Even lightly populated nonindustrial areas are subject to the effects of smog brought about by human activities. Particularly, the practice of burning savanna grasses for agricultural purposes causes smog. This burning produces NOx and reactive hydrocarbons that are required for smog formation. Furthermore, these grasses grow in tropical regions which have the intense sunlight required for smog formation. The net result is rapid development of smoggy conditions as manifested by ozone levels several times normal background values.