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Presentation Slides for
Atmospheric Pollution:
History, Science, and Regulation
Chapter 5: Aerosol Particles in Smog and the Global
Environment
By Mark Z. Jacobson
Cambridge University Press, 399 pp. (2002)
Last update: March 23, 2005
The photographs shown here appear in the textbook and are provided
to facilitate their display during course instruction. Permissions for
publication of photographs must be requested from individual
copyright holders. The source of each photograph is given below the
figure and in the back of the textbook.
Particle Characteristics
Mode
Diameter (mm)
Gas molecules
0.0005
Aerosol particles
Small
< 0.2
Medium
0.2-2
Large
>2
Hydrometeor particles
Fog drops
10-20
Cloud drops
10-200
Drizzle
200-1000
Raindrops
1000-8000
Number (#/cm3)
2.45x1019
103-106
1-104
<1 - 10
1-1000
1-1000
0.01-1
0.001-0.01
Particle Size Distribution
Variation of particle concentration (i.e., number, surface area,
volume, or mass of particles per unit volume of air) with size.
Size distribution usually divided into modes
Mode
Diameter Range (mm)
Nucleation
< 0.1
Accumulation
0.1 - 2
Submode 1 ~ 0.2
Submode 2 ~ 0.5 - 0.7
Coarse
>2
Lognormal Distribution
10
) / d log
D (m m)
10 2
1
10 0
-1
-3
dv m
(m
3 3 cm-3
10
10-2
-3
10
0.001
dv (mm cm ) / d log
10 10D (mm)
dv
-3)-3 /
3 cm
dv 3m
(m
(mm
cm
) / d log
m)
d log1010DD(m(mm)
Describes an individual mode of a size distribution
D1
D2
0.01
0.1
Particle diameter (D, mm)
1
10 2
10
1
10 0
10
-1
10-2
10
-3
0
0.05
0.1
0.15
Particle diameter (D, mm)
Figure 5.1
Ambient Size Distribution
10
2
10
1
10 0
10-1
0.01
2
n
250
x=a ( mm cm )
-3
200
x=v ( mm cm )
3
-3
150
10
dn (particles cm
) / d log
-3 -3
4
10
10 3
300
100
50
0
0.1
1
Particle diameter (D, mm)
dx / d log10DD (mm)
(m m)
10 6
10 5
dx / d log
D (10
dn (particles cm ) / d10log
D (mm)
m m)
Figure 5.2, Claremont,
California, Aug., 1987
Mode
Diameter Range (mm)
Nucleation
< 0.1
Accumulation
0.1 - 2
Submode 1 ~ 0.2
Submode 2 ~ 0.5 - 0.7
Coarse
>2
10
Sources of New Particles
Emission
Sea spray
Soil dust
Volcanic
Biomass burning
Fossil-fuel combustion
Industrial
Miscellaneous
Homogeneous nucleation
Homomolecular
Binary
Ternary
Sea Spray Emission
Form when winds and waves force air bubbles to burst at sea surface
Contain composition of sea water
Spume drops
Drops larger than sea spray form when winds tear off wave
crests.
Sea-spray acidification
Reduction in chloride in sea spray drops as sulfuric acid or nitric
acid enter the drops.
Dehydration
Water loss when drop evaporates in low relative-humidity air
Constituents of Sea Water
Constituent
Water
Sodium
Chlorine
Magnesium
Sulfur
Calcium
Potassium
Carbon
Mass percent
96.78
1.05
1.88
0.125
0.0876
0.0398
0.0386
0.0027
Table 5.3
Sea-Spray Acidification
SO
4
2-
(0.66)
+
Na (0.66)
+
NH (0.5)
4
2+
M g (0.23)
2+
Ca (1.47)
Figure 5.12
Particle composition
Riverside, CA
-
-
NO (4.06)
Cl (0.12)
3
HNO3(g) + ClNitric Chloride
acid gas
ion
HCl(g) + NO3Hydrochloric Nitrate
acid gas
ion
(5.5)
Soil Dust Emission
Soil
Natural, unconsolidated mineral and organic matter lying above
bedrock on the surface of the Earth. Originates from the
breakdown of rocks and decay of dead plants and animals.
