IB Option E
Methods of Atmospheric Pollution Removal
Thermal exhaust reactor
exhaust from the car engine is combined with more air and reacts due to the heat of the
exhaust gases. Carbon monoxide is converted into _______________________ and unburned hydrocarbons are also
Lean burn engines
by adjusting the carbure
tor the ratio of air:fuel can be altered. The higher the ratio the less carbon
monoxide emitted as more ____________________________________ occurs. Unfortunately, this produces higher
temperatures so more NOx is produced. At lower ratios ______________
___________________________ will be emitted.
the hot exhaust gases are passed over a catalyst of platinum, rhodium or palladium. These fully
oxidize _________ and unburned ____________, and also catalyze the rxn betwe
en CO and NO.
Alkaline scrubbing & limestone
based fluidized beds
Some sulfur is present in _________________ as metal sulfides (i.e. FeS) and can be physically removed by crushing coal
and mixing with water. The more dense sulfides sink to the bottom a
nd the cleaned coal can be skimmed off. Sulfur is
also removed from oil before it is refined by converting it into _____________________.
______________________________ can be removed
from the exhaust of coal burning plants by “
with an alkaline slurry of limestone (_________) and
lime (________). The resulting sludge is used for landfill
or as gypsum
A more modern method known as
involves burning the coal on a bed of
limestone which removes the sulfur as
__________________ or _______________ as the coal
Particulates are solid or liquid particles suspended in
the air. Larger particles can be allowed to settle under
the influence of ____________________ in
sedimentation chambers. For smaller particles, an
chamber can be used. The
charged particulates are attracted to the oppositely
charged electrodes, which are shaken periodically so
that aggregated particulates fall to the bottom of the
precipitator where they can be removed.
IB Option E
Acid deposition refers to the process by which acidic particles, gases and precipitation leave the atmosphere. Both wet
__) and dry deposition (______________________
Rain is naturally _________________ because of dissolved __________, but acid rain has a pH of < ______.
True “acid deposition”
is caused by oxides of nitro
gen and oxides of sulfur
Oxides of Sulfur (SO
Sulfur dioxide occurs naturally from volcanoes and is produced industrially from the combustion of sulfur
fossil fuels and the smelting of sulfide ores.
In the presence of
sunlight, sulfur dioxide is oxidized to sulfur trioxide.
The oxides can react with water in the air to form sulfurous acid and sulfuric acid:
Oxides of Nitrogen (NO
Nitrogen oxides occur naturally from electrical storms and bacter
ial action. Nitrogen monoxide is produced in the
internal combustion engine and in jet engines.
Oxidation to nitrogen dioxide occurs in the air.
The nitrogen dioxide then reacts with water to form nitric acid and nitrous acid:
…or is oxidized
directly by to nitric acid by oxygen in the presence of water:
Environmental effects of acid deposition
increased acidity in the soil leaches important nutrients, such as Ca
. Reduction of Mg
cause reduction in chloroph
yll and consequently lowers the ability of plants to photosynthesize. Many trees have been
seriously affected by acid rain. Symptoms include stunted growth, thinning of tree tops, and yellowing and loss of
leaves. The main cause is the aluminum leached
from rocks into the groundwater. The Al
ion damages the roots and
prevents the tree from taking up enough water and nutrients to survive.
IB Option E
Lakes and rivers
increased levels of aluminum ions in water can kill fish. Aquatic life is also highly sensiti
ve to pH.
Below pH 6 the number of sensitive fish, such as salmon and minnow, decline as do insect larvae and algae. Snails
cannot survive a pH less than 5.2 and below pH 5.0 many microscopic animal species disappear. Below pH 4.0 lakes are
dead. The nitrates present in acid rain can also lead to
stone, such as marble, that contains calcium carbonate is eroded by acid rain. With the sulfuric acid the
calcium carbonate reacts to form calcium sulfate, which can be
washed away by rainwater thus exposing more stone to
corrosion. Salts can also from within the stone that can cause the stone to crack and disintegrate.
the acids formed when NOx and SOx dissolve in water irritate the mucus membranes and
risk of respiratory illness, such as asthma, bronchitis and emphysema. In acidic water there is more probability of
poisonous ions, such as Cu2+ and Pb2+, leaching from pipes and high levels of aluminum in water may be linked to
disease (the jury is still out on this one).
