There's nobody in ILC 140 before our 2:00 class on Friday so
there's time for an additional song or two. Today you heard
"Stairway
to Heaven" and "Diablo Rojo"
from Rodrigo y Gabriela. Here are a couple more for the
weekend: "Tamacun",
"Vikingman".
Other than 1S1P reports that you can be working on, still no
additional assignments other than the suggestion that you read
through the Lecture Notes once they
appear online after each class.
A large metropolitan area like Tucson and Pima County is
required to continuously measure concentrations of several air
pollutants. The main ones are shown below (see the top of p.
8 in the ClassNotes). You can read more about air quality
monitoring done by the Pima County Department of Environmental
Quality here.
The concentration of lead in air has
decreased significantly since lead was removed from
gasoline (the
following quote is from a Wikipedia
article on gasoline: "In the US, standards to phase
out leaded gasoline were first implemented in 1973 .....
In 1995, leaded fuel accounted for only 0.6% of total
gasoline sales ...... From 1 January 1996, the Clean Air Act banned the sale
of leaded fuel for use in on-road vehicles. Possession and
use of leaded gasoline in a regular on-road vehicle now
carries a maximum $10,000 fine in the US.")
In Tucson, carbon monoxide, ozone, and particulate
matter are of primary concern and daily measurements are
reported in the city newspaper. If
I were to tell you that the measured carbon monoxide
concentration yesterday was 4.5 ppm (averaged over an 8 hour
time period) would you be able to tell me whether that was
high or low, hazardous or not? Most people wouldn't be
able to answer that question. So rather than report the
actual measured values, an Air Quality Index value is reported
instead. The AQI is the ratio of the
measured to accepted concentrations multiplied by 100%.
The acceptable levels are known
as the National Ambient Air Quality Standards (NAAQS)
for example, the NAAQS for carbon monoxide are:
9 ppm (average value over an 8 hour
period)
35 ppm (average over a 1 hour period)
The air quality in this case would be good. Air becomes
unhealthy when the AQI value exceeds 100%. The
units "ppm", by the way, stand for "parts per million." A CO
concentration of 4.5 ppm would mean that in 1 million air
molecules 4.5 of them would be carbon monoxide.
Current Air Quality Index
values for Tucson are available online.
Carbon monoxide is a
serious hazard indoors where is can build to much
higher levels than would ever be found outdoors.
This next link is to a newspaper article describing an
incident at Virginia Tech (that occurred near the
beginning of the school year in 2007). Carbon
monoxide
from
a malfunctioning hot water heater sickened 23 Virginia
Tech students in an apartment complex. The CO
concentration is thought to have reached 500 ppm.
You can get an
idea of what kinds of symptoms and effects that concentrations
this high could cause from the figure. on p. 9 in the
photocopied ClassNotes.
You would begin to show symptoms of carbon monoxide exposure
(headache, dizziness, nausea) after breathing 400 ppm CO
concentration after about 1 hour. After several hours
exposure you would approach the level where CO would cause coma
and death. At Virginia Tech several students were found
unconscious and one or two had stopped breathing but they were
revived.
Carbon monoxide alarms are relatively inexpensive (~$50) and
are available at most hardware stores. They will monitor
CO concentrations indoors and warn you when concentrations reach
hazardous levels. Indoors CO is produced by gas
furnaces and water heaters that are either operating improperly
or aren't being properly vented to the outdoors. A few
hundred people are killed indoors by carbon monoxide every year
in the United States. An operating carbon
monoxide alarm probably saved the lives of the
6 Tucson residents in December 2010. Several
people working in a meat storage warehouse in Scottsdale were
hospitalized last week after experiencing symptoms of carbon
monoxide poisoning (read more here).
The figure above can be found on p. 14a in the photocopied
ClassNotes. The ozone layer (ozone in the stratosphere) is
beneficial, it absorbs dangerous high energy ultraviolet light
(which would otherwise reach the ground and cause skin cancer,
cataracts, and eventually kill us).
Ozone in the troposphere is bad, it is toxic and a
pollutant. Tropospheric ozone is also a key component of
photochemical smog (also known as Los Angeles-type smog)
We'll be making some photochemical smog in a class
demonstration. To do this we'll first need some ozone; we'll
make use of the simple stratospheric recipe (shown above) for
making what we need instead of the more complex tropospheric
process (the 4-step process in the figure below). You'll
find more details a little further down in the notes.
At the top of this figure (p. 15 in the packet of
ClassNotes) you see that a more complex series of reactions is
responsible for the production of tropospheric ozone. The
production of tropospheric ozone begins with nitric oxide
(NO). NO is produced when nitrogen and oxygen in air are
heated (in an automobile engine for example) and react.