Rocks
Sedimentary: Cover 75 percent of Earth’s surface and form by
deposition and cementation of carbonates, sulfates, chlorides,
shell fragments. Example: chalk.
Igneous: Form by cooling of magma. Example: Granite.
Metamorphic: Form by structure transformation of existing
rocks due to high temperatures and pressures. Example: marble.
Breakdown of Rocks to Soil
Physical weathering
Disintegration of rocks and minerals by processes not involving
chemical reactions. Examples: when stress applied to a rock.
Stresses arise due to high pressure under soil or when rocks
freeze/thaw or when saline solutions enter cracks and cause
disintegration/fracture.
Chemical weathering
Disintegration of rocks and minerals by chemical reaction.
Example: Dissolution of gypsum in water:
CaSO 4-2H2O(s)
Calcium sulfate
dihy drate (gypsum)
Ca2+ + SO 4 2- + 2H2 O(aq)
(5.1)
Calcium Sulfate Liquid
ion
ion
water
Types of Minerals in Soil Dust
Quartz - SiO2(s) - clear, colorless, resistant to chemical weathering
Feldspars - 50 percent of rocks on Earth’s surface
Potassium feldspar - KAlSi3O3(s)
Plagioclase feldspar - NaAlSi3O3-CaAl2Si2O8(s)
Hematite - Fe2O3(s) - reddish brown
Calcite - CaCO3(s) - found in limestone
Dolomite - CaMg(CO3)2(s)
Gypsum - CaSO4-2H2O(s)- colorless to white
Clays - soft, compact, odorous minerals resulting from weathering
Kaolinite - Al4Si4O10(OH)8(s)
Illite
Smectite
Vermiculite
Chlorite
Organic matter - plant litter or animal tissue broken by bacteria
Dust Storm From Africa
(Feb. 28, 2000)
SeaWiFS Project, NASA/Goddard Space Flight Center and ORBIMAGE
Time For Particles to Fall 1 km
Diam. (mm)
0.02
0.1
1.0
10
100
1000
5000
Time to Fall 1 km
228 y
36 y
328 d
3.6 d
1.1 h
4m
1.8 m
Only particles smaller than 10 mm reach the global atmosphere
Table 5.4
Volcanic Emission
Over 500 volcanos currently active
Magma contains 1-4 percent gas by mass.
Water vapor makes up 50-80 percent of gas mass
Some other constituents:
CO2(g)
SO2(g)
OCS(g) N2(g)
CO(g)
H2(g)
S2(g)
HCl(g)
Cl2(g)
F2(g)
Particles
Most abundant are silicate minerals.
Range in size from <0.1 to 100 mm
Mount St. Helens (Fall, 1982)
Peter Frenzen, available from
Mount Saint Helens National
Volcanic Monument Photo Gallery
Biomass-Burning Emission
Burning of evergreen forests, deciduous forests, woodlands,
grasslands, agricultural land either to clear land, stimulate grass
growth, manage forest growth, or satisfy a ritual.
Gas constituents
CO(g)
CO2(g)
CH4(g)
NOx(g)
ROGs
SO2(g)
Particle constituents
Ash, plant fibers, soil dust, organic matter, soot (black carbon
plus organic matter)
Composition of soot
High temperatures: Higher ratio of BC:OM in soot.
Biomass Burning in South
Africa (September 7, 2000)
NASA/GSFC/JPL, MISR and Air MISR Teams
Ash, Combusted Plant Fiber,
Elongated Ash, Soil Dust
Reid and Hobbs (1998)
Prescribed Burn in Big Horn
National Forest, Wyoming (1981)
Fig. 5.7. U.S. Forest Service, available from National Renewable Energy Lab.
