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					College of Marine Studies

                                      October 4, 1998



 Atmospheric and Oceanic
      Aerosols
            and
              Climate
Magdalena Anguelova
Ph.D. Student           Advisor: Prof. Ferris Webster
                                       Duration: 45 min.
    A sunrise over the China Sea

                                            This photograph
                                            is taken by the
                                            crew of the
                                            Space Shuttle.


       Here the black shadows against the sunlit horizon are
high-peaking clouds. The colorful bands above are atmospheric
layers and their exceptional brightness is due to concentration
of dust in the atmosphere. Dust and other types of particles,
called aerosols, and their effect on climate are the subject of
this poster.
                                                        2 of 52
    Outline
   The big picture - climate elements   (18 screens)
   What are aerosols?                   (2)
   Why are aerosols so important?       (3)
   Aerosol properties                   (3)
   Aerosol types                        (3)
   Aerosol sources and formation        (12)
   Global distribution                  (5)
   Summary
   Hypothesis
                                                3 of 52
   The big picture:
       Sun, Earth, and Atmosphere
  The climate system on our planet is driven by the energy
coming from the sun. The sunlight reaches the Earth through
several atmospheric layers.
    The lowest one, from the
Earth surface to about 7miles                 Thermosphere
height, is called troposphere.
                                                  Mesosphere
     Next layer, from 7 up to
30 miles above the surface, is
called stratosphere.                             Stratosphere
     Mesosphere and
thermosphere follow above                      Troposphere
up to about 50 miles height.
     The layers of interest
for us are those where the aerosols reside:
the troposphere and stratosphere.
                                                         4 of 52
   The big picture:
                                         Sun spectrum
Recall: each body with some temperature emits radiation. We feel the
        radiation emitted from our bodies as heat.
        This law applies to all objects in the Universe.

    Solar spectrum                    The sun is a celestial body with a
                                  temperature of 6000 oC. Objects with such
                                  high temperature emit energy at the so called
               Near IR   Far IR
                                  short wavelengths of the electromagnetic
                                  spectrum visualized like this:

     Visible


  The Sun emission
peaks in the visible
range.
                                                                         5 of 52
    The big picture:
                                   Earth Spectrum
      Solar spectrum               Earth’s spectrum           In contrast, the Earth
                                                         is colder celestial body with
                                                         average surface
                Near IR   Far IR
                                                         temperature of 15oC.



short Visible                                   long          That is why Earth
                                                         emits at longer wavelengths,
Get oriented in Electromagnetic spectrum !               called infrared (IR),
 X-rays in medicine                 Radio broadcasting   visualized like this:
So, remember:
The Sun emits at
      short wavelengths (SW).
The Earth emits at
      long wavelengths (LW).
  The big picture:
          Solar energy at sea level
   Only a part of the SW solar radiation available at the top
of the atmosphere reaches the Earth.
                                      Some of it is scattered,
                                  absorbed and reflected within
                                  the atmosphere by the gases,
                                  aerosols, and clouds.
                               The absorbed radiation is re-
                          emitted by the atmospheric
                          constituents back as a LW radiation,
                          i.e., it is converted in heat.



                                                         7 of 52
     The big picture:
                        Greenhouse effect
         Similar process takes place at the surface of Earth: from the SW
solar radiation (A) left at the sea level, part is absorbed (B)
and then re-emitted back (C) to the atmosphere as LW IR radiation.
   If there were no atmosphere, the IR
radiation emitted by Earth would escape to
the space and the planet would cool down.
   But in presence of atmosphere, some
IR radiation is trapped and re-emitted
back (D) to Earth by naturally occurring
gases as CO2 , H2O vapors, and CH4.

   This is the so called natural greenhouse effect which keeps
the Earth’s surface about 33 oC warmer than it would be if
greenhouse effect were not present.                      8 of 52
     The big picture:
                       Climate System
   How fortunate for all living creatures ! For the natural
greenhouse effect makes our planet habitable. Otherwise the
Earth would be a frigid and inhospitable place.



