chapter 20. we live at the bottom of a thin layer of gases surrounding the earth atmosphere the...
TRANSCRIPT
Chapter 20
We live at the bottom of a thin layer of gases surrounding the earth• Atmosphere
The Atmosphere is made up of several layers
We live in the troposphere Above the troposphere is the
stratosphere
Troposphere 1st layer of
atmosphere Extends 11 miles
above Earth 78% N, 21% O Chemical cycling of
nutrients happens here
Weather & Climate happen here
Water vapor present
Stratosphere 2nd layer of
atmosphere Extends from 11 – 30
miles above Earth’s surface
More ozone (O3) present here
Less water vapor
Atmospheric Pressure• A measure of the mass per unit of air
Pressure of atmosphere increases at the density increases• A volume of air with a high density has more
gas molecules than air at a lower density (D = m/v)
• Atmospheric pressure decreases with altitude Ex: At sea level, your body is bombarded with more
gas molecules than your body would be at the top of a mountain
In the diagram, notice that as altitude decreases, the atmospheric pressure increases.
Another graph: As altitude decreases, atmospheric pressure increases.
Ozone (O3) • Found in 2nd layer
of atmosphere (stratosphere)
• Filters our most of the sun’s harmful UV rays Ultraviolet rays –
dangerous to organisms, can cause cancer
• Created when oxygen molecules interact with UV radiation emitted by the sun
How ozone is created
Air Pollution• Presence of chemicals in the atmosphere in
concentrations high enough to affect climate and harm organisms
• Range from annoying to lethal Sources
• Majority of air pollution comes from natural sources
• Ex: dust blowing across the land; organic chemicals released by plants, forest fires, volcanic eruptions, and sea spray
Primary Pollutants• Pollutants emitted directly into the
troposphere in a potentially harmful form Ex: soot, carbon monoxide (CO)
Secondary Pollutants• When some primary pollutants react with
one another or with the air to form a new pollutant Ex: SO2, H3SO4
U.S. cities typically have higher outdoor pollution levels than rural areas
Due to prevailing winds, the city pollutants are spread to rural areas
Indoor air pollutants come from infiltration of outdoor pollutions into the building
Most people believe CO2 is a pollutant
EPA (Environmental Protection Agency)disagrees
• Too much pressure from oil and coal companies?
• Repercussions if listed as pollutant by EPA?
CO2 IS a pollutant because:
1) It’s found in high concentrations in the air• ANY chemical in high concentrations in the air can become
a pollutant
2) We have been increasing CO2 concentrations in the troposphere by burning fossil fuels & clearing CO2-absorbing trees faster than they can grow back• No way to get rid of CO2
3) The troposphere is warming & there is considerable evidence that additional CO2 added by humans is the cause• Greenhouse gas – warms the Earth
UV Rays http://
www.youtube.com/watch?v=np-BBJyl-go
Air Pollution http://
www.youtube.com/watch?v=e19VoA2SApM&feature=related
Photochemical reaction
Any chemical reaction activated by light (photo= light)
Ex: Photochemical smog
Photochemical smog
• A mixture of air pollutants formed by the reaction of nitrogen oxides (NO and NO2 )and volatile organic hydrocarbons
• Activated by light
Photochemical Smog formation
Smog pollutants: NO2, NO3 (nitrogen
oxides) Ozone Nitric acid Aldehydes Peroxyacyl nitrates
(PANs)
Sources of smog pollutants:
Automobile engines Coal-burning plants Industrial plants Vegetation
Certain trees & plants can contribute to photochemical smog
Ex: oak, sweet gums, poplars, kudzu
They release volatile organic compounds (VOCs)• Ingredient in smog
Trees planted in nonurban areas release their VOCs, which are dispersed into the atmosphere• They do not make a significant contribution to
the formation of photochemical smog Trees planted in / near urban areas with
high levels of NOx (nitrogen oxides) and sunlight, will create high levels of VOCs
Environmentalists’ view: widespread planting of trees in urban areas BUT only those who emit low VOCs
Industrial smog• A mixture of sulfur
dioxide, droplets of sulfuric acid, and a variety of particles emitted by burning coal and oil
• When burned, carbon in coal and oil is converted to CO2 and CO Some of this ends up
in atmosphere as ingredient of smog
Industrial smog• Also known as: gray-air-smog
Not a big problem in developed countries• Good pollution control when coal & oil are
burned It IS a big problem in industrialized
urban areas of:• China, India, Ukraine, Slovakia, Poland,
Hungary, and Czech Republic
Factors that decrease outdoor air pollution:• Precipitation
Rain & snow help to cleanse the air, lowering pollution
• Sea Spray Can wash out particulates & water-soluble pollutants
from air that flows from land onto the oceans• Wind
Can sweep pollutants away or dilute them Pollutants are blown somewhere else Can be deposited onto surface waters, soil, buildings
Factors that increase outdoor air pollution:• Urban buildings
Slow wind speed Reduce dilution / removal of pollutants
• Hills and Mountains Reduced the flow of air in valleys below them
Allows pollutants to build up at ground level
• High temperatures Promote chemical reactions leading to photochemical smog
• Grasshopper effect Transfers air pollutants from tropical / temperate areas to
the earth’s poles Reason for high levels of pollutants, decreasing ozone in
poles
Keep in mind that the warm air rises in the temperate / tropical areas and will condense once it reaches the colder temperatures (earth’s poles).