Fossil Fuels
Coal
Combustible brown-to-black carbonaceous sedimentary rock
formed by compaction of partially decomposed plant material.
Stages of coal metamorphosis
Peat (unconsolidated, brown-black)
Peat coal (consolidated, brown-black)
Lignite coal (brown-black)
Bituminous (soft) coal (dark brown to black)
Anthracite (hard) coal (black)
Oil (petroleum)
Natural greasy, viscous, combustible hydrocarbon liquid that
forms from geological-scale decomposition of plants and
animals.
Fossil Fuels
Natural gas
Colorless, flammable gas, made primarily of methane, often
found near petroleum deposits.
Kerosene
Combustible, oily, water-white liquid with strong odor distilled
from petroleum
Diesel
Combustible liquid distilled from petroleum after kerosene.
Fossil-Fuel Combustion
Emission
Gases
NOx(g), ROGs(g), CO(g), CO2(g), CH4(g), SO2(g)
Particles
Soot (BC+OM), OM alone, SO42-, metals, fly ash
Fly ash
Contains O, Si, Al, Fe, Ca, Mg.
Industrial Emission
Source
Smelters
Oil-fired power plants
Coal-fired power plants
Metals in Fly Ash
Fe, Cd, Zn
V, Ni, Fe
Fe, Zn, Pb, V, Mn, Cr, Cu, Ni, As,
Co, Cd, Sb, Hg
Municipal waste incineration Zn, Fe, Hg, Pb, Sn, As, Cd, Co, Cu,
Mn, Ni, Sb
Steel-mill furnaces
Fe, Zn, Cr, Cu, Mn, Ni, Pb
Table 5.5
Miscellaneous Particle Sources
Tire-rubber particles
Pollen
Spores
Bacteria
Viruses
Plant debris
Meteoric debris
Processes Affecting Particle
Evolution
Homogeneous nucleation
Emission
Coagulation
Growth
Condensation/evaporation
Deposition/sublimation
Dissolution, dissociation, hydration
Solid precipitation
Dry deposition
Rainout
Washout
Coagulation
Occurs when two particles collide and stick together (coalesce).
Reduces number concentration but conserves volume concentration
Classic coagulation mechanisms
Brownian motion
Convective Brownian diffusion enhancement
Gravitational collection
Turbulent inertial motion
Turbulent shear
Additional mechanisms
Diffusiophoresis
Thermophoresis
Electric charge
van der Waals forces
Fractal geometry effects
80
4
10
10 3
10 2
10
60
After 1 day
40
1
0
10
10 -1
0.01
Initial
After
1 day
20
0
0.1
1
Particle diameter (D, mm)
10
(mm)
m
m)
m)
dn (particles cm-3) / d log10Dm(mm)
Initial
log10D
-3
100
( m cm
dv m
10
10 5
dv (mm3 3cm-3)-3/ d
6
) / d log10 D (
dn (partic. cm ) / d log10 D (
Effect of Brownian Coagulation
Figure 5.9
Condensation/Evaporation
Figure 5.10
Condensing Gases
Condensation occurs primarily on accumulation mode since it
contains the largest surface area concentration of all modes.
Water vapor
Condenses on accumulation and coarse-mode particles to form
cloud drops
Sulfuric acid
Condensation onto accumulation mode affects visibility
High-molecular weight organic gases
Products of toluene, xylene, alkylbenzene, alkane, alkene,
biogenic hydrocarbon oxidation condense onto accumulation
mode primarily.
80
60
40
Over liquid
water
20
0
-20 -10 0 10 20 30 40 50
o
Temperature ( C)
8
Vapor pressure (mb)
100
Vapor pressure (mb)
120
Vapor pressure (mb)
Vapor pressure (mb)
Saturation Vapor Pressure of Water
Over Liquid Water/Ice Surfaces
7
6
5
4
3
Over liquid
water
2
1
0
-50
Over ice
-40
-30 -20 -10
o
Temperature ( C)
0
Figure 5.11
Dissolution
Dissolution
Process by which a gas diffuses to and dissolves in a liquid on a
particle surface.
