Calculation of long term averaged ground level ozone concentrations

Abstract

Seasonal averaged ground level concentrations for O 3 have been calculated for The Netherlands by means of a two-layer Lagrangian long-range transport (LRT) model. The model includes emissions, nonlinear atmospheric chemistry, dry deposition, exchange between boundary layer (BL) and free troposphere (FT) and fumigation between a mixed layer and an aged smog layer. Concentrations of primary and secondary pollutants in the FT are obtained from a two-dimensional global model developed by Isaksen. In the reference calculation the modelled concentrations of Ox (sum of O 3 and NO 2) and O 3 are in fair agreement with measurements. The NO x (sum of NO and NO 2) and NO 2 concentrations are under-estimated by the model but there is a good temporal correlation between calculated and measured concentrations. Validation of other components involved in the chemical scheme is hardly possible due to the paucity of measured data. It can only be stated that the results presented in this paper are not in disagreement with measured or modelled data presented in the literature. In a number of sensitivity runs the influence of European anthropogenic emissions of NO x and volatile organic compounds (VOC) has been investigated. The calculations indicate that the influence of European emissions on the growing season, daytime averaged (May–September, 10–17 h) O 3 concentrations in The Netherlands is small. For European reductions in the order of tens of per cents a VOC emission reduction is more effective than a NO x emission reduction in lowering the O 3 concentrations. For strong reductions (about 70%) VOC and NO x are equally effective. The effects of the modelled underprediction of NO x concentrations on the production of O 3 on a European scale are probably small. On a local scale the effects are more pronounced due to the NO/O 3 titration (photostationary equilibrium). Therefore, an empirical correction is applied on the modelled O 3 concentrations. After this correction, it is shown that daytime O 3 levels during the growing season increase when European NO x emissions are reduced (2.0–7.7.% increase at 50% NO x emission reduction). A reduction in VOC emission leads to decreasing O 3 levels (9% reduction for 40% VOC emission reduction, 16% reduction for 70% VOC emission reduction). For a combined reduction of both VOC and NO x slightly decreasing ground level O 3 concentrations are expected.