Studying high ozone concentrations by using the Danish Eulerian model

The long-range transport of air pollutants (LRTAP) over Europe is studied by a mathematical model based on a system of partial differential equations (PDEs). The number of PDEs is equal to the number of species studied and the model contains 35 species at present. Among the species are NO, NO₂, NO₃⁻, HNO₃, NH₃, NH₄⁺, O₃, PAN, SO₂, SO₄²⁻ and may hydrocarbons. Most of the 70 chemical reactions involved in the model are nonlinear (including here many photochemical reactions).The model requires large sets of input data. Emissions of SO₂, NO_x, NH₃ and both natural and anthropogenic volatile organic compounds (VOC) are needed in the model. The meteorological data consist of fields of wind velocities, precipitation, surface temperatures, temperatures of the boundary layer, relative humidities and cloud cover, which are read in the beginning of every 6-h interval. Both daytime and nighttime mixing heights are used in the model.Many of the species in the model vary on a diurnal basis. An investigation of the main mechanisms that determine the diurnal variation of the ozone concentrations is performed. One of the important conditions that is necessary if one wants to represent correctly the diurnal variations of the concentrations is to have access to meteorological data that vary diurnally. This is especially true for the temperature and the mixing height.The use of modern numerical algorithms (which are combined with vectorization of the most time-consuming numerical procedures) allows one to perform long-term runs with the model on several high-speed computers. Results obtained in runs with meteorological data for July 1985 and August–October 1989 are discussed. The computed concentrations and depositions are compared with measurements taken at stations located in different European countries. The agreement between calculated concentrations and measurements is reasonably good.Results obtained with several scenarios, in which the NO_x emission and/or the anthropogenic VOC emissions are varied, are presented. Several main conclusions are drawn by studying the results obtained during the comparisons. Some plans for future development of the models are discussed.