Concentration and deposition of particles and vapors in a vertical profile through a forest canopy

Abstract

Vertical profiles of deposition and concentration of several particulate and gaseous species were measured in a mixed oak forest in eastern Tennessee. Deposition was measured to plastic petri plates and to paper filters, and atmospheric concentrations were measured by low-volume filtration. The results show that concentration of HNO 3 vapor and coarse particle-associated elements like Ca 2+ decrease markedly with depth in the canopy, but this is not true for substances associated with fine aerosols like SO 4 2−, NH 4 + and H +. Potassium showed a trend of increasing deposition to the petri plates with depth in the canopy, indicating a significant in-canopy source of particulate K +. The paper filters showed a strong decrease in deposition of SO 4 2−, NO 3 − and NH 4 + in the canopy, indicating that surfaces in the interiors of the canopy are subject to substantially less S and N deposition than those at the top. The deposition velocity of HNO 3 vapor to the paper filters was at a minimum in mid-canopy.