   The atmosphere sets the greenhouse effect at work, and
the climate system is created. The solar radiation powers it.
     The climate machine does not stop if something goes wrong
in it. If small perturbation in one of the elements appears, e.g.,
a change in solar emission, or a change in ocean shapes due to
plate tectonics, the system tries to readjust to the new
conditions.
                                                           9 of 52
  The big picture:
          Climate System Elements
                                         The main elements
                                      of the climate system
                                      are the atmosphere and
                                      the oceans.
                                         The fast heating
                                      and cooling of land,
                                      the strong reflection
                                      of the sunlight by ice
                                      and snow, the clouds
                                      and precipitation are
   Their interaction with the basic   the other elements of
elements makes the last touches in    this machine.
this almost perfect harmony.                           10 of 52
   The big picture:
                   How does it work?
   The warmth of the Sun is not distributed uniformly over
the globe. It is maximum at the equator and the tropics
and minimum at the polar regions.
   The climate
machine churns
relentlessly
attempting to
smooth out this
temperature
imbalance by cooling
the tropics and
warming the poles.
The wind system and ocean currents do the work.
                                                        11 of 52
The big picture:
                  Winds and Currents
    Unequal heating of the atmosphere sets up convection -
rising of warm air at the tropics and sinking of cold air at high
latitudes.

   This in turn sets
a regular system of
winds called Trades
(or Easterlies)
and Westerlies.
   These, together
with frontal storms,
transfer cold air
equatorward and
warm air poleward.
                                                             12 of 52
    The big picture:
                    Winds and Currents
                                              The winds drag
                                           the water in the
                                           oceans and form a
                                           system of immense
                                           ocean currents.
                                              They transport
                                           cold water toward
                                           the Equator and
                                           warm water to the
                                           poles.
   As a result of this heat transfer, the average temperature
anywhere on the Earth is quite stable over long time period.
                                                        13 of 52
     The big picture:
                            Radiation Budget
  So, on a long-time scale, the climate system is in equilibrium. This
usually is demonstrated with the radiation budget of the planet. Let see:

 The SW radiation coming
to the Earth is 340 W m-2.
                                      Reflected SW = 100 W m-2
 About 30% of it is directly
reflected back to the space.     Incoming SW               Emitted LW
                                 = 340 W m-2               = 240 W m-2
 The remaining 240 W m-2
are absorbed by the Earth-
atmosphere system.
                                                Climate
                                                system
 As the law requires, the same amount
is emitted as LW radiation back to space.     Absorbed SW
   This is the natural and                     = 240 W m-2
                    necessary balance !                             14 of 52
The big picture:
            Troubled Radiation Budget
The trouble is...                  We, humans, are adding
                                   more and more greenhouse
              gases into the atmosphere by burning fossil fuels.
    Even worse, we increase not only the concentration of the
 naturally occurring greenhouse gases, but add unnatural
 greenhouse gases, such as nitrous oxide (N2O) and
 chlorofluorocarbons (CFCs).
   In addition, we cut down thousands of trees for lumber,
making them unable to take CO2 out of the air.
   All this waste in the air is letting less and less heat to go
back to space. And, the more CO2 and other greenhouse
gasses in the atmosphere, the more IR radiation is trapped and
re-emitted back to the Earth, the warmer it becomes with
possible catastrophic effects.                                15 of 52
  The big picture:
                       Global Warming
       This greenhouse effect in excess of the natural one is
termed global warming. Scientists try to model and predict
the effect of global warming. They recalculate the radiation
budget with increased concentration of CO2.
       If the amount of CO2 doubles, the outgoing LW
radiation would decrease by 4 W m-2.
       This imbalance would induce a gradual change in order to
restore the amount of leaving radiation from 236 back to 240
W m-2. This would require an increase in global mean surface
temperature by 1.2 K.
 Instantaneous CO2 Doubling:                And this is
 Emitted LW = 236 W m-2
 Warm by 1.2 K to restore 240 W m-2         a trouble !
                                                         16 of 52
  The big picture:
            Modeling Global Warming
      The current models, however, produce both greater
warming and substantial disagreement: from 1.7 to 5.4 K.
       The main reason for the disagreement stems from the
different depiction of the climate feedback mechanisms in the
models. These can either amplify or moderate the warming.
       E.g., a warmer climate means a warmer atmosphere with
more water vapor, which itself is a greenhouse gas. So, water
vapor provides a positive (or amplifying) feedback mechanism.
Different models generally consent on this particular
feedback.
       The feedback associated with cloudiness, however, turns
out to be much more difficult matter.
                                                        17 of 52
The big picture:
       Radiation Budget Without Clouds
   Let track the radiation budget of a hypothetical planet with the same
surface temperature but without clouds:
 The same coming solar radiation;
 In absence of clouds less
SW radiation is reflected back
to space, only 50 W m-2 instead
of 100 W m-2 ;
 Earth-atmosphere system
absorbs the remaining 290 W m-2,
instead of 240 W m-2;
 At 15 degrees surface temperature
Earth-atmosphere system emits only
270 W m-2 and ...
There is surplus of 20 W m-2 !
Obviously, the clouds balance the system. How?                     18 of 52
   The big picture:
                          Cloud Feedback
    The effect of clouds on the Earth-atmosphere system is termed as
Cloud-Radiative Forcing (CRF).
    We see, the clouds enhance the SW reflection and cool the system by
50 W m-2. In this way the clouds exert negative feedback.
    But they also absorb LW radiation coming from the earth and re-emit
it back. So that simultaneously with the negative the clouds provide also
positive feedback and warm the Earth with 30 W m-2.
   The net result of these two opposite processes is cooling by 20 W m-2.

