Tuesday Sept. 3, 2019

Junius Meyvant "Be A Man" (3:05), "Mighty Backbone" (3:36), "Gold Laces" (3:51), "Color Decay" (4:28); Ylja "Ut" (3:33)

We'll use page 11, page12,  page14a, page 15, and page 16 from the ClassNotes today.  I'll probably also bring page 13c just in case we finish the material below with a little extra time left in class.

 A quick summary of the key points concerning carbon monoxide.  We'll cover sulfur dioxide and tropospheric ozone today.



The yellow star next to temperature inversions means it's a pretty important concept and well worth trying to remember.


Sulfur dioxide (SO2 )
 We'll turn now to another of the air pollutants, sulfur dioxide (SO2 ).  See page 11 in the 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 (one of the smells in a freshly struck match).  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.

US NAAQS in the figure above stands for United States National Ambient Air Quality Standards.  Air with a pollutant concentration that exceeds the NAAQS is considered unhealthy.  This is discussed further in an online Supplementary Reading section.

London-type smog



Sulfur dioxide has been involved in some of the world's worst air pollution disasters.  Still the deadliest, as best I can tell, is the Great London Smog of 1952.  At that time people burned coal in their homes and coal was burned in factories.  At the time of the 1952 event, the atmosphere was stable, SO2 and smoke from all the coal fires was being emitted into air at ground level and 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.  Perhaps 100,000 people became ill.

The inversion layer in this case lasted for several days and was produced in a different way than the surface radiation inversions we heard about when covering carbon monoxide.  Surface radiation inversions usually only last for a few hours.

The term smog, a contraction of smoke + fog, was invented to describe a mixture of smoke and fog, something that was fairly common in the winter in London.  The 1952 event was an extreme case.  Now we distinguish between "London-type smog" which contains sulfur dioxide and photochemical or "Los Angeles-type smog" which contains ozone.
Most of the photographs below come from articles published in 2002 and 2012, the 50th and 60th anniversaries of the event.   The dramatic drops in visibility are mostly being caused by fog.  Later in the semester we will learn that fog clouds that form in "dirty" containing certain types of smoke particles can be thicker than fog that forms in cleaner air.


The caption to this photo from The Guardian reads
"Arsenal goalkeeper Jack Kelsey peers into the fog. 
The 'smog' was so thick the game was eventually stopped."
The smog in this photo is the thickest I was able to find.  Visibility here is perhaps 10 or 20 feet. (source of this image)


Buses had to creep along to avoid hitting someone or something.
from: http://news.bbc.co.uk/1/hi/health/2545747.stm

Someone would often walk out ahead of a bus to be sure the way was clear.
from: http://news.bbc.co.uk/1/hi/england/2543875.stm


You can get a feel for the cause of the smog
in this photograph by Paul Lowry in an article in SAGEMagazine.


Smog masks from this reference
The masks would filter out the smoke but not the sulfur dioxide gas

Even though it is a little off topic, here are some interesting photographs of early and mid 20th century London.

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 to a Power Point presentation that discusses the event and its health effects in more detail.

The Clean Air Act of 1956 in England reduced smoke pollution and emissions of sulfur dioxide. 

Air pollution disasters involving sulfur dioxide have also occurred in the US.  One of the deadliest events was in 1948 in Donora, Pennsylvania.




The reference material that contained this photographed stated "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.  Not only where the factories adding pollutants to the air they were undoubtedly adding hazardous chemicals to the water in the nearby river.




source of this photo

The Cuyahoga River that runs through Cleveland was so polluted that it used to frequently catch fire (see https://time.com/3921976/cuyahoga-fire/).  It has been 50 years since the last fire and the river has been cleaned up and restored (see https://www.nytimes.com/2019/06/07/travel/cleveland-cuyahoga-river-pollution.html).

The US passed its own Clean Air Act in 1963.  There have been several major revisions since then.  The EPA began in late 1970 (following an executive order signed by President Nixon)

"When Smoke Ran Like Water" a book about air pollution is one of the books that you can check out, read, and report on to replace the Experiment Report writing requirement 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. 


Acid rain
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 also react with water to form nitric acid).  The formation and effects of acid rain are discussed on page 12 in the photocopied Class Notes.


Acid rain is often a problem in regions that are 100s even 1000s of miles from the source of the sulfur dioxide.  Acid rain in Canada could come from sources in the US, acid rain in Scandinavia came from industrialized areas in other parts of Europe. 

Note at the bottom of the figure above that natural "pristine" rain is slightly acidic with pH 5.6.  This is because the rain contains dissolved carbon dioxide gas.  Acid rain has a pH less than 5.6.

Some of the problems associated with acid rain are listed above.


