Atmospheric Atmospheric and and OceanicOceanic

AerosolsAerosols and and

ClimateClimateMagdalena AnguelovaMagdalena AnguelovaPh.D. Student Advisor: Prof. Ferris Webster

October 4, 1998

College of Marine StudiesCollege of Marine Studies

Duration: 45 min.

Here the black shadows against the sunlit horizon arehigh-peaking clouds. The colorful bands above are atmosphericlayers and their exceptional brightness is due to concentrationof dust in the atmosphere. Dust and other types of particles, called aerosols, and their effect on climate are the subject of this poster.

A sunrise over the China Sea

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

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OutlineOutline 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

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TroposphereStratosphere

MesosphereThermosphere

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 height, is called troposphere. Next layer, from 7 up to 30 miles above the surface, is called stratosphere. Mesosphere and thermosphere follow above up to about 50 miles height.

The layers of interest for us are those where the aerosols reside:

TroposphereStratosphere

the troposphereand stratosphere.4 of 524 of 52

The big picture: Sun spectrum

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

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.

The Sun emission peaks in the visible range.

Solar spectrum

Near IR Far IR

Visible

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The Sun emits at short wavelengths (SW).

The big picture: Earth Spectrum

In contrast, the Earth is colder celestial body with average surface temperature of 15oC.

That is why Earth emits at longer wavelengths, called infrared (IR), visualized like this:

Get oriented in Electromagnetic spectrum ! X-rays in medicine Radio broadcasting

So, remember:

The Earth emits at long wavelengths (LW). 6 of 526 of 52

Solar spectrum

Near IR Far IR

Visible

Earth’s spectrum

longshort

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.

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The big picture: Greenhouse effect

Similar process takes place at the surface of Earth:

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)

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 528 of 52

from the SWsolar radiation (A)left at the sea level, part is absorbed (B)and then re-emitted back (C)to the atmosphere as LW IR radiation.

to Earth by naturally occurring gases as CO2 , H2O vapors, and CH4.

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 big picture: Climate System

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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.

The big picture: Climate System Elements

The main elements of the climate system are the atmosphere and the oceans.

Their interaction with the basic elements makes the last touches in this almost perfect harmony. 10 of 5210 of 52

The fast heating and cooling of land, the strong reflection of the sunlight by ice and snow, the cloudsand precipitation are the other elements of this machine.

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 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.The wind system and ocean currents do the work.

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and minimum at the polar regions.

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)

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These, together with frontal storms, transfer cold air equatorward and warm air poleward.

and Westerlies.

The big picture: Winds and Currents

The winds drag the water in the oceans and form a system of immense ocean currents.

As a result of this heat transfer, the average temperature anywhere on the Earth is quite stable over long time period. 13 of 5213 of 52

They transport cold water toward the Equator and warm water to the poles.

The big picture: Radiation Budget

Climate systemAbsorbed

SW= 240 W m-2

Emitted LW = 240 W m-2

Incoming SW= 340 W m-2

Reflected SW = 100 W m-2

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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.

As the law requires, the same amount is emitted as LW radiation back to space.

About 30% of it is directly reflected back to the space. The remaining 240 W m-2 are absorbed by the Earth-atmosphere system.

This is the natural and necessary balance !

We, humans, are adding more and more

greenhouse gases into the atmosphere by burning fossil fuels.

The trouble is...The trouble is...

The big picture: Troubled Radiation Budget

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Even worse, we increase not only the concentration of Even worse, we increase not only the concentration of the naturally occurring greenhouse gases, but add the naturally occurring greenhouse gases, but add unnatural greenhouse gases, such as nitrous oxide (Nunnatural greenhouse gases, such as nitrous oxide (N22O) O) and chlorofluorocarbons (CFCs).and chlorofluorocarbons (CFCs). In addition, we cut down thousands of trees for lumber, In addition, we cut down thousands of trees for lumber, making them unable to take COmaking them unable to take CO2 2 out of the air.out of the air. All this waste in the air is letting less and less heat to All this waste in the air is letting less and less heat to go back to space. And, the more COgo back to space. And, the more CO22 and other and other greenhouse gasses in the atmosphere, the more IR greenhouse gasses in the atmosphere, the more IR radiation is trapped and re-emitted back to the Earth, the radiation is trapped and re-emitted back to the Earth, the warmer it becomes with possible catastrophic effects. warmer it becomes with possible catastrophic effects.

