The Nitrogen Cycle

Question 1

Most common form of Nitrogen?

Answer 1

• In the atmosphere as the “inert” gas N2
• 6 electrons are shared, 3 pairs
• three covalent bonds
• tripple bond
• very strong and unreactive

Question 2

About Nitrogen:

Answer 2

• Along with carbon, most important element for life
• In protein
• Limits photosynthesis (nutrient)
• Has more physical and chemical sttes than any other bioelement
• Has the most complex cycle
• Also large influence on climate and ozone (stratospheric and tropospheric)

Question 3

Breakdown of N2

Answer 3

• Microbes in soil use organic carbon CH2O as energy source to break down N2 into ammonia NH3
• That is called fixed nitrogen and can be absorbed by plants.

Question 4

What is the Haber-Bosch process?

Answer 4

• One of the greatest inventions ever
• N2 + 3H2 -> 2(NH3)
• Fossil gas currently provide the cheapest source of H, but could be produced from H2O with CO2 free electricity.

Question 5

Good and bad with nitrogen fertilization:

Answer 5

• More food

- 50% of human fixed N is lost, more GHG

Question 6

What does reactive N emissions come from?

Answer 6

• Food and trasport

- In EU 85% of N emissions from food (while only producing 50% of the eaten N in food)

Question 7

2 really bad emmitters:

Answer 7

• Diesel cars NOx

- Beef production (only a fraction of used N is left in end product)

Question 8

How inefficient is beef production?

Answer 8

23 N -> 1 N (22 units are lost)

- one reason is offspring rate (1 calf per year)

Question 9

Increase in N2O?

Answer 9

• 20% looking back 1 million years

Question 10

Possitive and negative effects from high N inputs:

Answer 10

• High food crop yields
• > spares land
• > good for climate and biodiversity
• 50% is lost -> detrimental env. changes
• > smog
• > ozon layer effects
• > eutrophication (övergödning)

Question 11

How is NOx produced?

Answer 11

• Thermal NOx: N2 + O2 2NO
  temp > 1300 degC
• Fuel NOx: (complex) Organic N -> NO & N2
  part that becomes NOx increse with temp
• Prompt NOx: Air N2 + CHrad (from fuel) -> NOx

Question 12

What is good and bad with high temp in combust engines?

Answer 12

• High temps are necessary for high efficiency
• High temps give more NOx
• Cleaning technologies can convert NOx into N2

Question 13

Why is there more NOx with diesel?

Answer 13

• More O2 than needed (Lots for N2 to react with)
• Very high temp (2000 degC)
• Hard to “clean” with high O2 conc in exhaust gas

Question 14

What is the cleaning process of N in combustion called?

Answer 14

• Pyrodenitrification