chapter 20. we live at the bottom of a thin layer of gases surrounding the earth atmosphere the...

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