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CH1301: Impact of Chemistry:
Environmental Chemistry
John TS Irvine
Room 216
Topics
1.
Principles.
2.
Analytical Chemistry.
3.
Hydrological cycle and acid rain.
4.
Global Warming
5.
Shale oil and gas.
6.
Recycling/ Sustainable elements.
7.
Indoor pollution.
LECTURE 1
– What is Environmental Chemistry?
– Some Concepts
Resources, Pollutants, Reservoirs,
Residence time and persistence
– Cycles
What is environmental chemistry?
• Pollution?
– Man-made and natural processes e.g. volcanoes release mercury into the
environment
• Chemical industry to blame?
– Chemistry has helped improve health and standard of living through
disinfection and medicines, agriculture etc
– Unforeseen effects of chemicals, e.g CFCs, or by-products (dioxins from
paper bleaching) or chemicals which don’t break down rapidly
– Most problems due to how used, not chemistry
Politics - global warming, acid rain, smog – Give up the car vs use catalytic
converters? Pay more for electricity?
Synthetic chemicals in products, food? – Most widespread, dangerous toxins
are natural
Human health - cancer? Smoking? Genetic?
Resources- critical elements, urban mining
Task of Environmental Chemist is to
• understand system,
• improve technology (e.g. dioxin by-product from
pesticide manufacture),
• manage resources (better energy efficiency, efficiency in
materials manufacture),
• control anthropogenic effects (man-made effects) by antipollution control (e.g. replacements for CFCs, catalytic
converters in cars)
• assess likely environmental impact of processes.
History of environmental chemistry
– "Silent Spring" (Rachel Carson) 1962 – chemicals such DDT termed
biocides. DDT used as insecticide against fire ants in US etc but also malaria
carrying mosquitoes.
– "Limits to Growth" (Meadows et al, 1972 - first to use. Predicted
exponential increase in human population and resulting catastrophic fall in
food production. - a mathematical simulation model
Scandals such as the dumping of toxic chemicals in Love Canal, in Niagra
Falls suburb, with subsequent covering and then building upon 1976
James Lovelock author of controversial Gaia hypothesis.
The Gaia hypothesis proposes that organisms interact with their
inorganic surroundings on Earth to form a self-regulating, complex
system that contributes to maintaining the conditions for life on the
planet.
e.g. biosphere and the evolution of life forms affect
the stability of global temperature,
ocean salinity,
oxygen in the atmosphere
Emergence of Global Environmental Crises: – Ozone Hole:
The ozone layer protects life on Earth from ultraviolet solar radiation and plays an
important role on the radiation budget of the atmosphere. Its evolution is intimately
coupled to climate change.
http://www.theozonehole.com/
ozoneholehistory.htm
Greenhouse effect and climate change
Pressures on natural Resources
ENERGY
o Renewable (solar, air, wind, water, tides)
o and non-renewable (fossil fuels - oil, coal, natural gas)
o Energy crisis in 1974
Material scarcity
o Renewable - plants, minerals
o Metals (iron, copper, aluminium)
o Rare Earths and Platinum Group Metals
o Non-metallic minerals (salts, phosphates)
Chemical industry and the general public
Public awareness
WWII: no environmental regulation (affected manufacturing, use and disposal of
chemical substances).
Early 60’s: Concern developed over how chemical substances can harm
humans and environment.
Mosquito - malaria, lice - typhus
The Nobel Prize in Physiology or Medicine 1948
Cl
DDT
Cl
Cl
was awarded to Paul Müller "for his discovery of
the high efficiency of DDT as a contact poison
against several arthropods".
Cl
Cl
Millions of lives saved
Dichlorodiphenyltrichloroethane
1962: Rachel Carson - Silent Spring
Pesticides effect birds eggs.
1972: US ban, 1984 UK ban, 2004 worldwide
ban (Stockholm Convention of 2001).
