Monitoring dry deposition of gases and particles over a forest

Abstract

Dry deposition fluxes of acidifying and eutrophying compounds are continuously determined at Speulder forest, a Douglas fir site in the centre of the Netherlands. The monitoring equipment, installed on a 36-m high tower, consists of a sonic anemometer, a cup anemometer, a wind vane, a Bowen ratio system, three temperature/r.h. sensors, and gas analyzers to measure gradients of SO 2, NO x and NH 3 and concentrations of HCl, HNO 2 and HNO 3. Particles are sampled in two size ranges (<2.5 mm and 2.5–10 mm) on filters, which are analysed for acidifying components and basic cations. Fluxes of SO 2, NO x and NH 3 are determined with the gradient method, while fluxes of the other components are estimated with the inferential method. Parameterizations of the surface resistance ( R c ) for gases are derived from measurements obtained during periods that meet criteria with respect to homogeneous fetch, stationary flow, etc. Parameterized R c values are used to estimate fluxes during periods that don't fulfil these demands. In this way, yearly average fluxes can be determined. In 1995, the total deposition fluxes of SO x(=SO 2+SO 4 2−), NO y(=NO x+NO 3 −+HNO 2+HNO 3) and NH x, (=NH 3+NH 4 +) were 450, 630 and 1620 eq. ha −1 a −1, respectively.