MONITORING THE DRY DEPOSITION OF SO2 IN THE NETHERLANDS - RESULTS FORGRASSLAND AND HEATHER VEGETATION

An automated system based on the micrometeorological gradient techniqu e has been developed to measure the dry deposition of SO2 on a routine basis. Measurements were made at two locations in the Netherlands. Fr om these results dry deposition fluxes, dry deposition velocities and surface resistances for a heathland and for an agricultural grassland site were estimated using a selected set of data and a calculation pro cedure based on micrometeorological considerations. An extensive analy sis was made to determine uncertainties in the resulting deposition pa rameters. From this analysis it has been concluded that the uncertaint y in these parameters is almost completely determined by the random er rors in measured concentrations. The meteorological surface exchange p arameters can be estimated sufficiently accurately (<20% uncertainty). At the grassland site, average surface resistances to deposition of 6 (+/- 8) and 13(+/- 12) s m-1 were calculated for wet and dry condition s, respectively. At the heathland site, a similar distinct difference between R(c) values for wet and dry conditions was found. These values are 20(+/- 21) and 70(+/- 90) sm-1, respectively. The yearly average dry deposition flux for SO2 at the grassland site amounts to 585(+/- 3 30) mol ha-1 yr-1, while at the heathland site the yearly average flux was 300(+/ 270) mol ha-1 yr-1. The yearly average dry deposition velo city at 4 m height was 1.2(+/- 0.3) cm s-1 at the grassland site and 0 .8(+/- 0.4) cm s-1 at the heathland site.