Tropospheric Aerosols

8/14/2019 Tropospheric Aerosols

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Tropospheric Aerosols

Devang.SMSc. PreviousM.S.University


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Global warming induced by greenhousegases gets most of the press coverage, butit is not the only climate change issue our

planet is dealing with. Emissions of tinyparticles, called aerosols , into ouratmosphere are disrupting our climate aswell.


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Lets take look atWhat are aerosols ?

What are different type of aerosols ?

Where do they come from ?

What roles do aerosols play in Earthsatmosphere?

What is global dimming and what role doaerosols play in this phenomenon


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Aerosols The basics:

Aerosols are

1.Small particles that drift in atmosphere

2. Aerosols are not gases they are usually solids or tinydroplets of liquid

3.They are sufficiently small and light that they donot fall out of the air under influence of gravity

5. They range in size from about 10 nanometersto 100 microns in diameter

4.Some aerosols remain for few hours whileothers can stay airborne for years


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Transportof Aerosols

Aerosols are transported by theairflows they encounter during the timethey spend in the atmosphere. Thetransport can be over inter-continentalor even global scales.E.g.. Sulpher dioxide (SO2) emitted from powerplants in the United Kingdom can be deposited assulfate far inland in continental Europe.


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Average Residence Time of Aerosols in Atmosphere

10

100

1000

10 4

10 5

10 6

10 7

10 8

0.0001 0.001 0.01 0.1 1 10 100 1000

Jaenicke, 1980

A v e r a g e

R e s i

d e n c e

T i m e ,

s e c o n

d s

Radius, micrometer

Below1.5 km

MiddleTroposphere

Tropopause

1 Day


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MeansAtmospheric Aerosol are

The ensemble of all liquid/solid systemssuspended in the atmosphere, exceptwater/ ice clouds.

Water and Ice clouds are conventionallyexcluded because of their tight involvementwith the hydrological cycle, short lifetimesand involvement in long- range latentenergy transport.


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Aerosols :Sources and Types

Natural Source- Continental/ Desert Aerosols- Marine Aerosols- Volcanic Aerosols- Organic Forest Hazes

Human Source

- Industrial Aerosols- Smoke/Biomass Burning Aerosols


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Dust

Soot

Sea-salt

Activation

Resuspension

Terpenes

O x i d a t i o n

ForestFir es

Sources

Hydrocarbons,NO x, SO 2, NH 3, POA

O x i d a t i o

n

H2SO 4, HNO 3,Organic aerosol


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Continental/ Desert Aerosols

Large wind storms over deserts and other arid regions canlift dust particles high into the atmsophere, allowing themto drift downwind hundreds of kilometers from their source


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Marine AerosolsSea spray accounts for the second most common natural source of aerosols in the form of various types of salts.


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Volcanic Aerosols

.

Large volcanic eruptions spew vast clouds of fine ash particlesinto the air, sometimes reaching the stratosphere. Ash fromvery large eruptions can stay aloft for months to a few years,and can spread around the globe


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Organic Forest HazesLikewise, land-based vegetation emits gases, such asvolatile organic compounds (VOSs), that contribute to

secondary emissions of aerosols .


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Industrial AerosolsAnthropogenic ( human produced ) aerosols make up about 10percent of the amount of aerosols in our atmosphere. Tiny particles of black carbon, or soot , are a major component of smoke producedby many kinds of burning. Coal-burning power plants generate lotsof black carbon and often loft it high into the atmosphere as emissionsfrom tall smokestacks. Internal combustion engines in cars, trucks, andconstruction vehicles also emit plenty of black carbon. Diesel enginesare especially prolific producers of this type of aerosol. Humansactivities also increase the amount of mineral dust aerosol generation


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Smoke/Biomass Burning Aerosols


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Concept of Emission of Aerosols

Primary emission-

Are aerosols sources thatdirectly project aerosols In theair

e.g. Dust, volcanic ashand Black CO2

Secondary emission

refers to substances that are not aerosols whenthey are originally emitted, but later undergosome reaction in the atmosphere that transformsthem into aerosols

e.g. sulfur dioxide (SO2) gas isemitted by volcanoes, forest fires,coal-burning power plants, refuseincineration, and other sources. Inthe atmosphere, chemical reactionsand combination with water can

transform sulfur dioxide into sulfuricacid droplets, a liquid aerosol thathelps form acid rain


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Roles of Aerosols in Earthsatmosphere?

