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Ultrafine Particles and Climate Change. Peter J. Adams. HDGC Seminar November 5, 2003. Overview. Introduction climate effects of aerosols aerosol size distribution, mass / number concentrations Ultrafine particles and clouds. Overview. Introduction climate effects of aerosols

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ultrafine particles and climate change

Ultrafine Particles and Climate Change

Peter J. Adams

HDGC Seminar

November 5, 2003

overview
Overview
  • Introduction
    • climate effects of aerosols
    • aerosol size distribution, mass / number concentrations
  • Ultrafine particles and clouds
overview1
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
theme
Theme
  • Regulations based on mass concentrations (PM10 and PM2.5)
    • less attention to modeling number concentrations (i.e. ultrafines)
theme1
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
theme2
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)
aerosols and climate direct effect
Aerosols and Climate: Direct Effect

Direct Effect:

Scattering and

absorption by

particles

photo: SeaWifs website

aerosols and climate direct effect1
Aerosols and Climate: Direct Effect

Direct Effect:

Scattering and

absorption by

particles

Roughly proportional

to aerosol mass

concentration

photo: SeaWifs website

indirect effect on climate
Indirect Effect on Climate

Aerosol Particles

Cloud Droplets

activation / nucleation

indirect effect on climate1
Indirect Effect on Climate

Aerosol Particles

Cloud Droplets

Clean Air

Polluted Air

indirect effect on climate2
Indirect Effect on Climate

Aerosol Particles

Cloud Droplets

“First” indirect effect: albedo

“Second” indirect effect: lifetime

Clean Air

Brighter, more persistent clouds

Polluted Air

aerosols and climate indirect effect
Aerosols and Climate: Indirect Effect

AVHRR observation of

indirect effect

Red: visible

Green: 3.7 mm solar IR

Blue: infrared

aerosols and climate indirect effect1
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

aerosol activation
Aerosol Activation

Diameter

  • “Activation” = formation of cloud droplet
  • involves a competition between solute

and surface tension effects

Number

aerosol activation1
Aerosol Activation

Diameter

  • “Activation” = formation of cloud droplet
  • involves a competition between solute

and surface tension effects

Depends on number

concentration above

“critical diameter”

Number

previous work
Previous Work

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

Ultrafine

CCN

Cloud Droplets (cm-3)

Boucher & Lohmann, 1995

Sulfate Mass (mg m-3)

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

previous work1
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]

aerosol microphysics
Aerosol Microphysics

Diameter

Nucleation

Emissions

Coagulation

Condensation

Deposition

Number

slide23

M1

N1

M2

N2

...

...

mo 2mo … Mass

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

slide24

M1

N1

M2

N2

...

...

mo 2mo … Mass

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

aerosol microphysics1
Aerosol Microphysics

Coagulation:

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

General Dynamic

Equation

Condensation:

model structure
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
slide29

Van Dingenen et al., 1995

JGOFS cruise

Sep/Oct, 1992

uncertainties
Uncertainties
  • Particulate Emissions
    • Most sulfate aerosol mass results from gas-phase SO2 emissions
    • Particulate sulfate: <5% 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
sensitivity scenarios
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
ultrafine particles and ccn1
Ultrafine Particles and CCN

Diameter

Condensation

to accumulation

mode does not

produce new

CCN

Condensation

Number

Growth

ultrafine particles and ccn2
Ultrafine Particles and CCN

Diameter

Additional ultrafine particles result in

enhanced CCN formation

Condensation

to accumulation

mode does not

produce new

CCN

Condensation

Number

Growth

impact of particulate emissions
Impact of Particulate Emissions

SO2 emissions

SO2/SO42- emissions

summary and conclusions
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?