Transcript Recent environmental crises

Climate Change:
the Tropospheric Aerosol Connection
Robert J. DELMAS
Laboratory of Glaciology and Environmental Geophysics
Grenoble, France
• Over the last 3 decades, I have
participated, on the national and
international levels, in the studies of
several environmental crises:
- Acid rain
- Stratospheric ozone (« ozone hole »)
- Tropospheric ozone
- Climate change
- Global change
This was an opportunity to learn a lot
about atmospheric chemistry
Trends in atmospheric chemistry
1970-1990 :
Major advances were in gas phase
photochemistry (except the case of
« nuclear winter »)
Antarctic ozone hole: reactions on ice and
particulate surfaces
From 1990, interest shifted to natural and
anthropogenic aerosols
IPCC: Radiative Forcing Estimates
WHAT ARE AEROSOLS ?
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
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Continental/ Desert Aerosols
Marine Aerosols
Industrial Aerosols
Volcanic Aerosols
Organic Forest Hazes
Smoke/Biomass Burning Aerosols
Stratospheric Aerosols
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.
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.
Aerosols and Climate: Direct Effect
Direct Effect:
Scattering and
absorption by
particles
photo: SeaWifs website
Aerosols and Climate: Direct
Effect
Roughly proportional
to aerosol mass
concentration
photo: SeaWifs website
Direct Effect:
Scattering and
absorption by
particles
Indirect Effect on Climate
Aerosol
Particles
Clean
Air
Polluted
Air
Cloud
Droplets
“First” indirect
effect: albedo
“Second”
indirect effect:
lifetime
Brighter,
more
persistent
clouds
Aerosol Indirect Effects (Clouds)
Change in cloud
reflectivity
Change in
rainfall
Aerosol research needs…
• Process studies both in the atmosphere and in
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the laboratories
Source and sink studies of aerosols
Chemical analyses of particulate matter (PM)
Modelling
Regional campaigns
Global observation (satellites)
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!!!
Past decade advances in aerosol
research lead to realize that:
• It will not be possible to understand (and
even less so to be able to predict) the
chemical state of the atmosphere without
taking into account its multi-component and
multi-phase nature
New studies are needed
because….
• Most of current climate models consider
generally only the sulphur cycle
• They need much more data on the global
scale to be tested
• There are always more evidences that
aerosols have significant climate effects
• Uncertainties are high in this field
Atmospheric aerosol features
vary considerably
• Size: from nanometer to micrometers
very small (Aitken particles): soot, sulfuric acid,
large: dust, sea salt, pollen,
• A wide range of shapes, from individual
particles to aggregates
• Chemical compositions differ widely
Typical Number Distribution
"CCN" Mode
Coarse Mode
dN / d log Dp
Ultrafine Mode
0.01
0.1
1
Particle Diameter (mm)
10
Typical Mass Distribution
"CCN" Mode
Coarse Mode
dM / d log Dp
Ultrafine Mode
0.01
0.1
1
Particle Diameter (mm)
10
Average Residence Time,
seconds
Average Residence Time of
Aerosols in Atmosphere
10
8
10
7
10
6
10
5
10
4
Jaenicke, 1980
Tropopause
Middle
Troposphere
1 Day
Below 1.5 km
1000
100
10
0.0001 0.001 0.01
0.1
1
10
Radius, micrometer
100
1000
How to characterize aerosols?
• Particle size is central to the description of the
radiative effects of aerosols and to their influence on
clouds
• Composition affects the hygroscopic growth of
particles and therefore their ability to form cloud
droplets
• All these properties have to be introduced into
large-scale chemical transport models
One single system…
• As aerosol particles are strongly coupled with
gas-phase chemistry and clouds, an
understanding of their properties and effects
requires that gases, aerosol particles, and
clouds be treated as a single system
• Scales: from molecules and nanometer-sized
aerosol particles to frontal cloud systems
spanning hundreds of km…
Example for the gas-particlecloud coupling
• Aerosol particles and cloud droplets can
influence gas-phase chemistry by acting as
sinks of reactive species and by
decreasing/increasing actinic flux
• Clouds can serve as « chemical reactor »,
producing new species
• Aerosol particles and cloud droplets affect
« the oxidising capacity » of the atmosphere
Clouds as « chemical reactors »
Example highlighting the range
of scales
• Clouds cover roughly half of the earth’s surface
• Each cloud is composed of billions of individual
droplets or crystals, each of which having started
its life as an aerosol particle
• Understanding clouds on a global scale needs an
understanding of the microscale processes that
create and control clouds
• Aerosol particles have a multitude of sources
Sources
Indirect Radiative
Forcing
Direct Radiative
Forcing
Nucleation
Activation
H2SO4, HNO3,
Organic aerosol
Forest Fires
Oxidation
Dust
Terpenes
Hydrocarbons,
NOx, SO2, NH3, POA
Soot
Resuspension
H2SO4, MSA
Oxidation
Sea-salt
Dimethylsulfide
Phytoplankton
Indirect Radiative
Forcing
Direct Radiative
Forcing
Activation
Transport
Resuspension
Dry Deposition
Sinks
Precipitation
(Wet Removal)
Natural
processes
anthropogenic
Present burden vs
pre-industrial
Elements of climate
affecting emissions
Mineral dust
Wind erosion
Land use change,
industrial dust
Incr.
