Geog. 310 Urban Climatology
Air Pollution
Introduction.
Air is our most vital resource. We can live without food or water for days, but
how long can we live without air? Pollution may be defined as a process of
contaminating a medium with impurities to a less desireable level of quality. And so it is
with air pollution. Most legal definitions deal with its effects on plants, animals, humans
and property…”condition of the surrounding atmosphere that is due to release of
substances by people into the atmosphere in concentrations sufficient to interfere directly
or indirectly with our comfort, safety or health, or with the full use and enjoyment of our
property.”
Main Pollutants.
2 main classes of air pollutants: particulate matter, PM-composed of solids and
liquids of varying sizes (.01-100μ or microns), and gases and vapors, which include any
increase in quantity of the constant gases. Two other sub-groups often discussed
separately: biological poisons and radioactive dust and gases.
A. Particulates
1. Only about 100 compounds emitted into air as identifiable particulates, because (a)
extremely complicated chemical nature, (b) low trace amounts, and (c) photochemical
reactions can alter pollutants-usually for the worst.
2. Largest single group is called dust, having size greater than 1 μ. Dust often from
natural sources such as soil particles from unvegetated surfaces, fires, volcanoes,
agriculture, vehicular movement. Larger particles settle fairly rapidly and do not travel
far except under gusty or strong winds.
3. Soot, a very finely divided carbon particle is urban nuisance. Released by burning
fuels, it attracts many other compounds, including water vapor, making it a potential
respiratory-system danger. Mostly a nuisance as it soils buildings and clothing.
Dust particles are an indicator of industrial pollution, or combustion. They can be soluble
or insoluble in water. Soluble dust may result in an acidic liquid.
4. Aerosols, under 1 μ in size, remain in air longer. They are formed and destroyed
through condensation and dispersion.
5. In cities, concentration of suspended particulates varies with (a) population density
and amount, (b) character and scale of public activity, (c) amount of combustion,
industry, transport, commerce, etc. However, the actual amounts also depend on extent of
ventilation, which is controlled by weather.
6. Chemical composition. 3 main types of PM:
a. sulfates. Formed from oxidation of sulfur in combustion of fuels, leading to
SO2 and SO3, which when combined with water forms H2SO4 (sulfuric acid). This acid
reacts with other chemicals to form sulfates. Sulfates indicates level of fuel combustion in
area.
b. nitrates. Forms from oxidation of nitrous oxide (NO). Nitrates increase the
corrosive power of the atmosphere.
c. Solid organic substances. These include hydrocarbons, aldehydes (both from
cars), phenols and industrial solvents. A majority of these are detrimental to biological
systems, a number being carcinogenic.
Also of health concern are lead and asbestos.
B. Gaseous pollutants
Gases are often the most dangerous offenders; there is a whole slew of them. The major
types are:
1. SO2 (sulfer dioxide) is one of the most dangerous, especially to humans. It attacks
the lungs and the other parts of the respiratory system, usually slowing down the cleaning
action of small hair-like cilia that line the main parts of the system. It is also an irritant to
eyes and skin. It can even destroy the enamel on teeth.
a. Many effects are permanent and irreparable.
b. Formed in industrial areas from combustion of coal or oil primarily, smelters.
c. Converted to sulfuric acid by action of oxygen and water in the air. Highly
corrosive, main form of acid rain. Also implicated in almost all air pollution disasters in
recent decades, including London’s Killer Smog, 1952, in which 4000 died.
d. Product of smelting of sulfide ores (copper, nickel, iron), refineries, pulp &
paper, other metal and chemical processes.
e. Highly corrosive-deteriorates stone (statues), paper, metals, fabric, leather.
f. Downwind of smelters, no vegetation, lakes dead, forests dying.
g. 1 ton coal yields 80 lbs SO2; 1000 gallons gas yields 17 lbs SO2.
2. Halides-flourides, chlorides, etc.
a. Flourides come from aluminium industry, brick plants, pottery works,
phosphate fertilizer plants. Extremely toxic. HFl is taken up by nearly all plants and
certain species damaged by concentrations as low as 1 ppb. Since plants concentrate
fluorides, even low levels in air can produce toxic levels in forage of animals.
b. Chlorine is not as big a problem as in past, although it is released in alkali
industrial plants and occasional tanker spills from water treatment plants.
c. Near source, Fl causes eye and skin irritation, respiratory inflammation and
breathing difficulties.