Temperature Inversion• Occurs when cool, dense air is trapped under a
warm, less dense air• These two air masses do not mix• As a result, pollutants in the air can be
concentrated in the lower layer of cool air (closest to the earth)
Effects of temperature inversion
Asian brown cloud (industrial smog) 2 miles thick Caused by huge emissions of ash,
smoke, dust, acidic compounds (from burning coal), burning trees (to plant crops), dust blowing from desserts
As the cloud travels it picks up many pollutants
Impacts: Effects the amount of solar energy hitting
earth• Impacts of crop production• Damage trees• Can kill organisms in lakes
Illnesses & premature deaths• Respiratory diseases
Particles in cloud are causing climate change• Changes temperature pattern, rainfall shifts• Can effect El Nino (which could affect North & South
America)
South Asia’s Brown Cloud
Acid deposition / acid rain:• Mixture of wet deposition & dry deposition• Wet deposition: acid rain, snow, fog, cloud
vapor pH is less than 5.6
• Dry deposition: acidic particles
Composed of:• Sulfur dioxide (SO2)• Nitrogen oxides (NO2 and NO)• Particulates
Acid Deposition / Rain
Some soils contain chemicals which buffer acidic deposition / rain:• Calcium carbonate
(CaCO3)• Limestone
Chemicals neutralize acids• Bring pH closer to 7
Harmful effects of acid deposition / rain:• Human respiratory diseases
Bronchitis, asthma
• Can leach toxic chemicals into drinking water Lead, copper
• Damages statues, monuments, buildings, metals Including car finishes, eats away / dissolve certain types of
rock
• Can kill aquatic life if pH drops too low
• Acid shock Damage to aquatic life due to runoff of large
amounts of highly acidic water
Effects of acid rain on plants and soil:• Can deplete soil nutrients
Calcium and Magnesium
• Release toxic ions into the soil
• Weaken plants If pH of soil drops below 5.1
• Calcium deficiencies in plants can be passed to the organisms who eat them Ex: birds eating these plants could have problems with
egg production (shell made of calcium)
Synergistic effect• When the interaction of two or more factors’
combined effect is greater than the sum of their separate effects
Clean Air Act
• Has helped reduce some of the harmful impacts of acid deposition
Solutions to acid deposition:
Prevention (BEST solutions)• Improve energy efficiency• Reduce coal use or burn low-sulfur coal• Increase natural gas use and renewable energy• Remove SO2 particulates and NOx from smokestack
gases• Fees for SO2 emissions
Cleanup• Add lime or phosphate fertilizer to neutralize acidified
lakes
Controlling acid deposition / rain is a challenge:• The people who cause acid rain and the people
or ecosystems affected by it are quite distant
• Countries with large supplies of coal (which produces acid rain) want to use coal for energy
• Coal-burning power plants say it’s too costly to install equipment to reduce harmful emissions
Environmentalists idea- Use alternative energy sources (wind turbines, natural gas)
Cleanup of acid rain in lakes & soil• Add limestone (or lime) to neutralize• Called “liming”
• Problems: Expensive Needs to be repeated annually (temporary fix) Can kill some aquatic plants, plankton, wetland
plants
• Possible solution: Add phosphate fertilizer to neutralize Effectiveness still being evaluated
Thermal Inversion demonstrationhttp://www.youtube.com/watch?v=LPvn9qhVFbM Thermal Inversion in the real worldhttp://www.youtube.com/watch?v=pkOuBUXwiyA Asia’s Pollution Super Cloudhttp://www.youtube.com/watch?v=qYYK-2sDN4U Coal combustion & Acid Rainhttp://www.youtube.com/watch?v=HE6Y0iEuXMQ
Go to hippocampus link
On the left-hand side of the screen click “Earth Science”
Click “Environmental Science for AP”
Scroll down the middle of the page
Watch the following videos:• Earth’s atmosphere• Ozone• Photochemical smog• Air pollution