ozone in the upper atmosphere - fremont...
TRANSCRIPT
May 18-22 Logan River Academy Chemistry
ENVIRONMENTAL CHEMISTRY
<< REFRESHER >>
May 18-22 Logan River Academy Chemistry
REVIEW• Environmental Chemistry deals with
chemical reactions happening in the:
– atmosphere … the sky
– hydrosphere … bodies of water
– lithosphere … rocks & soils
• Becoming more and more important -global warming, ozone hole, acid rain, etc.
• Today we begin with atmosphere
May 18-22 Logan River Academy Chemistry
May 18-22 Logan River Academy Chemistry
Intro - Atmosphere• Most of us have never been far from Earth’s
surface
• We probably take for granted the many ways that the atmosphere affects the environment we live in
• We will look at some of the characteristics of our planet’s atmosphere
May 18-22 Logan River Academy Chemistry
I. TEMPERATURE• The atmosphere’s temperature varies in a complex way as
a function of altitude
• Based on temperature, the atmosphere is divided into four regions
– TROPOSPHERE
– STRATOSPHERE
– MESOSPHERE
– THERMOSPHERE
May 18-22 Logan River Academy Chemistry
II. Composition• The atmosphere is a very complex system
• It is bombarded by radiation and energetic particles from the Sun
• All this energy pouring in to the atmosphere has extreme chemical effects, especially on the outer reaches
• Also, Earth’s gravity pulls heavier atoms and molecules to the bottom-- and allows lighter atoms and molecules to rise to the top-- of the atmosphere
• Because of all this, the composition of the atmosphere isn’t constant all across the board
May 18-22 Logan River Academy Chemistry
Molecular Composition
May 18-22 Logan River Academy Chemistry
More about “-spheres”
May 18-22 Logan River Academy Chemistry
TROPOSPHERE• This is where we live
• Mt. Everest (29,035 ft) scrapes the upper reaches
• This is where “weather” happens -- winds, breezes, rain, snow, sunny skies
• Temperature decreases with increasing altitude
• Commercial jets fly at 9 km above Earth, also scraping the top
May 18-22 Logan River Academy Chemistry
STRATOSPHERE• Temperature increases with higher altitude
• Most airplanes can’t fly here because the air is too thin to support them (except spy planes U-2 & SR-71)
• Ozone layer is here
• No clouds - no “weather”
• If you see an “anvil cloud” in a thunderstorm, it’s probably knocking up against the stratosphere
May 18-22 Logan River Academy Chemistry
May 18-22 Logan River Academy Chemistry
MESOSPHERE• Is found between 50 - 80 km above sea level
• Very thin air because air particles are far apart - very difficult to breathe
• Temperatures decrease greatly, and get as low as -100 degrees C at the top of the mesosphere - coldest place in the atmosphere. Called “mesopause”
• Least understood layer of atmosphere because it’s too low for spacecraft and too high for aircraft
• Contain “noctilucent clouds” - highest clouds in the atmosphere, made of ice crystals - visible only in deep twilight conditions
May 18-22 Logan River Academy Chemistry
May 18-22 Logan River Academy Chemistry
THERMOSPHERE• In the thermosphere, ultraviolet radiation
causes ionization (atoms lose or gain electrons)
• International Space Station found here
• Auroras originate here - produced by collision of charged particles (arriving via solar wind) with ions formed in the thermosphere
• Radio waves bounce off the ions in thermosphere
May 18-22 Logan River Academy Chemistry
May 18-22 Logan River Academy Chemistry
May 18-22 Logan River Academy Chemistry
EXOSPHERE• An upward traveling molecule can escape
to space if it has high enough velocity
• Low density - few molecular collisions
• No clear boundary between exosphere and space - sometimes referred to also as outer space
• Between 500 km above earth’s surface to 10,000 … 97,000 … 190,000 … km above surface
May 18-22 Logan River Academy Chemistry
Outer Regions of the Atmosphere
Processes and Reactions
May 18-22 Logan River Academy Chemistry
Intro• Beyond the stratosphere, the
atmosphere has only a small portion of
the atmospheric mass
• The meso-, thermo- and exosphere
form an outer defense against radiation
and high-energy particles that are
always bombarding Earth
• Chemical changes occur in these
particles and molecules
May 18-22 Logan River Academy Chemistry
PHOTODISSOCIATION• The Sun emits radiation over a wide range of
energies (gamma, UV, etc.)
