SENSITIVITY OF ADOM DRY DEPOSITION VELOCITIES TO INPUT PARAMETERS - A COMPARISON WITH MEASUREMENTS FOR SO2 AND NO2 OVER 3 LAND-USE TYPES

Dry deposition velocity measurements of SO2 and NO2 over a deciduous forest, a carrot field and a snow surface are compared with estimates obtained from the dry deposition module in the regional Eulerian Acid Deposition and Oxidant Model (ADOM). The comparison with measurements taken in the fall and winter shows large model overestimates, sometimes as large as a factor of 5. The NO2 estimates are particularly poor and support existing evidence that models that employ the constant flux assumption for NO2 are inadequate. The canopy and the snow surface resistances are the largest contributors to the total resistances for SO2 and NO2, except for situations in which some of the snow turns into liquid water, when the aerodynamic resistance becomes important. Increasing the magnitudes, taken from measurements, of the ADOM original values for the stomatal, cuticle, ground and snow resistances and decreasing the NO2 mesophyll resistance and the Leaf Area Index (LAI) yield improved model results, particularly for SO2, reducing the error by almost a factor of 5 at times. The new estimates compare favourably with those from a model that includes Wesely's canopy resistance parametrization. Over snow the NO2 estimates are improved by as much as a factor of 6. Observed deposition velocities for SO2 vary from 0 to 0.65 cm s-2 over a deciduous forest, 0 to 0.60 cm s-2 over a carrot field and are generally less than 0.05 cm s-2 over snow.