Particles and Clouds
Cloud albedo forcing, Cooling
The shortwave
rays from the
Sun are
scattered in a
cloud; many of
the rays return to
space,The
resulting "cloud
albedo forcing”,
taken by itself,
tends to cause a
cooling of the
Earth.
Cloud Greenhouse Forcing,Warming
Longwave radiation
When a cloud absorbs longwave radiation emitted by the Earth's
surface,the cloud re-emits a portion of the energy to space and a
portion back toward the surface,This process is called "cloud
greenhouse forcing" and,taken by itself,tends to cause a heating or
"positive forcing" of the Earth's climate.
Overall effect of all clouds
? Cloud albedo forcing ? cooling
? Cloud greenhouse forcing ? warming
? The overall effect of all clouds together is that
the Earth's surface is cooler than it would be if
the atmosphere had no clouds
? The dominate factor in the global albedo is
clouds.
Aerosol,Definition
? Aerosol is a suspension of solid or liquid particles in a gas.
? Atmospheric aerosols consist of small particles of liquid
and solid material suspended in the air.
? Bioaerosol,An aerosol of biological origin,(Examples,
viruses,bacteria,fungi,spores,and pollens.)
? Aerosol sizes are usually measured in the unit of
micrometer (mm)
– 1 mm = 10–6 m
– 1 mm = 104 angstrom (?)
Typical Particle Diameters (mm)
Photochemical aerosols 0.01-1
Tobacco smoke 0.25
Coal fly ash 1-50
Flour dust 15-20
Pollens 15-70
Human hair,~25-100 mm
Example images of atmospheric particles
Source,http://www.mpch-mainz.mpg.de/~kosmo/
Aerosol sources
Aerosol sources
? Windblown dust from Desert
? Sulfate aerosol from volcano eruption,fuel
combustion and microbial activities.
? Seasalt aerosol from seaspray and bubble
bursting
? Soot from fuel combustion
? Secondary organic aerosol from volatile
organic compounds
Aerosol Radiative Forcing,direct effect
? The effect of aerosol on the energy flux of
the atmosphere depends on particle size and
composition.
– Dark particles (soot–containing) tend to
absorb light,thus warming Earth’s
atmosphere.
– Small particles tend to scatter light,thus
increasing the albedo of the atmosphere.
Aerosol and cloud condensation nuclei (CCN)
? Cloud Condensation Nuclei (CCN) are particles
that can become activated to grow to fog or
cloud droplets in the presence of a
supersaturation of water vapor.
? If the Earth’s atmosphere were totally devoid of
particles,clouds could not form.
Aerosol radiative forcing,indirect effect
An increase in the
number of
atmospheric particles
would increase the
number of cloud
condensation nuclei,
therefore more cloud
cover and higher
albedo Ship tracking phenomenon
Volcanoes and climate change
Large volcano
eruptions provide
dramatic evidence
of the ability of
aerosols to affect
global climate.
Mt,Pinatubo eruption made 1992 the
coolest year since 1986
Red line,modeled temperature changes
Blue line,temperature changes observed from
meteorological ground stations
Volcanic Cooling
Large volcanic eruptions can cool the Earth by
increasing the albedo,Calculate the expected
temperature change if the albedo increases from 30
to 30.5 percent,Compare this estimate with the
temperature record after the Mt,Pinatubo eruption.
(Textbook,pp150).
1816-the year without a summer
? In 1815,Tambora in Indonesia exploded and the
volcano dust blanketed the Northern Hemisphere.
? The following year,1816,daily minimum
temperatures were abnormally low in the northern
hemisphere from late spring to early autumn.
? Famine was widespread because of crop failures,An
estimated 82,000 were killed indirectly by the
eruption by starvation,disease,and hunger,
Sulfate aerosol formation from volcano
eruptions
? Large amount of SO2 is injected into the atmosphere
from the force of the volcano eruption.
? SO2 can be converted to sulfate in gas and aqueous
phase.
? In gas-phase
SO2 +,OH + M ? HOSO2,+ M
HOSO2,+ O2 ? HO2,+ SO3
SO3 + H2O + M ? H2SO4 + M
Sulfate aerosol formation from volcano
eruptions (Continued)
? In aqueous phase,dissolved SO2 is oxidized to
sulfate by
– O3 (dominant pathway when pH>5)
– H2O2 (dominant pathway when pH<5)
– organic peroxides
– O2 catalyzed by iron and manganese
? The oxidation of SO2(aq) by H2O2 proceeds as
follows:
– HSO3- + H2O2 ? SO2OOH- + H2O
– SO2OOH- + H+ ? H2SO4
Sulfate formation from biogenic gases
? Dimethylsulfide (DMS),CH3SCH3
– Marine origin
– Produced in plankton by the enzymatic cleavage
of dimethylsulfonopropionate,a compound that
help plankton achieve osmotic balance in the salty
ocean water.
– Oxidation of DMS?SO2 ? sulfate
? H2S
– Terrestrial origin
– Produced by sulfate-reducing bacteria.
Example,Kuwait Oil Fires
? Air temperatures below the
plumes were reported to be
about 7oC lower than in
adjacent areas without smoke,
? Coldest May in 35 years,
? Average temperatures were
about 4oC lower than normal,
Aerosol Effects on Climate
Direct Effects
? Aerosols scatter and
absorb visible and
infrared radiation
? Overall effect,
cooling
? Light scattering
depends on size
distribution and
index of refraction of
the particles
Indirect Effects
? Serve as Cloud
condensation nuclei
? More CCN leads to more
cloud cover
? Possible effects include
changes in Earth's
albedo and changes in
hydrological cycle
Cloud albedo forcing, Cooling
The shortwave
rays from the
Sun are
scattered in a
cloud; many of
the rays return to
space,The
resulting "cloud
albedo forcing”,
taken by itself,
tends to cause a
cooling of the
Earth.