3. Oxides of nitrogen.
a. Of the 6 or 7 oxides of N, 2 are normally considered pollutants: nitric oxide
(NO) and nitrogen dioxide (NO2). These 2 called “jet-age pollutants” since only highly
advanced countries suffer seriously from them.
b. NO is colorless, odorless, formed when combustion takes place at temperatures
high enough for N2 and O2 to react in air. Formed primarily in auto cylinders, electric
power plants and other v. large energy-conversion processes. Cooling at exhaust of cars
prohibits return to N2 and O2.
c. While NO somewhat toxic, it may be converted to NO2, which is considered
more poisonous. Oxidation of NO to NO2 is very rapid at high concentrations in air, but
slow at low concentrations, except in presence of hydrocarbons and sunlight. Due to CA
sunlight, SF and LA have more NO2 while Chicago and cool climate cities have more
NO. Chemical changes are due to radiant energy of the sun, lumped together under the
name, photochemical smog. NO2 is also a by-product of numerous industries, including
fertilizer and explosives factories.
d. NO2 is only important and widespread pollutant that’s colored-yellow-brown,
as result it significantly reduces visibility. Also has a pungent, sweetish odor detectable at
1-3 ppm.
e. At sufficiently high concentrations, NO2 can be fatal, but quite rare. Prolonged
exposure at ordinary concentrations can lead to lung damage.
f. NO2 reacts with raindrops or water vapor forming nitric acid, HNO3, which
even in small concentrations can corrode metals. Causes vegetation damage as does N
oxides at high levels only.
4. Ozone.
a. Product of reaction between NO2 and hydrocarbons (HC) in the presence of
sunlight, a photochemical process.
b. Extremely toxic, ozone can cause coughing, choking, headache and severe
fatigue; can damage leaves of plants, crack rubber, deteriorate fabrics and fade colors.
c. O3 is used as an index for smog, as it indicates photochemical reactions taking
place. Also called an oxidant.
d. 0.15 ppm in 1-hr lead to tabacco damage in S. Ontario. In LA, O3 has exceeded
.50 ppm, 3rd stage alert, however has been a few years since last 1st stage alert (.2 ppm).
Ozone used in forecasting air pollution potential in various cities.
5. Carbon monoxide.
a. Next to CO2 is most abundant atmospheric pollutant. Like soot, CO is product
of incomplete combustion. Colorless, odorless, very toxic gas.
b. At 100 ppm most people get dizzy, develop headaches and feel other symptoms
of poisoning, as it interferes with oxygen-carrying capacity of red blood cells.
Hemoglobin has greater affinity for CO than oxygen. In traffic jams, CO may reach 370
ppm, inside vehicles. Lethal at high concentrations, as publicized in suicide or accidental
deaths in garages. Leads to brain damage. At lower concentrations may affect driving
performance (hard to tell in LA), leading to accidents. Tolerance in humans is 30 ppm for
max of 8 hrs or 120 ppm for 1 hr.
c. 1000 gallons gas yields 3000 pounds of CO.
6. VOCs-volatile organic carbons
a. Incomplete burning of gas products and sunlight lead to thousands of organic
compounds including hydrocarbons, aldehydes and PAN, peroxyacetyl nitrate.
b. Many hydrocarbons only harmful at high concentrations, but some very
harmful even at lower levels. Aromatics, such as benzopyrene known as carcinogenic.
PAN makes eyes burn and tear and irritates lungs; causes plant damage.
7. Hydrogen sulfide H2S.
a. Results from variety of industrial and other processes, usually as result of
accumulation of industrial wastes in stagnant waters, where bacteria reduce sulfurcontaining compounds to H2S.
b. Smells like rotten eggs, in high concentrations is lethal. Accidental release in
Poz Rica, Mexico led to many deaths. Sewage treatment have H2S alarm systems.
C. Main Sources of Pollutants
1. Cars are main source of air pollution in US through burning of organic fuels.
However industrial areas also contribute to regional amounts.
2. CO is the most abundant pollutant. Over 90% from motor vehicles.
3. Nearly half Nox also from motor vehicles, as is large % of VOCs.
4. SOx (sulfur oxides)-almost 50% from stationary fuel combustion, especially
electric power plants. In Canada, SOx from mining and pulp and paper industries.
5. Particulates from various sources, including transportation, industrial processes,
construction and fugitive dust (unpaved roads).
D. Effects.
1. Plants. Vegetation can signal the presence of pollutants. By examining certain
plants, it is possible to tell which pollutants are present in what amounts. Main pollutants
of plants: SOx, O3, fluorides, PAN, acid deposition-nitric and sulfuric acid. Particulates
can clog stomata, inhibit photosynthesis.
2. Animals. Effects on animals two-fold: affects animals directly making them ill or
dead; affects them indirectly by poisoning their food. Florides in low levels can cause
fluorosis, a crippling disease. Crop dusting with pesticides also hazardous to animals.
