Sources and Levels of Background Ozone and its Precursors and Impact at Ground Level

Abstract A number of significant sources of ozone exist in the planetary boundary layer, the free troposphere and the lower stratosphere. The contributions are estimated for each of these sources of ozone to ground level ozone concentrations. Both natural and anthropogenic sources are considered. Horizontal and vertical transport of ozone and its precursors also are important in determining the atmospheric distribution of ozone. The measurements of the concentration and composition of non-methane hydrocarbons and nitrogen oxides have been evaluated at both rural/remote continental sites and at tropospheric background locations. The effects discussed of the reactions of precursors with hydroxyl radicals, ozone and nitrogen trioxide radicals are discussed along with the lifetimes of organics and on their atmospheric composition. Ratios of non-methane hydrocarbons to nitrogen oxides are important in determining the efficiences of ozone production. Experimental and modeling approaches to estimating these efficiencies are reviewed.