Transcript Notes - UA Atmospheric Sciences

NATS 101
Lecture 23
Air Pollution Meteorology
AMS Glossary of Meteorology
• air pollution—The presence of substances in the
atmosphere, particularly those that do not occur
naturally.
• These substances are generally contaminants that
substantially alter or degrade the quality of the
atmosphere.
• The term is often used to identify undesirable
substances produced by human activity, that is,
anthropogenic air pollution.
• Air pollution usually designates the collection of
substances that adversely affects human health,
animals, and plants; deteriorates structures; interferes
with commerce; or interferes with the enjoyment of life.
Major Air Pollution Episodes
of Historic Significance
• Some of the worst events in the last two
centuries occurred in London
– Key ingredients: calm winds, fog, smoke particles
from coal burning
– 1873 - 700 deaths
– 1911- 1150 deaths
– 1952 - 12,000 deaths (Dec 5 - 9)
• Last event led to the Parliament passing a
Clean Air Act in 1956
http://www.atmos.washington.edu/2005Q4/212/Kaufman_health.pdf
Major U.S. Air Pollution Episodes
of Historic Significance
• U.S. air quality degraded shortly after the
beginning of the industrial revolution
• Coal burning in Central and Midwest U.S.
– 1939 St. Louis Smog Nov 28
– 1948 Donora, PA in the Monongahela River Valley
– 20 deaths, 1000’s took ill in 5 days Oct 27
• Prompted Air Pollution Control Act of 1955
– Ignored automobiles
Major U.S. Air Pollution Episodes
of Historic Significance
• 1960s - NYC had several severe smog episodes
• 1950s onward – LA had many smog alerts from
an increase in industry and motor vehicle use
• Led to passage of the Clean Air Act of 1970
(updated 1977 and 1990)
– Empowered Federal Government to set emission
standards that each state had to meet
U.S. Air Pollution Examples
Smog in San Gabriel Valley, 1972.
(Photo: EPA.)
1963 photo of a severe smog episode in
New York City. (Photo: AP/Wide World
Photo, EPA Journal Jan/Feb 1990.)
Air Pollution in Grand Canyon
Even remote areas are
affected by pollution
Canyon on a clear day
Canyon on a smog day
http://apollo.lsc.vsc.edu/classes/met130/notes/
Nice link to Lyndon Valley State College that has
useful material for a NATS-type course
Primary Pollutants
Injected directly into atmosphere
• Carbon Monoxide (CO)
– odorless, colorless, poisonous gas
– byproduct of burning fossil fuels
– body acts as if CO is O2 in blood, can result in death
• Nitrogen Oxides (NOx, NO)
– NO - nitric oxide
– emitted directly by autos, industry
Primary Pollutants
• Sulfur Oxides (SOx)
– SO2 - sulfur dioxide
– produced largely through coal burning
– responsible for acid rain problem
• Volatile Organic Compounds (VOCs)
– highly reactive organic compounds
– released through incomplete combustion and
industrial sources
• Particulate Matter (dust, ash, smoke, salt)
– 10 um particles (PM10) stay lodged in your lungs
– 2.5 um particles (PM2.5) can enter blood stream
Secondary Pollutants
Form in atmosphere from chemical-photochemical
reactions that involve primary pollutants
• Sulfuric Acid H2SO4
– major cause of acid rain
• Nitrogen Dioxide NO2
– brownish hue
L.A. Sky Colors
Dec 2000
Mark Z. Jacobson
Secondary Pollutants
• Ozone O3
– colorless gas
– has an acrid, sweet smell
– oxidizing agent
• Primary and secondary pollutants are found in
the two types of smog:
– London-type smog
– LA-type photochemical smog (LA AQMD)
SMOG = SMOKE + FOG
Human Response to One Hour
Pollutant Exposure (Turco, p194)
Pollutant
Concentration
Part per million
by mass
CO
10-30 ppmm
Symptom
Time distortion (typical urban level)
100 ppmm
Throbbing headache
(freeway background, 100 ppmm)
300 ppmm
Vomiting, collapse
smoke, 400 ppmm)
600 ppmm
Death
(tobacco
CO sticks to hemoglobin, forming carboxyhemoglobin (COHb),
which reduces the capacity of hemoglobin to carry O2 to cells
Physiology of Exposure to CO
COHb level is 5%-15% for cig puffers!