Solvent
A liquid in which a gas dissolves
Solute
Gas, liquid, or solid that dissolves in a solvent
Solution
One or more solutes plus the solvent.
Solubility
Maximum gas that can dissolve in a quantity of solvent
Common dissolving gases
HCl(g), HNO3(g), NH3 (g), SO2(g)
Dissociation
Dissociation
Breakdown of dissolved molecules into ions.
Cations
Positively-charged ions (e.g., H+, Na+, K+, Ca2+)
Anions
Negatively-charged ions (e.g., OH-, Cl-, NO3-, HSO4-, SO42-)
Electrolyte
Substance that undergoes partial or complete dissociation
Acidity
Measure of the concentration of hydrogen ions (H+) in solution
pH = -log10[H+]
[H+] = molarity (M, moles of H+ per liter of solution)
Higher [H+] --> lower pH --> more acidic solution
(5.2)
Acidity
In dilute water, the only source of H+ is
H2O(aq)
Liquid
water
H+ + OHHydrogen Hydroxide
ion
ion
[H+][OH-] = 10-14 M2 --> [H+]=[OH-]=10-7 M
--> pH = -log10[10-7M] = 7
(5.3)
Acid/Base
Acid
Substance that, when added to a solution, dissociates,
increasing [H+], decreasing pH
Strong acid: Substances that dissociate readily
(e.g., H2SO4, HCl, HNO3)
Weak acids: Substances that dissociate less readily
(e.g., H2CO3)
Base (alkalis)
Substances that, when added to a solution, reduce [H+],
increasing pH. (e.g., NH3, Ca(OH)2)
pH Scale
Figure 10.3
Dissolution/Dissociation
Addition of acid to solution increases [H+], decreasing pH
Hydrochloric acid
HCl(g)
HCl(aq)
H+ + ClHydrogen Chloride
Hydrochloric
Dissolved
ion
ion
acid gas
hydrochloric acid
Nitric acid
HNO3(g)
Nitric
acid gas
HNO3(aq)
Dissolved
nitric acid
H+ + NO3Hydrogen Nitrate
ion
ion
(5.4) - (5.6)
Soil-Particle Acidification
Addition of acid to calcite-containing soil dust removes
carbonate ion
CaCO 3(s) + 2HNO3(g)
Calcium
carbonate
Nitric
acid gas
Ca2+ + 2NO3- + CO2(g) + H 2O(aq)
Calcium Nitrate Carbon
ion
ion dioxide gas
Liquid
water
(5.7)
Hydration
Bonding of liquid water to solute (anions, cations, or
undissociated molecules).
The higher the relative humidity and greater the quantity of
solute, the greater the liquid water uptake due to hydration.
Hydration responsible for swelling of particles sufficiently to
cause a haze when the relative humidity is below 100
percent.
(5.3)
Sulfuric Acid
Condensation/Dissociation
H2SO4(g)
Sulfuric
acid gas
H2SO4(aq)
Dissolved
sulfuric acid
H+ + HSO4Hydrogen Bisulfate
ion
ion
2H+ + SO 42Hydrogen Sulfate
ion
ion
Condensation occurs primarily on accumulation mode
(5.8)
Ammonia Dissolution/Dissociation
Stationary-source fuel burning (2) Other stationary sources (3)
Mobile combustion sources (2)
Fertilizers (5)
Sewage treatment plants (8)
Livestock (52)
Soils (14)
Figure 5.13
Ammonia gas
emissions
Los Angeles
Humans/domestic animals (14)
NH3(g)
Ammonia
gas
NH3(aq)
Dissolved
ammonia
NH3(aq) + H+
Dissolved Hydrogen
ammonia
ion
NH4+
Ammonium
ion
(5.9) - (5.10)
Na
10
+
NH
4
8
2+
Long Beach, California
August 29, 1987
0500-0830 PST
Mg
2+
Ca
6
4
Cl
-
3
SO
2
-
NO
2-
4
0
0.075 0.14 0.27 0.52
1.04 2.15 4.35
Stage 50-percent cutoff diameter
mm)
(
8.2
-3
+
)
m-3)
Stage concentrationm g m(mg
12
Stage concentration (
-3
m g m(mg
)
m-3)
Stage concentration
Stage concentration (
Aerosol Particle Composition vs.
