Human Impact on the Environment

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Human Impact on the Environment

• Atmospheric Pollution
• Sergio A. Guazzotti
• Department of Chemistry and Biochemistry, UCSD

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Damaging the Ozone Layer

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Composition of Air
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Structure of Present-Day Ozone Layer
90 of O3 molecules reside in stratosphere
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Ozone Formation, Noncatalytic Destruction, and
the Chapman Cycle
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Model Calculated Ozone Abundance vs Typical 1960
Conditions
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Catalytic Processes of Ozone Destruction
Mostly Natural Contributors to X in non-polluted
stratosphere
NOx Catalytic ozone destruction
cycle NO. Responsible for shaping ozone profile
in the middle and upper stratosphere.
HOx Catalytic ozone destruction
cycle HO. Dominant role in ozone destruction at
very high stratospheric altitudes Together
with HOO. responsible for shaping ozone profile
in lower stratosphere
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Atomic Chlorine and Bromine as X Catalysts

• Cl. and Br. efficient in destroying O3
• Natural sources (CH3Cl, CH3Br)
• Anthropogenic sources (CFCs, HCFCs, halons)

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Chemicals That Cause Ozone Destruction

• Anthropogenic sources (CFCs, HCFCs, halons)
• Do not have a tropospheric sink
• Long lifetimes
• After a few years traveling in the troposphere
  they diffuse into the stratosphere where
  eventually they undergo photochemical
  decomposition (UV-C) liberating halogen atoms
• Molina and Rowland (1974) first recognized that
  anthropogenic Cl compounds can destroy ozone

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Simplified schematic of Clx catalytic ozone
destruction cycle
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CFCs Replacements Hydrochlorofluorocarbons (HCFCs)

• Contain H atoms bonded to C
• Majority of the molecules removed from the
  troposphere by reactions starting with H
  abstraction by HO.
• Delicate balance between H content to ensure
  efficient HO. attack and precluding flammability
• HCFC-22 (CFC-22) currently in major use
• Replacing all CFCs with HCFCs would eventually
  lead to build up of Cl

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CFCs Replacements Hydrofluorocarbons (HFCs)

• Main long term replacement for CFCs and HCFCs
• They absorb thermal IR radiation
• Can contribute to global warming
• One atmospheric degradation pathway can produce
  trifluoroacetic acid (TFA)

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Atomic Chlorine and Bromine as X Catalysts

• Cl. and Br. efficient in destroying O3
• Natural sources (CH3Cl, CH3Br)
• Anthropogenic sources (CFCs, HCFCs, halons)

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Regulation of CFCs

• October 1978 manufacture and sale of CFCs for
  spray cans banned in the US
• Montreal Protocol (1987)
• Amendments to accelerate phase-out (London, 1990
  Copenhagen, 1992)
• CFCs emissions have decreased
• HCFCs emissions have increased
• HCFCs reduction or phase-out under Copenhagen
  amendment

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Stratospheric chlorine (equivalent) concentrations
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Ozone Depletion and Ozone Hole
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Now larger
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Why/ How does this happen?

• (A) Special Antarctic Polar Winter Conditions
  Polar Stratospheric Cloud (PSC) Formation.
• (B) Heterogeneous reactions (PSC surface
  reactions). Convert relatively inactive forms of
  chlorine e.g., HCl, ClONO2 to photochemically
  active forms e.g., Cl2, HOCl, ClNO2. Chlorine
  activation
• (C) Springtime Polar Chemistry Cl-containing
  gases created by PSC reactions photolyze.

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(A) Antarctic Polar Winter

• June-September
• very cold much of the polar region exposed to 24
  hs of darkness
• Polar Vortex

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(B) Heterogeneous reactions on PSC surfaces

• During the dark winter months molecular
  chlorine accumulates and becomes the predominant
  chlorine-containing gas in the lower stratosphere

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(C) Springtime Polar Chemistry

• When the sun rises in early spring, Cl-containing
  gases, created by heterogeneous reactions on PSC
  during winter, photolyze.
• Once Cl has been released, it attacks ozone.
• Chlorine activation (during winter) and
  springtime photochemical reactions convert
  chlorine from reservoir forms e.g., HCl, ClONO2
  to active the active forms Cl. and ClO.