• Electromagnetic radiation can be pictured as a stream of photons
• Each photon has a certain amount of energy
• For chemical change to occur:
1) There must be photons with energy sufficient to accomplish the chemical reaction
2) Molecules must absorb the photons
May 18-22 Logan River Academy Chemistry
PHOTODISSOCIATION• Photodissociation = the rupture of a
chemical bond as a result of absorption of a photon by a molecule
• Photodissociation of the O2 molecule:
– O2(g) + photons --> 2O(g)
May 18-22 Logan River Academy Chemistry
PHOTOIONIZATION• 1901 - Guglielmo Marconi received a radio
signal in St. John’s, Newfoundland, Canada that had been sent from Land’s End, England
• Radio waves were thought to travel in straight lines, but this showed that the upper atmosphere can bounce radio waves … This experiment showed that there are electrons in the upper atmosphere.
May 18-22 Logan River Academy Chemistry
PHOTOIONIZATION• There must be a corresponding positively
charged ion for every electron
• Electrons in the upper atmosphere result from photoionization, caused by solar radiation
• In this process, a molecule absorbs radiation, and that absorbed energy causes an electron to be lost
May 18-22 Logan River Academy Chemistry
Important Photoionization Reactions
• N2 + photons --> N2+ + e-
• O2 + photons --> O2+ + e-
• O + photons --> O+ + e-
• NO + photons --> NO+ + e-
May 26-28 LRA Chemistry
OZONE in the UPPER ATMOSPHERE
O3
May 26-28 LRA Chemistry
Ozone• N2, O2, and O absorb photons with
wavelengths <240 nm
• Ozone is the key absorber of photons with wavelengths between 240 - 310 nm
• Between 30 - 90 km, the concentration of O2 is much greater than that of O
• Therefore, the O atoms in this region undergo frequent collisions with O2 molecules: O(g) + O2(g) --> O3(g)
May 26-28 LRA Chemistry
Ozone• The highest rate of O3 formation occurs at an
altitude of 50 km, near the stratopause
• 90% of Earth’s ozone is in the stratosphere
• The ozone molecule doesn’t last long; when it absorbs solar radiation, it decomposes back into O2 and O.
• If it weren’t for the ozone layer, high-energy photons (200-310 nm) would penetrate Earth’s surface, and plant and animal life could not survive
• OZONE IS A SHIELD
May 26-28 LRA Chemistry
OZONE DEPLETION• In 1974, scientists recognized that chlorine
from chlorofluorocarbons (CFCs) was depleting the ozone layer
• CFCl3 (Freon-11), CF2Cl2 (Freon-12), were widely used in aerosol cans, refrigerators, air conditioners, and plastics
• Are not very reactive molecules and are insoluble in water, which makes them commercially useful
• There are several million tons of CFCs in the atmosphere
May 26-28 LRA Chemistry
Ozone depletion reactions1. CF2Cl2(g) + hv --> CF2Cl (g) + Cl (g)
2. Cl (g) + O3 (g) --> ClO (g) + O2 (g)
3. 2ClO (g) --> O2 (g) + 2Cl (g)
May 26-28 LRA Chemistry
Environmental effects• The more CFCs that diffuse into the
stratosphere, the quicker the destruction of the ozone layer
• Representatives of babout 100 nations agreed to ban the production and use of CFCs by 1996
• But CFCs are unreactive and diffuse slowly into the stratosphere, so scientists estimate that ozone will be depleted for many years to come
May 26-28 LRA Chemistry
CHEMISTRY OF THE
TROPOSPHERE
(where we live)
May 26-28 LRA Chemistry
Troposphere Intro• Most of the troposphere is N2 & O2 - these
molecules make up 99% of Earth’s atmosphere at sea level
• There are other molecules, however, and there can be greater amounts of them in areas of human activity
• For example ...
May 26-28 LRA Chemistry
Sources of other Atmospheric molecules
Molecule Source
Carbon dioxide decomposition of organic matter, release from
oceans, fossil-fuel combustion
Carbon monoxide decomposition of organic matter, industrial
processes, fossil-fuel combustion
Methane decomposition of organic matter, natural gas
seepage
Nitric Oxide electrical discharges, internal combustion engines,
combustion of organic matter
Ozone electrical discharges, diffusion from the
stratosphere, photochemical smog
Sulfur Dioxide volcanic gases, forest fires, bacterial action, fossil-
fuel combustion, industrial processes
May 26-28 LRA Chemistry
Conc. of other Atmospheric molecules
Molecule Typical Concentrations
Carbon dioxide 355 ppm throughout troposphere
Carbon monoxide 0.05 ppm in air without pollution; 1 - 50 ppm in
areas of urban traffic
Methane 1 - 2 ppm throughout troposphere
Nitric Oxide 0.01 ppm in air without pollution; 0.2 ppm in smog
Ozone 0 - 0.01 ppm in air without pollution; 0.5 ppm in
photochemical smog
Sulfur Dioxide 0 - 0.01 ppm in air without pollution; 0.1 - 2 ppm
in polluted urban environment
May 26-28 LRA Chemistry
May 26-28 LRA Chemistry
Acid Rain• Combustion of coal and
oil accounts for 80% of SO2 released in the U.S.