Methods to lower or counteract the effects of acid deposition
Lower the amounts of NOx and SOx
formed (i.e. by improved engine design, use of catalytic converters, and
removing sulfur before, during and after c
ombustion of sulfur
Switch to alternative methods of energy
(i.e. wind and solar power) and reducing the amount of fuel burned (i.e.
by reducing private transport and increasing public transport and designing more efficient power station
Liming of lakes
adding calcium oxide or calcium hydroxide (lime) neutralizes acidity, increases the amount of
calcium ions and precipitates aluminum from solution. This has been shown to be effective in many, but not all,
lakes where it has been trie
Mechanism of acid deposition caused by NO
(memorize these rxns.)
In the atmosphere, NO
are converted into acids by a free radical mechanism involving hydroxyl free radicals,
. These hydroxyl free radicals are formed either by the
reaction of water vapor with ozone
…or by the reaction of water vapor with oxygen free radicals that are formed when ozone decomposes.
The hydroxyl radicals then react directly with NO
in the presence of water to give the dissolved acids.
The role of ammonia in acid deposition
The atmosphere contains trace amounts of ammonia. Ammonia can also be found in the soil due to the action of certain
bacteria known as rhizobia. These can be found in the root nodules of leguminous plants such as pe
as, beans, soy and
clover. The ammonia in the atmosphere can to some extent neutralize the acids to form ammonium sulfate,
______________, and ammonium nitrate, _______________. These ammonium salts, which are the product of a weak
base and a strong acid
, are slightly acidic. As they sink to the ground or are washed out by precipitation the ammonium
ion is deposited and enters the soil where acidification and nitrification can occur.
IB Option E
result of NOX rxns in the
presence of UV light (occurs in dry sunshine). This is responsible for the brown cloud of LA.
“pea soup smog”
result of carbon particulates and sulfur dioxid
e (occurs in cold, damp
weather). Creates yellow
due to env. controls, largely a thing of the past (thank goodness!!!)
when the normal temperature gradient is
when it is warm and dry
and there is
Mountains, buildings and other barriers around cities
can also promote the development of thermal
preventing horizontal movement of air.
(today’s air pollution problem)
aused by traffic exhaust fumes
Free radical rxns between
Examples of reactions leading to secondary pollutants:
(GOOD up high, BAD nearby)
2NO + O
+ sunlight (UV)
NO + O
Production of hydrocarbon
alkyl radicals and hydroxyl radicals produced
when VOCs are oxidized
hydroxyl radicals react with alkanes to produce further alkyl radicals
these alkyl radicals react with
Production of aldehydes
peroxy radicals react with nitrogen monoxide to produce nitrogen dioxide
radicals react with oxygen to form aldehydes
Production of PANs by hydroxyl radicals and aldehydes
atom is removed from an aldehyde
resulting radical reacts with oxygen molecule to produce a peroxide
Termination step: free radicals in step above + NO
IB Option E
Part 2: Smog, Greenhouse Effect & Ozone Depletion
reenhouse gases allow the passage of incoming solar short
wavelength radiation from the Earth. Some of the absorbed r
radiated back to Earth.