Cloud Greenhouse Forcing,Warming
Longwave radiation
When a cloud absorbs longwave radiation emitted by the Earth's
surface,the cloud re-emits a portion of the energy to space and a
portion back toward the surface,This process is called "cloud
greenhouse forcing" and,taken by itself,tends to cause a heating or
"positive forcing" of the Earth's climate.
Overall effect of all clouds
? Cloud albedo forcing ? cooling
? Cloud greenhouse forcing ? warming
? The overall effect of all clouds together is that
the Earth's surface is cooler than it would be if
the atmosphere had no clouds
? The dominate factor in the global albedo is
clouds.
Aerosol,Definition
? Aerosol is a suspension of solid or liquid particles in a gas.
? Atmospheric aerosols consist of small particles of liquid
and solid material suspended in the air.
? Bioaerosol,An aerosol of biological origin,(Examples,
viruses,bacteria,fungi,spores,and pollens.)
? Aerosol sizes are usually measured in the unit of
micrometer (mm)
– 1 mm = 10–6 m
– 1 mm = 104 angstrom (?)
Typical Particle Diameters (mm)
Photochemical aerosols 0.01-1
Tobacco smoke 0.25
Coal fly ash 1-50
Flour dust 15-20
Pollens 15-70
Human hair,~25-100 mm
Example images of atmospheric particles
Source,http://www.mpch-mainz.mpg.de/~kosmo/
Aerosol sources
Aerosol sources
? Windblown dust from Desert
? Sulfate aerosol from volcano eruption,fuel
combustion and microbial activities.
? Seasalt aerosol from seaspray and bubble
bursting
? Soot from fuel combustion
? Secondary organic aerosol from volatile
organic compounds
Aerosol Radiative Forcing,direct effect
? The effect of aerosol on the energy flux of
the atmosphere depends on particle size and
composition.
– Dark particles (soot–containing) tend to
absorb light,thus warming Earth’s
atmosphere.
– Small particles tend to scatter light,thus
increasing the albedo of the atmosphere.
Aerosol and cloud condensation nuclei (CCN)
? Cloud Condensation Nuclei (CCN) are particles
that can become activated to grow to fog or
cloud droplets in the presence of a
supersaturation of water vapor.
? If the Earth’s atmosphere were totally devoid of
particles,clouds could not form.
Aerosol radiative forcing,indirect effect
An increase in the
number of
atmospheric particles
would increase the
number of cloud
condensation nuclei,
therefore more cloud
cover and higher
albedo Ship tracking phenomenon
Volcanoes and climate change
Large volcano
eruptions provide
dramatic evidence
of the ability of
aerosols to affect
global climate.
Mt,Pinatubo eruption made 1992 the
coolest year since 1986
Red line,modeled temperature changes
Blue line,temperature changes observed from
meteorological ground stations
Volcanic Cooling
Large volcanic eruptions can cool the Earth by
increasing the albedo,Calculate the expected
temperature change if the albedo increases from 30
to 30.5 percent,Compare this estimate with the
temperature record after the Mt,Pinatubo eruption.
(Textbook,pp150).
1816-the year without a summer
? In 1815,Tambora in Indonesia exploded and the
volcano dust blanketed the Northern Hemisphere.
? The following year,1816,daily minimum
temperatures were abnormally low in the northern
hemisphere from late spring to early autumn.
? Famine was widespread because of crop failures,An
estimated 82,000 were killed indirectly by the
eruption by starvation,disease,and hunger,
Sulfate aerosol formation from volcano
eruptions
? Large amount of SO2 is injected into the atmosphere
from the force of the volcano eruption.
? SO2 can be converted to sulfate in gas and aqueous
phase.
? In gas-phase
SO2 +,OH + M ? HOSO2,+ M
HOSO2,+ O2 ? HO2,+ SO3
SO3 + H2O + M ? H2SO4 + M
Sulfate aerosol formation from volcano
eruptions (Continued)
? In aqueous phase,dissolved SO2 is oxidized to
sulfate by
– O3 (dominant pathway when pH>5)
– H2O2 (dominant pathway when pH<5)
– organic peroxides
– O2 catalyzed by iron and manganese
? The oxidation of SO2(aq) by H2O2 proceeds as
follows:
– HSO3- + H2O2 ? SO2OOH- + H2O
– SO2OOH- + H+ ? H2SO4
Sulfate formation from biogenic gases
? Dimethylsulfide (DMS),CH3SCH3
– Marine origin
– Produced in plankton by the enzymatic cleavage
of dimethylsulfonopropionate,a compound that
help plankton achieve osmotic balance in the salty
ocean water.
– Oxidation of DMS?SO2 ? sulfate
? H2S
– Terrestrial origin
– Produced by sulfate-reducing bacteria.
Example,Kuwait Oil Fires
? Air temperatures below the
plumes were reported to be
about 7oC lower than in
adjacent areas without smoke,
? Coldest May in 35 years,
? Average temperatures were
about 4oC lower than normal,
Aerosol Effects on Climate
Direct Effects
? Aerosols scatter and
absorb visible and
infrared radiation
? Overall effect,
cooling
? Light scattering
depends on size
distribution and
index of refraction of
the particles
Indirect Effects
? Serve as Cloud
condensation nuclei
? More CCN leads to more
cloud cover
? Possible effects include
changes in Earth's
albedo and changes in
hydrological cycle