Changing winds
and precipitation
Sea salt
Wind
Biolog. Part.
Wind, biolog.
processes
Agriculture
???
Changing winds
Carb. Part.
Vegetation fires
Fossil fuel & biomass
burning
Incr.
Changing precip.
More sulfate
Changing winds
Species
Primary particles
Changing winds
Secondary
DMS
Phytoplankton
degradation
SO2
Volc emissions
Fossil fuel comb.
More sulfate
NH3
Microbial activity
Agriculture
More ammonium
nitrate
NOx
Lightning
Fossil fuel comb.
Incr. nitrate
VOC
Vegetation
Industrial processes
Incr. Org. aerosol
Change in convective
activity
Integrated view of the present state
of knowledge of atmospheric aerosol
• It emerges from observations and field
campaigns that there is no such thing as a
global aerosol. Instead there exists a
superposition of largely independent
regional aerosol plumes and layers, each
having unique sources and correspondingly
differing spatial and seasonal patterns as
well as specific microphysical and chemical
characteristics
Soil-derived dust
• The majority of soil-derived dust particles is lifted
into the atmosphere by wind in arid and semi-arid
regions (1/3 of Earth’s land area).
• Fine dust particles are produced by grain saltation
• Surface properties (texture, roughness,
composition, moisture, vegetation) are key factors,
in addition to meteorological conditions
• Global annual mean dust production estimated to:
1000-5000 Tg a-1
Dust storm
Sahara dust over West Africa
and the Atlantic Ocean
Dust storm in the Gobi desert
(27/03/04)
From China to North America
Between April 20th
and 25th, 1998, a dust
cloud was rapidly
moving across the
Pacific Ocean.
It appeared as a yellow
dye on SeaWiFS
satellite images
visualizing its own
path across the Pacific.
Impact of Asian dust on North America
By April 27th, the dust
cloud rolled into North
America. Satellite images
show that one branch of
the dust plume was
heading southward along
the California coast and
another branch continued
eastward across the
Canadian Rockies.
MINERAL DUST PASSING OVER
LAND.
Chemical and mineralogical analysis
of individual mineral dust particles
A.Falkovich, E. Ganor, Z. Levin,
P. Formenti and Y. Rudich, JGR, 2000
Highly
Non- Spherical
Shapes!
During the dust event the
PM10 and PM2.5
concentrations in
Washington state reached
120 and 40 mg/m3,
respectively.
An example of material
exchange between
land and ocean via
atmospheric transport
of dust:
Iron rich dust from the Gobi
Desert fertilized a rapid algae
bloom in the North Pacific
Ocean in spring 2001.
Two robotic Carbon Explorer
floats recorded the rapid
growth of phytoplankton in
the upper layers after a
passing storm had deposited
dust from the Gobi Desert.
(Jim Bishop, Berkeley)
Still large uncertainties…
• Emissions schemes elaborated for Sahara
desert dust cannot be extended directly to
other source regions due to the lack of data
on surface properties
Anthropogenic dust is of special
interest in climate change studies
• Human activities such as land use practice and
construction, etc…, can modify the geographical
area of dust sources and increase the dust loading
of the atmosphere
• Recent estimates suggest that the anthropogenic
fraction of dust could be as much as 30 to 50% of
total dust production
• Note that erosion due to human activities is now
more important than natural erosion!
Anthropogenic aerosol produced
by industrial processes
• Fly ash production by combustion processes
• Particles emitted by cement manufacturing,
metallurgy,…
• Current estimates of industrial dust:
130 Tg a-1
Strong increase expected in developing
countries, e.g. in China…
Very new findings
•Asian dust is relatively non-absorbing. Prior to
ACE-Asia, Asian dust was expected to be relatively
light-absorbing at solar wavelengths due to its mixing
with soot aerosol during transport over downwind
industrial and urban regions. While there was soot
associated with the dust in the ACE-Asia
measurements, the data indicate that soot associated
with the dust does not appear to have had a large
effect on the single scatter albedo of the dust-pollution
mixture.
• The Northeast U.S. plume is comparable to the
Indian and Asian plumes in terms of aerosol mass,
surface extinction, and aerosol optical depth. This
runs counter to the perception that developing nations
are the source of the most significant aerosol plumes.
