Nitrogen And Phosphorus in the Atmosphere Flashcards
Why is nitrogen important ?
It is the most important nutrient for plants. Nitrogen availability plays a vital role in photosynthesis
Important component of the enzyme ( rubisco) that controls the rates of biochemical reactions( photosynthesis). Nitrogen are building blocks of Amino acids and the N in the DNA
How much of the atmosphere is nitrogen?
78 %
What is the total mass of nitrogen in the atmosphere?
- 9 x1015 tonnes
- 9 x 109 megatonnes
- 9 x106 gigatonnes
If you convert the 78 percent into parts per millio you get 780 000 ppm in the atmosphere
Why is there so much nitrogen in the atmosphere?
N2 is an ‘even’ nitrogen molecule - it’s relatively unreactive and therefore the nitrogen is not rly available to do used by biology so builds up in the atmosphere
The two N atoms have a triple bond ( 3 pairs of electrons shared between the 2 N atoms). The nitrogen triple bond is strong. Takes a lot of energy to break.
This makes N2 almost inert, except for high energy events such as lightning
What are the 6 stages of the nitrogen cycle ?
1) Nitrogen fixation
2) Ammonia assimilation
3) Nitrification
4) Assimilatory nitrate reduction
5) Ammonification
6) Denitrification
NANA :
D
What is nitrogen fixation? What different types of bacteria help the process? Give examples of specific bacteria for each example and the relationship
1)Nitrogen fixation is any process by which N2 (gas) in the atmosphere is converted to any form of nitrogen that is more useful to organisms. Biological fixation is the enzyme catalysed reduction of ammonia ( HN3-), Ammonium (NH4+) or any other organic nitrogen
Nitrogen fixation is carried out by nitrogen fixing bacteria. They convert the nitrogen into ammonia using a reduction reaction catalysed by the enzyme nitrogenase.
Can get Bacteria that are free living and live in soil or water. Many species such as Azotobacter colonise the rhizisohere ( rioting zone) of many plant species but do not depend directly on the plants
.Some of these bacteria live in special swellings on the roots (known as root nodules) of plants called legumes. The bacterium receives water and sugars from the plant and in return supplies the plant with ammonia. The ammonia can be used later to make proteins and other nitrogen containing organic compounds which are required by the plant, such as nucleic acids. This mutually beneficial relationship between the bacteria and the plant is an example of symbiosis.
First, the atmospheric N2 diffuses into the soil air. Then it is fixed by the bacteria in the soil.
The best known examples are Rhizobium species which form root nodules on peas, bean, clover
What is ammonia assimilation?
2)The process by which HN3- or NH4+ is taken up by an organism to become part of its biomass in the form of an organic nitrogen compound like amino acids or DNA.
What is nitrification?
3)Nitrification is the oxidation of ammonia (HN3-) or NH4+ to NO2- or NO3- by an organism, as a means of producing
This process is carried out by bacteria called nitrifying bacteria. These bacteria
transform ammonium ions into nitrates.This releases energy which they use for the synthesis of organic molecules such as carbohydrates. For this reason, these bacteria are described as autotrophs.
What is assimilatory nitrate reduction?
4)Assimilatory nitrate reduction is the reduction of NO3- followed by the uptake of nitrogen by the organism as biomass ( plants). Plants can then be consumed and nitrogen flows through food webs/chains
So uptake of NO3- or nh4+ as biomass
The inorganic nitrogen is taken up by plants from the soil, largely in the form of nitrates which is then used to synthesise nitrogen-containing organic molecules such as proteins or DNA. These move into other organisms when they eat the plants, and digest and absorb the organic compounds.
What is ammonification?
5)
This is the breaking down or organic nitrogen compounds to HN3- or NH4+
Nitrogen is passed through food chains in the form of organic compounds, e.g. proteins & DNA. When organisms die, excrete urea or egest faeces, decomposers such as bacteria and fungi convert the organic nitrogen locked up in these organic compounds into ammonia.
What is denitrification?
6)
This is the reduction of NO3- ( nitrates) to any gaseous nitrogen species, generally N2 or N2O
This often happens under anaerobic conditions
What is fixation again generally?
To make N available to plants and animals, it must be fixed (combined) in the form of ammonium (NH4)
Fixation is conversion of nitrogen from a relatively stable form to something that can be used by plants
This fixation may either be natural or anthropogenic (human)
What is Nitrification again generally?
