Zahn, A., Brenninkmeijer, C. A. M., Maiss, M., Scharffe, D. H., Crutzen, P. J., Hermann, M., et al. (2000). Identification of extratropical two-way troposphere-stratosphere mixing based on CARIBIC measurements of O3, CO, and ultrafine particles. Journal of Geophysical Research, 105, 1527-1535.