Size
40
35
+
Na
+
NH
4
30
2+
Mg
25
Riverside, California
August 29, 1987
0500-0830 PST
2+
Ca
20
Cl
15
NO
10
SO
-
3
2-
4
5
0
0.075 0.14 0.27 0.52
1.04 2.15 4.35
Stage 50-percent cutoff diameter
mm)
(
Figure 5.14
8.2
Solid Precipitation
When the relative humidity decreases, ions in solutions may
combine (crystallize) to form solids (solid precipitation).
Solids may also form by chemical reaction on the surface of
particles.
Common solids
Ammonium nitrate - NH4NO3(s)
Ammonium sulfate - (NH4)2SO4(s)
Gypsum - CaSO4-2H2O(s)
Composition, Sources of Particles
Nucleation Mode
Nucleation
H2O(aq), SO42-,
NH4+
Accumulation Mode
Fossil-fuel emission
BC, OM, SO42Fe, Zn
Fossil-fuel emission Biomass-burning
BC, OM, SO42-,
BC, OM, SO42-, ClFe, Zn
Fe, Mn, Zn, Pb, V,
Cd, Cu, Co, Sb, As,
Ni, Cr
Coarse Mode
Sea-spray emission
H2O(aq), Na+, Ca2+,
Mg2+, K+, Cl-, SO42-,
Br-, OM
Soil-dust emission
Si, Al, Fe, Ti, P, Mn,
Co, Ni, Cr, Na+, Ca2+
Mg2+, K+, SO42-, ClCO32-, OM
Table 5.6
Composition, Sources of Particles
Nucleation Mode
Biomass burning
BC, OM, SO42-,ClMn, Zn, Pb, V,
Cd, Cu, Co, Sb,As,
Ni, Cr
Accumulation Mode
Industrial emission
BC, OM, Fe, Al, S
P, Mn, Zn, Pb, Ba
Sr, V, Cd, Cu, Co
Hg, Sb, As, Se, Ni,
H2O(aq), NH4+, Na+,
Ca2+, K+, SO42-,
NO3-, Cl-, CO32-
Coarse Mode
Biomass-burning ash,
industrial fly ash,
tire-particle emission
Cond./dissolution
H2O(aq), SO42-,
NH4+, OM
Cond./dissolution
H2O(aq), SO42-,
NH4+, OM
Cond./dissolution
H2O(aq), NO3-
Coagulation
Coagulation
Particle Mixing State
External mixture
Particle composition is the same as that when the particle was
emitted.
Internal mixture
Particle composition differs from that when it was emitted due to
condensation, dissolution, coagulation, and other physical
processes affecting composition.
Internally- and Externally-Mixed
Soot
Particles
Soot inclusion
Pósfai et al. (1999)
Strawa et al. (1999)
Particle Health Effects
Hazardous compounds in particles
Benzene, PAHs, metals, sulfur compounds
Metals
Lung injury, bronchioconstriction, increased infection
PM10
Asthma, chronic obstructive pulmonary disease, increased
mortality, higher hospitalization and health-care visits for
respiratory and cardiovascular disease. May be no low threshold
for health-related problems due to PM10.
PM2.5
More respiratory illness and premature death than larger
particles. Long-term city exposure may reduce life by two years.
Total air pollution mortality (due mostly due to particles)
2.7 million deaths/yr worldwide from air pollution; 1.8 million in
rural areas, mostly due to indoor burning of biomass, coal.