A 2-DIMENSIONAL GLOBAL STUDY OF TROPOSPHERIC OZONE PRODUCTION

The ozone production in the troposphere has been studied by means of a zonally averaged model which consists of a two-dimensional transport model, a description of the emissions, wet and dry deposition, and chemical processes of importance for the ozone production in the troposphere. The transport model describes a closed circulation in the meridional plane below 10 hPa and has a resolution and a numerical solution which compares favorable with earlier two-dimensional studies. The transport model also takes into account the fast vertical mixing in convective clouds and in frontal circulation. The production of nitrogen oxides by lightning has been coupled to the convection parameterization by assuming that the:nitrogen oxides are transported vertically in the thunder clouds and released at the altitudes where boundary layer air entrained in the convective cells is released. Comparisons with observations indicate that the model is able to reproduce the seasonal variation of ozone in the meridional plane quite realistically. The calculated distributions of the chemical species which determine tropospheric ozone also compare well with measurements. The model estimated an annually averaged production of ozone in the troposphere over the northern hemisphere of 16.6x10(10) molecules/cm(2)/s and over the southern hemisphere of 5.1x10(10) molecules/cm(2)/s. The annually and globally averaged dry deposition is 14.9x10(10) molecules/cm(2)/s, and the corresponding injection from the stratosphere is 4.1x10(10) molecules/cm(2)/s. A 50% reduction of the man-made emissions from the industrialized society of nitrogen brides resulted in a reduction in the ozone production of 2.9x10(10) molecules/cm(2)/s in the lower troposphere over the northern hemisphere during the period of maximum photochemical production, June-August. The corresponding production decrease due to a 50% reduction of the emissions of volatile organic compounds and carbon monoxide from the same source, however, was 1.6x10(10) molecules/cm2/s. Elsewhere, the effects of reductions are less significant due to smaller influence of man-made emissions.