Topic 19: Air Pollution
Part 1
What is air pollution?
• Definition
• Natural sources: dust from wind
storms, soot and carcinogenic
materials from forest fires and
volcanoes, VOCs released by some
plants
• Anthropogenic sources: burning of
fossil fuels (power plants, factories,
motor vehicles, home heating
systems)
Types of pollutants
Two broad categories:
• Primary
• Secondary
Figure 19-3
•
•
•
•
•
The
Major
Players
Carbon oxides
Nitrogen oxides
Sulfur dioxide
Particulates
Volatile organic compounds (VOCs)
Carbon oxides
• CO (carbon monoxide) results from incomplete
combustion of carbon containing substances
– Sources: vehicle exhaust, clearing & burning of
forests/grasslands, tobacco smoke, cooking with fire or gas
stoves
– Effects: reacts with hemoglobin, reducing ability to carry oxygen
• CO2 (carbon dioxide)
– Sources: 93% natural carbon cycle, 7% human activities
(burning fossil fuels, clearing & burning forests/grasslands)
– Effects: increases greenhouse effect
Nitrogen oxides
• NO (nitrogen oxide)
– Source: reaction of atmospheric O2 and N2 at very
high temperatures (car engines, coal-burning power
plants)
– Effects: creates secondary pollutants
• NO2 (nitrogen dioxide)
– Source: 2NO + O2  2NO2
– Effect: Aggravate respiratory systems, suppress plant
growth; creates more secondary pollutants
• Both contribute to the formation of photochemical smog
• NO2reacts with water vapor to form nitric acid and nitrate
salts which are forms of acid deposition
Sulfur compounds
• SO2 (sulfur dioxide)
– Sources: 2/3 from human activities (burning of
S containing coal; oil refining; smelting of
sulfide ores)
– Effects: Combines with water vapor in the
atmosphere to make sulfuric acid, and sulfate
(SO42-) particles
• Acid deposition
• Aggravate asthma
• Reduce visibility
Acid Deposition
• What it is: fallout of sulfuric
(H2SO4) and nitric acid
(HNO3) as precipitation, or
sulfate (SO42-) and nitrate
(NO3-) salts as particulate
matter.
• Effects:
– Ecosystems: changes pH of
soil and aquatic systems
– Stuff: erodes statues and
stone buildings
Open Source
Types of acid deposition
• Wet deposition= rain, snow, fog, cloud vapor of pH
5.6 or lower
• Dry deposition= acidic particles like sulfate and
nitrate salts
• Together they are acid deposition, or more commonly
called acid rain (pH <5.6)
• Wet deposition tends to travel farther than dry.
Acid deposition: in-depth
• Sources: power plants,
factories, smelting plants,
vehicles
• Tall smokestacks reduce local
pollution, but increase
downwind pollution,
sometimes 1000s of miles
away (eg New England, from
mid-west)
• Eastern US has precipitation
of pH 4.4-4.7 on average. This
is due to wind borne acidic
compounds and urban areas
with lots of vehicles.
www.sourcewatch.org
© Cornell University
Regional effects
• Ecological
– Leaches nutrient ions from the soil
– Releases (toxic) heavy metal ions bound to soil
particles into aqueous solution in the soil
– Increases acidity (decreases pH) of water bodies
to fatal levels for animal life
• Human
– Chronic respiratory diseases
– Leach heavy metals into drinking water sources
• Bioaccumulation
– Damage to buildings, statues, metal finishes
Factors That Limit Organisms
• Organisms have a “range of tolerance” for numerous factors
• pH, temperature, salinity, UV radiation, heavy metal
concentrations, etc…
Figure 3-11
Aquatic organisms and pH
• Where in the world is the most acidic precipitation?
Asia (particularly China)
• How can we prevent acid rain?
Particulates
• Suspended particulate matter (SPM)
• Sources: 38% from human activities
(plowing, construction, unpaved roads,
tobacco smoke, burning of coal, vehicle
exhaust)
• Categories:
– Fine (PM-10): diameter< 10μm
– Ultrafine (PM-2.5): diameter< 2.5μm
• Effects: respiratory system aggravation;
mutations, reproductive problems,
Tropospheric Ozone
• O3
• Source: VOCs + NOx + UV + heat  O3
(and other stuff…to be discussed later)
• Major component of photochemical smog
• Effects: irritates respiratory system,
aggravates diseases such as asthma and
heart-related, damages plants, rubber,
paint, and fabrics
Volatile organic compounds
• VOCs
• Include methane (rice paddies, cows, landfills,
oil and natural gas wells), benzene, vinyl
chloride, trichlorethylene (TCE) come from
gasoline, plastics, industrial solvents, synthetic
rubber, tobacco smoke
• Volatile because they spontaneously evaporate
• Effects: long-term exposure can cause cancer,
short-term high dose exposure can cause
dizziness, unconsciousness, and death
Urban special cases: smogs
• Industrial smog
– Combo of sulfur dioxide, sulfuric acid
droplets, ammonium sulfate salts
(combo of sulfuric acid and
ammonia), and carbon particulates.
• Photochemical smog
– Mix of primary and secondary
pollutants formed when UV light
catalyzes reactants between nitrous
oxides and VOCs. One secondary
pollutant is ozone.
www.climatechange.org
Photochemical smog details
• Formation requires vehicles and sunlight
• Morning commuter traffic releases large amounts of NOx and
VOCs
• UV radiation promotes a series of reactions, that result in more
than 100 chemicals
• Ozone is the most abundant
• Warmer temperatures increase the rate of reaction
• Amount of smog peaks at noon when the sun rays are
strongest. They dissipate and fall to low/zero after midnight.
Cycle starts over again in the morning.
• Cities exacerbate the problem due to the heat island effect.
Factors Influencing Levels of
Outdoor Air Pollution
• Reductions occur due to:
– settling out, precipitation, sea spray, winds,
and chemical reactions.
• Increases occur due to:
– urban buildings (slow wind dispersal of
pollutants)
– mountains (trap polluted air)
– high temperatures (promote photochemical
reactions)
Lichens:
Atmospheric canaries in a coal mine
• Absorb air for photosynthesis and
respiration.
• Are stationary and long-lived.
• Different species are sensitive to
different pollutants.
• May store pollutants in their tissues or
die if pollution is severe.
• Old man’s beard: sicken or die in the
presence of too much SO2. Scientists
can monitor the health as an
inexpensive way to monitor pollution
levels.
Not so fun fact: lichens in Scandinavia
absorbed lots of radioactive outfall from the
Chernobyl disaster. 70,000 reindeer that ate
the lichens had to be euthanized due to
radioactive poisoning.