Who are we

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Using a global aerosol model to understand the
fate and characteristics of anthropogenic sulfate

P. T. Manktelow
K.S. Carslaw and G.W. Mann
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Talk Outline
INTRODUCTION What is Aerosol? Who
Cares? RESULTS The Tropospheric Sulphur
Cycle. Anthropogenic and Natural Sulfur. Changes
in Fate of Anthropogenic Sulphur between 1985 and
2000.

FUTURE DIRECTION Tagging and
tracking the intercontinental transport of aerosol
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What is aerosol?

• Definition A population of liquid or solid
  particles
• suspended in a gas.
• Two types
• Primary aerosol Emitted directly
• e.g. sea salt, dust, soot
• (2) Secondary aerosol Produced from
• gas to particle conversion
• e.g. sulfate, nitrate, organics
• Aerosol lifetime Days to weeks allowing aerosol
  transport
• 1000s km downwind from sources

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What is aerosol?
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Who Cares?
1. Direct Aerosol Radiative Forcing
Scattering Aerosol
Absorbing Aerosol
SW
eg. Sulphate, organic C, nitrate and dust
aerosols
- ? SW
eg. Black C and dust
? SW
- AGEING -
- ? SW
- ? SW
- MIXING -
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Who Cares?
2. Indirect Aerosol Radiative Forcing
Natural unperturbed cloud
Polluted perturbed cloud
Increased aerosol loading
Increased cloud albedo and lifetime
- Large cloud droplets
- Few in number
- Smaller cloud droplets -
Large in number
Figures http//terra.nasa.gov/FactSheets/Aerosols
/
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Who Cares?
From IPCC (2001)
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Who Cares?
3. Aerosol/particulate matter is associated with
a range of health effects depending upon size and
composition.
www.tropos.de/eng/PHYSICS/aerosol/urban.html
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GLOMAP Multicomponent

• Global TOMCAT CTM typically 2.8º by 2.8º
  resolution
• 20 Size Bins ranging from dry radii 2 nm 25
  µm.
• Full aerosol microphysics - Nucleation,
  condensation, coagulation, cloud processing, wet
  and dry deposition.
• Size distribution is simulated in detail.
  Anthropogenic/natural sulphate share the same
  distribution but carried as different components.
  Sea salt aerosol is also included but carried in
  a separate distribution.

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GLOMAP Tropospheric Sulphur Cycle
Upper Troposphere
Nucleation
H2SO4
Coagulation
H2O
Cloud Processing
Sulphur Emissions
H2O2
SO2
Nucleation Scavenging
Lower Troposphere
OH
Condensation
OH
Precipitation Scavenging
H2SO4
DMS
Dry Deposition
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Anthropogenic and natural sulfur in the
GLOMAP model
1)What contribution does sulfur from both sources
make to each process of the sulfur cycle, and
how does this translate into a sulfate production
efficiency?
2) Where does anthropogenic sulfur reside
across the aerosol size distribution?
3) What contribution does each source make to
sulfate number and mass?
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1)What contribution does sulfur from both sources
make to each process of the sulfur cycle, and how
does this translate into a sulfate production
efficiency?
DECEMBER
x Total Budget (Tg (S) yr-1)
Anthropogenic contribution
Cloud Processing 24.7 / 42
Sulfur Emissions 76.1 / 69
H2O2
SO2
SO4
Condensation 6 / 74
OH
Deposition 45.8 / 83
H2SO4
SO4
Nucleation 0.002 / 36
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1)What contribution does sulfur from both sources
make to each process of the sulfur cycle, and how
does this translate into a sulfate production
efficiency?
JUNE
x Total Budget (Tg (S) yr-1)
Anthropogenic contribution
Cloud Processing 26.4 / 74
Sulfur Emissions 65.7 / 80
H2O2
SO2
SO4
Condensation 11.3 / 87
OH
Deposition 29 / 83
H2SO4
SO4
Nucleation 0.003 / 79
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2) Where does anthropogenic sulfur reside across
the aerosol size distribution?
DECEMBER
Particulates (100)
Removal of Particulates stronger natural
contribution lt 100 nm
Cloud processing (42)
Nucleation (36)
Condensational growth (74)
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2) Where does anthropogenic sulfur reside across
the aerosol size distribution?
JUNE
Particulates (100)
Removal of Particulates stronger natural
contribution lt 100 nm
Cloud processing (74)
Nucleation (79)
Condensational growth (87)
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3) What contribution does each source make to
sulfate number and mass?
LT (850 1000 hPa)
UT (300 500 hPa)
Anthropogenic contribution
Omission of particulates
December

- Poor correlation exists between composition of
mass and number when primary particles are
emitted.
-
Strong natural contribution to mass in December
due to cloud processing.
June
-
Poor correlation exists between composition of
mass and number when primary particles are not
emitted.

