The Southern Oxidants Study (SOS) has developed and demonstrated the effectiveness of a new paradigm for policy-relevant, air-quality research in US. This new paradigm is based on a long-term commitment to improve scientific and public understanding of the fundamental chemical meteorological, biological, and sociological processes that lead to the formation and accumulation of ozone in the lower atmosphere of the earth. SOS uses the southern US as a natural laboratory for systematic observation-based testing and evaluation of essentially every assumption undergirding the US EPA's present emissions-based thinking and modeling, an approach which has yet to achieve significant progress in the abatement of photochemical ozone pollution over the past 20 years.