Research has shown that high school and college students have a lack of conceptual understanding of global warming, ozone, and the greenhouse effect. Most research in this area used survey methodologies and did not include concepts of atmospheric chemistry and ozone formation. This study investigates college students' understandings of atmospheric ozone formation using established clinical interview methodologies and qualitative data analysis techniques. Three prevalent naive conceptions were identified: (1) that there is only one atmospheric mechanism for ozone formation; (2) that pollutants and gases only react after being transported up high in the atmosphere; and (3) that concerns about ozone in the atmosphere are due primarily to its role as a greenhouse gas. The existence of these naive conceptions prevented students from forming correct mental models of atmospheric ozone formation. Existing conceptual change approaches may provide pathways for addressing these naive conceptions, but further research is required before specific solutions are proposed. (Contains 1 table, 1 box, and 2 figures.)