Trees in the Jizera Mountains (Czech Republic) killed by the effects of acid rain
(source: https://en.wikipedia.org/wiki/Acid_rain)
 		Acid rain damage to the Ulysses S. Grant Memorial in Washington, D.C.  The sculpture is made of bronze, a mixture of copper and tin.  Copper is dissolved by acid rain and produces the green stains on the marble base.
(source: https://www.nps.gov/nama/blogs/acid-rains-slow-dissolve.htm)


A chimera (left, photo source) and a strix (right, photo credit: Jawed Karim, photo  source) on Notre Dame Cathedral in Paris.  The rounded edges, grainy texture, and pitting are all characteristic of damage caused by acid rain.  You'll find many more photographs of Notre Dame gargoyles here.


We can fill in another column in our air pollutants chart:





Good (stratospheric) and bad (tropospheric) ozone
Ozone has a kind of Dr. Jekyll and Mr Hyde personality.


The figure above can be found on page 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 actually there are some forms of UV light that would quite simply kill us).

Here's a nice visual depiction of the role that stratospheric ozone plays.










Essentially all of the UV-C light, the most dangerous form, is absorbed by the ozone layer,  About 5% of the UV-B and perhaps 50% of the UV-A makes it to the ground. (Fig. source:
https://www.nasa.gov/larc/celebrate-world-ozone-day)
 The UV Index forecast for Tucson on Jan 10, 2019.  Available at https://www.epa.gov/sunsafety/uv-index-1. 
You can find explanation of the colors on the scale at https://www.epa.gov/sunsafety/uv-index-scale-0
 The UV index forecast for Tucson early in the Fall 2018 semester (Aug. 28).  Sunlight is much more intense in the summer.

Ozone in the troposphere (surface level ozone in the figure above) 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 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.



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 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 more intense than at other times of year.

The American Lung Association's 2019 State of the Air report mentions that 10 of the 25 cities with the highest tropospheric ozone concentrations are found in California (Los Angeles is at the top of the list).  Texas has 3 cities in the top 25, Colorado has two.  Arizona (Phoenix), Utah, and Nevada each have one city.    Here's a link to the full report (167 pages long).  Here's a shorter report with the lists of most polluted cities.  Here a list of the cities in the United States with the cleanest air.

Tucson exceeded the EPA NAAQS for ozone for the first time in August 2018. Phoenix had already exceeded the NAAQS 39 times that year.  Here's a link to the entire article.


The violation in Tucson, which could impact the availability of federal transportation funds, is partly because the allowed ozone concentration is lower than it used to be.  The 80 parts per billion (ppb) 8 hour average value was lowered to 75 ppb in 2008 and to 70 ppb in 2015.

Photochemical (LA-type) smog

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.

Photochemical smog demonstration
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 the bulb was).  The UV light and oxygen in the air produced a lot of ozone (you could have easily 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 of lemon 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   We shined a laser beam through the smog cloud to reinforce the idea that we are seeing the cloud because the drops or particles scatter light.

Here's a video that I found of a slightly different version of the demonstration (you really don't miss much if you don't come to class).  Instead of using UV light to produce the ozone the demonstration uses an electrical discharge (the discharge travels from the copper coil inside the flask to the aluminum foil wrapped around the outside of the flask).  The overall effect is the same.  The discharge splits an oxygen molecule O2 into two oxygen atoms.

O2  + spark  ---> O + O

One of the oxygen atoms reacts with an oxygen molecule to form O3 
O + O2  ---> O3 

The smog cloud produced in the video is a little thicker than the one produced in class.  I suspect that is because they first filled the flask with pure oxygen, 100% oxygen, before making the ozone.  I used air in the room which is 20% oxygen.  More oxygen in the flask means more ozone and a thicker cloud of Los Angeles type smog.

Here's the nearly completed air pollutants list.


A couple of smog related topics to finish up the day

Volcanic smog (vog) and laze (lava and haze)

Volcanic smog can form when the sulfur dioxide (SO2) from an erupting volcano reacts with oxygen and moisture.  The product of the reaction can form small drops or particles that  begin to scatter light and lower the visibility. 



Diamond Head is just visible in this picture of volcanic smog in Honolulu.  This picture (Marco Garcia, AP) was published in the Seattle Times on May 6, 2008 (http://old.seattletimes.com/html/nationworld/2004394494_hawaii06.html).  Kiluaea was erupting at that time also.  The volcanic smog can kill crops and cause respiratory problems.  The vog can also spread to nearby  islands. 

An entirely different type of haze cloud is formed when hot molten lava pours into the ocean as shown in the photo below (photo credit: Brocken Inaglory in https://en.wikipedia.org/wiki/Laze_(geology) ). 



In this case the hot lava splits water molecules into hydrogen and oxygen ions.  The hydrogen ions react with chlorine ions from dissociated salt (sodium chlorida NaCl splits into Na+ and Cl- ions) in the ocean water.  The sudden cooling of lave creates small fragments of glass.  You are left with a haze cloud consisting of small droplets of  hydrochloric acid and particles of glass.  The dangerous haze cloud can cause skin and eye irritation, lung damage, even death.

 We'll cover particulate matter fairly quickly at the start of our next class.