Very new findings
•Sea salt dominates sub- and supermicron
aerosol mass and light extinction in the
remote marine atmosphere. Prior to a series of
Pacific and Southern Ocean cruises, including ACE
1, it was commonly believed that sea salt was a
supermicron or coarse mode aerosol only. It was
further thought that the submicron aerosol was
dominated by sulfate derived from biogenic
dimethyl sulfide (DMS), but the ACE 1 data showed
that DMS-derived sulfur did not make a significant
contribution to aerosol mass or light extinction.
Instead it contributed to the growth of existing
particles (Bates et al., 1998) and the nucleation of
new particles in the free troposphere (Clarke et al.,
1998).
Primary particles from the oceans
• The ocean is a source of primary sea-salt
particles to the atmosphere through the
bursting of bubbles (yielding film and jet
droplets), mechanical tearing (spume
droplets) and spillover (splash droplets) of
wave crests
• Number dominated by sub-micrometer salt
particles
• Surface area dominated by jet drops
Super-micrometer
sea salt particles
• Their total number is small but they dominate the
mass size distribution
• They have therefore significant effects
- on chemical reactions occurring in the MBL
- on the nucleation of new particles
- on the formation of clouds
However their concentration sharply decreases with
elevation
Annual global mass
emission rate:
-1
Tg/a (Andreae,
1300
1995)
5900 Tg/a-1 (Tegen, 1997)
• Typically, number and mass concentrations
of sea-salt aerosol increase with wind speed
• Large uncertainty (one order of magnitude)
Further properties of sea salt
aerosol
• SS particles contain biological material
• Primary biological particles in the marine
environment usually contain long chain
fatty acids, alcohols, esters, soluble
proteins,…
• Some of these compounds are oxidized in
the atmosphere to form other products e.g.
oxalic acid, amino acids, …
Organic Carbon and Black
Carbon
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Two main sources of combustion aerosols:
-fossil fuel burning
-biomass burning
The formation of particulate matter depends
strongly on the conditions of combustion
(temperature, efficiency, nature of fuel)
• Black carbon (BC) is favoured by high
temperature, inefficient combustion increases total
particulate matter
Global BC emissions
1989
1997
0
1250
Bc
in
2500
3750
metric-ton/yr
5000
2100A2
0
Catherine Liousse
Air Pollution as a climate forcing : A Workshop, Honolulu, May 2002
125000
250000
375000
500000
BC
in
metric-tons/yr
Biomass burning sources
• Savannah & forests
• Quantification of emission factors based on
numerous field campaigns, statistics from
the FAO, data from satellites, vegetation
maps
TOTAL BIOMASS BURNING (dry mass) estimated
from 4000 to 10400 Tg a-1
Total soot production from 60 to 100 Tg a-1
Impact of forest fires
• Image shows the pollution over
Indonesia and the Indian Ocean
on October 22, 1997. White
represents the aerosols (smoke)
that remained in the vicinity of
the fires. Green, yellow, and
red pixels represent increasing
amounts of tropospheric ozone
(smog) being carried to the
west by high-altitude winds.
(TOMS satellite)
What about biomass burning emissions and trends?
Hao 1990
4000
Hao 1995
Liousse 2000
3500
EDGAR
3000
Seiler and Crutzen 1980
Andreae 1991
2500
Lobert 1999
2000
1500
1000
500
0
forest
savanna
biofuel
agricultural fires
extratropical
forest
Alaska
GRASSLAND
Canada
Mongolia
SHRUBLAND
Russia
Scandinavia
United States
TEM PERATE
Update is needed (agricultural maps ..)
Central Western europe
BOREAL
Southern, Western Europe
North Africa, Middle East
California
United States
Uncertainty on Russia
Mongolia
Lavoué et al., 2000
Catherine Liousse
Air Pollution as a climate forcing : A Workshop, Honolulu, May 2002
Fossil fuel combustion
• Emissions depend on burning practices in
individual regions and the type of fuels
burned
• The currently estimated range of emissions
of OC (organic carbon) is 10 to 30 Tg a-1
whereas estimates of fossil fuel BC range
from 2.3 to 7 Tg C a-1
VOC = Volatile Organic Compounds
• Natural biogenic and anthropogenic sources
• -Anthropogenic: alkane, alkenes, aromatics and
carbonyls
• -Biogenic: isoprene, mono-and sesquiterpenes, a
suite of O-containing compounds
• They produce secondary organic particles
• Based on emission inventories and laboratory data,
the production of secondary organic particulate
from VOC is estimated to:
30 to 270 Tg a-1
International Global Atmospheric Chemistry
Satellite
Evaluation/
Assimilation
PhotoChemistry
Transport,
Transformation,
Fate
StratosphereTroposphere
Exchange
Cloud
Chemistry
Aircraft Plumes
Turbulence
ILEAPS
Terrestrial
Exchange
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Polar l
Stratospheric
Clouds
A
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SPARC
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Heterogeneous
Aerosols
Chemistry
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SOLAS
Sea Surface
Snow
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Exchange
Exchange
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