Budget calculations for ozone and its precursors: Seasonal and episodic features based on model simulations
Instituut voor Milieuwetenschappen TNO
Results from two air quality models (LOTOS, EURAD) have been used to analyse the contribution of the different terms in the continuity equation to the budget of ozone, NO(x) and PAN. Both models cover large parts of Europe and describe the processes relevant for tropospheric chemistry and dynamics. One of the models is designed to simulate episodes in the order of 1-2 weeks (EURAD), the other is focussing on the seasonal scale (LOTOS). Based on EURAD simulations it is found that the atmospheric boundary layer (ABL) in Central Europe during a summer-smog episode in 1990 acts as a source of ozone, which is partly exported from the production region in Central Europe. About 40% of the ozone produced chemically in the ABL is lost from Central Europe due to net transport (large-scale and turbulent), 40% are deposited within the domain. Vertical mass exchange of ozone is dominated by the prevailing subsidence and averaged vertical mass fluxes are directed downward. Averaged mass fluxes of PAN, which has no stratospheric source, are upward in the upper part of the ABL. The results from LOTOS are discussed for the same episode and for a two month period (July/August 1990). The budget calculation show larger chemical production for the LOTOS model compared to EURAD. The relative importance of deposition and net transport, however, is in the same order. Differences between the two-month calculation and the one week episode are only important for Western Europe where the chemical production is enhanced by 30% during the summer-smog episode. The dependence of the results on initial and boundary values is discussed for ozone on the basis of a simple sensitivity study with EURAD where ozone in the FT is set to 10 ppb initially. This leads to a reversal in the direction of averaged ozone mass fluxes in the upper part of the ABL.
To reference this document use:
Ozone budgets for Europe
Journal of Atmospheric Chemistry, 28 (1-3), 283-317