Thursday Aug. 29, 2019

"Old Enough" featuring Ricky Skaggs & Ashley Monroe  (6:57), The XX Intro, City of the Sun cover (4:23), Gotye (feat. Kimbra) "Somebody That I Used to Know" on KCRW (4:07), Ashley Monroe on NPR Tiny Desk Concert "Weed Instead of Roses" (9:05 - 13:05 = 4:00)

We'll be using use page 7, page 105, and page 106 from the ClassNotes today.  You might also want to download and print out the Environmental and Physiological Causes of Death handout.  It is not in the ClassNotes. 

40 sets of Expt. #1 materials were checked out before class today.  If you checked out materials you should find your name on the Expt. #1 Signup list.   There are several students on the Expt. #1 Waiting list.  I'll have a limited number (~10 sets) of additional sets of materials in class next Tuesday.

Signup sheets for the remaining experiments were handed out in class today also.  Students that signed up for an Experiment or Scientific Paper or Book report should find their name on the relevant signup list soon.

The first of this semesters 1S1P Report topics have been posted.  See the 1S1P Report Assignments and Topics page for more details.

I distributed a short handout that describes the Packback Questions platform that we will be using for online discussion among students in this class this semester.  You can read more about Packback at https://www.packback.co/ .  You will probably receive an email from Packback inviting you to join (there is a $25 registration fee).  At this point my main objective is to get everyone signed up.  We'll start worrying about how to use Packback next week.

Dew point temperature continued

Here's a picture again of the cup of liquid nitrogen.  There are several things, both visible and invisible, to be aware of.






First of all the nitrogen.  We can see the liquid nitrogen.  Once the liquid has evaporated and turned to gas it is invisible.  You can't see the nitrogen gas.

The cloud that you can see is water vapor that has condensed to form small drops of water or crystals of ice.


Another invisible gas in the air, water vapor, is coming into contact with the cold cup of liquid nitrogen.  The moist air cools enough that water vapor is able to condense and form a cloud of very small drops of liquid water and small crystals of ice.  The cloud is visible.

We're seeing a demonstration of the dew point's "second job."  This is also where dew point temperature gets its name.





If you cool air next to the ground to its dew point, water vapor will condense and coat the ground (or your car) with water.  The ground will be covered with dew.  If a little thicker layer of air is cooled fog will form. 

A soda bottle in the refrigerator cools to about 40 F.  In the summer in Tucson the dew point will be in the 50s or 60s.  The soda bottle is cold enough that when removed from the refrigerator it can cool the air to and below its dew point and water vapor will condense onto the side of the bottle as shown below.  (source of the photo)


Except for the summer, the air is usually too dry in Tucson for this to happen.  Dew points are often only in the 20s. The 40 F soda bottle isn't able to get the air cold enough, the relative humidity stays below 100%,  and dew doesn't form on the bottle.

Trace gases in air - pollutants and greenhouse gases

 We are going to add a bunch of minor constituents, trace gases, to the list of the 5 most abundant gases in our present day atmosphere.

Trace gases are found in very low concentrations in air.  The concentrations often vary with location and time.  The fact that the concentrations are low doesn't mean the trace gases are not important.  We'll be concentrating on one sub-group of trace gases, air pollutants.  Air pollution (both indoors and outdoors) probably kills a few million people every year across the globe. 

Note in the top part of the list below that our present day atmosphere is completely different from the earth's original atmosphere.  This will be one of the topics that you can read about and report on in this semester's first 1S1P Report Assignment.




Water vapor, carbon dioxide, methane, nitrous oxide (N2O = laughing gas), chlorofluorocarbons, and ozone are all greenhouse gases.  The greenhouse effect warms the earth to a habitable temperature.  Increasing atmospheric concentrations of these gases though are responsible for the current concern over climate change and global warming.  We'll discuss this topic and learn more about how the greenhouse effect actually works later in the course.  Carbon dioxide will also be the subject of another 1S1P Assignment.

Carbon monoxide, nitric oxide, nitrogen dioxide, ozone, and sulfur dioxide are some of the major air pollutants  We'll cover 3 of these in more detail today and in our next class.

