Walter Ruijgrok

The dry deposition of particles to a forest canopy: A comparison of model and experimental results

Abstract This paper evaluates estimates of the dry deposition velocity (vd) for acidifying aerosol and particles with base cations based on the model by Slinn (1982, Atmospheric Environment, 16, 1785–1794) with experimental results from experiments in the Speulder forest (The Netherlands). Results point at two dominating driving forces for particle deposition: particle size and friction velocity. Model results obtained show largely similar relations to the measurements. On average for the Speulder forest, we obtained a vd for sulphate of 1.3 ± 1.2 cm s−1 during daytime and 1.0 ± 1.4 cm s−1 during nighttime. These values are about 2–3 times larger than for other inference methods available in the literature, however, they are in line with recent observations. For base cations we estimated an average vd of 5.1 ± 3.9 cm s−1. Based on model results we propose a simplified parametrisation of vd for sulphate, nitrate, ammonium and base cation aerosol, which can be used to calculate the dry deposition of the compounds to forests on a grid scale for deposition maps. The simplified parametrisation compares favourably with the more detailed model calculations.

Particle deposition to forests : Summary of results and application

Abstract Particle deposition to forest was studied at Speulder forest using experimental and modelling results. In this paper a short overview of the main results is given and they are applied in generalisation of deposition in The Netherlands. The results of the Aerosol project show that the deposition of particles to forests has been underestimated until now. Particle deposition makes a reasonable contribution to the total deposition of acidifying components and base cations to forests. Parametrisations of the deposition processes were derived from the experiments and model developed for particle deposition to Speulder forest. The parametrisations were used together with concentrations, meteorological observations and land-use data to determine the deposition on a 5 x 5 km basis in The Netherlands. Results of the canopy exchange experiments at Speulder forest and of the comparison of atmospheric deposition estimates and throughfall estimates at Speuld and other locations in The Netherlands show that throughfall fluxes and atmospheric deposition estimates are reasonably in agreement for all components, except nitrate. There is still large uncertainty in canopy exchange processes of oxidised nitrogen and in deposition estimates of the different gases contributing to the total oxidised nitrogen flux. The contribution of aerosol deposition to the total deposition in The Netherlands is 7% for SO42−, 11% for NH4+ and 9% for NO3−; for deciduous forests these numbers are 14,15 and 17%, and for coniferous forests 10, 17 and 20%, respectively. Dry deposition is estimated to amount to about 21% of total deposition for Na+, 20% for K+, 27% for Mg2+ and 25% for Ca2+.

Aspects of wet, acidifying deposition in Arnhem: Source regions, correlations and trends (1984–1991)

Abstract A time series of wet deposition in Arnhem, the Netherlands, was analysed for the period 1984–1991. Precipitation was collected with four samplers on a daily basis. A comparative study by the Dutch National Precipitation Network showed significant biases for the observations of the National Network station due to longer exposure to dry deposition. Simultaneous operation of wet-only and bulk collectors demonstrated a concentration bias of about 10% for daily bulk sampling. Using a cluster analysis of backward trajectories, clear distinctions could be made between precipitation from continental and maritime origin. Event-to-event variations in deposition seemed to be determined largely by meteorological influences. As major anthropogenic source regions, the U.K., France, Belgium and the Netherlands itself were identified. The contribution of Dutch sources to wet acid deposition in Arnhem was estimated at 30–40%. Trends and seasonal variations were analysed with an advanced time-series model based on Kalman filtering. Similar seasonal variations were found for SO 4 2− and NH 4 + . Also, seasonal variations in the concentrations of H + and NO 3 − corresponded. Significant long-term changes in deposition and concentration were found for SO 4 2− (about −3% yr −1 ) and H + (about −9% yr −1 ) only. The analysed trends were decreasing, but decreases were larger in the years 1984–1986 than in the following years. The relative decrease in the wet deposition of SO 4 2− was substantially smaller than decrease in dry-deposited SO 2 and SO 4 2− .

Atmospheric Particles and their Interactions with Natural Surfaces

The purpose of this short review will be to focus on those aspects of aerosol exchange which are of importance to the BIATEX community in order to aid in the assessment of acidic or alkaline deposition, from dry and wet aerosol (in the form of cloud or fog droplets) over Europe with an eye to the larger scale processes in which aerosols play a critical role. One of the important goals of the Biatex program, emphasised by its co-ordinator, has been the necessity to deliver information about these processes which are “useful” to wider interests, in particular the modelling community. In light of the co-ordinators plea for “immediately useful information” a detailed summary of parameterisations which have been forthcoming in BIATEX and related programmes for both dry and wet aerosol deposition are listed in the Appendix.

Particle deposition to forests.

Abstract Particle deposition to forest was studied using experimental and modelling results. Results show that the deposition of particles to forests has been underestimated until now. Particle deposition makes out reasonable contribution to the total deposition of acidifying components and base cations to forests. It was estimated that at Speulder forest the contribution of dry particle deposition to the total deposition was 18% for SO 4 , 38% for NO 3 , 23% for NH 4 , 56% for Na, 47% for K, 69% for Ca and 65% for Mg.. Deposition of compounds via fog at the Speulder forest was estimated to be small (

Dry deposition of acidifying and alkaline particles to forests: model and experimental results compared

This paper provides a comparison of modelling and experimental results on the dry deposition of acidifying and alkaline particles to forests. On average, a fair to good agreement is found between model and experimental results. Results show that the mean vd of acidifying aerosol (such as SO4) is around 1 cm s−1, while for base cations, (e.g. Ca) vd is approx. 5 cm s−1

Targets for mitigation of Greenhouse gases: Implications from a long-term perspective

Abstract This paper describes the implications of long-term climate change objectives (such as stabilization of CO 2 concentrations and of radiative forcing) for maximum allowable emissions of greenhouse gases and priorities for reduction strategies. It also briefly indicates some rough target values for technological developments which are based on these long-term objectives.