Singh, H., D. Herlth, D. O’Hara, K. Zahnleg, J. Bradshaw, S. Sandholm, R. Talbot, P. Crutzen, and M. Kanakidau (1990), Relationship of PAN to Active and Total Odd Nitrogen at Northern High Latitudes: Influence of Reservoir Species on NOx and O3, J. Geophys. Res..