Smog

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Smog

• To the right is Los Angeles on a smog-filled day
  and a smog-free day The haze is due to the
  presence of aerosols and particulates
• Two types of smog
• Industrial
• Photochemical

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Industrial Smog

• Occurs from oil or coal combustion
• Combustion products contain particulates (soot,
  fly ash) with adsorbed SO2
• SO2 is main ingredient in industrial smog
• Promotes aerosol formation
• In aerosol droplets
• 2 SO2 (g) O2 (g) 2 SO3 (g)
• SO3 (g) H2O (l) H2SO4 (aq)
• Sulfuric acid is corrosive and attacks bronchial
  passageways. Of special concern to
  asthma/emphysema sufferers

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Industrial Smog

• Source of SO2
• Sulfur containing compounds in coal and oil
• Non-ferrous smelters
• Smelters convert metals ores to free metals
• Example Nickel sulfide ores
• 2 NiS (s) 3 O2 (g) 2 NiO (s) 2 SO2 (g)
• Instead of releasing SO2 into aerosol droplets
• 2 SO2 (g) O2 (g) 2 SO3 (g)
• SO3 (g) H2O (l) H2SO4 (aq)
• SO2 can be captured, catalytically converted to
  SO3 and reacted with water to form concentrated
  sulfuric acid

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Primary Secondary Pollutants

• Primary Pollutants Pollutants directly emitted
  to a biogeochemical reservoir, such as the
  atmosphere.
• In the case of industrial smog, SO2 is the
  primary pollutant
• In aerosol droplets
• 2 SO2 (g) O2 (g) 2 SO3 (g)
• SO3 (g) H2O (l) H2SO4 (aq)
• Secondary Pollutants Pollutant(s) formed in
  biogeochemical reservoir by subsequent chemical
  reactions. In this case, sulfur trioxide and
  sulfuric acid are secondary pollutants.

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Photochemical Smog

• Photochemical Smog The primary pollutants of
  nitric oxide (NO) and gaseous hydrocarbons
  interact in the presence of sunlight, oxygen, and
  water vapor to form a hazy cloud, which is a
  collection of secondary pollutants
• First observed in Los Angeles in the 1940s. The
  pictures on the right are of the Gateway Arch in
  St. Louis. The top is a clear day in April, the
  bottom is a hazy smoggy August day.

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Three Ingredients Required for the Formation of
Photochemical Smog

• UV light
• Hydrocarbons
• Nitrogen oxides
• Photochemical pollution level (Stern et al.,
  1973)
• PPL (ROG) (NOx) (Light Intensity) (Temperature)
  / (Wind Velocity) (Inversion Height)
• where
• PPL photochemical pollution level
• ROG concentration of reactive organic gases
• NOx concentration of oxides of nitrogen

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(No Transcript)
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Two Types of Smog
Reducing smog Oxidizing smog
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Nature of Photochemical Smog
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Photochemical Smog

• Start of the Day
• Sun rises
• People get up
• Start their vehicles
• Drive to work
• Fill up their gas tank
• On the Right
• Distribution of trace atmospheric components that
  constitute photochemical smog
• Data taken from Los Angeles in 1960s (smoggy day

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Photochemical Smog

• During fuel combustion
• Formation of nitric oxide
• N2 O2 ? 2 NO

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Photochemical Smog

• Nitric oxide reacts with atmospheric oxygen
• Formation of nitrogen dioxide
• 2 NO O2 ? 2 NO2
• NO O3 ? NO2 O2
• ROO. NO ? RO. NO2

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Photochemical Smog

• Nitrogen dioxide is corrosive and reacts rapidly
  with water vapor
• Formation of nitrous acid and nitric acid
• 2 NO2 H2O ? HNO2 HNO3
• Nitrogen dioxide also forms ozone
• Sunlight necessary to supply enough energy to
  break one of the nitrogen-oxygen bonds
• Atomic oxygen also generates the hydroxyl radical
  by reacting with atmospheric water vapor
• O3 hn ? O2 O
• O H2O ? 2 .OH

.NO2 hn ? .NO O O O2 ? O3
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Photochemical Smog

• Notice that ozone (oxidant) concentration doesnt
  increase until most of NO is converted to NO2.
  This is due to the following competing
  atmospheric chemical reaction
• This is why sunlight is necessary component for
  smog.

