Singh, H., D. Herlth, D. O'Hara, K. Zahnle, J. D. Bradshaw, S. T. Sandholm, R. Talbot, G. L. Gregory, G. Sachse, D. R. Blake, and S. C. Wofsy (1994), Summertime Distribution of PAN and Other Reactive Nitrogen Species in The Northern High Latitude Atmosphere of Eastern Canada, J. Geophys. Res., 99, 1821-1835.