Proxy Climate Data

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Lecture 33 Air Pollution The Ozone Hole
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Air Pollution and The Ozone Hole

• We will discuss
• Air pollution types, sources, and trends
• Tropospheric and stratospheric ozone
• Pollution in the urban environment

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Types Sources of Air Pollution
Primary air pollutants enter the atmosphere
directly, while secondary pollutants form by
chemical reaction. Pollutant sources are both
natural, such as volcanoes and forest fires, and
human caused, such as cars and industry.
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Emission inventories
Area sources
Point sources
On-road and non-road mobile sources
Biogenic emissions
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Principal Air Pollutants
Carbon monoxide, sulfur oxides, nitrogen oxides,
volatile organic compounds, and particulate
matter are the most prevalent primary pollutants,
and transportation and power generation are the
primary sources for these pollutants.
VOC
SOX
NOX
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Definitions NOx oxides of nitrogen (NO NO2)

• NO colorless, odorless, nonflammable
• NO2 orange, toxic, corrosive, sharp odor
• Emitted by combustion processes
• National emission inventory (18,690 tons N/day)

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Definitions Volatile Organic Compounds, VOCs

• VOCs are a group of compounds, characterized by
  their ability to evaporate and their reactivity
  in the atmosphere
• National emission inventory (133,200 tons C/day)
• Emitted by combustion processes (especially
  vehicles), fuel and solvent evaporation

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Particulate Matter Pollution
Particulates (particles or droplets) are
classified as having diameters less than 10 µm
(PM10) and less than 2.5 µm (PM2.5). 1 inch
25,000 microns (µm). One larger PM2.5 particle
width30 times smaller than that of a human
hair. PM10 pollutants settle out of the
atmosphere relatively quickly compared with the
lingering PM2.5. Both can adversely affect human
health and reduce visibility.
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Visible Invisible Pollutants
Suspended hygroscopic particles may scatter light
and create a white wet-haze, while carbon
monoxide and sulfur dioxide are not visible. The
reaction of nitrogen dioxide and hydrocarbons in
the presence of sunlight may generate unsightly
photochemical smog.
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Ozone in the Troposphere
OZONE Volatile Organic Compounds Oxides of
Nitrogen Sunlight Stagnant Air
Human health is compromised by exposure to ozone
and photochemical smog, which is formed when on a
daily cycle when sunlight dissociates NO2. The
product O reacts with atmospheric O2 to create
O3. Usually, the product NO would then react
with and destroy the O3. Excessive hydrocarbons,
often from automobile exhaust, react with the
product NO and O3 concentrations increase to
harmful levels.
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Ozone in the Stratosphere
UV radiation has enough energy to adversely
impact the health of plants and animals,
including humans. Naturally occurring O3 in the
stratosphere can block the most harmful UV
radiation from entering the troposphere.
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Stratospheric Ozone Destruction
Naturally destructive agents of ozone include NO
and NO2, or oxides of nitrogen, which largely
originate from bacterial activity at the earth's
surface. Human released chlorofluorocarbons
(CFCs) have upset the balance of O3 production
and destruction, and have caused formation of
ozone holes and an increase in human UV exposure.
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CFCs and Ozone Depletion
Stratospheric ozone protects life on Earth from
harmful UV radiation
90 of ozone in atmosphere occurs in a layer
between 19 and 48 km altitude in stratosphere.
Natural production and destruction O2 O
UV ? O3 O3 UV ? O2 O
CFCs destroy ozone CFCs UV ? Cl O3
Cl ? ClO O2 No loose O to make O3
One Cl atom in a CFC molecule can destroy
thousands of O3 molecules
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Evidence of Ozone Depletion
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Short history of discovery of ozone problem
1970 P. Crutzen showed that nitrogen oxides are
involved in reactions that destroy ozone.
NO O3 ? NO2 O2
1976 M. Molina and F. Rowland theorized that
chlorine in chlorofluorocarbons (CFCs e.g.,
CH3Cl) also help destroy the ozone layer. Cl
O3 ? ClO O2
1985 Ozone "hole" above Antarctica discovered
1987 Montreal Protocol signed to restrict CFCs
emissions
1995 Crutzen, Molina and Rowland share Nobel
Prize.
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Ozone depletion is a global problem!
Ozone depletion is not just confined to the
stratospheric Arctic and Antarctic. Over the
United States in March, 1994, ozone levels fell
between 8 and 16 below the values observed
during March, 1979.
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Decline of CFCs
1987 Montreal Protocol signed to restrict CFCs
emissions 1992 more than half the worlds
nations called for a quicker-phase out 1996 NOAA
reported a 1 decline around the world from
ground stations 1997 stratospheric chlorine
concentrations peaked about 1997
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Air Pollution Patterns Trends
Air quality in the U.S. may have been at its
worst in the 1970s, but programs implemented by
the Clean Air Act have helped the U.S. move
toward primary ambient air quality
standards. Regional Air Quality Indices may
identify certain non-attainment areas, which are
then targeted by the Environmental Protection
Agency for improvement.
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Trends in Tropospheric Ozone
Yearly ozone trends are influenced by hot sunny
weather and light surface winds, but many cities
have demonstrated an overall decline in harmful
ozone levels during the 1980s.
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Air pollutants of concern in Texas
PM10 and PM2.5 - Fine particulate matter
suspended in the atmosphere degrades visibility
and has been associated with increased rates of
mortality





































O3 - Ozone at ground level is an irritant, and is
associated with increased incidence of
respiratory disease and decreased respiratory
function











Hazardous air pollutants A variety of health
impacts associated with exposure to HAPs



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Air Quality in Texas cities

• Houston, Dallas/Fort Worth Beaumont/Port Arthur
  and El Paso violate the current ozone standard
  and Austin, San Antonio and Longview would
  violate the new ozone standard.
• El Paso violates the current particulate matter
  standard. Houston and possibly DFW would likely
  violate the new particulate matter standard.

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32-Hour back trajectories for days with peak
8-hour ozone levels over 75 ppb in Austin
(1993-1999)