http://apollo.lsc.vsc.edu/classes/met130/notes/
Human Response to One Hour
Pollutant Exposure (Turco, p194)
Pollutant
Concentration
Parts per million
by mass
NO2
0.06-0.1 ppmm
Respiratory impact (long term
exposure promotes disease)
1.5-5.0 ppmm
Breathing difficulty
25-100 ppmm
Acute asthma
150 ppmm
Symptom
Death (may be delayed)
Human Response to One Hour
Pollutant Exposure (Turco, p194)
Pollutant
Concentration
Parts per million
by mass
O3
0.02 ppmm
Odor threshold (sweet)
0.1 ppmm
Nose and throat irritation in sensitive
people
0.3 ppmm
General nose and throat irritation
1.0 ppmm
Airway resistance, headaches
(long term lead to premature aging of
lung tissue)
Symptom
Human Response to One Hour
Pollutant Exposure (Turco, p194)
Pollutant
Concentration
Parts per million
by mass
SO2
0.3 ppmm
Taste threshold (acidic)
0.5 ppmm
Odor threshold (acrid)
1.5 ppmm
Bronchiolar constriction
Respiratory infection
Symptom
Table 12-2, p.328
Beijing Air Pollution
Record Pollution Levels
AQI > 300 - Hazardous
11-5-2005 AFP Photo
Where’s Beijing?
11-4-2005
NASA MODIS Visible
http://www.terradaily.com/news/pollution-05zs.html
Beijing smog during 2008 summer olympics
Pollution Knows No Boundaries
April 2001 China Dust
Transport Across Pacific
Fig. 12-4, p.322
U.S. Pollutant Trends
1940-1995
• Most pollutants
decreased after the
1970 Clean Air Act
Lead
Particulates
SO2
VOC’s
CO
NO2 is Leveling Off
Fig. 12-9, p.328
AQI > 150 for CO,
SO2, NO2, O3 and PM
Fig. 12-10, p.329
http://www.arb.ca.gov/research/health/fs/pm-03fs.pdf
90% total
pollutants
10% total
pollutants
Table 12-1, p.320
Percentage of
Primary
Pollutants
Fig. 12-2a, p.320
Percentage of
Primary
Sources
Fig. 12-2b, p.320
Air Pollution Weather
• Strong low-level inversion
Subsidence inversion that diurnal heating
does not break or weaken significantly
• Weak surface winds
Persistent surface anticyclone
• Sunny weather for photochemical smog
• Hot weather to accelerate O3 production
Fig. 12-12, p.333
Top of Mixing Layer
Fig. 12-13, p.333
Valleys Trap Pollutants
L.A. is in a basin surrounded by
mountains that trap pollutants
and usually has onshore flow that
creates frequent inversions.
Pollutants can only escape
through narrow canyons
Fig. 12-15, p.334
Leading Edge of Sea Breeze and “Smog Front” over Inland SoCal
Fig. 12-14, p.333
Air Pollution Dispersion
• Air pollution dispersion is often studied with simple models,
termed Box Models. How is a box defined for the LA basin?
Box Model Boundaries for the LA Basin
• Ventilation factor is a simple way of relating concentrations
of pollutants to parameters that modulate the dispersion of
pollutants in a local environments.
• An increase in either the mixing height or the wind speed
increases the effective volume in which pollutants are
allowed to mix.
• The larger the volume, the lower the pollution concentration.
• How does a box model work?
