School of somethingFACULTY OF OTHER
Lecture 1: Introduction
Ken Carslaw
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A short history of aerosol and climate1783 Laki Eruption. Benjamin Franklin attributes global cooling to volcanic haze
1800’s aerosols are the smallest known sub-division of matter
1859 Tyndall explains blue colour of sky in terms of light scattering by particles
1871 JW Strutt (3rd Lord Rayleigh) explains light scattering
1880 Aitken discovered role of aerosol in cloud drop formation
1898 Aitken: First evidence of new particle formation in the atmosphere.
1950s: Aerosol as pollution
1950s Aerosol is a regional pollution issue (LA, London…). Smog.
1958 CE Junge "unpolluted areas... no longer exist" in Western Europe
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A short history of aerosol and climate1960s-70s: Anthropogenic aerosol and climate?
1964 Nicolai Fuchs published The Mechanics of Aerosols
1967 Aerosol turbidity spread over 1000’s km. McCormick and Ludwig "Climate Modification by Atmospheric Aerosols."
1968-70. Aerosol cooling could counteract CO2 warming (Bryson).
1970: First calculation of cooling by aerosol (JM Mitchell). 2/3 of cooling since 1940 due to volcanoes
1970. Hubert Lamb “volcanic dust probably not main influence”
1970 Journal of Aerosol Science founded
1971 Potential aerosol cooling of 3.5K, bigger than CO2 (Rasool and Schneider)
BUT, discussion about whether aerosol cools or warms
1976 Wide regional effect of sulfate aerosol on climate (Bolin and Charlson)
1977 Aerosol effect on cloud albedo. Net cooling. (Twomey)
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A short history of aerosol and climate
1980s: First global models with aerosol effects
Late 1970s. First global models including aerosol. James Hansen and others.
1981. Climate model with volcanic aerosol, solar and CO2 forcings explains 20th C T changes (Hansen)
1982 The American Association of Aerosol Research formed
1990: First IPCC report: “neither the sign nor magnitude of the [aerosol] climatic feedback can be quantitatively estimated”
1990s: Aerosol a central part of climate models. Increasing confidence
1991: SO4 aerosols roughly balancing CO2 warming (Charlson et al., 1990, 1991, Hansen and Lacis, 1990)
1991: Pinatubo eruption. Hansen et al (1992) predict 0.5K cooling. Roughly correct.
1992. Biomass burning aerosol impacts (Penner)
1994/5: Model of 20th century climate with CO2 and SO4 aerosol (Taylor and Penner, Mitchell et al.)
1995. 2nd IPCC. Several aerosols in climate models. “Human influence on climate discernable”
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A short history of aerosol and climate
2000s: Sophisticated models and observations
2001. 3rd IPCC. “Most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations”. Aerosol most uncertain forcing.
2000/01: Potential large warming from soot aerosol
2001: First “microphysical” global aerosol models
2002: Term “Global dimming”
2005: Global brightening!
2007: 4th IPCC. Aerosol still most uncertain forcing…
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Aerosol distribution and properties
Spatial distribution
Mass, number
Size distribution
What’s important for climate?
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Global aerosol distribution
Dust
Biomass burning
Pollution
Sea spray
Remer et al., Global aerosol climatology from the MODIS satellite sensors, JGR, 2008
Aerosol Optical Depth
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Seasonal variability
MODIS satellite aerosol optical depth climatology
Remer et al., JGR, 2008
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Particle concentrations at the surface
LocationNumber (>3 nm)
cm-3
Mass<2.5 m
g m-3
Mass<10 m
g m-3
Urban 105-4x106 8-100 (12-20) 30-300 (40)*
Polluted continental
2000-10,000 2-8 10-40
Remote continental
50-10,000 0.5-2.5 2-10
Marine 100-400 1-4 10
European annual mean exposure limit
European recommended limit
1 g m-3 ~ 0.75 parts per billion (ppbm) at STP
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European surface level particulate mass <10 m
2004, European Environment Agency
From the European Air Quality monitoring network
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Aerosol vertical profile
Profile of aerosol extinction:
Decays from boundary layer to ~3-4km, then follows molecular
Typical for surface sources
Well mixed
exponential
constant
BOUNDARYLAYER
FREE TROPOSPHERE
Sasano, Applied Optics, 1996
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Aerosol number vertical profile
Number increases with altitude
Typical Z-shaped profile over continents
Numerous small particles are invisible
Z
Remote Pacific
Europe
POLLUTED BOUNDARYLAYER
CLEAN BOUNDARY LAYER
Clarke et al.
Schroder et al.
