CALCULATION OF LONG-TERM AVERAGED AND EPISODIC OXIDANT CONCENTRATIONS FOR THE NETHERLANDS

Ground-level ozone and oxidant (sum of O3 and NO2) concentrations in The Netherlands are calculated during the growing season (May-September) by means of a Lagrangian long-range transport model. Two air parcels-one representative of the mixed layer, the other representative of the polluted layer above the mixed layer (aged smog layer)-are followed along 96 h back trajectories. Long-term averaged and 98 percentile values of hourly averaged concentrations are estimated on the basis of concentrations calculated for four arrival times per day for all days in the period considered. In a number of sensitivity runs the influence of European anthropogenic NO(x) and VOC emissions on the oxidant concentrations in The Netherlands has been investigated. In general, the influence of European emissions on the 98-percentile values is 2-3 times as large as on the averaged concentrations. This indicates that long-term averaged concentrations more strongly depend on the concentrations in the free troposhere whereas the episodic concentrations are determined by photochemical production over Europe. VOC emission reduction is more effective in lowering episodic concentrations than NO(x) emission reduction. For long-term averaged concentrations, however, NO(x) and VOC emission reduction of 50% or more are nearly equally effective.