A Lagrangian Model of Long-Range Transport of Sulphur

A Lagrangian receptor-oriented one-layer model has been developed in order to simulate a synoptic-scale transport of airborne sulphur. Mass-balance equations for sulphur dioxide and particulate sulphate were integrated along 3-day backward trajectories arriving at 0000 and 1200 GMT at selected receptor points. Advective winds used in trajectory calculations were based on the wind profile from radiosonde reports, taking an average over the ground based layer up to an 850 hPa level. These vertically averaged winds were thereafter objectively analysed using the ‘1/r2 aligned’ technique (Kahl and Samson, 1986), which gives the greatest weight to observations upwind and downwind of the interpolation point. Sulphur emissions were taken from EMEP inventory (Sandnes and Styve, 1992). They were assumed to vary linearly over the year, with the maximum and minimum occuring in January (multiplication factor=1.3) and July (multiplication factor=0.7), respectively. Background concentrations proposed by Szepesi and Fekete (1987) were used. Other model parameters had diurnal variation and they were estimated from routine synoptic observations, where 1/r2 spatial and linear temporal interpolation techniques were employed. Parameters were calculated at the beginning of each 3-hour time step. Mixing height varied from 500 to 2000 m, depending on stability conditions. Dry deposition velocities of sulphur dioxide (v_d) and particulate sulphate (w_d) over the ground and transformation rate of sulphur dioxide to particulate sulphate were taken as proposed by Renner et al. (1985). Over the sea v_d=0.8 cm/s and w_d=0.1 cm/s were taken. Wet deposition rates for both pollutants depended on precipitation intensity and mixing height (Eliassen et al., 1988).