October 31, 2001 1

Atmospheric Aerosols and Climate

Crew Familiarization Talk Chapter 2Joachim H. Joseph

Aerosols?! Aerosols...????

Aerosols…!!!

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Contents of this Chapter

Outline the nature of aerosolsIntroduce the study of aerosolsDescribe their Importance in

Atmospheric Phenomena on all Time and Space Scales with particular emphasis on Climate and Remote Sensing

The Desert Aerosol

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Why study aerosols?Reduce/Increase GHG’s Warming,Affect Cloud and Rain,Interfere with Remote Sensing of EAS,Active in Atmospheric Chemistry,Supply Minerals to Ocean Biosphere,Affect Well- Being of Organisms on both Land

and Sea: Contain Spores, Microbes and Viruses, Acids

and other stuff.

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Aerosol Involvement in the EAS.“EAS”= Earth Atmosphere System

Spatial Scales: Local/ Regional/Global

Natural and Man- Made Air Pollution Radiation Balance Clouds, Precipitation and Hydrology Health Hazards

Time Scales: Diurnal/Synoptic/Seasonal/ Decadal, Climatic : Industrial plumes, Haboobs, Biomass Burning, Khamsins, Dust

Plumes, Continental Pollution “Mountains”, Volcanic Eruptions.

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The Earth- Atmosphere Thermodynamic System.

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F0

A

t At

Art

A2rt

A2r2t

At2Art2

rA

AtrAFFF

FAF

FrA

AtrF

Twomeyabsorptionofel

seriesgeometricStreamTwoSimple

noneaaerosolaa

aerosolowabsorbed

aerosolinabsorbed

1

1

11

1977mod

2

,,

0..

0

2

Radiative Effects of Aerosols in Solar Spectrum.Proving need for Space- based Observations.

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When does aerosol heat/cool?

Fa Fa,aerosol Fa,none A r t 2A

1 rA

0 : Heats

0 :Cools

From the previous slide we have:

The sign depends on and g, through t and r

BUT IN ADDITION ON A, THE LOCAL SURFACE ALBEDO!

THE SAME AEROSOL MAY HEAT OR COOL

DEPENDING ON THE SURFACE OVER WHICH IT IS LOCATED!!!

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The Study of Aerosols from Space.

The regional and global spatial distribution of any aerosol determines its climatic effect.

The combined climatic effect of all atmospheric aerosols together depends on their combined spatial distribution

Therefore the study of aerosols from space is

MANDATORY!!!

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Aerosols versus GHG’s

Aerosols are wide- spread, localized, transitory and highly variable on all space and time scales

Atmospheric GHG’s are globally distributed in a vastly more homogeneous manner and vary in time mostly on seasonal and longer time scales.

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What is an Atmospheric Aerosol?

Mixture of Particles and Gases with

Suitable Degree of Definability over

Time Span of Relevance to the

Observed System

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Elaboration on Definition- 1

“Particles” Liquid: Drops of Solutions Solid:

Single Chunks/ Aggregates /Flakes Solid/ Liquid

Drops with Solid Inclusions

Liquid Coated Aggregates “Gases”

Any mixture of gases Particle Mixture- External or Internal

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Elaboration on Definition- 2

“Suitable Degree of Definability over Time Span of Relevance to the Observed System” Having a set of measurable physical and chemical

properties that define its interactions with the ambient atmosphere;

These properties change slowly compared to the time constant of interaction of the aerosol with other components of or processes in the observed system.

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Examples of Aerosols

The Atmosphere: More exactly, it is a system of many different

aerosols existing simultaneously;

Wind- Blown Mineral or Soil DustNatural/Industrial Hazes/Fogs/Smogs/SmokesWater/Ice Clouds

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Atmospheric Aerosols:A Practical Definition

The ensemble of all liquid/solid systems suspended in the atmosphere, except water/ ice clouds.

Water and Ice clouds are conventionally excluded because of their tight involvement with the hydrological cycle, short lifetimes and involvement in long- range latent energy transport.

