The NARSTO-NE-OPS (North East Oxidant and Particle Study) is an investigation of the coupling of the meteorological and chemical processes that control the evolution of air pollution events. The project includes three major field programs which have been carried out at a field site in northeast Philadelphia during the summers of 1998, 1999 and 2001. The activity brings together the research groups from 13 universities, 5 government laboratories and a representative of the electric power industry to apply the most advanced measurement techniques to understanding the physical and chemical processes contributing to air quality issues. Results have been obtained from three prepared ground sites, from two instrumented aircraft, from many different instrumented balloon platforms and from several remote sensing techniques. In addition, the data base used includes the ground based measurements conducted using monitoring instruments by several surrounding states, Pennsylvania, New Jersey, Delaware, New York and Maryland. The results have shown the importance of developing the 3-dimensional regional scale picture of the atmosphere to understand and properly model air pollution events. It has been shown that only from such a perspective can one hope to properly model and predict ozone and particulate matter pollution because of the importance of dynamical transport processes, both horizontal and vertical, that accumulate, photochemically condition, and then mix with the locally produced chemical species to cause the more important periods of air pollution. Efforts have also focused on developmental testing of several new approaches improved measuring techniques for better understanding of the physical and chemical properties of the airborne particulate matter.