Table 2: Major greenhouse gases you should know
Heat Trapping Effectiveness
Compared With CO
Overall contribution to
increased global warming
Evaporation of oceans
Combustion of fossil fuels and biomass
Anaerobic decay of organic matter caused by
Artificial fertilizers and combustion of biomass
pollutant in photochemical smog
Effects of increasing amounts of greenhouse gases on the atmosphere:
hermal expansion of oceans
elting of the polar ice
Changes in precipitation and temperature of regions (causing
Changes in yield and distribution of commercial
Changes in distribution of
Stratospheric Ozone Depletion
Formation and depletion of stratospheric ozone
by natural processes
Mechanisms for ozone depletion by anthropogenic sources
(most common =
, a.k.a. Freon
Refrigerants, propellants for
aerosols, foaming agents for
expanding plastics and
High temperatures inside
combustion engines, power
stations and jet
IB Option E
Alternatives to CFCs for the future
should have the following characteristics
Similar properties to CFC’s, but
No weak C
bonds that can easily be broken by UV to form radicals
Inability to absorb infrared radiation (not greenhouse gases)
Most immediate replacements
Class of chemicals
Lewis structure of example
Decompose more readily than
CFCs and do not build up in
Still contains one C
in polar regions:
Small amounts of water vapor in air freezes to form
Crystals also c
ontain small amounts of molecules, such as
Catalytic rxns occur on the surface of the ice crystals to produce species such as hypochlorous acid (HClO) and
Each spring, the Sun causes these molecules to break down, gi
radicals catalyze the destruction of
Largest ozone layer holes occur during early spring.
As Sun continues to warm the air, ice crystals disperse and ozone concentrations gradually increase
IB Option E
One of the most important indicators of
Required by most aquatic plants and animals for
Consumed by microorganisms when they decompose
The presence of DO in natural water is a
The absence of DO can be a sign of severe pollution.
Fish such as trout require high levels of DO, while fish like carp and catfish can survive with lower levels.
s the type of organisms found in lakes and streams can be used as an indicator of the overall health of the
C, max solubility is 9 ppm (9 mg/L).
DO saturation levels vary with temperature (since oxygen is a gas), but here is a genera
l guideline for stream
supports some varied organisms
Biological Oxygen Demand (BOD)
Measure of the dissolved oxygen (in ppm) re
the organic matter in water biologically.
Water with a
without a means of replenishing oxygen (i.e. lakes or slow
moving streams) will not sustain aquatic life.
Fast flowing, churning that aerates water can help
as water is oxygenated.
Pure water BOD
Measurement of BOD
Sample of water is
Measured volume of the sample is incubated at fixed temp. for
in the water oxidize the organic material)
After 5 days, determine how much oxygen is left in the system
an excess of a manganese (II) salt to the sample.
Under alkaline conditions, Mn(II) ions are oxidized to Mn(IV) oxide by the remaining oxygen
(aq) + 4OH
(aq) + O
(s) + 2H
KI is then added which is oxidized by the Mn(IV) oxide in acid
ic sol’n to form iodine.
(s) + 2I
(aq) + 4H
(aq) + I
(aq) + 2H
The iodine released is then titrated with standard sodium thiosulfate sol’n
(aq) + 2S
(aq) + 2I
By knowing the #moles of iodine produced, the amt. of
oxygen that was present in the sample can be
calculated (thus you know how much oxygen was consumed over the 5 day period)
IB Option E
: too much of a good thing
lake with excess nutrients
Excess nitrates (from artificial fertilizers) and phosphates (from artificial fertilizers and detergents) accumulate in
These nutrients cause CRAZY growth of algae.
Excessive algal growth kills all life in the lake.
much decaying algae, insufficient DO, products of anaerobic decay poison life in the lake
(plus it blocks the
light from penetrating beneath the surface of the water)
, leading to more decay, etc.
Aerobic & Anerobic Decomposition
Aerobic decay product
Anaerobic decay product
Water that is removed from rivers by power stations can be returned with a temperature increase of up to 20
Concentration of D.O.
with rising temperature.
Oxygen in water may be insufficient for fish to survive.
Metabolic rate of organisms increases with temp., placing additional demand fo
in the water.
ning, fertilization and hatching of eggs, is very sensitive to temperature.
Thermal pollution can be reduced by trickling water through a porous material and blowing air in the opposite direction..
The heat is transferred to the
where it is le
Primary pollutants in waste water and
Enter the water from intensive animal farming, excessive use of artificial fertilizers and acid rain.
All nitrates are soluble, so it’s very diff
icult to remove them from water.
