2001 and 2002, particle formation and growth were observed at a forest ecosystem research site in the "Fichtelgebirge'' mountain range in NE Bavaria, Germany. Atmospheric nucleation events, identified through detailed analysis of the time evolution of submicron particle size distributions, differed considerably from nonevent days with respect to ultrafine particle concentrations and meteorological parameters. Particle diameter growth rates, as quantified through the geometric mean diameter development of the 3-60 nm particle fraction, ranged from 2.2 to 5.7 nm h(-1). While H2SO4 concentrations typically explained less than 10% of the observed growth rates, a significant fraction of particle growth may be explained through condensation of organic vapors from alpha-pinene oxidation. On several days, cocondensation of H2SO4 and alpha-pinene oxidation products was sufficient to fully explain the observed growth dynamics. While BVOC emissions from the tree vegetation may contribute to particle formation, the forest also acts as an effective sink for particles. This is reflected in the dominance of particle deposition to the forest over emission, with the strongest deposition fluxes occurring during particle formation events.