Первый слайд презентации: Nitrogen
(N) is an essential component of DNA, RNA, and proteins, the building blocks of life. All organisms require nitrogen to live and grow. The majority (78%) of the Earth’s atmosphere is N 2. Nitrogen
Слайд 2: Nitrogen’s triple bond
Although the majority of the air we breathe is N 2, most of the nitrogen in the atmosphere is unavailable for use by organisms. This is because the strong triple bond between the N atoms in N 2 molecules makes it relatively inert (like a noble gas).
Слайд 5: Forms of Nitrogen
Urea CO(NH 2 ) 2 Ammonia NH 3 (gaseous) Ammonium NH 4 Nitrate NO 3 Nitrite NO 2 Atmospheric Dinitrogen N 2 Organic N
Слайд 6: How can we use N 2 ?
In order for plants and animals to be able to use nitrogen, N 2 gas must first be converted to more a chemically available form such as ammonium (NH 4 + ) or nitrate (NO 3 -). WE CAN’T! But BACTERIA & … can…
Слайд 7: Nitrogen Fixation (N 2 --> NH 3 or NH 4 + )
ENVIRONMENTAL High-energy natural events which break the bond N 2 Examples: lightning forest fires hot lava flows
Слайд 9: Nitrogen Fixation N 2 --> NH 3 or NH 4 +
How? HUMAN IMPACT Burning fossil fuels, using synthetic nitrogen fertilizers, and cultivation of legumes all fix nitrogen.
Слайд 10: Ammonification or Mineralization
R-NH 2 NH 4 NO 2 NO 3 NO 2 NO N 2 O N 2
Слайд 11: Nitrogen Mineralization also called Ammonification Organic N --> NH 4 +
Decay of dead things, manure, etc. Done by decomposers (bacteria, fungi, etc.) During this process, a significant amount of the nitrogen contained within the dead organism is converted to ammonium (NH 4 + ).
Слайд 13: Nitrification NH 3 or NH 4 + --> NO 2 - --> NO 3 -
(Nitrifying) Bacteria add oxygen to nitrogen in two steps : STEP 1: Bacteria take in NH 3 or NH 4 + & make NO 2 - = nitrite Step 2: Bacteria take in NO 2 - & make NO 3 - = nitrate
Слайд 15: Denitrification NO 3 - --> N 2
(Denitrifying) Bacteria do it. Denitrification removes nitrogen from ecosystems, and converts it back to atmospheric N 2.
Слайд 16: Denitrification
Removes a limiting nutrient from the environment 4NO 3 - + C 6 H 12 O 6 2N 2 + 6 H 2 0 Inhibited by O 2 Not inhibited by ammonia Microbial reaction Nitrate is the terminal electron acceptor
Слайд 18: Nitrous oxide N 2 O
Nitrous oxide, commonly known as laughing gas, nitrous, nitro, or NOS is a chemical compound with the formula N 2 O. At room temperature, it is a colorless, odorless non-flammable gas, with a slightly sweet taste. It is used in surgery and dentistry for its anaesthetic and analgesic effects. It is known as "laughing gas" due to the euphoric effects of inhaling it, a property that has led to its recreational use as a dissociative anaesthetic. It is also used as an oxidizer in rocket propellants, and in motor racing to increase the power output of engines. At elevated temperatures, nitrous oxide is a powerful oxidizer similar to molecular oxygen. Nitrous oxide gives rise to nitric oxide (NO) on reaction with oxygen atoms, and this NO in turn reacts with ozone. As a result, it is the main naturally occurring regulator of stratospheric ozone.
Слайд 19: N 2 O/O 2 sedation
It is necessary to use oxygen with nitrous oxide so that the blood remains appropriately oxygenated. A mixture of 20% nitrous oxide and 80% oxygen has the same analgesic equipotence as 15 mg of morphine.
Nitrous oxide can be used as an oxidizer in a rocket motor In vehicle racing, nitrous oxide (often referred to as just " nitrous ") allows the engine to burn more fuel by providing more oxygen than air alone, resulting in a more powerful combustion. The gas itself is not flammable at a low pressure/temperature, but it delivers more oxygen than atmospheric air by breaking down at elevated temperatures. Therefore, it is often mixed with another fuel that is easier to deflagrate.
The gas is approved for use as a food additive (also known as E942), specifically as an aerosol spray propellant. Its most common uses in this context are in aerosol whipped cream canisters, cooking sprays, and as an inert gas used to displace oxygen, to inhibit bacterial growth, when filling packages of potato chips and other similar snack foods.
