Sleep oriented studies:

• Ayas, N.T., Brown, R., & Shea, S.A. (2000). "Hypercapnia can induce arousal from sleep in the absence of altered respiratory mechanoreception". AmericanJournal ofRespiratory andCriticalCare Medicine, 162(3 Pt 1), 1004-1008.
• Berry, R.B., Mahutte, C.K., & Light, R.W. (1993) "Effect of hypercapnia on the arousal response to airway occlusion during sleep in normal subjects". Journal of Applied Physiology, 74(5), 2269-2275
• Berthon-Jones, M., & Sullivan, C.E. (1984). "Ventilation and arousal responses to hypercapnia in normal sleeping humans". Journal of Applied Physiology, 57(1), 59-67
• Frey, M. A., Sulzman, F. M., Oser, H.,& Ruyters, G. (1998). "Joint NASA-ESA-DARA study, part one: the effects of moderately elevated ambient carbon dioxide levels on human physiology and performance". Aviation, Space, and Environmental Medicine, 69(3), 282-284
• Gundel, A., Drescher, J., & Weihrauch, M. R. (1998a). "Joint NASA-ESA-DARA Study, part three: cardiorespiratory response to elevated CO2 levels during sleep". Aviation, Space, and Environmental Medicine, 69(5), 496-500
• Samel, A., Vejvoda,M., Wittiber, K., & Wenzel, J. (1998). "Joint NASA-ESA-DARA study. Part three: circadian rhythms and activity-rest cycle under different CO2 concentrations". Aviation, Space, and Environmental Medicine, 69(5), 501-505.
• Laverge & Janssens 2011; 6 students over 1 month with 2-week periods of open/closed windows, comparing peaks of 1000-2500PPM to 3000-4500PPM. Some evidence for improvement.
• Strøm-Tejsen et al 2014a; within-subject comparison of 14 students sleeping in 660PPM vs 2585PPM conditions
• Strøm-Tejsen et al 2014b; within-subject comparison of 16 students sleeping in 835PPM vs 2395PPM conditions (as controlled by a fan with a CO2 sensor; very quiet but blinding may not've succeeded)