Dry deposition of sulfur dioxide or nitric acid to oak, elm and pine leaves

Abstract

To improve our knowledge of atmospheric inputs to forests, experiments were performed in the field to measure the dry deposition of SO 2 and HNO 3 to oak, elm, and pine leaves. A thee branch was enclosed in a Teflon chamber, through which SO 2 or HNO 3 flowed. The dry deposition characteristics of SO 2 and HNO 3 were very different. The SO 2 deposition occurred primarily through stomatal openings for the oak and pine leaves, and equal stomatal and cuticular deposition was observed for the elm leaves. The deposited SO 2 could not be removed from the branch by extracting in water or by revolatilization. In contrast, over 90% of HNO 3 dry deposition occurred to the cuticle. Most of the deposited HNO 3 could be extracted from the leaves. Revolatilization of HNO 3 was negligible from an active branch, but increased from a dormant or detached branch. A deposition velocity was derived from the ratio of the flux of the gas to the leaves and the gas concentration in the chamber. Deposition velocities ranged from 0·02 to 0·11 cm s −1 for SO 2 and from 0·2 to 1·2 cm s −1 for HNO 3 to individual leaf surfaces.