Cirrus
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Particle size distributionsModesNucleation, Aitken, accumulation and coarse
Not always present
Air qualityParticulate matter (PM), particulates
PM1 – mass less than 1 mm aerodynamic diameter
PM2.5 and PM10
Air quality and healthCoarse > 2.5m
Fine <2.5mm
Ultrafine < 0.1m
Cloud Physics:Giant > 2m
Ultra giant > 10 m
0
4e3
8e3
0
50
100
0
4
8
0.01 0.1 1.0 10.0
Diameter / m
NucleationAitken
Accumulation
Coarse
PM1 PM10PM2.5
Ultrafine fine coarse
cm-3
m2 c
m-3
m3 c
m-3
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Size distribution representation
1-3- mcm particles/)( rfdr
dN 1-3- mcm particles/)( rf
dr
dN
1-3- mcm particles/)( rfdr
dN
0
3000
6000
0
100
200
0
60
120
0.01 0.1 1.0 10.0
Diameter / m
0
5e4
1e5
0
300
600
0
8
16
0 2 4 10
Diameter / m6 8
cm-3 m-1
m2 cm-3 m-1
3-
10
cm particles/10ln)1(
10lnlog dr
dNr
drr
dN
rd
dN1-3- mcm particles/)( rf
dr
dN
m3 cm-3 m-1
cm-3
m2 cm-3
m3 cm-3
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Urban
0
105
2.105
0
500
1000
020
40
60
0.01 0.1 1.0 10.0
Diameter / m
Dominated by emissions
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Polluted continental
0
4000
8000
0
50
100
0
4
8
0.01 0.1 1.0 10.0
Diameter / m
Accum. modeEmitted particles plus complex regional processes
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Remote continental
0
4000
8000
0
100
200
0
4
8
0.01 0.1 1.0 10.0
Diameter / m
Remote doesn’t mean clean!
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Free troposphere and stratosphere
0
50
100
0
10
20
0
2
4
UT
0.01 0.1 1.0 10.0
Diameter / m
0
10
20
0
1
2
0
0.05
0.1
0.01 0.1 1.0 10.0
Diameter / m
Volcanically perturbed
20
3
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Arctic
0.01 0.1 1.0 10.0
Diameter / m
0
100
200
0
2
3
0
0.2
0.4
Arctic haze
Very aged aerosol
Two periods:
Spring: polluted (Arctic haze)
Summer: clean
G. Shaw, Bull. Am. Meteorol. Soc., 76, 2403-2413, 1995.
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Marine
0
100
200
0
50
100
0
10
20
0.01 0.1 1.0 10.0
Diameter / mHeintzenberg et al., Size distribution and chemical composition of marine aerosols: a compilation and review, Tellus, Ser. B, 52B, 1104–1122, 2000.
Varies strongly between clean and polluted
Multiple modes from sea spray production processes
…but there are other sources even in clean regions
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Desert
0
100
200
0
500
1000
0
1000
2000
0.01 0.1 1.0 10.0
Diameter / m
Aged dust plume
Dominated by emissions
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Composition
0.01 0.1 1.0 10.0
Diameter / m
FINE
H, NH4, SO4, NO3
Organic carbon
Elemental carbon
Metals
(Fe, Pb, Cd, V, Zn etc)
COARSE
Dust (CaCO3, Mg, Si, Al, Fe)
Coal dust
NaCl
Pollen, spores
Biological debris
See lectures by Sandro Fuzzi.
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What’s important for climate?
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Light extinction
0.01 0.1 1.0 10.0
Diameter / m
Continental
Arctic
Marine
Ext
inct
ion
Effi
cie
ncy
volu
me
volu
me
volu
me
n = 1.5-0.005i
n = 1.37-0.01i
Number
Light scattering efficiency depends in a complex way on • size distribution of
particles• chemical composition
(refractive index)• particle shape (sphere
or not)
Light absorption efficiency depends on• mass of absorbing
material• mixing of absorber with
other material
Area
See later lectures
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Cloud drop formation
Cloud drop number depends on (in order of
importance):
• Particle numbers and sizes
• Cloud dynamics
• Particle chemical composition
0.01 0.1 1.0 10.0
Diameter / m
See lectures by Graham Feingold
cloud condensation nuclei
0.01 0.1 1.0 10.0
Diameter / m
Only a subset of particles affect climate
Only a subset of particles affect climate
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Long term change
IPCC, 2001
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CCN change?
1850
2000
Leeds GLOMAP model
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Next 2 lecturesSources and sinksFactors that control the size distribution
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Definition
An aerosol is a dispersion of solid and liquid particles suspended in gas
It is a singular noun describing the mixture of particles. E.g. “the aerosol over Asia…”
Refer specifically to aerosol particles or particles.
E.g., the “the particle growth rates…” rather than “the aerosol growth rate…”.