                 So, Cloud Radiative Forcing (CRF)

    SW CRF = -50 W m-2             closes the balance of absorbed
    LW CRF = 30 W m-2              and emitted radiation.
    NET CRF = -20 W m-2
                                                                    19 of 52
  The big picture:
               Modeling Cloud Feedback
 How exciting ! The cooling by clouds would mitigate the global warming !
  However, the cooling by clouds may change as the climate changes due to
global warming.
  Scientists constructed and ran
                                                     2.0



models again to see how the cloud                    1.5


radiative forcing would change.

                                     Cloud forcing
                                                     1.0


   Here 19 (!) different models                      0.5

show quite different results for
cloud feedback :                                     0.0




from modest cooling                                  -0.5




                                                                  MRI
                                                                CCM0
                                                                CCM1
                                                                BMRC




                                                                 DNM




                                                                 LMD
                                                                  CCC


                                                               CNRM
                                                                  CSU




                                                                 GICC


                                                              OSU/IAP
                                                              ECMWF



                                                                 MGO
                                                              ECHAM

                                                              GFDL II




                                                               UKMO
                                                               GFDL I




                                                            OSU/LLNL
                                                            CCM/LLNL
       through almost missing

               to strong positive.                            Model name

                                                                           20 of 52
   The big picture:
               What about Aerosols?
       The discrepancies in modeling the cloud feedback pointed out
that we need to know well the cloud properties and their global
pattern. So, since the beginning of 90s studies of clouds have priority
and many programs for measuring the global cloud coverage and
properties have been initiated.
You probably ask yourself already impatiently:
   Where in this long story are the aerosols?
   Well, the findings about clouds gradually showed that the cloud
properties and lifetime are significantly affected by aerosols.
    How exactly? It turned out we do not have enough knowledge about
aerosols in order to know how they do that.
        So, for the last 2 years the aerosols, not the clouds, are
     the Gordian knot of the climatic studies.
                                                                     21 of 52
    What are Aerosols?
   Aerosols are minute stable particles, solid or liquid,
suspended in the atmosphere.