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.

Instantaneous CO2 Doubling:Emitted LW = 236 W m-2

Warm by 1.2 K to restore 240 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.

If the amount of CO2 doubles, the outgoing LW radiation would decrease by 4 W m-2.

And this And this isisa trouble !a trouble !

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The current models, however, produce both greater The current models, however, produce both greater warming and substantial disagreement: from 1.7 to 5.4 K. warming and substantial disagreement: from 1.7 to 5.4 K.

The big picture: Modeling Global Warming

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The main reason for the disagreement stems from The main reason for the disagreement stems from the different depiction of the climate feedback the different depiction of the climate feedback mechanisms in the models. These can either amplify or mechanisms in the models. These can either amplify or moderate the warming. moderate the warming. E.g.E.g., a warmer climate means a warmer atmosphere , a warmer climate means a warmer atmosphere with more water vapor, which itself is a greenhouse gas. with more water vapor, which itself is a greenhouse gas. So, water vapor provides a positive (or amplifying) So, water vapor provides a positive (or amplifying) feedback mechanism. Different models generally consent feedback mechanism. Different models generally consent on this particular feedback. on this particular feedback.

The feedback associated with cloudiness, however, The feedback associated with cloudiness, however, turns out to be much more difficult matter.turns out to be much more difficult matter.

The big picture: Radiation Budget Without Clouds

ClimateSystem(without clouds)Absorbed SW

= 290 W m-2

Reflected SW = 50 W m-2

Emitted LW = 270 W m-2

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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-2There is surplus of 20 W m-2 !

Obviously, the clouds balance the system. How?Obviously, the clouds balance the system. How?

and ...

Incoming SW= 340 W m-2

SW CRF = -50 W m-2 LW CRF = 30 W m-2

NET CRF = -20 W m-2

The effect of clouds on the Earth-atmosphere system is termed as Cloud-Radiative Forcing (CRF).

The big picture: Cloud Feedback

The net result of these two opposite processes is cooling by 20 W m-2.

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.

So, Cloud Radiative Forcing (CRF)

closes the balance of absorbed and emitted radiation.

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How exciting !

The big picture: Modeling Cloud Feedback

However, the cooling by clouds may change as the climate changes due to global warming. Scientists constructed and ran models again to see how the cloud radiative forcing would change. Here 19 (!) different models show quite different results for cloud feedback :

from modest coolingthrough almost missing

to strong positive.

The cooling by clouds would mitigate the global warming !

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Where in this long story are the Where in this long story are the aerosols?aerosols? Well, the findings about clouds gradually showed that the cloud

properties and lifetime are significantly affected by aerosols.

The discrepancies in modeling the cloud feedback The discrepancies in modeling the cloud feedback pointed out that we need to know well the cloud properties pointed out that we need to know well the cloud properties and their global pattern. So, since the beginning of 90s and their global pattern. So, since the beginning of 90s studies of clouds have priority and many programs for studies of clouds have priority and many programs for measuring the global cloudmeasuring the global cloud coveragecoverage and properties have and properties have been initiated.been initiated.

The big picture: What about Aerosols?

You probably ask yourself already impatiently:You probably ask yourself already impatiently:

So, for the last 2 years the aerosols, not the clouds, are the Gordian knot of the climatic studies.

How exactly? It turned out we do not have enough knowledge about aerosols in order to know how they do that.

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What are Aerosols? Aerosols are minute stable particles, solid or liquid, suspended in the atmosphere.

rural site

urban site22 of 5222 of 52

Samples of clean (rural) and polluted (urban) air under microscope show different particle

shapes (spherical or arbitrary) and concentrations.For the scale: 1 m = 10-6 m

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.

