Tropospheric Pollution Part II:Aerosols - Atmospheric and Oceanic ...

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Tropospheric Pollution Part II:Aerosols - Atmospheric and Oceanic ...

Tropospheric Pollution

Part II: Aerosols

AOS 171

04/04/13


Outline

• Review last class…

• Where do sulfate aerosols come from?

• Natural and man-made

• How are they produced?

• Worldwide production of aerosols

• Climactic Effects of aerosols

• Acid rain

• Summary of Tropospheric Pollution


Tropospheric Ozone

• Result of air pollution from internal

combustion engines and power plants

• Exhaust and emissions release NOx (Nitrous

Oxide gases), SOx (Sulfur Oxide gases), and

VOCs (volatile organic compounds), which are

bi-products of burning gas and coal

• NOx, SOx and VOCs combine chemically with

oxygen to form ozone during sunny warm days


Tropospheric Aerosols

Aerosols enter the lower atmosphere

through...

1) factory and auto emissions (human

induced)

2) agricultural burning (human induced)

3) dust storms, forest fires, sea spray and

volcanoes (naturally)


Sulfate Aerosols

• The majority of these particles come from

the combustion of sulfur containing fossil

fuels


Another Source

• Over the oceans is a major source of sulfate aerosols

• Phytoplankton produce dimethylsulphide gas (DMS)

when they die

• DMS slowly diffuses into the atmosphere where it

oxidizes to form sulfur dioxide, then converts to

sulfate aerosols


Thermoregulation of the planet through

DMS – James Lovelock

• DMS emitted by phytoplankton in sunlight can

create effective cloud condensation nuclei

(CCN) and form clouds

• If there is too much sunlight and CCN, clouds

will shut off the sunlight and DMS formation

so that the clouds will go away and the sun

will come out again


By regulating clouds and sunlight phytoplankton help

keep the planet’s temperature near an equilibrium


Air Quality Standards

• In 2010 the EPA revised the primary SO2

NAAQS by establishing a new 1-hr standard at

a level of 75 ppb


How do sulfate aerosols affect the

temperature of the planet?

• By absorbing and emitting infrared, sulfate

aerosol keeps the nighttime warmer than it

would be without them

• By reflecting sunlight during the day, sulfate

aerosol keep the daytime cooler than it would

be without them


Diurnal Range

• The diurnal range has decreased by more than

1 K in the last century

• In major fossil fuel burning regions, radiative

observations show that anthropogenic aerosol

reflects 2 – 10 W m^2 of solar energy back to

space across N. America and Eurasia


Box model - Sulfur over the eastern U.S.

• Amount of a constituent is a reservoir (kg)

• The flux of a constituent from one reservoir to

another is given in (kg/s)

• 1 Tg = 10^6 tons (the mass of a million cars)

• Smokestacks and vehicles in the eastern U.S.

emit 12 Tg S/yr (flux into the atmospheric

reservoir)

• ~8 Tg S/yr fall back to the ground as acid rain

(flux out of the atmospheric reservoir)


1 Teragram = 1X10^9 kilograms


1 KTonne = 1,000

metric tons


1 Gg (Gigagram) = 1 million kg


1 Gg (Gigagram) = 1 million kg


1 DU = 2.69 10x16

molecules/cm2


Acid Rain

• Rainfall that has been mixed with elements

and gases that have caused the moisture to

become more acidic

• Pure water has a pH of 7

• Generally rainfall has a pH of about 6

• Acid rain can have a pH of 5.0-5.5 and in some

parts of the world it can have a pH of 4


What causes acid rain?

1. Primary emissions of sulfur dioxide (SO2) and

nitrogen oxides (NOx) resulting from fossil fuel

combustion

2. Sulfur in the air combines with oxygen to form

sulfur dioxide (SO2)

3. Car exhaust causes nitrogen oxides in the air

(NOx)

4. From (SO2) and (NOx) airborne sulfuric acid

(H2SO4) and nitric acid (HNO3) can be formed

and dissolved in water vapor


H2SO4 (sulfuric acid)

HNO3 (nitric acid)

Degrades waxy coating

Destroys chlorophyll

Causes necrotic tissue

Mycorrhiza (root hairs) are

killed by acid rain

Nutrients are leached

out of water


Acid rain and statue degradation

• Calcium carbonate, the main component of

marble, is not soluble in water.

• Acids contained in acid rain transform CaCO 3 ,

by chemical reactions, into soluble salts

which are washed away, giving rise to the

formation of holes on the surface of the

artifacts


Sandstone figure over the

portal of a castle in

Westphalia, Germany,

photographed in 1908

(left) and again in 1968

(right)


Tropospheric Aerosols Summary

Aerosols enter the lower atmosphere

through...

1) factory and auto emissions (human

induced)

2) agricultural burning (human induced)

3) dust storms, forest fires, sea spray and

volcanoes (naturally)


Summary

• Anthropogenic aerosol reflects 2 – 10 W m^2

of solar energy back to space across N.

America and Eurasia

• Acid rain - From (SO2) and (NOx) airborne

sulfuric acid (H2SO4) and nitric acid (HNO3)

can be formed and dissolved in water vapor


Next Class…

• Homework 2 is due

• Biodiversity and climate stability

• Gaia hypothesis

• Daisy World

• Chaos Theory and Climate Stability

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