• Some oil (Middle East) is low in sulfur. Other oil (Venezuela) is higher in sulfur
• Coal east of the Mississippi is higher in sulfur content. Western states coal has less sulfur content
• SO2 itself is harmful to human health & property
• SO2 can be oxidized to SO3, and combine w/ water to make sulfuric acid (H2SO4)
• pH of mo0st natural waters with living organisms is 6.5 - 8.5. pH below 4.0 means all vertebrates, most invertebrates, and many microorganisms are destroyed
• Acid rain is a pH of about 4 (normal rainwater is 5)
May 26-28 LRA Chemistry
CO (carbon monoxide)• Formed by incomplete
combustion of fossil fuels
• Most CO from the U.S. comes from automobiles
• An unreactive molecule
• No direct threat to vegetation or materials
• But it affects humans, because it has an ability to bind very strongly to hemoglobin, the protein in red blood cells that transports blood oxygen
• Normally O2 binds to hemoglobin, but human hemoglobin likes CO 210 times better than O2!
• So a small amount of CO can inactivate a lot of the hemoglobin the blood
• A nonsmoker breathing unpolluted air has about 0.3 - 0.5% COHb in the bloodstream
• If COHb level becomes too high, oxygen transport is shut down and death occurs
• CO is colorless & odorless
May 26-28 LRA Chemistry
OCEANSWeather generators
Climate stabilizers
Living reservoirs
The last frontier
May 26-28 LRA Chemistry
SEAWATER• Water covers 72% of
Earth’s surface. It makes up 65% of our body mass
• Salty water is connected and usually constant in composition
• There is really a “world ocean,” not separate ones
• Seawater = saline water
• The salinity of seawater is the mass in grams of dry slats present in 1 kg seawater
• World ocean average salinity is 35; seawater has about 3.5% dissolved salts by mass
• If a substance is present in seawater to the extent of 1 ppb, there is 5 x 109 of that substance in the ocean
• The list of elements found in the ocean is very long
May 26-28 LRA Chemistry
ELEMENTS in SEAWATER
May 26-28 LRA Chemistry
Desalination• Seawater can’t be drunk by humans
• The removing of salts from seawater or brackish water is desalination
• Distillation is one way to carry out desalination, but presents problems
• Another way, quite expensive, is reverse osmosis = moving solvent molecules (not solute molecules) through a semipermeable membrane
May 26-28 LRA Chemistry
Desalination plant in Jubail, Saudi Arabia -provides 50% of the country’s drinking water
How soils supply plant nutrients
An Introduction to Soil Chemistry
Prepared by:
Richard Stehouwer
Department of Agronomy
What is soil?
Soil is the unconsolidated cover on the surface of the earth.
Soil is made up of
mineral particles,
organic particles,
air, and
water.
Soil is capable of supporting plant growth.
Functions of agricultural soils
• Anchor plant roots• Supply water to plant roots• Provide air for plant roots• Furnish nutrients for plant
growth• Release water with low levels of
nutrients
Soil ComponentsThe 4 parts of soil
MineralMatter45%
SoilWater25%
SoilAir
25%
OrganicMatter
5%
About ½ of the soil volume is
solid particles
About ½ of the soil volume is pore space
Soil Texture• The mineral part of soil consists of sand, silt, and
clay particles
• The amounts of each size particle determines the textural property of the soil– Coarse textured, loose (more sand, less clay)
– Fine textured, heavy (more clay, less sand)
– Loamy (more even mix of sand, silt and clay
Sand0.1 – 0.002 in
2 – 0.05 mm
Silt0.002 – 0.0001 in
0.05 - 0.002 mm
ClayLess than 0.0001 in
Less than 0.002 mm
1/100 in
Soil StructureThe arrangement of sand, silt, and clay particles to
form larger aggregates.
• Organic matter is the glue that holds the aggregates together
• Large pores (spaces) between aggregates are filled with air in a moist soil.
