Northern Hemisphere ozone (O3) measurements in the lower stratosphere made from 1989 to 1997 are presented along with simultaneous measurements of the conserved tracer nitrous oxide (N2O) to help separate O3 changes due to photochemistry from those due to transport. This model-independent analysis represents 139 flights aboard the ER-2 aircraft and 12 profiles from balloons and uses zonal, isobaric, and isentropic seasonal averages of O3 and N2O to examine seasonal changes in O3 distributions. The resulting seasonal families of curves at constant latitude are somewhat intertwined, while the families of isobaric and isentropic curves are not. Although some of the isobaric curves cross, the isentropic curves are sufficiently separated to confidently estimate O3 by specifying season, N2O, and potential temperature, then interpolating between the curves. Such estimates may be useful for testing of photochemical models with transport, and perhaps more importantly, the families of curves could serve as baseline references for estimating high latitude photochemical O3 loss and as an indicator of O3 recovery in the lower stratosphere.