The presence of aerosols in Earth'satmosphere influences climate inthree key ways.

1. Aerosols alter albedo (reflectivity).2. Formation of clouds of various types.3. Various types of chemical reactions

in the atmosphere.


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To know Roles of Aerosols in Earthsatmosphere we should know


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Role 1: Aerosols alter albedo (reflectivity)

Changing the amount of solar energy that reaches theplanet's surface and the amount that is absorbed at

various levels within the atmosphere.


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2. Cloud formation

Clouds arenothing more

than watervapor thatcondenses and accretes into a visibleform.

F i f


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Formation of clouds& aerosols

The particles around whichcloud droplets coalesce arecalled cloud condensationnuclei (CCN) or sometimes"cloud seeds

under normal circumstances,these droplets form only wherethere is some disturbance

In general, aerosolparticles providethis "disturbance".

CCN thatactivates

into a clouddrop

Aerosol particle

that does notactivate

Cloud


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Formation of clouds (animation)

h l


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3. Chemical reactionsin the atmosphere

The dispersal of volcanic aerosolshas a drastic effect on

the Earth's atmosphere

1. sulphur dioxide (SO2),hydrochloric acid (HCL)

and ash

2.heterogeneous chemistry

3. which can react with nitrogen

in the stratosphere,

To stratosphericozone destruction.


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AEROSOL-CLIMATE CONNECTION


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global dimming &role of aerosols

Global dimming isthe gradual reductionin the amount of

global directirradiance ( radiantemittance , and radiantexitance ) at the Earth

's surface
http://en.wikipedia.org/wiki/Irradiancehttp://en.wikipedia.org/wiki/Earthhttp://en.wikipedia.org/wiki/Earthhttp://en.wikipedia.org/wiki/Irradiance


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Effect ofglobal dimmingover India

The aerosols that contribute to poor air quality overmuch of the Indian subcontinent are believed tooriginate from industrial smoke, vehicle emissions, and

biomass burning


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Polluted haze layer seen by Terra satellite overnorthern parts of India and Bangladesh.

04 January 2008 26 January2008


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Summary of Problems

The effects of aerosols are difficult to assessAerosols are a very very minor component of the atmosphere and very difficult to measure

Aerosols are very varied and complex innature at any time and locationAerosols are highly inhomogeneouslydistributed and highly episodic in occurrence

Aerosols need to be studied simultaneously fromspace, air and ground and in the lab.


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International Research EffortsSome Recent Comprehensive Campaigns. ACE1- US Air Pollution, ACE2- European Air Pollution & Desert Aerosol, ACE3- ACE-ASIA) East AsianAerosols, and Desert Aerosols.TARFOX- US Air Pollution,SCAR- A,- Eastern Seaboard Air Pollution, SCAR- B-Biomass Burning in Brazil , SCAR-C- CA Air PollutionSAFARI 2000, etc.

Satellite Programs : SAGE, EOS, ADEOS, SEAWIFS,Pegasus, Robotic Surface Photometer Network : AERONET

AMIP- Climate Model Comparisons

AVHRRAERONETMISR


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Very fine aerosols from the WorldTrade Center.


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References:

The Science of climate change J.T. Houghton, L.G.Meria Filhio,B.A.Callander, N.Harris

National Aeronautics and SpaceAdministration (NASA)National Research Council (U.S.)

Space and Atmospheric SciencesDivision, Physical ResearchLaboratory, Ahmedabad, India


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Documents

Tropospheric Aerosols