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Conclusions
Natural sulfate is produced much more efficiently
than that derived from anthropogenic sources as

• It is cloud processed with a high efficiency
  
  
• Natural SO2 resides at higher altitudes and so is
  dry deposited less freely.

Anthropogenic sulfur tends to reside across sizes
below 50 nm. Natural sulfur predominates across
sizes extending from 50 nm and above. This would
suggest that

• Anthropogenic sulfur may contribute to the
  radiative forcing of sulfate less than modern day
  emissions would suggest.
• 2) Indirect forcing may have been strongly
  perturbed by anthropogenic sulfur, as CCN has an
  anthropogenic contribution similar to the
  fraction of emissions.

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UKCA Model

• Built into TOMCAT CTM.
• Full aerosol microphysics - Nucleation,
  condensation, coagulation, cloud processing, wet
  and dry deposition.
• Two moment modal scheme. Mean particle radius
  allowed to evolve and aerosol number carried as a
  prognostic variable.
• Multicomponent system sulfate, sea salt, BC, OC
  and dust carried as an internal mixture in each
  mode.

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Changes in the Fate of Anthropogenic Sulfur
Change in the global distribution of
anthropogenic SO2 emissions over last several
decades. Emissions W.Europe/USA ? Asia.
Different responses observed in atmospheric
sulfur concentrations following the change in
sulfur loading
Long term measurements suggest that for

Sulfate lt Emissions
BUT ...
Sulfate Emissions
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Changes in the Fate of Anthropogenic Sulfur
GEIA 1985 vs AEROCOM 2000
1985
GEIA seasonality imported into AEROCOM inventory
High (gt100 m) and low (lt 100m ) level source
emission heights consistent.
Particulate fraction and sizes consistent
2000
Year 2000 meteorology and oxidants for June and
Dec.
UNITS106 molecules cm-2 sec-1
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Changes in the Fate of Anthropogenic Sulfur
Large decrease in SO2 emissions simulated across
NH mid latitudes. Slight increase across NH
subtropics/tropics
SO2 Emission
Decrease in sulfate production from 40 N 90 N.
Increase simulated from 40 N to equator. Almost a
global net balance in sulfate production.
Wet oxidation
Dry oxidation
Extremely large decrease in SO2 deposition across
NH mid latitudes, compared to the increase
simulated across tropics/subtropics.
Sulfate deposition
SO2 deposition
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Regional Changes in Sulfur
Budget terms mg (S) m -2 day -1
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Global Changes in Sulfur
1985 Column Sulfate (mg (S) m-2)
Global Sulfur Budget/Burden
Change Column Sulfate by 2000
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Conclusions
Sulfate has declined across Europe and North
America at a much slower pace than emissions due
to oxidant limitation in cloud. High oxidant
concentrations at latitudes where emissions have
increased, lead to a more proportional
relationship between emission and sulfate
production. 2 Consequences


Global sulfate production has only
decreased by a small amount following a
substantial decrease in the global sulfur
source. Sulfate concentrations have increased
across latitudes where the annual flux of solar
radiation is greater. Global average radiative
forcing of sulfate has probably increased over
last several decades despite over a 12 reduction
in sulfur emissions!



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FUTURE DIRECTION Understanding the Fate and
Radiative Forcing Efficiency of Sulfate Formed
from North American and Asian Emissions
How does SO2 emitted from North America and Asia
contribute to the formation and fate of sulfate
aerosol?
This will depend on Background aerosol
concentrations (e.g. natural sulfates and sea
salt), the concentration of oxidants and
meteorology (e.g. cloud volume, precipitation and
convective transport to the upper troposphere).
Which will determine SO2 lifetime and burden,
sulfate aerosol production efficiency, lifetime
and microphysical properties.
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Why is this Important? It determines the
potential of SO2 to form CCN (cloud condensation
nuclei) or optically active aerosols.
Implications for Climate
How will this be Investigated?
Sulfate can be tagged using the GLOMAP model
according to the source region of the SO2
emitted.
The region of the size distribution in which the
tagged sulfate resides will determine the
contribution it makes to CCN number and aerosol
direct radiative forcing. This will allow a
radiative forcing potential per unit sulfur
emission to be determined for each region.
MOA
CCN
MOA Most Optically Active