I put ozone in a group by itself.  It has sort of a Dr. Jeckyl and Mr. Hyde personality
(i)  Ozone in the stratosphere (a layer of the atmosphere between about 10 and 50 km altitude) is beneficial because it absorbs dangerous (sometimes deadly) high energy ultraviolet (UV) light coming from the sun.  Without the protection of this ozone layer, life as we know it would not exist on the surface of the earth.  It was only after ozone started to buildup in the atmosphere that life could move from the oceans onto land.  Chlorofluorocarbons are of concern in the atmosphere because they destroy stratospheric ozone.

(ii)  Ozone in the troposphere (the bottom 10 kilometers or so of the atmosphere where we live) is a pollutant and is one of the main ingredients in photochemical smog.

          (iii)  Ozone is also a greenhouse gas.

Gases like water vapor, oxygen, and nitrogen are invisible.  Some gases are colored and can be seen; some examples are shown below.  I would love to bring some actual samples to class, but most of these gases are toxic and require very careful handling. 





Bromine in both liquid and gaseous phases. Bromine and mercury are the only two elements that exist as liquids at room temperature.  The bromine is in a sealed glass ampoule inside an acrylic cube.  Bromine could be safely brought to class in a container like this.  I actually have a sample of mercury in a cube like this and will bring it to class during the semester.

Here's what Webelements.com says about bromine: " It is a serious health hazard, and maximum safety precautions should be taken when handling it."  I'm not sure what maximum safety precautions are, so I probably shouldn't be bringing it to class.

This photo was taken by Alchemist-hp and was Picture of the Day on the English Wikipedia on Oct. 29, 2010.
 Chlorine (Cl2)
I found this image here
 Iodine
Also an element that is normally found in solid form.  The solid sublimes, i.e. it changes directly from solid to gas (you would probably need to heat the solid iodine to produce gas as deeply colored as seen in the picture above).  source of this image

I think we could probably handle iodine safely and might bring some to class.
 Nitrogen dioxide  (NO2)
An important pollutant.  I used to make this in class but I've read that you can inhale a fatal dose of  NO2 before showing any symptoms.  NO2 also has an anesthetic effect - it can deadens your sense of smell.


Air Pollution

Air Pollution is a serious health hazard in the US and around the globe  (click here to download a copy of the information below including references).  The lists below try to give you some idea of how serious a threat it is.
  

The list above shows the external or environmental agent that causes death.  Of interest are the 80,000 deaths thought to be due to air pollution.  More than half are probably due to exposure to particulate matter, something we will cover also.  This year I added an estimate of deaths due to skin cancer caused by exposure to ultraviolet (UV) light and deaths due to lung cancer caused by long term exposure to radioactive radon gas.

The second list, below, is the physiological or internal bodily function that ultimately leads to your demise.  Keep in mind that many of these numbers are difficult to measure and some may contain a great deal of uncertainty.



Here's some information about the global effects of unhealthy environments and air pollution (ref: https://www.who.int/news-room/detail/15-03-2016-an-estimated-12-6-million-deaths-each-year-are-attributable-to-unhealthy-environments)


A more recent 2018 reference (https://www.who.int/airpollution/en/) estimates that outdoors air pollution kills 4.2 million people per year.   3.8 million people are killed by indoors air pollution, largely due to smoke from cooking fires and burning dirty fuels for heat.  91% of the world's population lives in regions where the air quality doesn't meet World Health Organization (WHO) standards

Here are links to a couple of other interesting sites: Institute for Health Metrics and Evaluation (http://www.healthdata.org/) and Our World in Data (https://ourworldindata.org/ and https://ourworldindata.org/air-pollution)
_______

We will be looking at three gaseous air pollutants and particulate matter.  They're listed below together with an idea of the number of main points you should try to remember and understand about each.
 

Today's class will feature a light scattering demonstration.  It's a fairly simple concept and explains how/why we are able to see things like smog, clouds, and particulate matter in the air.  I'm planning a photochemical smog demonstration in class next Tuesday (safely confined inside a glass bottle); you'll be able to see the smog because it scatters light.
Carbon Monoxide (CO)

We'll start our section on air pollutants with carbon monoxide.  You'll find additional information on carbon monoxide and other air pollutants at the Pima County Department of Environmental Quality website and also at the US Environmental Protection Agency website.


