1. Dr. Pieter Tans, NOAA/ESRL, www.esrl.noaa.gov/gmd/ccgg/trends/ and Dr. Ralph Keeling, Scripps Institution of Oceanography, scrippsco2.ucsd.edu/.
2. Intergovernmental panel on climate change. http://www.ipcc.ch/.
3. U.S. Environmental Protection Agency. http://www.epa.gov/cleanenergy/energy-resources/refs.html.
4. Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity (Recommendations 1984)
5. International Zeolite Association. http://www.iza-online.org/.