.NO O3 ? .NO2 O2
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Other Mechanisms for .OH Formation
NO2 H2O ? NO 2 .OH NO NO2 H2O ? 2
HNO2 2 HNO2 hn ? 2 NO 2 .OH NO2 H2O ? NO
2 .OH
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The Formation of Free Radicals OH

• (1) HONO h? ? OH NO
• (2) H2O2 h? ? 2OH
• (3) O H2O ? 2OH
• (O from O3)
• (4) HO2 NO ? OH NO2
• (HO2 from HCHO)

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Photochemical Smog

• VOCs
• The presence of hydrocarbons and hydrocarbon-like
  organic compounds called volatile organic
  compounds (VOCs)
• These compounds correspond to the curve labeled
  Non-methane hydrocarbons
• VOCs come from
• Anthropogenic sources
• Gasoline pumps
• Cold starts leading to incomplete combustion
• Natural sources
• Trees, plants

Most reactive VOCs have double bonds They were
anti-knock agents but contribute to reactive VOC
emissions
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Oxidation of Hydrocarbons Initiated by OH

• RCH3 ? RCHO
• OH RCH3 (hydrocarbon) ? RCH2 (alkyl) H2O
• RCH2 O2 M? RCH2OO (peroxyalkyl) M
• RCH2OO NO ? RCH2O (alkoxyl) NO2
• RCH2O O2 ? RCHO (aldehyde) HOO
  (hydroperoxyl)
• HOO NO ? NO2 OH
• Note that each step in the sequence produces a
  new radical. The sum of the reactions is
• RCH3 2O2 2NO ? RCHO 2NO2 H2O

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Oxidation of Hydrocarbons Initiated by OH

• CH3CHO ? PAN
• CH3CHO OH ? CH3CO H2O
• CH3CO O2 M ? CH3C(O)OO (acetylperoxy)
• CH3C(O)OO NO2 ? CH3C(O)OONO2 (PAN)
• Peroxyacetic nitric anhydride and related
  compounds, PANs, are the major eye irritants in a
  photochemical smog. PAN is relatively stable
  molecule, especially at low temperature, and
  therefore may be transported over long distances
  by air currents.
• The last equation is also the chain-terminating
  reaction

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Termination Reactions for Removal of .OH
.OH .NO2 ? HNO3 2 HOO. ? H2O2 O2 .OH HOO. ?
H2O O2
or else the conc. would continue to increase and
increase the rate of hydrocarbon oxidation
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Night-Time Smog-Forming Reactions Role of
Nitrate Radical (NO3)
Formation of nitrate radical NO2 O3 ? NO3
O2 Dissociation during daylight NO3 h? (? lt
700 nm) ? NO O2 NO3 h? (? lt 580 nm)? NO2
O NO3 has a lifetime only 5 seconds at noon
time Reactions involving nitrate
radical Nitrate radical adds across the double
bonds in alkenes (CC) leading to the formation
of reactive radical species that participate in
smog formation
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Effects of Photochemical Smog

• Human health
• There are some 100 urban areas with a combined
  population of approximately 100 million people
  that do not meet the existing ambient air quality
  standards for O3 (Spensley 1992)
• O3 at 0.15 ppm causes coughing, wheezing,
  bronchial constriction, and irritation to the
  respiratory mucous system
• Oxidant peroxyacyl nitrates and aldehydes are eye
  irritants
• Damage to materials
• O3 causes cracking and aging of rubber by
  oxidizing and breaking double bonds in the
  polymer
• Effects on the atmosphere
• Reduced visibility

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Effects of Photochemical Smog

• Toxicity to plants
• NOx Toxicity of NOx itself is low compared to
  its secondary products.
• PAN Highest toxicity to plant, damaging
  vegetation at 0.02-0.05 ppm. However, PAN is
  normally present at low concentration.
• O3 Reduction to plant growth and yield. In
  California (mostly located n san Francisco and
  Los Angles), crop damage from O3 and other
  photochemical air pollutants alone is estimated
  to be millions of dollars each year.

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Ozone and PAN damage

• To right Tobacco leaf showing chlorosis
  (yellowing of leaf) due to ozone exposure.
• To right Potato leaves showing bronzing due to
  PAN exposure.

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The Origins of NO and HCExhaust Gases from
Internal Combustion Engines
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Engines
4 Cycle (Stroke) 2
Cycle (Stroke)
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Limiting Vehicle Emissions

• Catalytic Converter
• Platinum-Rhodium catalyst
• Accomplishes the following reactions
• Conversion of Nitric Oxide to original reactants
• 2 NO (g) N2 (g) O2 (g)
• Conversion of carbon containing gases to CO2 and
  H2O (in other words, completing the oxidation!)
• 2 CO (g) O2 (g) 2 CO2 (g)
• hydrocarbons O2 (g) CO2 (g) H2O (g)

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Clean Air Act (CAA)

• First passed in 1970
• Amended in 1977 and 1990
• Places strict limits on emission of pollutants
  from
• Point sources
• Factories
• Power plants
• Mobile sources
• Motorized vehicles
• Plain English guide to CAA on the web
• http//www.epa.gov/oar/oaqps/peg_caa/pegcaain.html

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Pollutants

• U.S. Environmental Protection Agency (EPA)
  established National Ambient Air Quality
  Standards (NAAQS) for pollutants considered
  harmful to public health and the environment.
  This is part of the Clean Air Act.

