Ultrafine Particles and Climate Change

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Ultrafine Particles and Climate Change

• Peter J. Adams

HDGC Seminar November 5, 2003
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Overview

• Introduction
• climate effects of aerosols
• aerosol size distribution, mass / number
  concentrations
• Ultrafine particles and clouds

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Overview

• Introduction
• climate effects of aerosols
• aerosol size distribution, mass / number
  concentrations
• Ultrafine particles and clouds
• Theme
• Aerosol (particulate matter) models developed for
  PM regulations / visibility are inadequate for
  newer issues

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Theme

• Regulations based on mass concentrations (PM10
  and PM2.5)
• less attention to modeling number concentrations
  (i.e. ultrafines)

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Theme

• Regulations based on mass concentrations (PM10
  and PM2.5)
• less attention to modeling number concentrations
  (i.e. ultrafines)
• Ultrafines cause concern
• health effects
• climate change

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Theme

• Regulations based on mass concentrations (PM10
  and PM2.5)
• less attention to modeling number concentrations
  (i.e. ultrafines)
• Ultrafines cause concern
• health effects
• climate change
• Sources of ultrafines poorly understood
• direct (primary) emission by combustion
• atmospheric formation from supersaturated gases
  (nucleation)

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Earths Energy Budget
Anthropogenic GHGs 2.5 W m-2
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Aerosols and Climate Direct Effect
Direct Effect Scattering and absorption
by particles
photo SeaWifs website
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Aerosols and Climate Direct Effect
Direct Effect Scattering and absorption
by particles
Roughly proportional to aerosol mass
concentration
photo SeaWifs website
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Indirect Effect on Climate
Aerosol Particles
Cloud Droplets
activation / nucleation
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Indirect Effect on Climate
Aerosol Particles
Cloud Droplets
Clean Air
Polluted Air
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Indirect Effect on Climate
Aerosol Particles
Cloud Droplets
First indirect effect albedo Second indirect
effect lifetime
Clean Air
Brighter, more persistent clouds
Polluted Air
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Aerosols and Climate Indirect Effect
AVHRR observation of indirect effect
Red visible Green 3.7 mm solar IR Blue
infrared
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Aerosols and Climate Indirect Effect
AVHRR observation of indirect effect
Power plant
Lead smelter
Port
Oil refineries
Red visible Green 3.7 mm solar IR Blue
infrared
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Aerosol Activation

• Activation formation of cloud droplet
• involves a competition between solute
• and surface tension effects

Number

• Diameter

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Aerosol Activation

• Activation formation of cloud droplet
• involves a competition between solute
• and surface tension effects

Depends on number concentration above critical
diameter
Number

• Diameter

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Source IPCC Third Assessment Report
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Typical Number Distribution
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Typical Mass Distribution
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Previous Work
Ultrafine
Cloud Droplets (cm-3)
CCN
Boucher Lohmann, 1995
Sulfate Mass (mg m-3)

• Mechanistic number of cloud drops depends on
  number of particles large enough to activate

Empirical number of cloud drops correlated with
sulfate mass based on observations
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Previous Work

• I Martin et al. 1994
• -0.68 W/m2
• II Martin et al. with background CCN
• -0.40 W/m2
• III Jones et al. 1994
• -0.80 W/m2
• IV Boucher and Lohmann 1995
• -1.78 W/m2

Cloud Droplets (cm-3)
Sulfate Mass (mg m-3)
It is argued that a less empirical and more
physically based approach is required
Kiehl et al. 2000
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Aerosol Microphysics
Nucleation Emissions
Coagulation Condensation
Deposition
Number

• Diameter

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Two-Moment Sectional Algorithm

• This work two moments of the size
• distribution (mass and number)
• are tracked for each size bin.
• Air quality regulatory model
• tracks mass in each size bin

Tzivion et al., JAS 44, 3139 3149, 1987 Adams
et al., JGR 10.1029/2001JD001010, 2002
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Two-Moment Sectional Algorithm

• This work two moments of the size
• distribution (mass and number)
• are tracked for each size bin.
• Air quality regulatory model
• tracks mass in each size bin
• Two-moment method conserves
  both mass and number precisely
• Prevents numerical diffusion present in
  single-moment methods
• Excellent size resolution 30 sections from .01
  mm to 10 mm

Tzivion et al., JAS 44, 3139 3149, 1987 Adams
et al., JGR 10.1029/2001JD001010, 2002
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Aerosol Microphysics

• 30,000 grid cells
• 1 year
• Adaptive time steps

General Dynamic Equation

• Coagulation

Condensation
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Model Structure

• Aerosol composition
• Current Sulfate / Sea-salt
• Development Organic / Elemental carbon
• Future Mineral dust
• Processes
• Emissions
• Chemistry
• Microphysics
• Cloud processing
• Size-resolved dry / wet deposition

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Size Distributions
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Size Distributions
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Van Dingenen et al., 1995 JGOFS cruise Sep/Oct,
1992
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CCN (cm-3) 0.2 Supersaturation
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Uncertainties

• Particulate Emissions
• Most sulfate aerosol mass results from gas-phase
  SO2 emissions
• Particulate sulfate lt5 of anthropogenic sulfur
  emissions
• Nucleation of new aerosol particles
• Important uncertainties in mechanism and rate
• Both processes contribute significant numbers of
  small particles
• insignificant contribution to sulfate mass
• important contribution to aerosol number
  concentrations and size distributions

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Sensitivity Scenarios

• Base Case
• 1985 sulfur emissions
• all emissions as gas-phase SO2
• nucleation based on critical concentration from
  binary (H2SO4-H2O) theory
• Primary Emissions
• 3 of sulfur emissions as sulfate
• Enhanced Nucleation
• critical H2SO4 concentration factor of 10 lower
• Pre-industrial
• no anthropogenic emissions

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Vertical Profiles
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CCN Vertical Profiles
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CCN Vertical Profiles
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Ultrafine Particles and CCN
Number

• Diameter

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Ultrafine Particles and CCN
Condensation to accumulation mode does
not produce new CCN
Condensation
Number
Growth

• Diameter

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Ultrafine Particles and CCN
Additional ultrafine particles result in
enhanced CCN formation
Condensation to accumulation mode does
not produce new CCN
Condensation
Number
Growth

• Diameter

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Impact of Particulate Emissions
SO2 emissions SO2/SO42- emissions
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Summary and Conclusions

• A regulatory model (mass concentrations) omits
  important physics
• Ultrafine particles have a significant impact on
  clouds via CCN number concentrations
• Require better knowledge of sources of ultrafines
• nucleation
• primary emissions from combustion
• Future changes in ultrafine emissions?