Some of the toxic compounds

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Air Pollution

• Some of the toxic compounds
• Ambient standards
• Atmosphere in general
• Measurements exposures
• Smog chemisty and modeling

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Air pollution

• One of the most significant sources of air
  pollution is combustion
• Coal
• Diesel
• Natural gas
• Gasoline
• Wood and biomass

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Mastery of Fire

• 400,000 years ago in Europe
• 100,000 years ago in Africa
• M. N. Cohne, 1977

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When fire was brought inside the home very large
smoke exposures resulted

• These exposures are often much higher in the
  developing world than in the industrialized
  world
• Women tend to spend more time around unvented
  fires than men

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• In Nepal females and their very young children
  receive much higher exposures to indoor fires
  than males (Kirk Smith, 1983)
• Average cooking time is 2.8 hours
• Prevalence of chronic bronchitis is related to
  hours spent near the stove

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Ozone

• ozone is a form of oxygen it has three atoms of
  oxygen per molecule
• It is formed in the lower troposphere (the
  atmosphere we live up to 6 km) from the
  photolysis of NO2
• NO2 light --gt NO O.
• O. O2 -----gt O3 (ozone)
• its concentration near the earths surface ranges
  from 0.01 to 0.5 ppm

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Ozone Health Effects

• Ozone causes dryness in the throat, irritates the
  eyes, and can predispose the lungs to bacterial
  infection.
• It has been shown to reduce the volume or the
  capacity of the lungs for air
• School athletes perform worse under high ambient
  O3 concentrations, and asthmatics have difficulty
  breathing
• The current US standard has been reduced from
  0.12 ppm to, 0.08 ppm for one hour, to 0.08 ppm
  for 8 hours

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Lung function before exposure to O.32 ppm O3
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Lung function after exposure to O.32 ppm O3
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Killer Particles
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Particle Health Studies

• Dockery et al., N. Eng .J. Med, vol 329, p1753,
  1993)
• looked at 6 American cities with different annual
  PM2.5 concentrations
• From 1974 to 1990, they followed 8111 males and
  females.
• Subjects were 25-74 years old

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Mortality rates were estimated from

• Survival times (date of death minus the start
  date for that person in the study)
• Raw mortality rates are computed, for each city,
  which are the number of deaths/year/100,000
  people
• These were adjusted for smoking, education, body
  mass index, and other risk factors

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Mortality vs. particle exposure
1.3
1.2
mortality ratio
1.1
1.0
10 20 30 40
2.5 mm particle conc. in mg/m3
Watertown, Mass.Harriman, Tenn. Steubenville,
Ohio St. Louis Portage, Wis Topeka, Kansas
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ChiangMai, Thailand
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Carbon Monoxide (CO)

• Generated from incomplete combustion
• C2H4 3O2 ? heat 2H2O 2CO2 (complete
  combustion)
• C2H4 2.5O2 ? less heat 2H2O CO2 CO
  (incomplete combustion)

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Carbon Monoxide (CO)

• Typical rural concentrations are 0.1 ppm
• Urban concentrations as high as 360 ppm have been
  reported
• The US ambient air quality standard is 9 ppm for
  8 hours not to be exceeded more then once /year
• CO Hb ? CoHb normal blood level O.5 smokers
  (3-10) ambient standard based on 1.4
• CO ambient x 0.16 COHb

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The atmospheric compartment

• Temperature and pressure
• Circulation and mixing

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Two important features the atmosphericCompartme
nt aretemperature and pressure
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The atmosphere is usually divided into the
following

• Troposphere 0-10 km
• tropopause 10km
• Stratosphere 10-50km
• stratopause 50 km
• mesosphere 50-80kn
• Thermosphere 80 km

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These divisions come about because of temperature
differences as one increases in altitude
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Air Circulation

• The troposphere contains about 80 of the
  atmospheric mass.
• Air cools with altitude in the troposphere. The
  top 10-15 km is at -60oC which means very
  little water vapor.
• In the stratosphere, temp. increases with height
  because O3 absorbs uv radiation.
• Thermal mixing of air (heat) is responsible for
  global circulation in the lower atmosphere.

