If you have any questions with what I post leave a commen and I will try to give you references on the subject. It seems that some links are not working properly while others are restricted from academic journals. Nonetheless I found 2 that might work.
http://webapi.prosperity.com/download/pdf/Country_FactSheets_Web_2012.pdf
Some links here: Sangha, K K; Butler, JRA; Delisle, A; Stanley, O. Journal of Environmental Science and Engineering5.7 (Jul 2011).