Wednesday, Aug. 28, 2019

Beginning of Quiz #1 Material

"Chapter 1" - the earth's atmosphere

If we were using a book we'd start in Chapter 1 and here's some of what we would first be looking at in this course (it will probably take the better part of a month to cover all this).

 


The 5 most abundant gases in our atmosphere
Let's start with the most abundant gas in the atmosphere.  I poured some of that material (in liquid form) into a Styrofoam cup.  Here's a photo I took back in my office.






You can see the liquid, it's clear, it looks like water.  Probably a lot of you knew this was nitrogen (liquid nitrogen).  Liquid nitrogen is very cold and begins to boil (evaporate) at -321o F.  The cloud that you see surrounding the cup is not nitrogen gas, nitrogen gas is invisible.  We'll learn more about the visible cloud later.

The most abundant gas in the earth's atmosphere is nitrogen.  We'll use liquid nitrogen in several class demonstration this semester mostly because it is so cold. 

Nitrogen was discovered in 1772 by Daniel Rutherford (a Scottish botanist).  Atmospheric nitrogen is relatively unreactive and is sometimes used to replace air in packaged foods to preserve freshness.  You don't really need to worry about remembering details like this.

Oxygen is the second most abundant gas in the atmosphere.  Oxygen is the most abundant element (by mass) in the earth's crust, in ocean water, and in the human body.  In liquid form it also becomes visible.








from: http://www.webelements.com/oxygen/
The web elements site credits Prof. James Marshall's Walking Tour of the Elements.
 from: http://en.wikipedia.org/wiki/Oxygen
Wikipedia credits U.S. Air Force Staff Sgt. Jim Araos.
 A nice picture of liquid oxygen's pale blue color from this source.


Some photographs of liquid oxygen (O2) are shown above (it boils at -297o F).  It has a (very faint) pale blue color (I was pretty disappointed when I first saw it because I had heard it was blue and imagined it was a deeper more vivid blue).    I'd love to bring some liquid oxygen to class and it's probably available on campus but you probably need to be careful with it because it is reactive.

I recently learned that liquid ozone (O3) does have a nice deep blue color. 


Liquid ozone (source of this photograph).

Sorry I don't have any liquid ozone which is probably a good thing because it's also very (probably dangerously) reactive.  Ozone gas is also poisonous.
 
 Here is a complete list of the 5 most abundant gases in air.  And a note about the figures you'll find in these online notes.  They may differ somewhat from those drawn in class.  I often redraw them after class, or use neater versions from a previous semester for improved clarity (and so I can get the notes online more quickly).  





With a little practice you should be able to start with a blank sheet of paper and reproduce the list above.

Water vapor and argon are the 3rd and 4th most abundant gases in the atmosphere.  A 2% water vapor concentration is listed above but it can vary from near 0% to as high as 3% or 4%.  Water vapor is, in many locations, the 3rd most abundant gas in air.  In Tucson most of the year, the air is dry enough that argon is in 3rd position and water vapor is 4th.   Water vapor and carbon dioxide are circled because they are greenhouse gases.

Water vapor, a gas, is invisible.   Water is the only compound that exists naturally in solid, liquid, and gaseous phases in the atmosphere.

Argon is an unreactive (inert) noble gas (helium, neon, krypton, xenon, and radon are also inert gases).  Here's a little more explanation (from Wikipedia) of why noble gases are so unreactive.  You can gloss over all these additional details if you want to, we won't cover this in class. 

The noble gases have full valence electron shells.  Valence electrons are the outermost electrons of an atom and are normally the only electrons that participate in chemical bonding.   Atoms with full valence electron shells are extremely stable and therefore do not tend to form chemical bonds and have little tendency to gain or lose electrons (take electrons from or give electrons to atoms of different materials).

Noble gases are often used used in "neon signs"; argon produces a blue color.  The colors produced by Argon (Ar), Helium (He), Kryton (Kr), Neon (Ne) and Xenon (Xe), which are also noble gases, are shown above (source of the images).




An electric current is traveling through and heating the gas in the tube causing it to emit light.  You're seeing the light emitted by the gas itself.  The inert gases don't react with the metal electrodes in the bulbs.

Here are some of some of the "best neon signs" in Tucson from an article in the Arizona Daily Star (https://tucson.com/news/retrotucson/of-tucson-s-best-neon-signs/collection_87671166-5f90-11e4-bf0c-63bc9770ccfc.html#1 )








The "diving lady" sign was recently restored.
photo credit: Michael McKisson
 A sign at the Hotel Congress
photo credit: David Sanders, Arizona Daily Star
 King Fisher restaurant
photo credit: David Sanders, Arizona Daily Star
 Rialto Theater in downtown Tucson
photo credit: Rich Facun, Arizona Daily Star

Most, if not all, of the examples above are probably more properly called fluorescent signs.  The bulbs contain mercury vapor rather than one of the noble gases.  An electric arc causes the mercury vapor to emit invisible ultraviolet light.  The UV light strikes a phosphor coating on the inside of the bulb.  The phosphor then fluoresces, different colors are emitted depending on the composition of phosphor used in the bulb.