Unpolluted water is generally
Max limit of nitrates in drinking water is
) as determined by the World
High nitrate levels in drinking water can poison babies under
It makes it difficult for them to get enough oxygen and they my turn blue and suffocate
methaemoglobinaemia, a.k.a. blue
IB Option E
Ions in polluted water may include cadmium, mercury, lead, chromium, nickel, copper
Table 7: Sources and hazards of some heavy metals
Causes severe damage to the
nerves and the brain.
up food chain;
causes reproductive system failure
in fish; inhibits growth and kills fish
Lead pipes, lead paint
glazes, leaded fuel
banned in US)
Can cause brain damage,
especially in young children
Biomagnification up food chain;
toxic to plants and domestic
igments, byproduct of
Makes enzymes ineffective by
replacing zinc; causes brittle
bones; can lead to lung and
Toxic to fish; produces birth
Include insecticides, fungicides and herbicides, which kill insects, fungi and weeds respectively.
Since they are poisonous, they can be problematic when washed off land into water.
(derived from old imprecise name
introduced into environment at low levels harmless to birds and
animals (including humans), but because it is stable and fat soluble it
accumulated and became concentrated over time via
. Has been banned in many countries because
it had disastrous effects on bird life.
Group of compounds whose structure con
sists of two benzene rings connected via one or two oxygen
atoms. Each benzene ring can have up to four chlorine atoms.
times more poisonous than the cyanide ion.
Sources: one of the herbic
ides present in Agent Orange used during the Vietnam war, and also forms
when waste materials containing organochloro
compounds are not incinerated at high enough
and liver cells and therefore persist in environment
ms of exposure include cirrhosis of the liver, damage to the heart and memory
malfunctions in fetuses.
Polychlorinated biphenyls, PCBs
Can have up to
Source: used in electrical transformers and capacitors because of
their chemical stability and high electrical
Persist in environment and accumulate in fatty tissue.
Reproduce reproductive efficient, impair learning in children and
are thought to be carcinogenic.
IB Option E
Waste Water Treatment
before the water is returned to the environment.
aste water passed through screens and grids to filter out debris.
ater is then passed into a sedimentation tank where it is allowed to
is removed from the bottom of
organic material is oxidized and broken down.
Involves introduction of bacteria and aeration. Large blowers are used to bubble air, or air enriched with oxygen,
through waste w
ater mixed with bacteria
laden sludge. Thus bacteria help to aerobically decompose the contents. The
water, containing decomposed suspended particles, is passed through another sedimentation tank and the sludge is
removed for further processing. After s
econdary treatment, about 90% of the organic oxygen
demanding wastes and
suspended particles have been removed.
specialized chemical, biological or physical processes which further treat the water and
heavy metals, phosphates and nitrates by chemical or biological processes.
: Heavy metals such as Cd, Pb and Hg can be removed as sulfide salts, which have low solubility.
: all nitrates are soluble and are thus more dif
ficult to remove. Resins or zeolites can be used to exchange the nitrate ions in
polluted water with hydroxide ions. Positive ions can also be exchanged with H+ ions. The resulting OH
and H+ will then combine for
: algal p
onds can also be used to remove nitrate ions
by using the nitrate ions as nutrients which are then converted
back into atmospheric nitrogen.
Activated carbon bed method
: activated carbon consists of tiny carbon granules with large surface area which have
been treated and
activated by high temperatures. Activated carbon readily adsorbs organic chemicals from the water.
Obtaining fresh water from sea water
sea water is heated in a series of coiled popes and then
evacuated chamber. Under reduced pressure, the water boils instantly. The water vapor produced
condenses when it makes c
ontact with cold
es carrying sea water. In this way, heat released when water
condenses is used
to preheat more sea water.
pressure (up to 70 atm) is applied to seawater and pure water
is pushed through a semipermeable membrane made of cellulose ethanoate, leaving the salts behind.
IB Option E
Soil & W
soil quality has been altered in such a way that it lowers crop production. Can be caused by changing
weather patterns, or by anthropogenic factors such as acidification, contamination, erosion and salinization (from
industrialization, irrigation, overgr
azing, overharvesting of trees).
from constant or excess irrigation. Salts from irrigated water accumulate in soil long after the
water evaporates. Plants die from toxic levels of salt or inability to take up water from salty soil with
no time for fields to be fallow; no organic fertilizers used
can be caused by industrial discharge, use of pesticides and fertilizers, illegal dumping of spent
engine oil, etc.; all leads
to groundwater pollution.
