1: SOURCES OF PRIMARY AIR POLLUTANTS
Objective: to describe the natural as well as human sources of pollution life cycles.
1. Sulfur oxides:
Also known as SOx, its natural sources include volcanoes,
oceans, and general microbial degradation. Human sources are
primarily from combustion of fuels containing sulfur.
We often refer to crude oils as sweet and sour (sour crude is
high in sulfur, while sweet crude is low).
2. Particulates:
Also known as solid and liquid aerosols, particulates are the
various non-gaseous pollutants in air. Natural sources include
volcanoes, oceans (sea salt), general erosion processes (creating dust), and
fires. Human sources are primarily from fuel combustion .
3. Carbon monoxide (CO):
CO is colorless, odorless, and tasteless. Due to these
characteristics, CO can be undetected even at dangerous levels.
Natural sources of CO are primarily from the oceans -- mostly
from the partial oxidation of chlorophylls and methane. Human
sources of CO are from incomplete combustion of fuels (from both
motor vehicles and industrial processes). Carbon monoxide is
usually, by mass, the largest of the criteria pollutants.
4. Hydrocarbons:
Hydrocarbons are in various combustible fuels. Natural sources
include bacterial decomposition, and emissions from plants and
animals. Human sources are primarily from the oil industry
(from incomplete combustion as well as evaporation). Since it is
a category (rather than a specific chemical), the source of
hydrocarbons depends on the type of hydrocarbon.
5. Nitrogen Oxides:
Also known as NOx, natural emissions of NOx are mostly from
microbial action. Human sources are from virtually any
combustion process. The heat of combustion combines nitrogen and
oxygen (both naturally present in air) by the following equation:
N2 + xO2 ---> NOx
(NOx is primarily in the form of NO).
6. Lead:
Lead comes from a wide variety of natural and human sources.
Since the development of unleaded gasoline, combustion emissions
of lead have dropped dramatically. Nevertheless, total lead
sources continue to be a major concern.
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2: HEALTH EFFECTS FROM AIR POLLUTANTS
Objective: to consider the basic evidence in evaluating health effects. Such methods are
discussed in greater detail in other classes (e.g., air pollution, toxicology, and risk analysis).
1. Acute episodes:
Occupational exposures , often at much higher concentrations
than community levels, can provide evidence of health effects.
One major problem is extrapolating this evidence from a
population of relatively healthy workers to a general
population that includes the very young, the very old, and the
very sick. These special populations are usually not found
in a worker population, yet they are much more vulnerable.
Acute community episodes are another sub-category. The most
notorious examples of acute community episodes include London,
Donora PA., and the Meuse Valley in Belgium (for a more
complete list, see Salvato, p. 769). In each of these
episodes, sudden and severe changes in pollution (usually from
inversions) were followed by sudden and severe changes in
mortality rates. These episodes tell us a great deal about
higher concentrations, but the challenge is to extrapolate
what this means at lower concentrations and chronic exposures.
2. Toxicological studies:
In the previous category, we typically start with an increase
in health effects and try to associate that with the higher
community concentrations. In this category, by contrast, we
can start with well defined exposures (e.g., concentrations of
recognized toxics in the air), and then test animals for dose
response relationships. Ultimately, we want to extrapolate
what this means to humans.
There are various problems with toxicological studies that are
best left for other courses to discuss. However, some obvious
issues include:
1) the differences between humans and other animals, and
2) most air pollution is chronic (i.e., low concentrations)
and mixed (not just one pollutant but many, and they may have
synergistic interactions).
More subtle is the issue that most test animals are quite
homogeneous, while humans are far more heterogeneous.
Therefore, it can be difficult to translate what animal
evidence means to the most sensitive humans.
3. Chronic studies
Much of these principles are covered in your studies of
epidemiology and statistics. We generally start with effects
and look for relationships with chronic exposures (e.g., in
epidemiology, this could be a retrospective study).
A statistical approach can use regression analysis to
establish associations between tiny increases in exposures and
tiny increases in effects. Because the increases and their
relationships are not readily apparent, we need the tools of
statistics to test these associations.
These studies can be very powerful and useful, but they have
their own set of limitations. For example, they are more
expensive to conduct, they take more time to establish
definitive evidence, and they are subject to many confounding
variables that are the focus of epidemiological study.
What have these studies told us? To summarize, tiny
increases in pollution are associated with:
1) increased incidence of colds and sore throats; and
2) increased mortality, especially in sensitive persons
(e.g., "COPD" stands for Chronic Obstructive Pulmonary
Diseases, which include asthma, bronchitis, emphysema, and
lung cancer.)
The most important principle in using these three areas of
evidence is that they can be used to corroborate each other. For
example, if independent toxicological and epidemiological studies
both suggest health effects, we have much greater confidence in
our conclusions than if we relied on only one approach to
evidence. Also, the weaknesses of one approach may be assisted
by the strengths of another approach.
Review Questions
1. Contrast the 3 categories of evidence of health effects.
2. Describe 2 sub-categories of evidence from acute episodes.
3. Discuss 2 problems with animal toxicological studies.
4. Name 2 effects associated with small increases in air pollution.
5. Why do we need more than one category of evidence in studying
health effects?
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3: CONTROLS OF AIR POLLUTANTS
Objective: to analyze natural and manmade controls of air pollution.