   Samples of clean
(rural) and polluted rural site
(urban) air under
microscope show
different particle
shapes (spherical
or arbitrary) and
concentrations.
 For the scale:
   1 m = 10-6 m                            urban site
                                                            22 of 52
      We see Aerosols as...
   Aerosols are too small to be observed by naked eye.
   We do not see the air molecules too.
But we see the result of scattering of
the sunlight by them as blue sky.
   Similarly, the red sunsets and
sunrises are result of scattering and
absorbing of the sunlight by aerosols.
    The red color comes from the fact that
the aerosols are larger than the air molecules
and scatter more effectively the red light
than the blue one.
   Another manifestation of the
presence of aerosols is haze.                            23 of 52
Why are Aerosols so Important?
   Atmospheric aerosols influence the climate in two ways:
 directly - through the reflection and absorption of solar
                 radiation. The mechanisms are well understood:
     scattering of coming SW solar radiation back to space;
     absorption of coming SW solar radiation.
     In both cases less radiation reaches and heats the Earth,
i.e., the aerosols cool the Earth-atmosphere system.
 indirectly - through modifying the optical properties and
                lifetime of clouds.
   Aerosols act as cloud condensation nuclei (CCN) on which
H2O vapors in the atmosphere condense and form cloud
droplets. Two scenarios are at work:                    24 of 52
   Cloud/Aerosol Scenarios
   When there are more aerosols (i.e., more CCN), more
droplets form in the cloud. We observe:
                 1) more surface available to reflect the light.
                 Net result: cloud albedo (reflection) increases.

                                      2) inhibition of the
                                      growth of the existing
                                      droplets, hence
                                      condensation and rain
                                      are delayed.


                    Net result: prolonged cloud lifetime.
                                                          25 of 52
   More Roles for Aerosols
   Aerosols act as sites for chemical reactions to take place.
The most significant example: destruction
                                     of stratospheric ozone.
                               During winter in the polar regions,
                             aerosols grow to form polar
                             stratospheric clouds.
                              The cloud particles provide huge
                             surface area for chemical reactions.
                               These reactions lead to the formation
                             of large amount of reactive chlorine,
                             which ultimately leads to destruction of
                             the ozone in the stratosphere.
                                Increased aerosol pollution from 1979
                         to 1989 resulted in ozone hole over Antarctic.
                                                               26 of 52
      Aerosol Properties
The effect of aerosols on climate is termed aerosol radiative forcing.
   To estimate aerosol radiative forcing we need to know
which aerosol properties control the different processes.
   Aerosols represent only a small part of the mass of the atmosphere.
Yet, they have the potential to influence the heat budget of the planet.
  The reason is that most processes involving aerosols are
controlled by the aerosol surface, not by the aerosol mass.
That is, many small particles do better than few large.
Thus, the most important aerosol properties are:
              size and shape
              concentration
and
              lifetime                                             27 of 52
Aerosol properties:
             Size and Shape
                  Typical distribution of aerosol mass and
                  number by size.

                  We see 2 peaks over coarse
                                  and fine particles.
                    The size controls the physical
                 and chemical processes !
                 Particles with diameter:
                 • 0.01 - 0.05 m act as cloud nuclei;
                 • 0.08 to 0.5 m accumulate mass;
                 • 0.1 - 2 m efficiently scatter the light;
                 • above 1 m provide medium for chemical
                         reactions.
                                                    28 of 52
Aerosol properties:
     Concentration and Lifetime
Concentration is defined as the total number of particles
                                   per unit volume;
             Concentration changes with height and site,
             being higher where the aerosols form:
             • look - there are more aerosols close to the Earth
             surface, and their number decreases with height;
             • there are more aerosols close to the continents,
             and their number decreases in remote oceanic places.

                       Lifetime is the time aerosols reside in the
                       atmosphere before being removed by
                       precipitation or conversion in something else;
                Aerosol lifetime ranges from 2-3 years to 3-5 days;
                Most aerosols are short-lived.              29 of 52
 Aerosol Types
There are many types of aerosols
                          classified by different criteria.