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Pollutants

• These standards are related to Recommended
  Exposure Limits (REL) set by National Institute
  of Occupational Safety and Health (NIOSH).
• RELs are maximum concentrations of airborne
  compounds a person can be exposed to for a short
  time without suffering adverse health effects.

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NAAQS Pollutants
See the EPA Website http//www.epa.gov/air/urban
air/6poll.html for additional information. A
1999 federal court ruling blocked implementation
of these standards, which EPA proposed in 1997.
EPA has asked the U.S. Supreme Court to
reconsider that decision. All challenges to the
EPA ruling were removed in March 2002.
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Effects of NAAQS Pollutants

• CO
• Binds more strongly to hemoglobin than O2.
• Hemoglobin Protein in red blood cells that
  enables oxygen transport
• Carbon Monoxide interferes with oxygen transport.
• Heart must work harder to supply oxygen to cells
• Colorless, odorless
• Symptoms dizziness, fatigue, headache
• Confused with flu-like symptoms
• Present in second-hand smoke
• Effect is reversible
• Exposure to gas higher in oxygen concentration
  than air will slowly replace CO in blood.

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Effects of NAAQS Pollutants

• SO2
• Forms acidic compounds upon reaction with water
  vapor and O2.
• Sharp odor
• Constricts bronchial tubes
• Causes respiratory distress
• Can trigger asthma
• NO2
• Forms acidic compounds upon reaction with water
  vapor
• Constricts bronchial tubes
• Irritates lungs, more susceptible to respiratory
  infections

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Effects of NAAQS Pollutants

• O3
• Reactive molecule
• Inflames lung tissue
• Reduces lung function
• Causes chest pain, coughing, congestion
• Lead
• Neurotoxin
• Diminishes mental function
• Interferes with enzymes that produce hemoglobin -
  leads to anemia

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Effects of NAAQS Pollutants

• Particulates (lt 10 µm diameter)
• Coarse particles from windblown dust from roads
  and fields
• Accumulates in respiratory system
• Damages lung tissue
• Aggravates asthma
• Particulates (lt 2.5 µm diameter)
• Fine particles emitted from industrial
  combustion, residential combustion, vehicle
  emissions
• Penetrates deeper into respiratory system
• Damages lung tissue
• Decreases lung function
• Places stress on cardiovascular system

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Assessing Air Quality

• EPA developed the Air Quality Index (AQI)
• Definition of AQI There are six categories
• 0 - 50 Good
• 51 - 100 Moderate
• 101 - 150 Unhealthy for Sensitive Groups
• 151 - 200 Unhealthy
• 201 - 300 Very Unhealthy
• 301 - 500 Hazardous
• AQI of 100 corresponds to NAAQS for the pollutant

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Assessing Air Quality

• So AQI of 100 is the level EPA has set to protect
  public health
• Example A carbon monoxide concentration of 9 ppm
  would result in an AQI of 100 for CO
• AQI is set to most offending pollutant (i.e.
  pollutant with largest AQI
• To look at Medfords air quality, go to
• http//www.deq.state.or.us/aq/index.htm
• click on Air Quality Index (AQI)

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Air Quality - Particulates

• Another quality index for particulates is called
  a particulate matter index (PM index)
• PM10 index total concentration of all particles
  lt 10 µm diameter
• PM2.5 index total concentration of all particles
  lt 2.5 µm diameter
• Units of PM index µg/m3
• That is, micrograms of particulate matter per
  cubic meter of air

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• NIOSH - National Institute for Occupational
  Safety and Health. Part of the Center for Disease
  Control (CDC). Conducts research and makes
  recommendations to prevent work related injury
  disease.
• OSHA - Occupational Safety and Health
  Administration. Part of U. S. Department of
  Labor. Enforces laws regarding worker safety.
• For Pocket Guide, see http//www.cdc.gov/niosh/npg
  /npg.html

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• REL - Recommended Exposure Limit. A time-weighted
  average (TWA) of exposure up to a ten-hour
  workday for a 40-hour workweek. C means ceiling,
  Ca means potential carcinogen
• PEL - Permissible Exposure Limit. A time-weighted
  average over an eight-hour workday for a for a
  40-hour workweek.
• IDLH - Immediately Dangerous to Life and Health.
  Above this limit, a worker cannot escape with
  loss of life or irreparable harm to health.