The Elspeetsche Veld experiment on surface exchange of trace gases: Summary of results

A three-year experiment for the determination of deposition fluxes on heathland was conducted at the Elspeetsche Veld involving several research groups. Micro-meteorological measurements of SO 2, NH 3 and NO 2 were made using different techniques. Furthermore, throughfall and bulk precipitation fluxes of SO 4 2−, NH 4 + and NO 3 − were also measured. From these measurements, deposition parameters were derived to yield a generalized description of the surface exchange of these trace gases, including possible interactions. For SO 2, generally low surface resistances were found; the annual average dry deposition velocity ranged from 0.8 to 1.0 cm s −1. The annual flux of SO 2 was estimated as 250 mol ha −1 yr −1. For NH 3 also, low R c values were observed, yielding annual average V d of 0.8 cm s −1. The annual flux of NH 3 was estimated as 850 mol ha −1 yr −1. Under the environmental conditions prevailing in the Netherlands, co-deposition between SO 2 and NH 3 was estimated to be irrelevant. Surface wetness was found to be the dominating factor influencing dry deposition of the two gases. R c values for NO 2 stomatal behaviour, V d for this gas ranged from 0.1 to 0.4 cm s −1. Fluxes measured with the throughfall method are compared with fluxes derived using micro-meteorological methods. The yearly average net throughfall flux for SO 4 and the dry deposition flux (SO 2 and SO 4 particles) amounted 500 and 350 mol ha −1 yr −1, respectively. For NH 4 this was 1180 and 930 mol ha −1 yr −1, respectively. The correlation between the two on a monthly basis is significant ( r=0.50 for SO 4 and r=0.52 for NH 4, n = 12, p