3. Human health. There are volumes of literature on health aspects of air pollution.
Many show highly significant correlations between certain ailments and high
concentrations of air pollution.
a. Research methods: epidemiological surveys study a disease as affects a
community rather than individuals; clinical studies look at the disease process in living
subject; industrial research uses hygiene data in long-term records to see chemicals
effects on workers; accidents and pollution episodes reveals a great deal.
b. Air pollution episodes, like London Killer Smog, Meuse Valley, Belgium
(1930), Donora, PA (1948), and others reveal:
1’effects of incidents were anatomically localized and limited to respiratory tract;
2’ people most vulnerable were elderly and those with pre-existing cardiorespiratory ailment;
3’ meteorological conditions important-often stagnant air
4’ Not 1 but 2 or more interacting pollutants responsible-SOx, particulates, fog
droplets. Combined effects greater than individual effects-synergy.
c. Lung cancer, asthma, bronchitis, heart disease have higher incidence in polluted
cities and follow same seasonality as pollution levels.
4. Economy. Air pollution leads to billions in losses through agricultural losses,
health, soiling, property values, material corrosion, lowered visibility, which impacts
transport, and most importantly in air pollution controls.
5. Weather and climate. Air pollution decreases sunshine and visibility; increases
cloudiness, fog and days of rain through condensation nuclei. Acid rain created by
polluted air. Possible leads to severe weather, such as in LaPorte, IN.
E. How Weather & Climate Affect Air Pollution
1. “The solution to pollution is dilution.” Pollution concentrations are controlled by
how well atmosphere disperses chemicals, both vertically and horizontally.
2. Horizontal dispersion depends on wind speed. Doubling the speed spreads pollution
twice as far.
3. Vertical dispersion depends on term, “mixing depth”: the expanse in which warm
air rises and mixes freely with cooler air. It limits the upward boundary for pollution
dispersion. Mixing depth varies with season and time of day. It is usually lower in winter
and early morning, while higher in summer and afternoon.
a. Inversion. In the lower atmosphere, temperatures normally decrease with
height. In certain regions and under certain weather conditions, the opposite occurs with
warm air sitting over cooler air. A case in which temperature increases with height is
called an inversion. Inversions act as a lid to any vertical mixing and its base becomes the
top of the mixing layer.
1’radiation inversion, which occurred with pollution episodes of Donora, Meuse
Valley. Land looses heat at night until lower layer is colder than air above.
2’ subsidence inversion (LA) occurs when a high pressure weather system causes
air to sink and warm, while air below remains cool. Typical of LA in summer, with
warm, dry air sitting above the cool marine layer.
b. The stronger and lower the inversion, the less volume of air available to mix
pollutants and the higher its concentration. Persistent low inversions lead to increasing
pollution levels, especially if horizontal winds are absent as well.
4. Greater sunshine and higher temperatures lead to faster photochemical reactions
and more smog formation. In LA, highest ozone levels are usually on the hottest days of
summer. Photochemical reactions are minimal once temperatures are below 72oF.
F. Air Pollution Controls
1. Usually not until a disaster takes place before any action taken. Not until smog
episode in London, 1952, that that country initiated the Clean Air Act, which prohibited
open burning and led to change of fuels from soft sea coal to natural gas. Since the
problem disappeared, so too the famous London fog.
2. CA and LA have been leaders in smog control and anti-pollution legislation. 1948,
LA first to establish air pollution control districts. Studied photochemical process. 195758 prohibited home incinerators and restricted fuel-oil burning during smog season. Set
standards for HC, CO amounts from exhausts. Smog devices required on all cars that
didn’t meet CA standards-although Detroit claimed it was not possible.
3. Solutions: cleaner cars, strict burning permits, rapid transit, more efficient catalytic
converters, alternatives to infernal internal combustion engine.
4. Controlling pollution at its source. 2 ways:
a. Separation. Pollutants separated from harmless gases and disposed of without
discharging into atmosphere.
1’ filter bags
2’ cyclone-vortex or impingers
3’ electrostatic precipitators, thermal precipitators
4’ scrubbers. Liquid sprayed through gas, washes out particles or gas bubbled
through liquid and pollution adsorbed, such as with activated charcoal.
b. Conversion. Most important conversion by oxidation of pollutants. When
organic substances, containing C, H, O are completely oxidized, products are CO2 and
H2O. Needs high temperature.
5. Catalytic converters, using platinum and palladium convert HC and CO into CO2
and H2O. Needs lead-free fuel. Problem is with Nox. At high temperatures, more
efficient, but produces more Nox. Low temperatures, less efficient, less Nox, but more
HC and CO unburned. Cars use precise control on air/fuel ratios to maximize pollution
reduction.
6. Other controls: zoning-place polluters in area of better dilution or downwind of
residences. Meteorological controls-require less burning, more controls when weather
“bad” for dispersion.
7. Regulations, legislation. LA has strictest regulations in world. Hurts economy?