The material above is from page 7 in the ClassNotes.  We will mostly be talking about carbon monoxide found outdoors, where it would only rarely reach fatal concentrations.  CO is a serious hazard indoors also where it can (and does) build up to deadly concentrations (several people were almost killed in Tucson in December 2010 for example).  Carbon monoxide from a malfunctioning heating system is also suspected to have caused the deaths of four people spending the recent holidays in a cabin near Flagstaff (more information).  Between 1999 and 2010  an average of 430 people were killed per year in the US from unintentional, non-fire-related carbon monoxide poisoning according to the Centers for Disease Control and Prevention (ref).

Carbon monoxide is insidious, you can't smell it or see it and it can quickly kill you (Point 1).  Once inhaled, carbon monoxide molecules bond strongly to the hemoglobin molecules in blood and interfere with the transport of oxygen throughout your body.  The article about carbon monoxide poisoning in Tucson mentions that the victims were put inside a hyperbaric (high pressure) chamber filled with pure oxygen.  This must force oxygen into the blood and displace the carbon monoxide molecules.

CO is a primary pollutant.  That means it goes directly from a source into the air,  CO is emitted directly from an automobile tailpipe into the atmosphere for example. The difference between primary and secondary pollutants is probably explained best in a series of pictures.   The distinction between primary and secondary pollutants is a relatively minor point.







In addition to carbon monoxide, nitric oxide (NO) and sulfur dioxide (SO2), are also primary pollutants.  They all travel directly from a source (automobile tailpipe or factory chimney) into the atmosphere.  Ozone is a secondary pollutant (and here we mean tropospheric ozone, not stratospheric ozone).  It wouldn't be present in the exhaust coming out of a car's tailpipe.  It shows up in the atmosphere only after a primary pollutant has undergone a series of reactions with other chemical compounds in the air.



Point 2 explains that CO is produced by incomplete combustion of fossil fuel.  Basically there isn't enough oxygen.  More oxygen and complete combustion would produce carbon dioxide, CO2.  

Because cars and trucks produce much of the CO in the atmosphere in Tucson, special formulations of gasoline (oxygenated fuels) are used during the winter months in Tucson to try to reduce CO emissions.  The added ingredient, ethanol, has the effect of adding more oxygen to the combustion process.
 
Vehicles are also fitted with a catalytic converter that will change CO into CO2 (and also NO into N2 and O2 and hydrocarbons into H2O and CO2).  In Pima County, vehicles must also pass an emissions test every year to insure that the car is burning fuel as cleanly as possible (my older automobile failed its test earlier this month).

Flames resulting from the combustion of natural gas (methane) in a Bunsen burner are shown below.  The air intake is completely closed in the picture at left.  There isn't enough oxygen in this case and the flame is yellow.  This is incomplete combustion and will produce more carbon monoxide and also a lot of black soot (carbon).  The intake is partially opened in Picture 2, opened a little more in Picture 3 and completely open in Picture 4.  The blue flame in Picture 4 results from complete combustion.  The flames on a gas stove or the pilot light in a hot water heat or a furnace should have this blue color.  (source of the photo: https://commons.wikimedia.org/wiki/File:Bunsen_burner_flame_types.jpg)


Dirty (incomplete) at left and clean (complete) combustion of natural gas at right.
In the atmosphere CO concentrations peak on winter mornings (Point 3).  The reason for this is surface radiation inversion layers.  They are most likely to form on cold winter mornings. 

When we say inversion layer (Point 4), we mean a temperature inversion, a situation where air temperature increases with increasing altitude.  That's just the opposite of what we are used to (you would expect it to be colder at the summit of Mt. Lemmon than here in the Tucson valley).  This produces stable atmospheric conditions which means there is little up or down air motion.

 The lack of vertical air motions means there is very little vertical mixing in a stable air layer.