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The atmosphere is held to earths surface

• by the gravitational attraction of the earth
• At a given altitude the downward force (F) is
  related to the mass (M) of the atmosphere above
  that point. F M (g) where g is the
  gravitational acceleration constant

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The pressure or force per unit area

• decreases with increasing altitude
• The decline in pressure (P) with altitude is
  approximately to log P - 0.06 (z) where z
  is the altitude in km and P is bars

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How thin is the air at the top of Mt. Everest?

• Mt. Everest is 8882 meters high or 8.88 km high
• log P -0.06 x 8.88
• P 10-0.06x 8.88 0. 293 bars
• Assume there are 1.01bars/atm.
• This means there is lt 1/3 of the air

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• Where does log p - 0.06 (z) come from
• Force mass x accelerationacceleration g
• The mass of air over a surface, A, equals height
  x A x mass/volume the mass / volume density,
  r
• So Force -z x A x r x g
• The change in force at any altitude
• dF -dz x A x r x g F/A pressure, p
• So the change in pressure with height isdp -dz
  x r x g

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• dp -dz x r x g
• What is the ideal gas law
• pV nRT
• Show that r Mw x p/RT
• Substituting for r in dp -dz x r x g
• dp -dz x Mw x p/RT x g
• So dp/p -dz x Mw /RT x g
• Integrating
• So p po exp -Mw g z /RT

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• p po exp -Mw g z /RT
• If we set H (Mw g /RT)-1 it has the units of
  length
• and we get a simple expression p po exp -z
  /H
• Solving for H at 290K R 8.3 joules/(K mole)
  one joule 1kg meter2/sec2 average Mw of air
  28.9 g/mole g 9.8 meter/sec2
• H 8.5 km people actually find that 7km works
  best when 7 km is used we end up with
• log p - 0.06 (z)

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Is it possible in the troposphere to calculate
the rate that temperature of the air decreases
with altitude?
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To do this we need to start with simple
thermodynamics

• The first law of thermo says that the change
  internal energy of a system is the sum of its
  changes in heat content and work that is done.
• dU dq - dw
• A change in work can only occur if a force moves
  through a distance dw d (fxz) d (pV) for
  work there must be movement
• Hence dw Vdp and dU dq - Vdp
• Another form of energy is call enthalpy (H) which
  is the sum of the internal energy and pV from
  pVnRT
• so H U PV or dH dq Vdp Vdp pdV Vdp
  (dq is assumed to be zero for a process that does
  not have a heat loss)
• The change in the heat of a mass, per change in
  a degree centigrade, is called its specific heat
  Cp and Cp dH/dT

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• we said the enthalpy dH Vdp
• specific heat capacity Cp dH/dT
• So Cp dT dH Vdp
• Before we said that the change in pressure with
  height, z was dp -dz x r x g
• So substituting for dp we get
• Cp dT - V x dz x r x g
• So the change in temp with height is dT/dz - V
  x r x g/ Cp
• Density r is mass/V so for an air mass of one
  gram, r 1/V
• This puts Cp in units of energy gram-1
  deg-1 for dry air this is 0.24 cal gram-1 o
  K-1 and we will call it cp
• So - dT/dz g/ cp where g 9.8 m sec-2
• 1 cal 4.1 joules so cp 1 joule gram-1 o K-1
  
• One joule 1 kg m2sec-2
• So - dT/dz g/ cp 0.0098 oK/meter or 9.8
  oK/kilometer

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• - dT/dz g/ cp 9.8 oK/kilometer
• This is called the dry adiabatic lapse rate so
  that - dT/dz ?d
• When - dT/dz gt ?d the atmosphere will be
  unstable and air will move (convection) to
  re-establish a stability

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The quantity ?d is called the dry adiabatic lapse
rate

• Air that contains water is not as heavy and has a
  smaller lapse rate ? and this will vary with the
  amount of water
• If the air is saturated with water the lapse rate
  is often called ?s
• Near the surface ?sis -4 oK/km and at 6 km and
  5oK/km it is -6K/km at 7km high

