Aerosols

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AEROSOLS IN THE CLIMATE CHANGE

• PRESENTED BY
• ANKITA MANGAL

Los Angeles, CA
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WHAT ARE AEROSOLS?

• An Aerosol is a colloidal suspension of fine
  solid particles or liquid droplets in a gas.
  Examples clouds, and air pollution such as smog,
  smoke.

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HOW ARE AEROSOLS RELEVANT TO US?

• Aerosols can pose a serious respiratory hazard.
• Aerosols reduce visibility.
• Climate is influenced by aerosols. They scatter
  and absorb radiation generally cooling and
  warmimg of climate.
• They alter the sizes and number of cloud drop.
• They provide sites for atmospheric chemistry
  (e.g. stratospheric ozone depletion, acid rain).
• They are one of 3 elements required for cloud
  formation (other 2 are H2O and a cooling
  mechanism).

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Aitken mode 0.01-0.1 ?m hours to days
The Aerosol Modes
Coarse mode gt1 ?m hours to days
Accumulation mode 0.1-1 ?m weeks
Nucleation mode- lt0.01 ?m minutes to hours
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sources
NATURAL
ANTHROPOGENIC
Natural inorganic materials dust, sea salt,
water droplets. Natural organic materials
pollen, spores,bacteria
anthropogenic products of combustion such as
smoke, ashes oder dusts
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CHEMICAL COMPOSITION
The bimodal nature of the size-number
distribution of atmospheric particles suggests at
least two distinct mechanisms of formation, and
the chemical composition of the particles
reflects their origins.
Fine particles have a diameter smaller than
about 2.5 mm, and are produced by the
condensation of vapors, accumulation, and
coagulation. They have a chemical composition
that reflects the condensable trace gases in the
atmosphere SO2, NH3, HNO3, VOCs, and H2O. The
chemical composition is water with SO4-2, NO3-,
NH 4, Pb, Cl-, Br-, C(soot), and organic
matter where biomass burning is prevalent, K.
Coarse Particles have a diameter greater than
about 2.5 mm, are produced by mechanical
weathering of surface materials. Their
lifetimes, controlled by fallout and washout, are
generally short. The composition of particles in
this size range reflects that of the earth's
surface - silicate (SiO2), iron and aluminum
oxides, CaCO3 and MgCO3 over the oceans , NaCl.
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ORIGINS OF ATMOSPHERIC AEROSOLS

• Condensation and sublimation of vapors and the
  formation of smokes in natural and man-made
  combustion.
• Reactions between trace gases in the atmosphere
  through the action of heat, radiation, or
  humidity.
• The mechanical disruption and dispersal of matter
  at the earths surface, either as sea spray over
  the oceans, or as mineral dusts over the
  continents.
• Coagulation of nuclei which tends to produce
  larger particles of mixed constitution.

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ORIGIN OF THE ATMOSPHERIC AEROSOL
Aerosol dispersed condensed matter suspended in
a gas Size range 0.001 mm (molecular cluster) to
100 mm (small raindrop).
Environmental importance health (respiration),
visibility, radiative balance, cloud formation,
heterogeneous reactions, delivery of nutrients
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AEROSOL NUCLEATION
1 2 3
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molecules
DG
Surface tension effect
cluster size
Critical cluster size
Thermo driving force
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Seinfeld and Pandis
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On the basis of origin
Primary aerosol atmospheric particles that are
emitted directly into the atmosphere.
Secondary aerosol atmospheric particles that
are created by in situ aggregation or nucleation
from gas phase molecules (gas to particle
conversion).
Aerosol Either type may be natural or
anthropogenic or both
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MAIN TYPES OF AEROSOLS

• Continental/ Desert Aerosols
• Marine Aerosols
• Industrial Aerosols
• Volcanic Aerosols
• Organic Forest Hazes
• Smoke/Biomass Burning Aerosols
• Stratospheric Aerosols

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Each Type has several Components

• Wind- Blown Mineral Dust
• Sea Spray
• Natural or Man- Made gas to particle conversion
  products- e.g. volcanic/ industrial emissions,
  DMS
• Natural Hazes from organic volatiles- e.g.
  terpenes , isoprenes
• Natural /Industrial direct emissions- e.g. soot,
  ash, smoke, biomass burning

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AEROSOL DISTRIBUTIONS

• Number
• cloud formation
• Surface
• visibility
• Volume
• mass
• Mass Number
• human health

