Neufeld, Howard S., E. H. Lee, James R. Renfro, and David W. Hacker. "Seedling Insensitivity to Ozone for Three Conifer Species Native to Great Smoky Mountains National Park." Environmental Pollution 108, no. 2 (2000): 141-151.

Neufeld, Howard S., Henry E. Lee, James R. Renfro, David W. Hacker, and Ben-Hui Yu. "Sensitivity of Seedlings of Black Cherry (Prunus serotina Ehrh.) to Ozone in Great Smoky Mountains National Park. I. Exposure-Response Curves for Biomass." New Phytologist 130, no. 3 (1995): 447-459.

Hacker, David W., and James R. Renfro. "Great Smoky Mountains Plants Studies for Ozone Sensitivity." Park Science:  A Resource Management Bulletin 12, no. 1 (1992): 6-7.

Hacker, David W., James R. Renfro, and Howard S. Neufeld. Sensitivity of Native Plant Species to Elevated Levels of Ozone In Third Annual Southern Appalachian Man and the Biosphere Conference. Gatlinburg, TN: Tennessee Valley Authority, 1992.

Hacker, David W., and James R. Renfro. Ozone Response of Selected Plant Species from the Great Smoky Mountains National Park In First Annual Southern Appalachian Man and the Biosphere Conference. Gatlinburg, TN: Tennessee Valley Authority, 1990.