Experimental and numerical analysis of stomatal absorption of sulphur dioxide and transpiration by pine needles

Atmospheric Environment
Volume 29, No. 7, Pages 825-836
1995

T. Vesala¹, K. Hameri¹, T. Ahonen¹, M. Kulmala¹, P. Hari², T. Pohja², E. Krissinel'³, N. Shokhirev⁴ and A. A. Lushnikov⁵

¹Department of Physics, P.O. Box 9, FIN-00014, University of Helsinki, Finland
²Department of Forest Ecology, P.O. Box 24, FIN-00014, University of Helsinki, Finland
³Institute for Water and Environmental Problems, Russian Academy of Sciences, Papanintsev 105, Barnaul 656099, Russia
⁴Institute of Chemical Kinetics and Combustion, Russian Academy of Sciences, Institutskaya 3, Novosibirsk 630090, Russia
⁵Karpov Institute of Physical Chemistry, 10 ul. Obukha, 103064 Moscow K-64, Russia

Received for publication April 16, 1994; Accepted September 23, 1994

Abstract

We present the experimental results of flow chamber measurements on SO₂ dry deposition, and of separate field measurements on transpiration of Scots pine (Pinus sylvestris L) twigs under typical northerly summertime conditions. These results are interpreted by a numerical model, which solves the steady-state diffusion equation for a single stoma approximated to have cylindrical symmetry. An analytical method to estimate the maximal effect of interference (merging concentration fields of adjacent stomata) between stomatal pores is introduced. As a result, a functional pore radius is found to be of order of 2-3 microns, which is significantly smaller than the maximal anatomical size of stomatal aperture. This indicates that stomata are capable to transfer vapours to different degrees. If the obtained estimates for needle resistances are divided by a factor of 4, the leaf area index of local pine canopy, the bulk stomatal resistance for SO₂ is of the order of 200-300 s^.m^-1.

Key words

Stomatal resistance, SO₂ deposition, transpiration, Scots pine needles, gas-phase diffusion.