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So what does lambda give us???
At midday, there is generally a reasonably
well-mixed layer lying above the surface layer
into which the direct emissions are injected.
As the sun goes down, radiative cooling results
in the formation of a stable nocturnal boundary
layer, corresponding to a radiation inversion.
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What happens to the material above the inversion
layer??
more cooling at surface at night

residual layer
altitude

Inversion layer
temp
These materials are in a residual layer that
contains the species that were well-mixed in the
boundary layer during the daytime. These species
are trapped above and do not mix rapidly during
the night with either the inversion boundary
layer below or the free troposphere above.
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When the sun comes up the next day it heats the
earth an the air close to the earth.
During the next day heating of the earth's
surface results in mixing of the contents of the
nocturnal boundary layer and the residual layer
above it
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How does air circulate

• At the equator air is heated and rises and water
  is evaporated.
• As the air rises it cools producing large amounts
  of precipitation in equatorial regions.
• Having lost its moisture the air mass moves north
  and south.
• It then sinks and compresses (30oN and S
  latitude) causing deserts

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Circulation currents
30oN
Hadleycell
equator
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• The air in each hemisphere mixes with a time
  constant , t, of a few months.
• The air between the north and south hemispheres
  completely mix on the order of one year.
• Air mixes into the stratosphere from rising
  Hadley cells in the tropics, storms and eddy
  diffusion.
• exchange between the troposphere and the
  stratosphere can be thought of in terms of mean
  residence times (MRT)

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• The mean residence time (MRT) can be expressed
  as MRT mass / flux where flux is
  mass/time
• If 75 of the mass/year in the stratosphere comes
  from the troposphere
• 1 MRT ----------------- 1.3 years
• 0.75/year

41
So are we doing this???

• Mt. Pinatubo in the Philippines erupted in June
  1991, and added a huge amount of SO2 and
  particulate matter the stratosphere. After one
  year how much SO2 was left?
• For a 1st order process C Coe -1
  year/ MRT
• C/Co e -1 year/ MRT e -1/1.3 0.47 or 50
• in 4 years, C/Co e -4 years/1.3 years
  5

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• What happened to global temperatures after the
  Pinatubo eruption
• A lot of SO2 was injected into the atmosphere
• SO2 forms fine sulfate particles that reflect
  light back into the atmosphere and this cools the
  upper troposphere

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Atmospheric Composition

• N2 78.084 3.87x1021 grams
• O2 20.946 1.19x1021
• Ar 0.934 6.59x1021
• CO2 0.036 2.80x1018
• Ne 18.2 ppm 6.49x1016
• H2 510 ppb 1.82x1014
• CFC 11 280 ppt 6.79x1012
• MeBr 11 ppt 1.84x1011

45
Where does oxygen come from in our atmosphere?

• 3.8 billion years ago the earliest bacteria
  were able to take acetic acid and metabolize it
  to CO2 and water.
• CH3COOH -gtCO2 H2O
• A later form of bacteria could obtain energy from
  the reduction of H2S to S

46

• CO2 2H2S-gtCH2 O 2S H2O
• As supplies of H2S were consumed in the oceans
  other energy generating metabolic processes
  became more competitive
• one was photosynthesis
• H2O CO2 -gt CH2O O2

47
A good summary of the Rise of Life on Earth

• is given in National Geographic, vol 193, p 54,
  March 1998

48

How do we estimate exposure?

• Measurements
• Models
• Once we know exposures these concentrations can
  be compared to ambient air quality standards and
  controls or emission standards calculated.

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Particle measurements
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Activities that generate aerosols in Kamens home
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Cooking stir-fried vegetables Kamens house,
1987, EAA data
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Vacuuming in Kamens House
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Kamens house at night
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Chemilumenescence measurement of Ozone
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Using UV photometry to measure Ozone

• This is the most modern technique for measuring
  ozone
• sample air with O3 enters a long cell and a 254
  nm UV beam is directed down the cell.
• at the end of the cell is a UV photometer which
  is looking at 254 nm light
• we know that light Intensityout light
  intensityin e- a L Conc

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Modeling exposure
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c concentration at a certain distance down
wind Q emission rate in mass/ time m wind
speed sy variable representing the spread of
the plume in the y direction (depends on
stability) sz variable representing the spread
of the plume in the z direction (depends on
stability)
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Photochemical Reactions?Smog

• What is the key reaction that generates ozone at
  the surface of the earth?
• What is the main reaction that generates it in
  the stratosphere?
• How would you control O3 formation?