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WHY SIZE MATTERS
(1) Toxicity
(2) Light Scattering
(3) Particle Lifetime
Seinfeld Pandis
Finlayson-Pitts Pitts
NARSTO, 2003
(4) Surface Reactions smaller particles have
greater relative surface area
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SIZE, COMPOSITION AND IMPACTS
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OPTICAL PROPERTY VISIBILITY
The optics of aerosol science follow the most
rigorous physics, but traditionally defined
visibility is the distance at which a large dark
object, such as a hill or a barn can just be
seen. A more quantitative definition can be
obtained by considering the change in intensity
of light reflecting off an object as a function
of the scattering of light by the atmosphere.
DI/I e(-bDX) Where I is the intensity of
light, b (or bext) is the extinction coefficient
with units of m-1, and X is the distance in m.
The limit to visibility for the human eye is a 2
change in intensity relative to the background
or DI/I 0.02
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ATMOSPHERIC VISIBILITY (absorption scattering)
1.Residual 2.Scattered away 3.Scattered
into 4.Airlight
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Example Visibility improvement during the 2003
North American Blackout
Normal conditions over Eastern US during an air
pollution episode bsp 120 Mm-1 1.2 x 10-4
m-1 at 550 nm bap 0.8 x 10-5 m-1 bext
1.28 x 10-4 m-1 Visual Range 3.9/bext 30
km During blackout bsp 40 Mm-1 0.4 x 10-4
m-1 bap 1.2 x 10-5 m-1 bext 0.52 x 10-4
m-1 Visual Range 3.9/bext 75 km
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AEROSOL OPTICAL DEPTH (GLOBAL MODEL)
Annual mean
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AEROSOL OBSERVATIONS FROM SPACE
Fire locations in red
Biomass fire haze in central America (4/30/03)
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BLACK CARBON EMISSIONS
DIESEL
DOMESTIC COAL BURNING
BIOMASS BURNING
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AEROSOLS IN THE ATMOSPHERE

• Aerosol concentration is highly variable in space
  and time. Concentrations are usually highest near
  the ground and near sources.
• A concentration of 105 cm-3 is typical of
  polluted air near the ground, but values may
  range from 2 orders of magnitude higher in very
  polluted regions to several lower in very clean
  air.
• Radii range from 10-7 cm for the for small ions
  to more than 10 µm (10-3 cm) for the largest salt
  and dust particles.
• Small ions play almost no role in atmospheric
  condensation because of the very high
  supersaturations required for condensation.
• The largest particles, however, are only able to
  remain airborne for a limited time

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TOXIC METALS IN PARTICULATE MATTER.

• MERCURY enters into atmosphere from coal
  combustion volcanoes in elemental form, gets
  associated with particulate matter, mono
  dimethyl mercury compounds occur in atmosphere.
• LEAD lead halide from automotive exhausts are
  common form of atmospheric lead
• BERYLLIUM used mostly in electrical equipments
  its presence is hazardous.

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POLAR STRATOSPHERIC CLOUD (PSC)
g, gas s, particle
ClONO2 (g) HCl (s) (PSC) ? Cl2(g)
HNO3(s) Cl2 hv ? 2Cl Leads to the Ozone
Hole every Spring
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- Effect of aerosol on climate Cooling past
climates, possibly warming future climates -
Effect of aerosol on hydrologic cycle Less
evaporation from cooler land and ocean, more
stable atmosphere, less clouds and
precipitation. - Effect of aerosol on health
May be more important than ozone in causing
cancer and heart problems. - Effect on
agriculture, vegetation Shift of precipitation
away from polluted land, less sunlight to
vegetation
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AEROSOLS AND CLIMATE INDIRECT EFFECT

• Aerosols are the seeds upon which water vapor
  condenses to form a cloud (these are called
  cloud condensation nuclei, or CCN).
• If people make more aerosols, we make more cloud
  droplets, but because there is a fixed amount of
  water vapor in the air these droplets will be
  smaller.
• Smaller droplets scatter light more efficiently!
• Smaller cloud droplets may also impact rain from
  these clouds.
• Very difficult effect to observe and model!

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AEROSOL INDIRECT EFFECT ON CLIMATE

• clean cloud (few particles)
• large cloud droplets
• low albedo
• efficient precipitation

• polluted cloud (many particles)
• small cloud droplets
• high albedo
• suppressed precipitation
• (very controversial)

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AEROSOLS AND CLIMATE

• Drives
• Global Warming

Direct effect Light is scattered and absorbed
IPCC, AR4
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AEROSOLS AND HUMAN HEALTH
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AGRICULTURE IMPACTS
Aerosols cause decrease in solar radiation in the
photo synthetically active region (0.4-0.7 µm)
reducing photosynthesis.
Reduction in productivity
Deposition of particles on the plants shields
solar radiation
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We have in this fine dust aerosols a most
beautiful illustration of how the little things
in the world work great effects by virtue of
their numbers. -John Aitken, 1880
Thank you