The NO can then react with oxygen in the air to make nitrogen
dioxide, the poisonous brown-colored
gas that I used to make in class.
Sunlight can dissociate (split) the nitrogen dioxide molecule
producing atomic oxygen (O) and NO. O and O2react in a 4th step to make ozone (O3) just like happens in the
stratosphere. Because ozone does not come directly from an
automobile tailpipe or factory chimney, but only shows up after a
series of reactions in the air, it is a secondary
pollutant. Nitric oxide (NO) would be the primary
pollutant in this example.
NO is produced early in the day (during the morning rush
hour). The concentration of NO2 peaks somewhat later. Because sunlight is
needed in step #3 and because sunlight is usually most intense at
noon, the highest ozone concentrations are usually found in the
afternoon. Ozone concentrations are also usually higher in
the summer when the sunlight is more intense than at other times
of year.
Once ozone is formed, the ozone can react with a hydrocarbon of
some kind to make a product gas. The ozone, hydrocarbon, and
product gas are all invisible, but the product gas sometimes
condenses to make a visible smog cloud or haze. The cloud is
composed of very small droplets or solid particles. They're
too small to be seen but they are able to scatter light - that's
why you can see the cloud.
Here's a pictorial summary of the photochemical smog
demonstration.
We started by putting a small "mercury vapor" lamp
inside a flash. The bulb produces a lot of ultraviolet light
(the bulb produced a dim bluish light that we could see, but the
UV light is invisible so we had no way of really telling how
bright it was). The UV light and oxygen in the air produced
a lot of ozone (you could easily have smelled it if you had taken
the cover off the flask).
After a few minutes we turned off the lamp and put a few pieces
of lemon peel into the flash. Part of the smell that comes
from lemon peel is limonene, a hydrocarbon. The limonene gas
reacted with the ozone to produce a product gas of some
kind. The product gas condensed, producing a visible smog
cloud (the cloud was white, not brown as shown above). After
the flask had filled with a smog cloud I shined the laser beam
through the flask and you could see the beam. Just as was
the case in Wednesday's demonstration.
Back to the summary list started on Wednesday.
We can add 3 key points for tropospheric ozone.
Time now to turn to a 3rd air pollutant - sulfur dioxide (SO2
).
Sulfur dioxide is produced by the combustion of sulfur
containing fuels such as coal. Combustion of fuel also
produces carbon dioxide and carbon monoxide. People
probably first became aware of sulfur dioxide because it has
an unpleasant smell. Carbon dioxide and carbon monoxide
are odorless. That is most likely why sulfur dioxide was
the first pollutant people became aware of. I have read
that sulfur dioxide is one of the odors you smell just after
striking a match.
Volcanoes are a natural source of sulfur dioxide.
Sulfur dioxide has been involved in some of the world's worst
air pollution disasters. If not the deadliest, The Great
London Smog of 1952 is in the top two or three. Because the
atmosphere was stable, SO2 emitted into air at ground
level couldn't mix with cleaner air above. The SO2
concentration was able to build to dangerous levels. 4000
people died during this 4 or 5 day period. As many as 8000
additional people died in the following weeks and months.
Some of the photographs below come from articles published in
2002 on the 50th anniversary of the event.
The sulfur dioxide didn't kill people directly.
Rather it would aggravate an existing condition of some
kind. The SO2
probably also made people susceptible to bacterial infections
such as pneumonia. Here's
a link that
discusses
the event and its health effects in more detail.
Some other air pollution disasters also involved high SO2concentrations. One of the deadliest
events in the US occurred in 1948 in Donora, Pennsylvania.
"This eerie photograph was
taken at noon
on Oct. 29, 1948 in Donora, PA as deadly smog enveloped the
town. 20 people were asphyxiated and more than 7,000 became
seriously ill during this horrible event." (from: http://oceanservice.noaa.gov/education/kits/pollution/02history.html)
The photograph below shows some of the
mills that were operating in Donora at the time. Not only
where the factories adding pollutants to the air they were
undoubtedly adding hazardous chemicals to the water nearby.
"When Smoke Ran Like Water," a book about
air pollution is among the books that you can check out, read,
and report on to fulfill part of the writing requirements in
this class (though I would encourage you to do an experiment
instead). The author, Devra Davis, lived in Donora
Pennsylvania at the time of the 1948 air pollution
episode. Another book that I've just learned about "Killer
Smog: The World's Worst Air Pollution Disaster" by William Wise is
an account of the London Smog of 1952 (I don't yet have a copy of
that book)
Sulfur dioxide is one of the pollutants that can react with
water in clouds to form acid rain (some of the oxides of nitrogen
can react with water to form nitric acid). We'll cover that
in class next Monday.
