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