The Catatumbo Lightning in Venezuela is the world's largest single generator of ozone.[1] It is a cloud storm that forms a voltaic arc at more than 5 km of height, during 140 to 160 nights a year, 10 hours per day and up to 280 times per hour, over the bog area that forms where the Catatumbo River flows into the Lake Maracaibo.
http://en.wikipedia.org/wiki/Catatumbo_lightning