Aerosols - PowerPoint PPT Presentation

Loading...

PPT – Aerosols PowerPoint presentation | free to download - id: 43cbc7-MjYyY



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Aerosols

Description:

Aerosols: General Comments Any solid, liquid (or mixture) in the atmosphere Sources Natural Anthropogenic (urban, construction, agriculture) Primary ... – PowerPoint PPT presentation

Number of Views:526
Avg rating:3.0/5.0
Slides: 23
Provided by: Marty56
Learn more at: http://www.met.sjsu.edu
Category:
Tags: aerosols

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Aerosols


1
Aerosols
2
Atmospheric Aerosols Bibliography Seinfeld
Pandis, Atmospheric Chemistry and Physics, Chapt.
7-13 Finlayson-Pitts Pitts, Chemistry of the
Upper and Lower Atmosphere, Chapt. 9. Classic
papers Prospero et al. Rev. Geophys. Space
Phys., 1607, 1983 Charlson et al. Nature 1987
Charlson et al., Science, 1992. Recent Papers
Ramanathan et al., Science, 2001 Andreae and
Crutzen, Science, 1997 Dickerson et al., Science
1997 Jickells et al., Global Iron Connections
Between Desert Dust, Ocean Biogeochemistry and
Climate, Science, 308 67-71, 2005.
3
Aerosols General Comments
  • Any solid, liquid (or mixture) in the atmosphere
  • Sources
  • Natural
  • Anthropogenic (urban, construction, agriculture)
  • Primary (introduced directly into the atmosphere)
  • Secondary (formed in the attmosphere)

4
(No Transcript)
5
Aerosol Effects
  • Climate
  • Weather
  • Visibility
  • Health Effects

6
Saharan Dust affects the West African Monsoon
7
Natural Sources and Estimates of Global
Emissions of Atmospheric Aerosols
Source Amount-range (Tg yr-1) Amount -best estimate (Tg yr-1)
Soil Dust 1000-3000 1500
Sea Salt 1000-10000 1300
Botanical Debris 26-80 50
Volcanoes 4-10000 30
Forest Fires 3-150 20
Gas conversion 100-260 180
Photochem 40-200 60
Total 2200-24000 3100

8
Anthropogenic Sources of Aerosols
Source Amount Range (Tg yr-1) Best Estimate
Direct Emission 50-160 120
Gas to particle 260-460 330
Photochemistry 5-25 10
Total 320-640 460
Reference W.C. Hinds, Aerosol Technology, 2nd
Edition, Wiley Interscience
9
Gas-to-particle conversion
  • Certain gas phase reactions result in formation
    of low-vapor-pressure reaction products.
  • Because of their low vapor pressure, they exist
    at high supersaturations and can form particles.

10
Natural Background Aerosol
  • Stratospheric
  • Major volcanic activity injects sulfur dioxide
    (SO2) into the stratosphere
  • Gas to particle conversion, SO2 into sulfuric
    acid (H2SO4)
  • Tropospheric
  • Vegetation, deserts and ocean
  • Primarily in the lowest few km

11
Mount Pinatubo, 1991
12
Urban Aerosol
  • Dominated by anthropogenic sources
  • Three Modes
  • Nuclei Aitken
  • Accumulation Large
  • Coarse Giant

What is meant by the size of an aerosol? What
does a size distribution mean?
13
ORIGIN OF THE ATMOSPHERIC AEROSOL
AerosolSize range 0.001 mm (molecular cluster)
to 100 mm (small raindrop)
Soil dust Sea salt
Environmental importance health (respiration),
visibility, radiative balance, cloud formation,
heterogeneous reactions, delivery of nutrients
14
AEROSOL NUCLEATION
1 2 3
4
molecules
DG
Surface tension effect
cluster size
Critical cluster size
Thermo driving force
15
Atmospheric Aerosols
16
Question?
  • Considering the Urban Aerosol, where are most of
    the particles? Where is the most mass?
  • How many 0.01 ?m particles are necessary to have
    the same mass as one 1?m particles?

17
Urban Aerosol Size Distribution
18
Nuclei Mode (lt0.1?m)
  • Consist of
  • Direct combustion particles emitted
  • Particles formed by gas-to-particle conversion
  • Usually found near sources of combustion (e.g.
    highways!)
  • Due to their high number concentration
  • Coagulate rapidly.
  • End up in accumulation mode
  • Relatively short lifetime

Aitken Particles
19
Accumulation Mode (0.1 µm lt particle size lt 2.5
µm)
  • Includes combustion particles, smog particles,
    and coagulated nuclei-mode particles.
  • (Smog particles are formed in the atmosphere by
    photochemical reactions)
  • Particles in this mode are small but they
    coagulate too slowly to reach the coarse-particle
    mode.
  • they have a relatively long lifetime in the
    atmosphere
  • they account for most of the visibility effects
    of atmospheric aerosols.
  • The nuclei and accumulation modes together
    constitute fine particles.

Large Particles
20
Coarse-particle mode (particle size gt 2.5 µm)
  • Consist of
  • Windblown dust, large salt particles from sea
    spray,
  • Mechanically generated anthropogenic particles
    such as those from agriculture and surface
    mining.
  • Due to their large size
  • Readily settle out or impact on surface,
  • Lifetime in the atmosphere is only a few hours.

Giant Particles
21
Dynamic Processes of Atmospheric Aerosol
  • Formation
  • Gas to particle conversion
  • Photochemical processes
  • Growth
  • Coagulation, condensation, evaporation
  • Removal
  • Settling
  • Deposition
  • Rainout, washout

22
Global Effects of Aerosols
  • Global Cooling
  • Direct effect
  • Indirect effect
  • Ozone depletion
  • Polar stratospheric clouds (PSC)
  • Surfaces of PSC act to catalyze Cl compounds to
    atomic Cl
About PowerShow.com