Ventilation Factor (VF)
Mixing
Height
Volume ~ Length  Height
Length = Wind Speed  Time
VF = Mixing Height  Wind Speed
Acid Rain and Deposition
• Sulfur dioxide (SO2) and oxides of nitrogen
(NOx) within clouds (including fog) form acidic
particles when they react with water:
SO2 + H2O  H2SO4 (sulfuric acid)
NOx + H2O  HNO3 (nitric acid)
• Acid Rain is worse downstream of the point
sources of pollution
• Acid Rain affects Trees, Lakes, Structures
• Acid Deposition is a world-wide problem
pH is logarithmic scale.
An one unit change
denotes a factor of 10
difference.
Fig. 12-17, p.338
pH = 5.6 for pristine rain
Acidified Forest in Czechoslovakia
http://www.atmos.washington.edu/2005Q4/212/AcidDepositionSlides.pdf
Fig. 12-19, p.339
Impact on Aquatic Organisms
http://www.epa.gov/airmarkets/acidrain/effects/surfacewater.html#fish
Sandstone Figure in Germany
Herr Schmidt-Thomsen
1908
Herr Schmidt-Thomsen
1968
http://www.atmos.washington.edu/2005Q4/212/AcidDepositionSlides.pdf
Summary
• Air Pollutants – Long History
– Primary: CO, NOx, SOx, VOC, PM
– Secondary: H2SO4, NO2, O3
• Global Problem - Knows No Boundaries!
– Serious Health Consequences
• US Air Improving - Clean Air Act
But It is Degrading in Emerging Economies
• Air Pollution Weather and Air Dispersion
• Acid Rain
NATS 101
Lecture
Ozone Depletion
Supplemental References for
Today’s Lecture
Danielson, E. W., J. Levin and E. Abrams, 1998: Meteorology. 462 pp.
McGraw-Hill. (ISBN 0-697-21711-6)
Moran, J. M., and M. D. Morgan, 1997: Meteorology, The Atmosphere
and the Science of Weather, 5th Ed. 530 pp. Prentice Hall.
(ISBN
0-13-266701-0)
UV Visible
Review:
Ultraviolet (UV)
Absorption
IR
Ahrens, p 36
O2 and O3 absorb UV
(shorter than 0.3 m)
Therefore, reductions in
the level of O3 would
increase the amount of
UV radiation that
penetrates to the surface
Hazards of Increased UV
•
•
•
•
•
Increase number of cases of skin cancers
Increase in eye cataracts and sun burning
Suppression of human immune system
Damage to crops and animals
Reduction in ocean phytoplankton
Natural Balance of Ozone
Disassociation of O2
absorbs UV < 0.2 m
O2 + UV  O + O
O3 forms when O2 and O
molecules collide
O2 + O  O3
Disassociation of O3
absorbs 0.2-0.3 m UV
O3 + UV  O2 + O
Balance exists between O3
creation-destruction
CFC’s disrupts balance
Danielson et al, Fig 2.28
Sources of CFC’s
• CFC’s make up many
important products
Refrigerants
Insulation Materials
Aerosol Propellants
Cleaning Solvents
Commonly Used CFC’s
Name
Formula
Primary Use
Residence Time
(50% decrease)
CFC-11 CCl3F
Propellant
~55 years
CFC-12 CCl2F2 Refrigerant
~100 years
CFC-113
C2Cl3F3 Cleaning Solvent
~65 years
It would take 10-20 years for CFC levels to start falling if
all production ended today due to leakage of CFC’s from
old appliances, etc.
Chronology of Ozone Depletion
1881 Discovery of ozone layer in stratosphere
1928 Synthesis of CFC’s for use as a refrigerant
1950s Rapid increase in use of CFC’s
1974 Description of ozone loss chemical reactions
1979 Ban of CFC use in most aerosol cans in U.S.
1980s Growth of CFC use worldwide
1985 Discovery of Antarctic ozone hole
1987 Adoption of Montreal Protocol calling for a 50%
reduction in use of CFC’s by 1998
Chronology of Ozone Depletion
1989
Confirmation of ozone declines in mid-latitudes of Northern
Hemisphere and in the Arctic
1990
Montreal Protocol amended to require a complete phase out of
all ozone depleting chemicals by 2000
1990
U.S. requirement for recycling of CFC’s
1992
Discovery of high levels of ClO over middle and high latitudes
of Northern Hemisphere
1992
Further amendment of Montreal Protocol calling for an
accelerated phase out by ozone depleting chemicals
2100
Time needed for ozone layer to heal completely?