Still used in India (Indoor residual spraying)
In 2010, malaria caused an estimated 655 000 deaths,
mostly among African children - WHO
Environmental Cycles
Series of linked reservoirs usually at steady state with one or more sources and sinks for each.
Consider processes in
 Atmosphere
 Geosphere
 Hydrosphere
 Lithosphere
 Biosphere - where life exists close to Earth’s surface be it in geosphere or atmosphere
 endogenic - sub surface
 exogenic - surface exchanging with atmosphere/hydrosphere
Environment is a special chemical reactor: aqueous/gas phase reactions, very dilute (trace)
transport important,
synergy between processes and with living systems, non-chemical factors (politics).
 Cycles can be based on pollutants or any chemical substance (e.g. elements).
Biosphere
 Biosphere: Section of environment where life exists.
 Troposphere: Lower portion of atmosphere
 Soil: Upper portion of Lithosphere
(Topmost part of Earth’s structure)
 Hydrosphere: All the rivers, lakes, oceans
 Biota: All life contained within these sections
of the environment
These sections of the biosphere are closely linked.
Residence Time
Residence time = amount of substance in reservoir
total rate of inflow or outflow
Also known as the Box Model
Steady-state and fluxes
Mass balance: dM/dt = 0 at steady state
– Define residence time as mass in reservoir/flux in (or out)
Should use same mass units for reservoir amount and flux
Steady-state analogy is traditionally the leaky bucket – Will
find a level/volume when the outflow from the leaks is equal
to the inflow (cannot predict this unless you know how
many holes at each depth and variation of leak rate with
depth/pressure!)
Residence time is volume of water/rate of inflow (or
outflow)
Definitions
 Reservoir
– Body of matter which has a relatively uniformly distributed physical, chemical or
biological properties e.g. ocean, atmosphere, biosphere. It should be homogeneous (wellmixed)
 Flux – Amount of material entering or leaving per unit time (e.g. rain into the ocean)\
 Source
– Flux of material going in to a reservoir plus rate of creation within the reservoir (if
any), e.g. creation of ozone in ozone layer.
 Sink
– Flux of material leaving reservoir plus rate of destruction within reservoir (e.g.
destruction of ozone)
 Steady-state
– When sources and sinks are in balance and do not change with time so that the
concentration M does not change with time.
Numbers for O2 cycle
 Principal source (input) from photosynthesis
– 4 x 1014 kg y-1
 Principal sink (output) from respiration of plants and animals
and burning fuel
– Roughly the same as the above
– 0.1% if this from rock weathering (e.g. Fe2+ --> Fe3+)
 Reservoir size is very large (21 % atmosphere) – 1.2 x 1018 kg
 Hence residence time is
– 1.2 x 1018 kg/4 x 1014 kg y-1
=3000 y
Amsel, Sheri. “Ecology.” Oxygen Cycle. Exploring Nature Educational Resource.
© 2005 - 2013. October 25, 2013.
<http://exploringnature.org/db/detail.php?dbID=27&detID=1186>
Pollutants distinguished by residence time
Those with high residence time compared to mixing
processes cause global change through widely circulating
materials in the atmosphere (chlorofluorocarbons - CFCs,
carbon dioxide). Chemicals with long residence times will
be more widespread, i.e. global problem, especially in
atmosphere
Low residence time compared to mixing processes operating
at local level (carbon monoxide, ozone and, in general,
pollutants within the hydrosphere (acids, metals, pesticides,
nitrates).
Acid rain pollutants have a shorter residence time (days)
compared to atmospheric mixing time (years) than CFCs so
the problem is more local.
Pollutants distinguished by residence time
Pollutants with residence times longer than animal lifetimes
may not be dispersed evenly in biosphere
- often concentrated in plants or higher animals since they
are soluble in fatty tissues (bioconcentration) and/or
accumulate (bioaccumulation) in the animal as they are only
slowly removed from the body.