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Main Types of Aerosols

Continental/ Desert AerosolsMarine AerosolsIndustrial AerosolsVolcanic AerosolsOrganic Forest HazesSmoke/Biomass Burning AerosolsStratospheric Aerosols

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Each “Type” has several “Components”

Wind- Blown Mineral Dust Sea Spray Natural or Man- Made gas to particle conversion

products- e.g. volcanic/ industrial emissions, DMS Natural Hazes from organic volatiles- e.g. terpenes ,

isoprenes Natural /Industrial direct emissions- e.g. soot, ash,

smoke, biomass burning

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Average Residence Time of Aerosols in Atmosphere

10

100

1000

104

105

106

107

108

0.0001 0.001 0.01 0.1 1 10 100 1000

Jaenicke, 1980A

vera

ge

Re

sid

ence

Tim

e,

seco

nd

s

Radius, micrometer

Below 1.5 km

MiddleTroposphere

Tropopause

1 Day

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Present Main Foci of Research:

Aerosol Processes: Sources, Sinks, Transport, Components of Types, Relation of Size/Shape/Composition, Time Constants, …

Direct /Indirect Radiative Forcing of EAS

Effects on Remote Sensing of EAS

Biosphere/ Atmosphere Interactions e.g. NMHC, VAT, Fires and Biomass Burning Aerosols

Oxidants and Photochemistry:e.g. tropospheric ozone and its precursors, Radicals

Health Hazards

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International Research Efforts

Some Recent Comprehensive Campaigns. ACE1- US Air Pollution, ACE2- European Air Pollution & Desert Aerosol, ACE3- “ACE-ASIA”) East Asian Aerosols, 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

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The 2D distribution of the average value of positive TOMS AI for each pixel for the period from August, 1996 to April, 2000 (top panel). Main source regions of the UV-absorbing aerosols can be inferred, and these regions are marked in the bottom panel.

The North African Desert Aerosol Sources.(Alperovich, Joseph, Levin and Ganor, JGR 2001)

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Top panel: The distribution of the highest observed TOMS AI. The largest values occur along the main trajectories of the dust plumes. Bottom panel:Schematic of the main routes of the desert aerosol transport.

Desert Aerosol Transport over North Africa and the Mediterranean.

(Alperovich, Joseph, Levin and Ganor, JGR 2001)

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The Desert AerosolGlobal Phenomenon with Regional Implications.

Sub- Tropical Sources:Sahara and its Boundary Regions, ME, Saudi, Indian Deserts;South- African and Australian Deserts

Middle & High Latitude Sources:Mongolia, Siberia, Gobi, Afghanistan

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Chemical and mineralogical analysis

of individual mineral dust particles

A.Falkovich, E. Ganor, Z. Levin,

P. Formenti and Y. Rudich, JGR, 2000 (in press

MINERAL DUST PASSING OVER LAND.

Mark! Highly Non- SphericalShapes!

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Why are DA’s, in contrast to others, so irregularly shaped?

Rain on Mountain Massifs; Run- off of silt into wadis and playas; Formation of playa soil- hollow spherules with a

range of radii from tens to hundreds of microns, weakly cemented by water or other materials;

Dry Out of soil; Turbulent weather systems mobilize particles; Saltation leads to break- up of spherules; The broken air- borne fragments: Desert Aerosol.

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ANALYSIS OF THE SLOPE - FRACTAL DIMENSION- OF THE LOG PERIMETER VS. LOG AREA GRAPH AT 08:00 AM.(Koren and Joseph, JGR 2001)

Average particle diameter in mSample No.

SimpleShapes

ComplexShapes

Fractal D

imension

Fractal Dimension (Calculated Diameter, m)Fractal Dimension ( Area in Pixels)

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A Multi- Resolution Look at the Desert Aerosol

QuickTime™ and aSorenson Video decompressorare needed to see this picture.

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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 measureAerosols are very varied and complex in nature at any

time and locationAerosols are highly inhomogeneously distributed and

highly episodic in occurrence Aerosols need to be studied interdisciplinarily Aerosols need to be studied simultaneously from space, air

and ground and in the lab.

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