How O3 is Measured: Dobson Unit
• Ozone can be measured by the depth of ozone if all
ozone in a column of atmosphere is brought to sea-level
temperature and pressure.
• One Dobson unit corresponds to a 0.01 mm depth at
sea-level temperature and pressure
• The ozone layer is very thin in Dobson units.
There are only a few millimeters (few hundred
Dobsons) of total ozone in a column of air.
Mean Monthly Total Ozone
Huge decrease in O3 over Antarctica during the period 1979-92.
Setting the Stage
Conditions over Antarctica promote
ozone loss.
Circumpolar vortex keeps air over
Antarctica from mixing with
warmer air from middle latitudes.
Temperatures drop to below -85oC
in stratosphere.
Chemical reactions unique to
extreme cold occur in air isolated
inside vortex.
Williams, The Weather Book
How Ozone is
Destroyed
June: Winter begins.
Polar vortex strengthens and
temperatures begin to fall.
July-August: The temperatures fall to
below -85oC.
Ice clouds form from water vapor
and nitric acid.
Chemical reactions that can occur
on ice crystals, but not in air, free
chlorine atoms from the CFC.
Williams, The Weather Book
How Ozone is Destroyed
Sept: As sunlight returns in
early Spring, stratospheric
temperatures begin to rise.
Clouds then evaporate,
releasing chlorine atoms
into air that were ice locked.
Free chlorine atoms begin
destroying ozone.
Oct: Lowest levels of ozone are
detected in early spring.
Nov: Vortex weakens and
breaks down, allowing ozone
poor air to spread.
Danielson et al, Fig 2.29
Chemistry of the Ozone Hole
CFC-11
Moran and Morgan, Fig 2.19
Chlorine atoms can be freed from
CFC’s by UV reaction
CCl3F + UV  CCl2F + Cl
CCl2F2 + UV  CClF2 + Cl
C2Cl3F3 + UV  C2Cl2F3 + Cl
Once a chlorine atom is freed, it can
destroy thousands of ozone
molecules before being removed
from the air
Cl + O3  O2 + ClO
ClO + O  O2 + Cl
Annual Cycle of Ozone over SP
http://www.cmdl.noaa.gov/ozwv/ozsondes/spo/index.html
http://www.cmdl.noaa.gov/ozwv/ozsondes/images/ozone_anim2001.avi
Mean Monthly Total Ozone
NASA web site
Decrease in O3 over N.H. during the period 1979 to 1993.
Ozone Hole
Statistics
• Daily max ozone hole area
(2009): 24 million km2 on
17 September.
• Daily min ozone value
area (2009): 94 DU on 26
September.
• Largest ozone hole
ever observed: 24
Sept 2006.
Key Points: Ozone Hole
• Chlorofluorocarbons (CFCs) disrupt the
natural balance of O3 in S.H. stratosphere
CFCs responsible for the ozone hole over SP!
Responsible for lesser reductions worldwide.
• Special conditions exist in stratosphere over
Antarctica that promote ozone destruction:
Air trapped inside circumpolar vortex
Cold temperatures fall to below -85oC
Key Points: Ozone Hole
• CFCs stay in atmosphere for ~100 years
One freed chlorine atom destroys thousands
of O3 molecules before leaving stratosphere
• Montreal Protocol mandated total phase out
of ozone depleting substances by 2000.
• Even with a complete phase out, O3 levels
Would not increase for another 10-20 years
Would not completely recover for ~100 years