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Arctic Ozone Depletion

• Ozone dent over the Arctic is not nearly so large
  or regular as is that over the Antarctic.
• Atmospheric temperature over the Arctic does not
  fall as low and not for as long as over the
  Antarctic.
• Vortex is much weaker.
• Air circulation to surrounding areas is not as
  limited.
• PSCs form less frequently.
• BUT springtime conditions over the Arctic are
  changing for the worse

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March Average of total overhead O3 63oN to 90oN
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Global Decreases in Stratospheric Ozone

• Between 1979 and 2000, global stratospheric O3
  column abundance decreased by approximately 3.5.
• Decrease between 60oS and 60oN was 2.5
• Decrease between 60oN and 90oN was 7.0
• Decrease between 60oS and 90oS was 14.3
• Unusual decreases observed following the El
  Chichon volcanic eruption in April 1982 and the
  Mount Pinatubo eruption in June 1991.

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Changes in Monthly-Averaged Global Ozone
Percent difference in global ozone from 1979
monthly average
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The second-largest volcanic eruption of this
century, and by far the largest eruption to
affect a densely populated area, occurred at
Mount Pinatubo in the Philippines on June 15,
1991. The eruption produced high-speed
avalanches of hot ash and gas, giant mudflows,
and a cloud of volcanic ash hundreds of miles
across. The impacts of the eruption continue to
this day. U.S. Geological Survey
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Mt. Pinatubo SO2 cloud
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Observed Global Annual Surface Air Temperature
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Ground-Level Air Pollution

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SMOG

• Smog combination of smoke and fog
• London-type Smog
• results from the burning of coal and other raw
  materials in the presence of a fog or a strong
  inversion
• Photochemical (Los Angeles) Smog
• results from the emissions of hydrocarbons and
  oxide of nitrogen in the presence of sunlight

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London-type smog

• Several deadly London-type smog events in the
  19th and 20th centuries, such as the one on
• December 1952 (London) 4000 excess deaths
  occurred

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Photochemical (LA) smog

• soup of gases and aerosol particles
• some of the substances are emitted (primary
  pollutants) whereas others form chemically or
  physically in the air (secondary pollutants)
• involves hundreds of different reactions (giant
  chemical reactor)
• sunshine vital ingredient
• relatively little movement of the air masses
  (inversions)
• relatively high levels of ozone at ground level
  (ozone in the wrong place)

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Temperature Inversion
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Source/Receptor Regions in Los Angeles
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Particulates in Air Pollution
Although most regulations of air pollution focus
on gases, aerosol particles cause more
visibility degradation and possibly more health
problems than gases.
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Aerosols liquid and solid particles suspended in
the air - Natural and Anthropogenic Sources
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Size Distribution
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Visibility Degradation
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Health Effects of Air Pollutants
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Health Effects of Air Pollutants

• Lung functions
• Lung growth
• Irregularities in heartbeats
• Long-term chronic exposure
• Respiratory illness
• Asthmatic attacks
• Angina pain
• Hospital admissions
• Emergency room visits
• Pulmonary deaths
• Cardiovascular deaths

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London-type smog

• Several deadly London-type smog events in the
  19th and 20th centuries, such as the one on
• December 1952 (London) 4000 excess deaths
  occurred

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Health Effects of Outdoor Air PollutantsGaseous
Pollutants
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Regulation in the U.S.

• Air Pollution Act of 1955
• Clean Air Act of 1963
• Motor Vehicle Air Pollution Control Act of 1965
• Air Quality Act of 1967
• Clean Air Act Amendments of 1970
• Clean Air Act Amendments of 1977
• Clean Air Act Amendments of 1990
• Clean Air Act Revision of 1997
• New Clean Air Act Regulations (2002/2003)
• New Source Review (NSR) modification

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INDOOR AIR POLLUTION

• Although epidemiological studies have found an
  association between short-term exposure to
  outdoor particulate air pollution and health
  problems, people spend most of their times
  indoors, and concentrations of aerosols particles
  are often greater indoors than outdoors.

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Sources of Major Indoor Air Pollutants
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