Total reactive nitrogen (NOy), ozone (O3), the tracer nitrous oxide (N2O), and carbon monoxide (CO) were measured in situ as part of the Polar Stratosphere Aerosol Experiment (POLSTAR 1 and 2). In total, 14 missions were performed in January and February 1997 and 1998 in the Arctic subvortex region, by using the Deutsches Zentrum f¿r Luft- und Raumfahrt research aircraft Falcon. During the two campaigns, no signatures of nitrification events in the lowermost stratosphere, due to sedimentation and evaporation of aerosol particles containing HNO3, were found. Compact correlations were observed between NOy and O3, between NOy and N2O, and between O3 and N2O. Mean NOy/O3 ratios observed in the lowermost Arctic stratosphere in 1997 and 1998 were 0.0046 and 0.0030, respectively. During POLSTAR 1, NOy-N2O and O3-N2O slopes compare quite well with results of previous measurements in the lowermost stratosphere. However, indications for a nonstratospheric NOy source, possibly aircraft emissions, were found. During POLSTAR 2, inferred NOy-N2O and O3-N2O slopes were significantly lower than those previously observed in this region. This might indicate transport from lower latitudes to the Arctic subvortex region. ¿ 2000 American Geophysical Union