Nitrous Oxide in Ag, Part 2: Nitric Acid Production

I am trying to do a life cycle analysis of synthetic fertilizers and their impacts on climate change. I am having to do a rough analysis of production process and ingredients to start.

As previously discussed, Nitrous Oxide (N2O) is a major source of greenhouse gas emissions:

• Nitrous Oxide (N2O) emissions from ag make up over 75% of the U.S.'s total N2O emissions.
  
• N2O is found in ag primarily from fertilizer application and management of solid waste from animals.
• N2O has 296 times more impact on the climate than CO2.

Let's add a defintion by the EPA: "Nitric acid (HNO3) is an inorganic compound used primarily to make synthetic commercial fertilizers. It is also a major component in the production of adipic acid⎯a feedstock for nylon⎯and explosives."(1)

So this shows pretty solidly that synthetic fertilizer production has a major impact on climate change.

A few questions come to mind:

1. What are the source ingredients for Nitric Acid? Can we find a replacement for Nitric Acid and still grow enough food and materials?
2. What is the power source for the industrial plants?
   
3. What are the best substitutes and are there enough of them?
   
4. Which crops receive the most? Which the least?
   
5. What industrial processes have more impact on the climate?

To answer the last question first (since it is the easiest), we can turn to the EPA's U.S. Inventory Report chapter for Industrial Processes.

The top 10 Industrial Processes for Greenhouse Gas (GHG) emissions are listed below. The numbers represent teragrams (tg) of CO2 Eq, with 1Tg equal to 1 million metric ton (MMT CO2 Eq.)(2)

Top 10 GHG Emitting Industrial Processes (3)

1. Substitution of Ozone Depleting Substances (123.3)
2. Cement Manufacture (45.9)
3. Iron and Steel Production (45.2)
4. HCFC-22 Production (16.5)
5. Ammonia Manufacture & Urea Application (16.3)
6. Nitric Acid Production (15.7)
7. Lime Manufacture (13.7)
   
8. Electrical Transmission and Distribution (13.2)
9. Limestone and Dolomite Use (7.4)
10. Adipic Acid Production (6.0)

Major source ingredients for Nitric Acid production are:

• Ammonia
• Nitric oxide

And as we can see, ammonia manufacture is the #5 highest emitter.

Sources:
1) EPA, Inventory of U.S. Greenhouse Gas Emissions and Sinks,1990-2003", :1990 – 2003, April 2005, p.161.
2) U.S. Energy Information Administration, "Emissions of Greenhouse Gases in the United States 2000", Appendix F (Common Conversion Factors), 2000
3) EPA, "U.S. Greenhouse Gas Inventory Reports", Chapter 4 "Industrial Processes", April 2007, http://epa.gov/climatechange/emissions/usinventoryreport.html