Another manifestation of the presence of aerosols is haze.

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.

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Why are Aerosols so Important?

directly - through the reflection and absorption of solar radiation. The mechanisms are well understood:

Atmospheric aerosols influence the climate in two ways:

indirectly - through modifying the optical properties and lifetime of clouds.

absorption of coming SW solar radiation.absorption of coming SW solar radiation. scattering of coming SW solar radiation back to scattering of coming SW solar radiation back to space;space;

Aerosols act as cloud condensation nuclei (CCN) on which H2O vapors in the atmosphere condense and form cloud droplets. Two scenarios are at work:

In both cases less radiation reaches and heats the Earth, In both cases less radiation reaches and heats the Earth, i.e., i.e., the aerosols cool the Earth-atmosphere systemthe aerosols cool the Earth-atmosphere system..

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Cloud/Aerosol Scenarios

1) more surface available to reflect the light.

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

Net result: cloud albedo (reflection) increases.

When there are more aerosols (i.e., more CCN), more droplets form in the cloud. We observe:

Net result: prolonged cloud lifetime.25 of 5225 of 52

During winter in the polar regions, aerosols grow to form polar stratospheric clouds.

Aerosols act as sites for chemical reactions to take place.

More Roles for Aerosols

The most significant example: destruction of stratospheric

ozone.

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 Increased aerosol pollution from 19791979to 1989to 1989resulted in ozone hole over Antarctic.resulted in ozone hole over Antarctic.

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Aerosol Properties

To estimate aerosol radiative forcing we need to know which aerosol properties control the different processes.

The effect of aerosols on climate is termed aerosol radiative forcing.

Thus, the most important aerosol properties are:

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 That is, many small particles do better than few large.large.

size and shape concentration

and lifetime 27 of 5227 of 52

Aerosol properties: Size and Shape

The size controls the physical and chemical processes !

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Typical distribution of aerosol mass and number by size.

coarsecoarseand and fine fine particles.particles.

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.

We see 2 peaks over

Aerosol properties: Concentration and Lifetime

Concentration is defined as the total number of particles per unit volume;

Lifetime is the time aerosols reside in the atmosphere before being removed by precipitation or conversion in something else;

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.

Aerosol lifetime ranges from 2-3 years to 3-5 days;Most aerosols are short-lived. 29 of 5229 of 52

Aerosol Types There are many types of aerosols

classified by different criteria.

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

Depending on their size aerosols are (we already know this):

coarse and fine;

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Examples of natural aerosols are:

Primary(formed directly as particles)

Secondary(formed in the atmosphere from

gases)

Soil dust (mineral aerosol)

Sulfates from biogenic gases

Let talk about some of these !

Sea salt Volcanic dustOrganic aerosols

Sulfates from volcanic SO2 Organic matter from biogenic CNitrates from NOx

Most numerous are

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Aerosol Types: Natural Aerosols

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.

experiences the highest frequency of dust storms in the world: over 30 dust storms per year.

Imagine, this village endures such a messtwice, sometimes more, a month !

As a result,

The area joining Iran, Afghanistan and Pakistan

the deposition rate of mineral aerosols in the Indian Ocean is more than 5 times any other region of the world oceans. 32 of 5232 of 52

There are 4 mechanisms of detachment and lifting of soil particles by wind:

The number of aerosols delivered by extreme events as dust storms dominates the number of aerosols created by continuous lower wind.

Natural Aerosols Formation: Soil Dust Lifting

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.

(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 5233 of 52

Natural Aerosol: Source of Sea Salt Aerosols On a windy day, when even a skillful Hawaiian surfer On a windy day, when even a skillful Hawaiian surfer may flip, the ocean is covered with whitecaps. Whitecaps may flip, the ocean is covered with whitecaps. Whitecaps are the major source for sea salt particles. They produce are the major source for sea salt particles. They produce numerous drops, which evaporate, shrink to a smaller numerous drops, which evaporate, shrink to a smaller size, and form sea salt aerosols.size, and form sea salt aerosols.