This is solid carbon dioxide, better known as dry ice (source of the image above)..  It doesn't melt, it sublimes, i.e. it changes directly from solid to gas without first melting (evaporation is a liquid to gas change).  The spoon holding the piece of dry ice has cooled enough that frost has formed on the spoon.  Just as with the liquid nitrogen earlier, the cloud that you see below the spoon is not carbon dioxide gas.

The concentration of carbon dioxide in air is much smaller than the other gases (it's about 0.04% but you don't need to remember the actual value).  That doesn't mean it isn't important.  We'll spend a lot of time this semester talking about water vapor and also carbon dioxide.  Water vapor and carbon dioxide are the two best known and most important greenhouse gases.  The greenhouse effect warms the earth.  Concentrations of greenhouse gases such as carbon dioxide are increasing and there is concern this will strengthen the greenhouse effect and cause global warming.  That's a topic we'll look at during the semester.

Here's a  link that explains how you can make your own dry ice.  I may well attempt this demonstration later in the semester as it illustrates another important concept.

Dew point temperature

Water plays many important roles in the atmosphere.  One of them is the formation of clouds, storms, and precipitation.  Meteorologists are very interested in knowing and keeping track of how much water vapor is in the air.  One of the variables they use is the dew point temperature.  The value of the dew point gives you an idea of how much water vapor is actually in the air.  A high dew point value means a higher the water vapor concentration.





The chart below gives a rough equivalence between dew point temperature and percentage concentration of water vapor in the air.


Note that for every 20 F increase in dew point temperature, the amount of water vapor in the air roughly doubles. 

Air temperature will always be equal to or warmer than the dew point temperature.  Experiencing 80o F dew points would be very unpleasant and possibly life threatening because your body might not be able to cool itself ( the air temperature would probably be in the 90s or maybe even warmer).  You could get heatstroke and die.

Click here to see current dew point temperatures across the U.S.  Here's a link concerning unusually high, even record setting dew point temperatures. 


Tucson's summer monsoon

Tucson usually gets between 11 and 12 inches of rain per year.  About half of that comes during the summer monsoon, i.e. the summer thunderstorm season.  Many people mistakenly think the term monsoon is just another word for thunderstorm. 


For most of the year in SE Arizona winds come from the west and are relatively dry.  For 2 or 3 months every summer the winds switch direction and start to blow from the east, southeast, and south.  This air is generally much moister.  The combination of moist air and summertime heating make it much easier for thunderstorms to form. 



Tucson residents generally look forward to the start of the summer thunderstorm season because the rain brings some relief from the hot dry weather of May and June.  Recall that the dew point temperature gives you an idea of how much water vapor is in the air.  The switch in wind direction and the arrival of moister air is often indicated by a fairly abrupt increase in the daily average dew point temperature.

The figures below are from the Tucson National Weather Service Office and show a plot of average daily dew point temperatures (red curve) for June - September.


 
"Traditional" start of the summer monsoon season.
The figure above shows average dew point values (probably a 30 year average).  Traditionally the summer monsoon would start when the daily average dew point reached and remained at or above 54 F green line for 3 days in a row.  Using the chart above we can see that occurs on July 9 on average.  The average dew point temperature drops below 54 F around Sept. 11.  Using this traditional definition, the summer monsoon season normally extends from July 9 through September 11.

In any given year the measured daily dew point values can depart appreciably from average.  The figures below show monthly variations of the measured daily dew point values from this summer, 2018.  Measured values are in blue.  The red line again shows average daily dew point values and the green line is 54 F.
 



The average dew point value remained below 54 F in June this year. 
The dew point reached 56 F on July 6 but only remained there for one day.  On July 13 the dew point reach 54 F and remained at or above 54 F for several days.  July 13 was the "traditional" start of the summer monsoon this year.  Dew points have mostly remained above 54 F for the remainder of the month.


data for September 2019 will be added later in the semester                              


                                                                    





This last figure shows data for the 4 month period, June 1 - Sept. 30, 2018.  I'll replace it with the 2019 data at some point later in the semester.  As you can see there are brief periods once the summer monsoon is underway when Td dips below 54 F.  I am not sure what defines the end of the monsoon.  It's usually pretty obvious; something will cause a sharp and dramatic drop in Td and it will stay below 54 F.

There is a newer and now official definition of the start and end of the summer monsoon season.  To avoid the uncertainties in the beginning and end of the summer monsoon period, the National Weather Service has, since 2008, just assumed a summer monsoon season of fixed duration, June 15 through Sept. 30, regardless of what the actual dew point values were. 

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 air, water vapor, is coming into contact with the cold cup of liquid nitrogen.  The moist air cools enough that water vapor begins to condense and forms a cloud consisting 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."





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 kill a few million people every year across the globe.




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 an upcoming 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 in the next few days.

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 like 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 can probably handle iodine safely and might well 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 examine soon.  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 a links to a couple more 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 four air pollutants this week and next.  They're listed below together with an idea of the number of main points you should try to remember and understand about each.