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 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  Regulations based on mass concentrations (PM 10 and PM 2.5 ) less attention to modeling number concentrations (i.e. ultrafines)

Theme  Regulations based on mass concentrations (PM 10 and PM 2.5 ) less attention to modeling number concentrations (i.e. ultrafines)  Ultrafines cause concern health effects climate change

Theme  Regulations based on mass concentrations (PM 10 and PM 2.5 ) 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)

Earth’s Energy Budget J.T. Houghton: “The science of climate change” Anthropogenic GHGs 2.5 W m -2

Aerosols and Climate: Direct Effect Direct Effect: Scattering and absorption by particles photo: SeaWifs website

Aerosols and Climate: Direct Effect Direct Effect: Scattering and absorption by particles photo: SeaWifs website Roughly proportional to aerosol mass concentration

Indirect Effect on Climate Aerosol Particles Cloud Droplets activation / nucleation

Indirect Effect on Climate Clean Air Polluted Air Aerosol Particles Cloud Droplets

Indirect Effect on Climate Clean Air Polluted Air Aerosol Particles Cloud Droplets Brighter, more persistent clouds “First” indirect effect: albedo “Second” indirect effect: lifetime

Aerosols and Climate: Indirect Effect AVHRR observation of indirect effect Red: visible Green: 3.7  m solar IR Blue: infrared

Aerosols and Climate: Indirect Effect AVHRR observation of indirect effect Red: visible Green: 3.7  m solar IR Blue: infrared Power plant Lead smelter Port Oil refineries

Aerosol Activation Diameter Number  “Activation” = formation of cloud droplet  involves a competition between solute and surface tension effects

Aerosol Activation Diameter Number  “Activation” = formation of cloud droplet  involves a competition between solute and surface tension effects Depends on number concentration above “critical diameter”

Source: IPCC Third Assessment Report

Typical Number Distribution

Typical Mass Distribution

Previous Work Sulfate Mass (  g m -3 ) Cloud Droplets (cm -3 ) Boucher & Lohmann, 1995 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 Ultrafine CCN

Previous Work I: Martin et al. [1994]: W/m 2 II: Martin et al. with background CCN: W/m 2 III: Jones et al. [1994]: W/m 2 IV: Boucher and Lohmann [1995]: W/m 2 “It is argued that a less empirical and more physically based approach is required…” Cloud Droplets (cm -3 ) Sulfate Mass (  g m -3 ) Kiehl et al. [2000]

Aerosol Microphysics Diameter Number Nucleation Emissions Coagulation Condensation Deposition

 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 Sectional Algorithm m o 2m o … Mass M1N1M1N1 M2N2M2N2... Tzivion et al., JAS 44, 3139 – 3149, 1987 Adams et al., JGR /2001JD001010, 2002

 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  m to 10  m Two-Moment Sectional Algorithm m o 2m o … Mass M1N1M1N1 M2N2M2N2... Tzivion et al., JAS 44, 3139 – 3149, 1987 Adams et al., JGR /2001JD001010, 2002

Aerosol Microphysics Coagulation: General Dynamic Equation Condensation:  ~30,000 grid cells  1 year  Adaptive time steps

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

Size Distributions

Van Dingenen et al., 1995 JGOFS cruise Sep/Oct, 1992

CCN (cm -3 ): 0.2% Supersaturation

Uncertainties  Particulate Emissions Most sulfate aerosol mass results from gas- phase SO 2 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  Base Case 1985 sulfur emissions all emissions as gas-phase SO 2 nucleation based on critical concentration from binary (H 2 SO 4 -H 2 O) theory  Primary Emissions 3% of sulfur emissions as sulfate  Enhanced Nucleation critical H 2 SO 4 concentration factor of 10 lower  Pre-industrial no anthropogenic emissions

Vertical Profiles

CCN Vertical Profiles

Ultrafine Particles and CCN Diameter Number

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

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

Impact of Particulate Emissions SO 2 emissions SO 2 /SO 4 2- emissions

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?