Depending on their size aerosols are (we already know this):
   coarse and fine;
Depending on their source aerosols are:
   • natural - produced by volcanic emission or oceans;
   • anthropogenic - result of the human activities;
Depending on their mechanism of formation aerosols are:
   • primary - delivered to the atmosphere directly as particles;
   • secondary - formed within the atmosphere from gases;
Depending on their residence site aerosols are:
   tropospheric and stratospheric
                                                           30 of 52
  Aerosol Types:
                   Natural Aerosols
 Examples of natural aerosols are:

        Primary
(formed directly as particles)
                                     Most numerous are

Soil dust (mineral aerosol)
Sea salt                             Secondary
Volcanic dust             (formed in the atmosphere from gases)
Organic aerosols
                            Sulfates from biogenic gases
                            Sulfates from volcanic SO2
                            Organic matter from biogenic C
                            Nitrates from NOx
Let talk about some of these !
                                                           31 of 52
Natural Aerosols:
                           Soil Dust Sources
    Major sources of soil dust are arid regions such as deserts of Northern
Africa and Asia. One of the largest source is Sahara desert.
This photograph is a good example: We see a dust storm north of Arabian
                                                    Sea - a basin surrounded
                                                    by arid terrain. The area
                                                    joining Iran, Afghanistan
                                                    and Pakistan experiences
                                                    the highest frequency of
                                                    dust storms in the world:
Imagine, this                                       over 30 dust storms per
                                                    year.      As a result,
village endures                                      the deposition rate of
such a mess                                          mineral aerosols in the
twice, sometimes                                     Indian Ocean is more
more, a month !                                      than 5 times any other
                                                     region of the world
                                                     oceans.           32 of 52
Natural Aerosols Formation:
                                  Soil Dust Lifting
   The number of aerosols delivered by extreme events as dust storms
dominates the number of aerosols created by continuous lower wind.
   Though the particles produced in this way are relatively large, they are
found all over the globe: the strong winds lift them at high altitudes and
the atmospheric circulation transports them over thousands of kilometers.
                                          There are 4 mechanisms of
                                          detachment and lifting of
                                          soil particles by wind:
                                         (a) creeping - one large particle
                                         bounces several times creating many
                                         smaller particles;
                                         (b) turbulent lifting - strong
                                         wind projects particles directly in air;
                                         (c) surface collision;
                                         (d) soil splashing.             33 of 52
  Natural Aerosol:
    Source of Sea                  Salt Aerosols
    On a windy day, when even a skillful Hawaiian surfer may
flip, the ocean is covered with whitecaps. Whitecaps are the
major source for sea salt particles. They produce numerous
drops, which evaporate, shrink to a smaller size, and form sea
salt aerosols.
                                       Interestingly enough, the
                                    vast oceans produce a bit
                                    less aerosols than deserts
                                    produce dust.
     The reason is that the formation of sea salt drops,
parenting the sea salt aerosols, includes several processes
requiring more energy than mere lifting of a dust particle.
   Let see these processes.
                                                          34 of 52
   Natural Aerosol Formation:
                                               Sea Salt
Air entrained into the water after wave breaking creates bubble clouds.
The large bubbles rise to the surface and burst.
Their caps shatter in thousands small droplets called film drops.

Upon bursting, bubble cavity collapses, a water jet
rises from its bottom, and several small drops,
called jet drops, are pinched from the tip.

Under high winds so called spume drops
are torn from the crests of breaking
waves and blown directly into the air.

