Lecture XI
Physics 367
Pollution from Fossil Fuels
We have previously discussed how energy is
generated for electricity and other purposes from fossil fuels.
We now consider how pollution is generated,
what the health consequences are and whether it is possible to
reduce the effects of pollution.
Pollution is an unavoidable
consequence of energy and materials production. Our
response must take this into account!
Pollutants come in two classes:
those which take part in natural
cycles
those which do not take part ...
It is the second class which does the most damage as they
accumulate.
Given these statements it makes sense to:
determine the pollutant level that
will not cause injury (global/local)
aim to produce no more than this
amount
Air in urban areas can be considered
local, in the same sense that
weather is local. Although each city may
be different, cities as a class are different than rural areas.
How?
cities have 2-3°C higher temperatures
than rural areas in the afternoon
cities are 5-6°C warmer at
night
cities are getting 0.5°C warmer
per decade
cities have ten times more dust
particles
cities have 100% more fog in
winter
cities have 20-30% lower winds
cities have 5-10% more rainfall
Local pollution in cities comes from cars, trucks, evaporation
of paint and solvents, industrial processing, power plants, ... Local
pollution added together becomes regional.
Example: visibility in the western US is
150 km, in the eastern US it is 20 km. Why?
sulfur + water = sulfate = haze
temperature inversions
What is a temperature inversion? How does it happen? Do we care?
PV=nRT
adiabatic lapse rate = 10°C/km
if actual lapse rate > adiabatic
rate air unstable
if actual lapse rate < adiabatic
rate air stable
In an air inversion the
temperature of the air increases with altitude. This
air is, see above, stable!
How does this happen? Night time in the city.
Air inversions keep the air trapped in the local
region preventing mixing with upper air... (a dilution solution).
If there are sources of pollution there then the
air becomes more and more polluted.
These are real occurrences:
Donora, PA (1948) - 20 extra
deaths
New York City (1966) - 270 deaths
Clairton, PA (1975) - 14 deaths
London (1952) - 4000 deaths *
London (1956) - 1000 deaths
London (1957) - 900 deaths
London (1962) - 700 deaths
Heath effects include:
acute respiratory disease
bronchitis
premature births
still births
kidney disease
cancer
lung disease
damage to plants, trees (ozone, smog)
Cigarette smoking is a form of pollution, especially in
cities. As such it is
bad for all of us.
How many of you smoke?
smokers death rates are 60% higher
than non-smokers
Pollution risks are quantified by
dose:
dose is the amount of pollutant that enters the body:
dose = potency x exposure
health risk = dose x exposed population
= potency x
exposure x exposed population
In order for atmospheric pollutants (which?) to affect us they must
enter our bodies
lungs via ENT system
the bodies defenses include
nose - large particles
lungs - small particles
Particles smaller than 10 µm (PM10
level) are dangerous to health
30% of particles < 1 µm stay in lungs once they are
there
Small particles are most heavily concentrated in urban areas:
cars and trucks
coal and oil combustion
The air is really better in the country!!!
How do we handle the problem?
Pollution control systems:
Particulates
electrostatic precipitators
baghouses
Sulfur, sulfur dioxide
precleaning (coal)
wet scrubbers (bubble gas thru
lime-slurry)
dry scrubbers (add chemicals
to flue gases)
Nitrogen oxides (higher T more
NOx)
staged combustion control
flue gas recirculation
(lower T)
thermal denoxification
(NOx
N2)
The cost to implement the 1990 Clean Air Act was
$7 Billion
Is pollution local?
For many years it was believed that tall chimneys reduce pollution.
They do not - they just spread out the effect (pollution dillution
once again!!). Effects of tall chimneys:
Britain causes sulfur dioxide in Norway
How do we know this? Heavy metal tracers are characteristic of
production - i.e. they form a chemical fingerprint!!! Results:
Ohio pollutes Tennessee
NY pollutes Massachusetts
Russia and Europe pollute Canada
So local pollution has turned into
global pollution!
It is important
for every group and country to meet standards!
Acid Rain is the deposition of sulfur
and nitrogen oxides by rain or other processes on plants, buildings, lakes,
ground.
Acid - concentration of hydrogen ions in liquid.
In distilled water there are 10-7 moles
hydrogen ions per liter of water.
More hydrogen ions acid;
less base.
PH = -log10(concentration of hydrogen
ions)
PH water = -log10
(10-7) = 7
Vinegar has a PH = 3
Lemon Juice has a PH = 2
Normal Rain has a PH = 5.6 (due to CO2)
Acid rain occurs when the PH < 5.6. Note the average PH of
rainfall in the US is 4.5 due to NOx and
SO2.
NOx + H2
HNO3
+ oxygen
SO2 + O3
SO3
+ O2
SO3 + H2O
H2
SO4
It now appears that 70-90% of the acid rain is man-made.
Control of sulfur is the issue.
Ohio is the worst producer of sulfur in the US!
Economic impact of sulfur emission abatement program in Ohio:
scrubbers cost $3-4 billion to install
scrubbers jobs gained
switch fuel jobs lost
in either scenario profits of $400-600 million after 10 years
In Ohio 95% of all electricity comes from coal. Are you prepared
to pay more for scrubbers? for switching fuel?
Problem of the day: How thick is the
atmosphere?
Imagine a cube of air:
In equilibrium SF= 0
Balance forces
Weight of cube: W = density x Ah x g
then
PtopA + W = PbotA
or
PtopA + rAhg = PbotA
or
Ptop + rhg = Pbot
or
h = (Pbot-Ptop)/rg
What do we do with pressure terms?
to get the height of the atmosphere assume
Pbot = surface pressure
Ptop = 0 (Pbot/e, Pbot/10)
then using r = 1.29 kg/m3
Pbot= 1x105N/m2
h = (1x105N/m2
)/(1.29kg/m3)
(9.8m/s2
h = 7900 m = 7.9 km