ozone in the upper atmosphere - fremont...

May 18-22 Logan River Academy Chemistry

ENVIRONMENTAL CHEMISTRY

<< REFRESHER >>

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

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

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

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

Molecular Composition

More about “-spheres”

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

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

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

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

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

Outer Regions of the Atmosphere

Processes and Reactions

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

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

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)

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.

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

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

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)

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

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

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)

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

CHEMISTRY OF THE

TROPOSPHERE

(where we live)

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 ...

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

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

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)

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

OCEANSWeather generators

Climate stabilizers

Living reservoirs

The last frontier

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

ELEMENTS in SEAWATER

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

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

OrganicMatter

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

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.

Ni Ca Mg Cu

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

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

ozone in the upper atmosphere - fremont...

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