Least drops are formed by
splashing mechanism, when
some small unstable projections
of water form drops.
                                                                   35 of 52
        Natural Aerosol:
                                Volcanic dust
   This photograph of the eruption of Mt. St. Helens in 1980 is a
good example for the huge clouds of ash particles and gases, including
sulfur dioxide, that volcanoes blast into the atmosphere as they erupt.
                                 Short-term global cooling often has been
                             linked with such events.
                                The year 1816 has been referred to as “the
                            year without a summer.” It was a time of
                            significant weather disruption in New England
                            and in Western Europe with killing summer
                            frosts in the United States and Canada.
                                The unusual weather was attributed to a
                            major eruption of the Tambora volcano in 1815
                            in Indonesia.
                                The volcano threw sulfur dioxide gas into
                            the stratosphere, and the aerosol layer that
                            formed led to brilliant sunsets seen around
                            the world for several years.             36 of 52
    Natural Aerosol:
                Cooling by Volcanic Dust
   Aerosols in atmosphere increase after major eruptions
  The relative global cooling of 1993 is ascribed to the eruption of Mount
Pinatubo in 1991. Several weeks after spreading of volcanic dust across the
Pacific, the sulfur dioxide had spread all over the world.
The red color shows maximum aerosol                  Not all large volcanic
                                                  eruptions produce global-
concentration                                     scale cooling. Mount Agung in
                                                  1963 caused a considerable
                                                  decrease in temperatures
                                                  around much of the world,
                                                  whereas El Chichón in 1982
                                                  seemed to have little effect.
                                                 It is believed the 1982 El
                                             Niño cancelled out the effect of
                                             the El Chichón eruption.
SO2 cloud from Mt. Pinatubo, September 23, 1991                       37 of 52
      Natural Aerosol Formation:
                                   Volcanic dust
   Millions of tons of ash and SO2 gas can reach the stratosphere from a
                                                     major volcano.
                                                         The ash is soon
                                                     washed out by rain.
                                                         SO2 stays and
                                                     under the action of
                                                     light converts to tiny
                                                     aerosols of sulfuric
                                                     acid.
                                                        These aerosols are
                                                     persistent, and after
                                                     the stratospheric
                                                     winds spread them
                                                     over the globe, they
These particles reflect the sunlight,                stay there for several
thereby cooling the Earth.                           years.
They grow slowly and are regularly removed by rain for a long time.
                                                                   38 of 52
Natural Aerosols:
       Sulfates and organic matter
    The living creatures in the oceans and on land are involved
in the creation of organic aerosols and sulfates.
                                      Bubble bursting in oceans and
                                   burning of terrestrial vegetation
                                   deliver organic carbon and other
                                   particles.
                                      Phytoplankton in the oceans
                                   emits gas called Dimethylsulphide
                                   (DMS). DMS is transferred into
                                   the atmosphere where organic
                                   aerosols form by gas-to-particle
The biosphere from satellites.     conversion.
    Emissions of natural organic aerosols from
 oceans dominate the terrestrial sources.
                                                             39 of 52
   Aerosol types:
             Anthropogenic Aerosols
 Examples of anthropogenic aerosols are:

        Primary
(formed directly as particles)
                                         Most numerous are

Industrial aerosols
Biomass burning
                                      Secondary
Soot                        (formed in the atmosphere from gases)
                             Sulfates from industrial SO2
                             Organic matter from biogenic C
                             Nitrates from NOx

Let talk about some of these !
                                                                40 of 52
Anthropogenic Aerosols:
   Sources of Industrial Pollution
                  The primary industrial aerosols originate from inorganic
                these sources increase or
            Allimpurities in the fuel we use : from incomplete fuel
               combustion.
                • carbon dioxide (CO )  2
                • methane (CH4)
                • nitrous oxide (N2 O)
                • halocarbons (CFCs)
Airplanes and factories
               Most dangerous are the sulfate aerosols
release water vapor
            formed from these gases, because they are
forming additional
            persistent.
clouds and reflecting
the incoming sunlight.
               About 90% of the sulfur emissions are
                  Recent estimates show that
                   industrial able to change Plants, cars,
            fromcontrails are regions in the Northern and aircraft
            hemisphere. locally in regions emit directly soot, and
                  the climate
                  with heavy airplane traffic. nitrogen oxides.
                                                                41 of 52
Anthropogenic Aerosols:
Biomass Burning - natural and...
 Biomass burning refers to the burning of the world's forests,
                   grasslands, and agricultural lands. It
                   releases significant quantities of gases and
                   particles into the atmosphere.
                 There are natural fires like this one in
                 Arizona, but it is generally believed that
                 most biomass burning
                 is human-initiated.
                   The oil fires
                 in Kuwait is one
                 such example.
The Hochderffer fire,
Coconino National Forest, AR                             42 of 52
Anthropogenic Aerosols:
    Man-initiated Biomass                    Burning
   The biomass burning has increased significantly over the
last century. Regular measurements and monitoring from
space helped in the last few years to understand that biomass
burning is much more widespread than previously thought.
   Biomass burning is a
 widespread practice
 for land clearing and
 land use change such as
 conversion of forest
 regions to grazing and
 agriculture areas.