Natural Controls
Just as we considered natural sources of pollution, we should
also consider natural sinks :
1. rain washes out pollutants;
2. gravity settles out particulates; and
3. wind can disperse pollutants.
On the other hand, these very same forces can act to accumulate
pollutants:
1. rain can become acid rain;
2. gravity can increase exposures at ground level; and
3. wind can trap pollutants horizontally.
Man-made controls
When natural controls are insufficient, manmade controls are
needed. It's impossible to give a complete list of air
pollution controls within this class, so I offer the following
generic classification. These nine generic alternatives can
be derived from basic systems theory (i.e., input, process, output).
|
|
input |
process |
output |
|
isolation |
1 |
2 |
3 |
|
treatment |
4 |
5 |
6 |
|
substitution |
7 |
8 |
9 |
Using cars as an example, gasoline is the input, engines are the
process, and exhaust is the output. Strategies for reducing air
pollutants are to isolate, treat, or substitute these factors.
Therefore, items 1-9 are defined below with some examples (some
of these examples will be explained in lecture).
1. isolate the input: gas rationing
2. isolate the process: PCV valves
3. isolate the output: national parks
4. treat the input: unleaded gas
5. treat the process: tune-ups
6. treat the output: catalytic converter
7. substitute the input: electric cars
8. substitute the process: bicycling
9. substitute the output: carpooling
Which method is the best? It depends, of course, on costs,
reliability, and other economic/technological factors.
Review :
1. Explain natural controls of air pollution.
2. Use systems theory to analyze indoor air pollution.
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4: Gasoline and Engines
Objective: to explain different components of crude oil, and explain their relationship with octane rating, knocking, and engine compression ratio.
Source
The source of gasoline is petroleum (also known as "crude oil" or
"fossil fuel"). Petroleum is formed over millions of years from
decayed plants and animals. Processing of the crude oil is based on
distillation (generally in huge towers), which separate
components by their volatility (longer chain hydrocarbons tend to
have higher boiling point). These components include (starting with
the lowest boiling point):
1. natural gas 4. aviation gasoline 7. kerosene
2. liquefied gas 5. auto gasoline 8. fuel oil
3. petroleum ether 6. naphtha 9. lubricating oils
Processing :
Among the above components, auto gasoline carries a huge
consumer demand. Therefore, various processing steps can
increase the gasoline yield. For example:
1. Cracking refers to the breaking down of long chains.
2. Polymerization is connecting of smaller chains.
3. Alkylation builds slightly larger chains and helps increase
octane rating (see below).
Output from Engines
Several terms relate gasoline structure to engine performance:
1. Knocking refers to ignition at wrong time. In general, aromatic
hydrocarbons have the best antiknock properties, and straight
chain hydrocarbons are worst. However, knocking may be a
function of many things, and so we rate anti knocking properties
by a measure called octane.
2. Octane is a measure of the tendency to produce knocking.
According to a 0-100 scale, n-heptane has a rating of 0, and
iso-octane has a rating of 100.
3. Within engines, the compression ratio is a critical measure.
By squeezing the air-fuel mixture during combustion, this high
compression increases the efficiency of engines but increases
knocking. In other words, high compression engines needs higher
octane fuels.
In the past, we increased octane by adding tetraethyl lead.
This technique was relatively cheap but ultimately dangerous because
of the health issues surrounding lead. Today, we build octane with such
additives as ethanol and MTBE.
Review :
1. List some of the distillation components of petroleum.
2. How can we increase the gasoline yield from petroleum?
3. Explain knocking, octane, and compression ratio.
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Objective: 1. To identify pollutants from gas stoves and space heaters.
2. To identify controls for these indoor air pollution exposures.
1. Gas Stoves
Most American homes rely on gas stoves. By itself, this does not necessarily
translate into an indoor air problem. However, a survey in New York City
found that half the population used gas stoves for supplemental
heating (turning on the stove to warm the house or apartment).
This habit translates into increased exposures.
What kind of exposures? Incomplete combustion releases
hydrocarbons and carbon monoxide. Furthermore, combustion
releases nitrogen oxides. Depending on other conditions,
particulate exposures can be significant, too.
Simple dispersion usually reduces the pollutants within an hour,
but ventilation techniques are critical. In one experiment,
investigators installed a new stove and turned two burners on
full for 35 minutes. With a standard ventilation fan above the
stove, there was no significant problem. However, when the fan
was not turn on, levels reached 2/3 of the federal standards for
carbon monoxide. This is assuming no outdoor air pollution.
The lessons are simple: 1) keep equipment in good repair,
2) do not use it in inappropriate ways, and 3) turn on the fan.
2. Home heating
Most American homes use natural gas for heating. Usually, it is centralized
heating with external venting, and therefore poses no significant indoor air
problem. However, many problems can arise with the use of portable "space
heaters." Improperly vented, they can be significant sources of
carbon monoxide and nitrogen oxides. Kerosene heaters (normally
reserved for outdoor use) can release the same pollutants along with sulfur
oxides.
Even the traditional fireplace can be a significant source. Ever
curl up by the fireplace and, as time passes, start to feel
relaxed and maybe a little sleepy? It could be initial symptoms
of carbon monoxide exposure! If it is followed by a headache,
the evidence is even stronger.
Of course, I am not suggesting we ban fireplaces or all space
heaters. However, simple recognition of sources followed by
common sense application of controls (such as ventilation) can
be our most important tools in controlling indoor air pollution.
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