In the left figure above, notice how temperature increases from 40 F to 50 F in the thin air layer next to the ground.  That's the inversion layer.  Temperature then begins to decrease as you move further up.  That's what we normally see.  When CO is emitted into the thin stable layer during the morning rush hour, the CO remains in the layer and doesn't mix with cleaner air above.  CO concentrations build.  Later in the day the ground and air in contact with the ground warms.  The inversion disappears and air at the ground mixes with cleaner air above.  The evening rush hour adds CO to the air but it is mixed in a larger volume of air and the concentration doesn't get as high.



Thunderstorms like we see this time of year contain strong up and down air motions.  Thunderstorms are an indication of unstable atmospheric conditions.



Scattering (splattering) of light

You are able to see a lot of things in the atmosphere (clouds, fog, haze, even the blue sky) because of scattering of light.  We'll try to make a cloud of smog in class later this week.  The individual droplets making up the smog cloud are too small to be seen by the naked eye.  But you will be able to see that they're there because the droplets scatter light.  That's true also of the little water droplets that make up a cloud.  So we need to take some time for a demonstration that will hopefully explain what light scattering is. 

In the first part of the demonstration a narrow beam of intense red laser light was directed from one side of the classroom to the other. 

The following 3 figures are on page 105 in the ClassNotes.  The red laser that I used to use quit working last fall.  The demonstration now uses violet, green, and red laser pointers.


 


We're looking down from above  in the the figure above.  Neither the students or the instructor would see the beam of light.  To see the laser light some of it would need to be traveling toward you rather than from one side of the room to the other. 



The instructor would have been able to see the beam if he had stood at the end of the beam of laser light where it hit the wall and looked back along the beam of light toward the laser.  The insert at upper right shows what the instructor would see, a bright spot of light originating at the end of the laser tube itself.   That wouldn't have been a smart thing to do, though, because the beam was strong enough to possibly damage his eyes (there's a warning on the side of the laser). 

Most everyone was able to see a bright red spot where the laser beam struck the wall. 




This is because when the intense beam of laser light hits the wall it is scattered (I think splattered is a more descriptive term).  The original beam is broken up into a multitude of weaker rays of light that are sent out in all directions.  There is a ray of light sent in the direction of every student in the class.  They see the red spot of light because they are looking back in the direction the ray came from.  It is safe to  look at this light because the original intense beam is split up into many much weaker beams.

Next we clapped two erasers together so that some small particles of chalk dust fell into the laser beam. 

The next 2 figures are on page 106 in the ClassNotes.




Now instead of a single spot on the wall, students saws lots of points of light coming from different positions along a straight segment of the laser beam.  Each of these points of light was a particle of chalk, and each piece of chalk dust was intercepting laser light and sending light out in all directions.  Each student saw a ray of light coming from each of the chalk particles.  With a cloud of chalk dust you are able to see segments of the laser beam.

We use chalk because it is white, it will scatter rather than absorb visible light.  What would you have seen if black particles of soot had been dropped into the laser beam?

In the last part of the demonstration we made a cloud by pouring some liquid nitrogen into a cup of water.  The cloud droplets are much smaller than the chalk particles but are much more numerous.  They make very good scatterers.
The beam of laser light was very bright as it passed through the small patches of cloud.  The cloud droplets did a very good job of scattering laser light.  So much light was scattered that the spot on the wall fluctuated in intensity (the spot dimmed when lots of light was being scattered, and brightened when not as much light was scattered).  Again the insert shows what you would see if you stood at the wall and looked back toward the laser.  Some of the light passes through the cloud so you would still be a spot of red light, but it would be weaker and more diffuse.  Then you would see red scattered light coming from the cloud surrounding the beam of laser light.

Here's a side view photo that I took back in my office.


The laser beam is visible in the left 2/3 rds of the picture because it is passing through cloud and light is being scattered toward the camera.  There wasn't any cloud on the right 1/3rd of the picture so you can't see the laser beam in that part of the photograph.

The air molecules in the room are actually scattering laser light but it's much too weak for us to be able to see it.  When a stronger light source (sunlight) shines through much more air (the entire atmosphere) we are able to see the scattered light.  The blue light that you see when you look at sky is sunlight being scattered by air molecules.  This will probably be the topic of yet another 1S1P assignment.