   Roughly 175 million acres of forest and grassland are
burned each year world-wide.
                                                           43 of 52
Anthropogenic Aerosols Formation:
                                      Biomass Burning
   Combustion gases include CO2, CO, hydrocarbons, NxO, etc. CO2 and CH4
are direct addition to the greenhouse gases. The other gases are chemically
active and impact the composition and chemistry of the troposphere, leading
to destruction of ozone.
      80% of the total
biomass burning occurs
in tropical rain forests      2/3 of the
and savanna grasslands        Earth's savannas
                              are located in
                              Africa,
                              recognized as the
                              "burning center"
                              of the planet.
   Biomass burning extends to fire-free regions as
smoke and aerosol particles rise high into the
troposphere and are carried long distances by winds.               44 of 52
  Aerosol global distribution
  Satellite observations reveal that there is no "global aerosol" that fills
the troposphere with a uniform background aerosol.

  • The global aerosol distribution is a collection of independent aerosol
  regions each having its own source and unique spatial temporal pattern.

  • Marine aerosols dominate large areas, but continental aerosol plumes
  show more intense reflection of sunlight. Hence, the aerosol impact
  over the continents is likely to be much higher than over the oceans.

  • The aerosol reflection is strongest in the Tropics where most of the
  solar radiation is absorbed and aerosol-cloud interactions are intense.

  • There is a pronounced seasonality in each aerosol region; the higher
  aerosol levels appear in the summer.

                                                                      45 of 52
 Aerosol global distribution:
                       Oceanic aerosol



                          summer                            winter
   Indeed, aerosols are concentrated in the Tropics and their reflection is
higher in summer than in winter.
                                    Even more aerosols are present
                                 during phytoplankton bloom in spring.




                     spring
                                                                     46 of 52
  Aerosol global distribution:
                      Oceanic CloudCondensationNuclei
Recall: the more aerosols, the more nuclei for forming cloud drops (CCN).
   We see, most CCN are around the continents where the aerosols
produced by human activity are most.




                                                                    47 of 52
Aerosol global distribution:
 Continental aerosol over oceans
                      Once again the same seasonal
                    pattern: more aerosols in summer
                    than in winter.
                      Note 2 places we considered:
           winter   • The pronounced plume from
                    Africa - Sahara and savanna fires
                    produce enormous quantity of
                    aerosols;
                    • Indian ocean - the arid areas
                    around Arabian sea with strong
           summer   dust storms.

                                                48 of 52
 Aerosol global distribution:
                         Volcanic aerosols
   This is animation showing the spreading of aerosols after 3
volcano eruptions in period 1985 - 1997; rate - every 3 months.
Red: high aerosol reflection.
Eruptions :
• Nevado del Ruiz, Columbia, 1985
Most of the volcanic aerosols were
high in the stratosphere and
remained obvious for several years.
• Kelut, Indonesia, February, 1990
small increase;
• Mt. Pinatubo, 1991: the
dominant event in this animation,
aerosols in stratosphere
increased by a factor of 30.
                                                         49 of 52
Aerosol global distribution:
                         Sulfur emissions
  As expected, the industrial regions are the major sources of
anthropogenic sulfate aerosols.




                                                        49 of 52
   Summary
• Aerosols influence the climate
   directly via scattering of sunlight
   indirectly via changing clouds’
          optical properties
• Aerosols provide medium for chemical
         reactions in the atmosphere
• Aerosols are unevenly distributed over the
         globe
• Aerosols are short lived with exception of
         the volcanic dust               50 of 52
   Hypothesis
      There is a hypothesis: aerosol cooling,
mainly due to man-produced sulfates, may
cancel the effect of global warming.
      Calming but not yet proven idea…
      While uniformly distributed greenhouse
gases over the globe may cause global
warming, the uneven aerosol distribution may
only cool places here and there. This may
still be not enough to outweigh the warming.
        We have much more work to do ...   51 of 52
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