1. Ceresana Online, http://www.ceresana.com/en/market-studies/chemicals/ammonia/ceresana-market-study-ammonia.html, accessed January 2015
2. FAO Global Estimates of Gaseous Emissions of NH3, NO and N2O from Agricultural Land Online, http://www.fao.org/docrep/004/Y2780E/y2780e00.htm, accessed January 2015
3. Estimation of anthropogenic ammonia emissions in asia
4. Ammonia emissions from non-agricultural sources in the UK
5. ISO 22241-4:2009 Online, https://www.iso.org/obp/ui/#iso:std:iso:22241:-4:ed-1:v1:en, accessed January 2015