A corona-type, air-cooled ozone generator has a cluster of ganged cylindrical generator units (100) packed into a cylindrical pipe (10). Each unit has an inner electrode (101), a dielectric tube around the inner electrode (103), and a concentric outer electrode (102 with side wall openings (112). The corona air gap is between the dielectric and the outer electrode. The inner electrode and dielectric tube are held in each respective outer electrode with silicone end pieces (152, 151). Voltage is put on the inner electrodes while air is blown through the pipe from a blower (30); the air passes through the gaps between the units' ends and circulates through side wall openings, passing over the dielectric tubes and cooling them. Because the dielectric tubes are small, for example 0.25 inches across, they lose heat quickly and do not reach a high temperature. The generator is compact.