Some gypsy jazz (Caravan at the Django Reinhardt "Live at Birdland" Festival in New York in 2004) to take us into the weekend.
Something new in class today, an Optional In-class Assignment (you work on the assignment and turn it in at the end of class). If you weren't in class and would like to do the assignment and earn a little extra credit, you can download the assignment and turn it in at the start of class next Monday.
We're almost done with air pollutants and some new topics have been added to the Upcoming Material page.
We returned briefly to carbon monoxide at the start of class to look at the symptoms of CO poisoning. This information was included in the Wed., Jan. 18 online notes but wasn't discussed in class on Wednesday.
Here's a summary of what we've covered and what we will be covering today and next week. Items in red will be covered today, topics in green next Monday.
1. secondary pollutant
2. summer afternoon pollutant
3. key ingredient in
Los Angeles-type smog
1. 1st recognized air pollutant
2. key ingredient in London type smog
3. acid rain (demonstration)
1. health hazard
2. affects visibility
We'll start class today with ozone.
The figure above can be found on p. 14a in the photocopied ClassNotes. Ozone has a Dr. Jekyll (good) and Mr. Hyde (bad) personality. 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, etc. There are some types of UV light that would quite simply 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've been thinking about making in class. Sunlight can dissociate (split) the nitrogen dioxide molecule producing atomic oxygen (O) and NO. O and O2 react 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 most intense.
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). I meant (but forgot) to shine the laser beam through the smog cloud to reinforce the idea that we are seeing the cloud because the drops or particles scatter light.
We had time to start a short section on sulfur dioxide, the 3rd and last of the (gaseous) air pollutant we will be concerned with.
The following information is on p. 11 in the photocopied ClassNotes.
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.
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.
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 SO2 concentrations. 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." The photograph below shows some of the mills that were operating in Donora at the time. The factories were not only emitted pollutants into the air but probably also discharging pollutants into the river.
"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.