It is the bacterial conversion of NH4+ intro nitrites NO2–) then nitrates (NO3-)which is a form than can be used directly by plants
Describe the anthropogenic nitrogen fixation
Main human processes ( 1/3 of total -2/3 is natural processes) are fertiliser production and combustion
Driven by our desire to increase agricultural production
Fertilisers ( planned fixation) Ammonium sulphate -21 Ammonium nitrate -33.5 Urea (NH2)2CO - 45 Liquid ammonia -82
Trace amount of accidental fixation which occurs due to combustion
Some N in fuel is oxidised to NO or NO2
Some of the N2 in the fuel is oxidised to NO or NO2
How much non biological N and biological N is fixed Global, MT:year
Non biological - 80
Biological -175
What is the rate of use per year of nitrogen ? Why doesn’t nitrogen run out?
200 Mt per year
Total N in atmosphere = 4 x109 Mt
Should all have been used up since should only take 20million years Nd earth is 5000 million years
Because denitrification!
Bacterial process which converts nitrates into N2 and returns it to the atmosphere)
This also produces N2O and NO
Why doesn’t the N2O concentration keep increasing?
N2O has a long lifetime in the troposphere (the lowest region of the atmosphere, extending from the earth’s surface to a height of about 6–10 km (the lower boundary of the stratosphere)
Eventually it diffuses up into the stratosphere
In the stratosphere there is a high UV flux density and the N2O Is bombarded with UV radiation
( above stratospheric ozone layer) Interacts with photons less than 250 nm ( UV-C light) and this high amount energy can break up the N2O molecule into N2 and O
What are odd nitrogen in the atmosphere ?
Present both in gases and particles
The particles may be solid or liquid, and they may be small enough to remain suspended in the air for days ( aersols), or large enough to fall out
Nitric oxide ( gas)- N2O IMPORTANT
Nitrogen dioxide (gas)
HNO2 - nitrous oxide (gas/liquid)
HNO3 - nitric acid (gas/liquid)
How does the odd nitrogen get back out of the atmosphere? What are the different types of these and describe them
Diffusion - diffusion of gas molecules and particles from the atmosphere to surfaces ( area of high concentration to low) down a concentration gradient
Note this is dry deposition:
Turbulent diffusion: the bulk movement of large number of molecules; cannot operate close to surfaces - close to sources or in remote areas
Molecular diffusion; important close to surfaces, but only for gases deposition of particles by impactation from the wind onto surfaces ( leaves etc)
Describe wet deposition
Deposition by incorporation into cloud droplets and then rain drops
Gases can be dissolved into the cloud water droplets
Particles can be the nuclei around which cloud droplets form
Falling raindrops can collect particles and dissolve more gases
Cloud droplets May impact onto surfaces ( e.g leaves) without forming raindrops
How are nitrogen compounds involved in climate change?
N2O is a very potent greenhouse gas
GWP ( greenhouse warming potential) of 109 years, compared to GWO of 30 for methane
Most N2O is derived from bacterial denitrification so its associated with land use and agricultural practices
Discuss stratospheric ozone destruction with nitrogen oxide
N2O = nitrous oxide NO = Nitric oxide
O3 + NO = O2 + NO2
NO2 + O = NO + O2
O3 + O = 2O2
Chemistry don’t rly need to go over?
NO is derived from the photolysis of N2O
However, not all the NO is reacted with O3 some reacts to with the hydroxyl radical (•OH) to produce nitrous acid ( HNO2)
This is not involved in O3 ( ozone destruction) so overall there is a reduction in O3 removal by NO
Not a fully closed system - NO used up so not a perfect catalyst
Polar stratospheric clouds?
They form in high altitudes.
You have CLOx —-> NO2 (dioxide
|
CH4
Outside stratospheric clouds which can reacts to form ClONO2 (chloro-nitrate) which is relatively stable and inert and HCl which is relatively soluble and rapidly rains out on the system.
So no real build up of chlorine in atmosphere when outside of the polar stratospheric clouds
In Winter the atmosphere in Antarctica gets really cold which leads to the formation of high altitude of polar stratospheric clouds
Within these clouds you have the process of denitrification. Where the chloronitrate and HCl denitrify yo give you HNO3 ( nitric acid) which forms as ice crystals on the surfaces of the clouds. And the denitrification liberates chlorine
Discuss stratospheric ozone destruction with nitrogen oxide
N2O = nitrous oxide NO = Nitric oxide
O3 + NO = O2 + NO2
NO2 + O = NO + O2
O3 + O = 2O2
Chemistry don’t rly need to go over?
NO is derived from the photolysis of N2O
However, not all the NO is reacted with O3 some reacts to with the hydroxyl radical (•OH) to produce nitrous acid ( HNO2)
This is not involved in O3 ( ozone destruction) so overall there is a reduction in O3 removal by NO
Not a fully closed system - NO used up so not a perfect catalyst
