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 che mical processes of importance for the ozone production in the troposph ere. The transport model describes a closed circulation in the meridio nal plane below 10 hPa and has a resolution and a numerical solution w hich compares favorable with earlier two-dimensional studies. The tran sport model also takes into account the fast vertical mixing in convec tive clouds and in frontal circulation. The production of nitrogen oxi des by lightning has been coupled to the convection parameterization b y 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 observ ations indicate that the model is able to reproduce the seasonal varia tion of ozone in the meridional plane quite realistically. The calcula ted distributions of the chemical species which determine tropospheric ozone also compare well with measurements. The model estimated an ann ually averaged production of ozone in the troposphere over the norther n hemisphere of 16.6x10(10) molecules/cm(2)/s and over the southern he misphere of 5.1x10(10) molecules/cm(2)/s. The annually and globally av eraged dry deposition is 14.9x10(10) molecules/cm(2)/s, and the corres ponding injection from the stratosphere is 4.1x10(10) molecules/cm(2)/ s. A 50% reduction of the man-made emissions from the industrialized s ociety of nitrogen brides resulted in a reduction in the ozone product ion of 2.9x10(10) molecules/cm(2)/s in the lower troposphere over the northern hemisphere during the period of maximum photochemical product ion, June-August. The corresponding production decrease due to a 50% r eduction of the emissions of volatile organic compounds and carbon mon oxide from the same source, however, was 1.6x10(10) molecules/cm2/s. E lsewhere, the effects of reductions are less significant due to smalle r influence of man-made emissions.