– e.g. PCBs(polychlorinated biphenyls) still at high level in
environment even though production was stopped in 1970 they are very unreactive to the usual degradative processes
(air
oxidation,
photolysis,
micro-organisms
"biodegradable").
Approaches to pollution control
Dilution
– Works for chemical easily broken down in the environment
– Not for persistent chemicals: (CFCs, some pesticides and
herbicides, PCBs , DDT
End-of-pipe
– Collect waste (e.g. SO2 from chimneys and convert to solid
form to dispose of safely e.g. landfill)
Green chemistry – Re-formulate process so as not to
discharge (alternative route or use closed cycle)
Change consumer habits - Use less waste (packaging), recycle
Cradle-to-grave analysis
– e.g. suggests polystyrene cup has less environmental impact than
a paper cup
Many of the above driven by legislation and public opinion
19
The ideal chemical process is that which a onearmed operator can perform by pouring the
reactants into a bath tub and collecting pure
product from the drain hole
Sir John Cornforth
Nobel Laureate
Introduction: the 12 principles of green chemistry
Paul T. Anastas and John C. Warner
1. Prevention
It is better to prevent waste than to treat or clean up waste after it is formed.
2. Atom Economy
Synthetic methods should be design to maximise the incorporation of all
materials used in the process into the final product.
3. Less Hazardous Chemical Synthesis
Whenever practicable, synthetic methodologies should be designed to use and
generate substances that pose little or no toxicity to human health and the
environment.
4. Designing Safer Chemicals
Chemical products should be designed to preserve efficacy of the function while
reducing toxicity.
P. T. Anastas, J. C. Warner, Green Chemistry: theory and practice, Oxford University Press, 1998.
Introduction: the 12 principles of green chemistry
5. Safer Solvents and Auxiliaries
The use of auxiliary substances (eg solvents, separation agents, etc.) should be
made unnecessary whenever possible and, when used, innocuous.
6. Design for Energy Efficiency
Energy requirements of chemical processes should be recognised for their
environmental and economic impacts and should be minimised. Synthetic
methods should be conducted at ambient temperature and pressure if no heat
utilisation.
7. Use of Renewable Feedstocks.
A raw material or feedstock should be renewable rather than depleting
whenever technically and economically practical.
8. Reduce Derivatives
Unnecessary derivatisation (use of blocking groups, protection/deprotection,
temporary modification of physical/chemical processes) should be minimised
and avoided if possible, because such steps require additional reagents and
can generate waste.
P. T. Anastas, J. C. Warner, Green Chemistry: theory and practice, Oxford University Press, 1998.
Introduction: the 12 principles of green chemistry
9. Catalysis
Catalytic reagents (as selective as possible) are superior to stoichiometric
reagents.
10. Design for Degradation
Chemical products should be designed so that at the end of their function they
break down into innocuous degradation products and do not persist in the
environment.
11. Real-Time Analysis for Pollution Prevention
Analytical methodologies need to be further developed to allow for real-time, inprocess monitoring and control prior to the formation of hazardous substances.
12. Inherently Safer Chemistry for Accident Prevention
Substances and the form of a substance used in a chemical process should be
chosen to minimise the potential for chemical accidents, including releases,
explosions, and fires.
P. T. Anastas, J. C. Warner, Green Chemistry: theory and practice, Oxford University Press, 1998.
Question to ponder
Assuming world energy usage is 150 x 1015 Wh pa
If all this was supplied by methane and all the CO2 sequestered
CH4 +2O2  CO2 + 2H2O
∆‫ ܪ‬௢ = −891 kJ/mol
How many years would this take to reduce the oxygen content of
the atmosphere by 1%, assuming no other processes affect oxygen
content. (We will consider these in discussion in lecture 2)
Suggested data
The oxygen in the atmosphere has a mass of about 1.2 x 1018 kg
Use enthalpy of combustion to estimate amount of oxygen lost in
combustion and 32 g as mass of 1 mole of O2