Soil Organic Matter (SOM)
organic constituents of the soil
humus provides source of energy and source of essential nutrient elements nitrogen, phosphor
and sulfur to sustain healthy growth.
s soil retain moisture; dark color of humus absorbs heat.
acts like clay with its cation exchange capacity. Contains active sites which enable it to bind to
nutrient cations. Also acts as acid
Hydrocarbons and other VOCs
esticides, herbicides & fungicides
Polyaromatic hydrocarbons (PAHs)
Polychlorinated biphenyls (PCBs)
Methods of Waste Disposal
Efficient method to deal with large volumes
Filled land can be used for building or other
Local residents may object to new sites
Once filled, needs time to settle, and
require maintenance as methane released
Convenient (for the dumper)
Causes air and ground water pollution
Health hazard: encourages rodents and insects
Source of nutrients
Convenient and inexpensive
Danger to marine animals
Pollutes the sea
Requires minimal space
Produces stable, odor
Can be used as a source of energy
Expensive to build and operate
Can cause pollutants, e.g. dioxins, if inefficiently
Provides a sustainable environment
Difficulty in separating different materials; not
possible in all cases
IB Option E
Mainly aluminum and steel. The metal are sorted, then
melted and either reused directly or added to the
purification stage of metals formed from their ores
Particularly important for metals such as
aluminum, which require large amounts
of energy to produce directly from ore
Taken to the plant, sorted i
n grades. Washed to remove
inks, etc., made into a slurry to form new types of paper,
such as newspaper and toilet rolls.
Energy required to transport. Composting
may be as efficient.
Sorted by color, washed, crushed, then melted and
Glass is not degraded during the recycling
process, so can be recycled many times
Industrial plastic is already sorted, but household waste
plastic must first be sorted. Degraded to monomers by
pyrolysis, hydrogenation, gasification,
cracking, then repolymerized
Fewer pollutants formed, and energy
used to recycle rather than to make from
crude oil. Better to reuse than to recycle.
: Plastics Recycling Codes
(no need to memorize, just an “FYI” item)
Fizzy drink bottles and oven
ready meal trays
Bottles for milk and washing
Food trays, cling film, bottles for squash, mineral
water and shampoo
Carrier bags and bin liners
Margarine tubs, microwavable meal trays
Yogurt pots, foam meat or fish trays, hamburger
boxes, vending cups, plastic cutlery, protective
packaging for electronic goods and toys
Any other plastics that don’t fall
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IB Option E
Water and Soil
When a salt is
labeled “insoluble,” it really means that it has a very low/slight solubility in water.
Solubility product, k
Many metal sulfides have very low solubility products, but can still be precipitated out by bubbling other compounds
through the water, ma
king use of the common ion effect.
IB Option E
Cation exchange capacity (CEC)
Both soil organic matter (SOM) and the clay particles in soil have a negative charge and will attract and bond to
positively charged cations.
Basic cations: Ca
Acidic cations: H
exchange capacity (CEC) = the amount of positively charged cations that a soil can hold.
These cations are exchanged with cations such as hydrogen ions on the root hairs of plants and thus provide
nutrients to the plant.
Low pH = high concentratio
n of acidic cations
High pH = more basic ions
Below 5 is bad for most plants (acid ions such as Al3+ are harmful to plants)
Acid rain increases amount of aluminum cations by lowering pH of soil (above pH 5 aluminum ions are
virtually all precipitated out o
f the soil solution).
Soil has a buffering capacity, but it is still sometimes necessary to add lime to soil to raise the pH and
increase the concentration of basic ions held by the clay and SOM.
In addition to capturing nutrient cations
needed by plants, the SOM can also bind to organic and inorganic
compounds in the spoil
helps to reduce the
environmental effects of
ions and other pollutants.