References
1. Portland Cement Associaltion (2013). self-cleanig concrete. Retrieved from http://www.cement.org/tech/self_cleaning.asp
2. Barabara P. (2013, April 14) Chicago, Frist U.S City to Line Streets with Smog-Eating Cementhicago, First U.S. City to Line Streets with Smog-Eating Cement. Retrieved from http://www.archdaily.com/359756/
3. Christie N. (2013, July 31) Pollution-killing Material: Smog eating cement. Retrieved from http://www.core77.com/blog/materials/pollution-killing_material_smog-eating_cement__25281.asp
4. David Suzuki Foundation. Greenhouse gases. Retrieved from http://www.davidsuzuki.org/issues/climate-change/science/climate-change-basics/greenhouse-gases/
5. Larry West. (2013) What causes smog? Retrieved from http://environment.about.com/od/smogfaq/f/smog_faq_five.htm
6. Gretchen Weber. (July 23, 2010) Another Climate Change Impact: Smog. Retrieved from: http://blogs.kqed.org/climatewatch/2010/07/23/another-climate-change-impact-smog/