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Interestingly enough, Interestingly enough, the vast oceans produce a the vast oceans produce a bit less aerosols than bit less aerosols than deserts produce dust.deserts produce dust.

The reason is that the formation of sea salt drops, The reason is that the formation of sea salt drops, parenting the sea salt aerosols, includes several parenting the sea salt aerosols, includes several processes requiring more energy than mere lifting of a processes requiring more energy than mere lifting of a dust particle. dust particle. Let see these processes.Let see these processes.

Natural Aerosol Formation: Sea SaltAir entrained into the water after wave breaking creates bubble clouds. Their caps shatter in thousands small droplets called film drops.

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

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

Least drops are formed by splashing mechanism, when some small unstable projections of water form drops. 35 of 5235 of 52

The large bubbles rise to the surface and burst.

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.

Natural Aerosol: Volcanic dust

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 5236 of 52

SO2 cloud from Mt. Pinatubo, September 23, 1991

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. Not all large volcanic

eruptions produce global-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.

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The red color shows maximum aerosol concentration

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 stay there for several years.

These particles reflect the sunlight, thereby cooling the Earth. They grow slowly and are regularly removed by rain for a long time. 38 of 5238 of 52

Natural Aerosols: Sulfates and organic matter

Emissions of natural organic aerosols from oceans dominate the terrestrial sources.

The biosphere from satellites.

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 conversion.

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Examples of anthropogenic aerosols are:

Primary(formed directly as particles)

Secondary(formed in the atmosphere from

gases)

Industrial aerosols

Sulfates from industrial SO2

Let talk about some of these !

Biomass burning Soot

Organic matter from biogenic CNitrates from NOx

Most numerous are

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Aerosol types: Anthropogenic Aerosols

Anthropogenic Aerosols: Sources of Industrial Pollution

The primary industrial aerosols originate from inorganic impurities in the fuel we use or from incomplete fuel combustion.

Recent estimates show that contrails are able to change the climate locally in regions with heavy airplane traffic.

Plants, cars, and aircraft emit directly soot, and nitrogen oxides.

Airplanes and factories release water vapor forming additional clouds and reflecting the incoming sunlight. Recent estimates show

that contrails are able to change the climate locally in regions with heavy airplane traffic.

Plants, cars, and aircraft emit directly soot, and nitrogen oxides.

The primary industrial aerosols originate from inorganic impurities in the fuel we use or from incomplete fuel combustion.

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Airplanes and factories release water vapor forming additional clouds and reflecting the incoming sunlight.

Most dangerous are the sulfate aerosols formed from these gases, because they are persistent. About 90% of the sulfur emissions are from industrial regions in the Northern hemisphere.

All these sources increase :• carbon dioxide (CO2)• methane (CH4)• nitrous oxide (N2 O)• halocarbons (CFCs)

Anthropogenic Aerosols:Biomass Burning - natural and...

The Hochderffer fire, Coconino National Forest, AR

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.

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Roughly 175 million acres of forest and grassland are burned each year world-wide.

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.

Anthropogenic Aerosols: Man-initiated Biomass Burning

Biomass burning is a widespread practice for land clearing and land use change such as conversion of forest regions to grazing and agriculture areas.

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80% of the total biomass burning occurs in tropical rain forests and savanna grasslands

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.

2/3 of the 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.

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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.

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Aerosol global distribution: Oceanic aerosol

spring

wintersummer 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.

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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.

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Aerosol global distribution: Continental aerosol over oceans

winter

summer

Once again the same seasonal pattern: more aerosols in summer than in 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 dust storms.

Note 2 places we considered:

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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. 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.

Red: high aerosol reflection.

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Aerosol global distribution: Sulfur emissions As expected, the industrial regions are the major sources of anthropogenic sulfate aerosols.

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• Aerosols are short lived with exception of the volcanic dust

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

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HypothesisThere is a hypothesis: aerosol

cooling, mainly due to man-produced sulfates, may cancel the effect of global warming.

We have much more work to do ... 51 of 5251 of 52

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.

That’s it!

questions?

Still here? Reading?

Puzzled?Then please,