Of the entire anthropogenic N 2 O emission (5.7 teragrams N 2 O-N per year ), agricultural soils provide 3.5 teragrams N 2 O–N per year. Nitrous oxide is produced naturally in the soil during the microbial processes of nitrification, denitrification, nitrifier denitrification and others. The production of adipic acid is the largest source to nitrous oxide. It specifically arises from the degradation of the nitrolic acid intermediate derived from nitration of cyclohexanone.
Слайд 23: Cumulative effect
Recent experiments show that interaction between water vapor, N 2 O and cosmic radiation increases cloud production.
Слайд 24: Other Effects on Climate
Tropospheric Ozone Anthropogenic emissions have lead to increase Increases are heterogeneous, plus hard to determine pre-industrial concentrations Stratospheric Ozone Loss in Stratosphere leads to cooling (more loss of energy out to space) However, loss of stratospheric ozone also leads to greater UV absorption (and heating) in troposphere As ozone loss is reversed, some heating may occur
Слайд 25: Climate Change - Other Effects on Climate
Aerosols Light Scattering Aerosol Light Absorbing Aerosol Indirect Effects of Aerosol
Слайд 26: Other Effects on Climate
Aerosol Effects – Light Scattering Aerosol Aerosol particles of diameter 0.2 to 1 m m is very efficient in scattering light A significant fraction is scattered in the backwards direction, so this effectively increases planetary albedo Increase in albedo leads to cooling Notice how smoke from Star fire is whiter vs. forest background
Слайд 27: Other Effects on Climate
Aerosol Effects – Light Absorption Most aerosol constituents do not absorb significantly in the visible region (where light is most prevalent) A big exception is soot (elemental carbon emitted in inefficient combustion) Soot clouds lead to atmospheric warming (even if cooling the surface over short-term) Notice how smoke from Kuwait oil fires is black vs. desert background http://www.lpi.usra.edu/publications/slidesets/humanimprints/slide_16.html
Слайд 28: Other Effects on Climate
Indirect Effect of Aerosols One type is through modification of cloud reflectivity Clean Case: fewer but larger droplets Polluted Case: more but smaller droplets
Слайд 29: Climate Change - Other Effects on Climate
Indirect Effect of Aerosols Larger droplets reflect light more poorly per g of cloud water Polluted clouds look whiter from space Source: http//www-das.uwyo.edu/~geerts/cwx/notes/chap08/contrail.html Ship tracks are indicative of localized pollution Most apparent where: clouds are normally clean and with thin clouds (thick clouds have high albedos regardless)
Слайд 30: Outdoor Air Pollution Can Temporarily Slow Atmospheric Warming
Aerosol and soot pollutants Can enhance or counteract projected global warming Sulfate particles reflect sunlight Soot particles absorb sunlight Outdoor Air Pollution Can Temporarily Slow Atmospheric Warming
Слайд 31: Feedback Effect
The climate system is very complicated. A change in one component of the system may cause changes in other components. Sometimes the changes in other components enhance the initial change, then we say that these changes have positive feedback to the system. If the changes result in the reduction of the original change, then they have negative feedback. Both positive and negative feedback processes may exist in the climate system. In studying the global climatic change, we cannot make conclusions based on intuition, but have to take all such possible complicated effects into account. A good climate model would have treated all of them realistically.
Слайд 32: An example of positive feedback
When the climate becomes warmer (either due to the increase of CO 2 in the atmosphere or other unknown mechanisms), the ocean may also become warmer. A warmer ocean has lower solubility of CO 2 and hence will release more CO 2 into the atmosphere. This may cause the climate to become even warmer than before. Thus the dependence of solubility of CO 2 on temperature has a positive feedback on the climate system.
Слайд 33: An example of negative feedback
Consider a clear region over the ocean. Since there is no cloud, the sun shines on the ocean surface, causing it to warm up. This makes this part of the ocean warmer than other parts and the air over it tends to rise (causing convection). Rising air expands and cools, causing clouds to form. The formation of clouds will block out the sun and the solar heating of the ocean surface will cease. The surface will start to cool down. Thus the cloud formation due to surface heating and convection is a negative feedback to the climate system.
Последний слайд презентации: Nitrogen
Atmospheric Feedbacks Increased CO 2 Higher temperature More water vapor POSITIVE NEGATIVE More water vapor & other changes Increased cloud cover More reflected solar radiation Lower temperature Less water vapor More absorbed infrared radiation Higher temperature More water vapor + + + + + –