• Small pores are filled with water in a moist soil. Even smaller pores inside the aggregates (not shown) are also filled with water.
1/10 inch
Supplying Plant Nutrients
Macronutrients:(needed in large amounts)
• Nitrogen (N)
• Phosphorus (P)
• Potassium (K)
• Calcium (Ca)
• Magnesium (Mg)
• Sulfur (S)
Micronutrients:(needed in small amounts)
• Chlorine (Cl)
• Cobalt (Co)
• Copper (Cu)
• Iron (Fe)
• Manganese (Mn)
• Molybdenum (Mo)
• Nickel (Ni)
• Zinc (Zn)
Nutrients that plants obtain from the soil
Where do plant nutrients come from?
• Decaying plant litter
• Breakdown of soil minerals
• Addition by humans– Commercial fertilizer
– Manure
– Lime
– Other
Recycling plant nutrients
Breakdown of soil minerals
Acid
Ca
Mg
K
CuNi
Zn
Water
Nutrient additions by humans
• Commercial fertilizers– Nutrients are in a form that is available to plants
– Dissolve quickly and nutrients go into soil water
• Lime– Dissolves slowly as it neutralizes soil acidity
– Releases calcium and magnesium
• Organic nutrient sources – Manure, compost, sewage sludge
– Decay and nutrient release is similar to crop litter
The soil solution
• Soil water is a complex solution that contains– Many types of nutrients
– Other trace elements
– Complex organic molecules
• Nutrients in the soil solution can be readily taken up by plant roots
• If nutrients remained in solution they could all be quickly lost from the soil.
P
Ni Ca Mg Cu
KN
Zn
Adsorption• Adsorption refers to the ability of an object to attract and hold particles on its surface.
• Solid particles in soil have the ability to adsorb
– Water
– Nutrients and other chemicals
• The most important adsorbers in soil are
– Clays
– Organic matter
+ -
Surface area of clay
¼ cup¼ cup of clay has more surface area than a football field
The large surface area of clay allows it to
• Adsorb a lot of water• Retain nutrients• Stick to other soil particles
Properties of Soil Clays
Clay particles are stacked in layers like sheets of paper.
Each clay sheet is slightly separated from those on either side.
Each sheet has negative charges on it.
Negative charges have to be balanced by positive charges called cations.1/20,000 in
Cation Retention onSoil Clays
Copper, +2
Magnesium, +2
Ammonium, +1
Potassium, +1
Sodium, +1
Calcium, +2
Aluminum, +3
Hydrogen, +1
Cation Retention onOrganic Matter
Low pH, 4 - 5(acidic soil)
Neutral pH, 7(“sweet” soil)
Hydrogen
Nutrients
Increasing pHincreases cation exchange capacity of organic matter
Cation Exchange Capacity• Cation exchange capacity
(CEC) is the total amount of cations that a soil can retain
• The higher the soil CEC the greater ability it has to store plant nutrients
• Soil CEC increases as– The amount of clay increases
– The amount of organic matter increases
– The soil pH increases
Negatively Charged Nutrients(Anions)
• Some very important plant nutrients are anions.
• Soils are able to retain some of these nutrient anions.
• Retention of nutrient anions varies from one anion to another
Nitrate Phosphate Sulfate Chloride
Phosphate retention in soil
+Phosphate Aluminum
Aluminum phosphatesolid
1. Formation of a new solid material
2. Anion exchange
Phosphate
Phosphate retention in soil
Iron oxide surface
Phosphate anions -Each held by two chemical bonds to theiron oxide surface
3. Adsorption on oxide surfaces
Nitrate (NO3-)
retention in soils
If nitrate is not taken up by plants it is very likely to be lost from the soil
Unlike phosphate, nitrate is very weakly held by soils
• Nitrate does not react to form new solids
• Nitrate is not held by oxide surfaces
NO3-
Moving nutrients from soil to plants
PlantRoot
Nutrients on soil clay and organic matter
Nutrients in soil solution
Excessive Nutrient Loading
PlantRoot
Nutrients on soil clay and organic matter
Nutrients in soil solution
Nutrient loss in drainage water
The black box is open• Soil consists of mineral and organic matter,
air and water
• Soils are able to adsorb nutrients and other chemicals
• The most important adsorbers are clay and organic matter
• Adsorbed nutrients are available to plants
• Adsorbed nutrients are not prone to loss in drainage water
• Soil adsorption capacity can be exceeded leading to greater nutrient loss