62

• Photochemical Reactions
• In the stratosphere O3 is good, because it
  filters uv light.
• At the earth's surface, because it is so
  reactive, O3 is harmful to living things

63

• In the stratosphere O3 mainly forms from the
  photolysis of molecular oxygen (O2)
• O2 uv light -gt O.
• O. O2 M --gt O3 M
• In the troposphere nitrogen dioxide from
  combustion sources photolyzes
• NO2 uv or visible light -gt NO O.
• O. O2 M --gt O3 (M removes excess energy and
  stabilizes the reaction)

64

• O3 can also react with nitric oxide (NO)
• O3 NO -gt NO2 O2

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What happens in urban air??

• In urban air, we have the same reactions as we
  discussed before
• NO2 uv light -gt NO O.
• O. O2 M --gt O3 M
• O3 NO -gt NO2 O2
• This is a do nothing cycle (Harvey Jeffries)

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In the urban setting there are a lot of ground
base combustion sources
Exhaust
hydrocarbonsNO NO2 CO
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• Emissions of organics, and especially aldehydes,
  can photolyze and generate radicals
• H2CO hn -gt .HCO H.
• H. O2 -gt .HO2
• if we go back to the cycle NO2 uv light -gt
  NO O. O. O2 M --gt O3 M O3 NO -gt NO2
  O2
• .HO2 can quickly oxidize NO to NO2
• NO .HO2 -gt NO2 OH.This is a key reaction in
  the cycling of NO to NO2
• (Why??)

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• OH. can now attack hydrocarbons such which
  makes formaldehyde and other radical products
• for ethylene CH2CH2 OH. -gt OHCH2CH2.
  OHCH2CH2. O2 -gt OHCH2CH2O2.
• OHCH2CH2O2. NO -gtNO2 OHCH2CH2O.
• OHCH2CH2O. O2 -gt H2CO .CH2OH
• O2 .CH2OH -gt H2CO .HO2

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These reactions produce a host of radicals which
fuel the smog reaction process
First OH radicals attack the electron rich double
bond of an alkene
Oxygen then add on the hydroxy radical forming a
peroxy-hydroxy radical
the peroxy-hydroxy radical radical can oxidize NO
to NO2 ,just like HO2 can
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• There is similar chemistry foralkanes
• OH. H 3-C-CH3 --gt products
• and for aromatics
• OH. aromatics --gt products

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Aromatic Reactions
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Nitrogen Storage (warm vs. cool)
OH
H
C-CO
H2O
H
C-CO
.
3
3
H
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• To help develop some of this chemistry in 1972
  (Jeffries, Fox, Kamens) we built the first large
  outdoor smog chamber, which had an interior
  volume of 300 m3.
• We wanted to predict oxidant formation in in the
  atmosphere.
• The idea was to add different hydrocarbon
  mixtures and NO NO2, to the chambers early in
  the morning, and then watch the chemistry.

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New UNC outdoor smog chamber, August 2002
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The Chamber had two sides
Or Darkness
300 m3 chamber
Teflon Film walls
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The Chamber had two sides
Or Darkness
300 m3 chamber
Teflon Film walls
propylene
Formaldehyde
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The Chamber had two sides
Or Darkness
300 m3 chamber
Teflon Film walls
propylene
Formaldehyde
Mercedes
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The Chamber had two sides
Or Darkness
NO NO2
300 m3 chamber
Teflon Film walls
propylene
Formaldehyde
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Example experiment with the following chamber
concentrations

• NO 0.47
• NO2 0.11 ppm
• Propylene 0.99 ppmV
• temp 15 to 21oC

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Solar Radiation Profile
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Example Mechanism

• NO2 hn -gt NO O. k1 keyed to
  sunlight
• O. O2 --gt O3 k2
• O3 NO2 --gt NO O3 k3
• H2CO hn --gt .HCO H. k4 keyed to sunlight
• H. O2 --gt HO2. k5
• HO2. NO --gt NO2 OH. k6 (fast)
• OH. CC ---gt H2CO HO2 H2COO. k7
• dNO2/dt -k1NO2 DNO2-k1 NO2 Dt

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Photochemical System
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• The model can then be applied to urban or
  regional airsheds to predict observed ozone,
  given realistic emissions of Hydrocarbons and NOx
• We we can then try different control scenarios
  for HC and NOx to achieve reductions in ambient
  ozone formation.