Class Session XI>

I. Up in the Air

So far in the course, we’ve gazed into the future, taken a look at how the world came to be the way it is, and you told your story. We defined the “environment”, thought about whether humans were natural and looked to see if humans are consuming the world. Last week, we focused on technological changes as part of the industrial revolution, learned about the eco-technological revolution and checked out what Bill McDonough and Michael Braungart refer to as the Next Industrial Revolution.

We have also learned about the formula for environmental impact. Environmental impact, as you may remember, is a function of population times consumption times technology, and we’ve looked at population, consumption, and technology. Now it’s time to learn about what kinds of environmental impacts are underway and what changes you can make everyday to minimize impact and/or improve the environment.

We will look at environmental impacts as a function of the resources we use – air, biomass, chemical, energy, land, materials, mineral, waste and water – and learn about how the way we use resources yields different kind of impacts. So, the decision you, I, all of us, make everyday about the food we eat, the cars we drive, how we heat our homes and what we do with our trash are enormously important in determining environmental impact. So, before we begin looking at resource use and environmental impacts, let’s talk a little bit about how we, as humans, make decisions.

II. Things Are Looking Up

The objective of this section is to introduce the basics characteristics of the atmosphere and, in doing so, provide some understanding of the atmosphere's endless variations. Much of what happens in the atmosphere is invisible and so humans generally don't have an understanding of the flows of matter in the atmosphere in the same way that we see rivers run and oceans swell. By the end of this section, you should have keener insight into how the atmosphere works and, hopefully, a genuine compulsion to look out the window and up at the sky more often.

The word “atmosphere” comes from the Latin “atmosphaera”, which was cobbled together from the from Greek word “atmos”, meaning “vapor”, and the Latin word “sphaera” translated as sphere. Quite literally then, the atmosphere is the “vapor-sphere”. In this first unit, we will explore the basic characteristics, components, processes, and dynamics of the atmosphere. Knowledge of these basic concepts is critical to understanding how human activities are changing the very chemistry of the atmosphere, and what we can do to prevent it.

III. Take a Deep Breath

To begin with, take a deep breathe. We take breathing, and the atmosphere, for granted. Yet, breathing “clean” air is the single most important biological need. That breath you just took, what we call “air” is actually a mixture of gases. The composition of “air”, otherwise known as the atmosphere, is usually expressed by percentage volume, that is, each gas’ relative part of the total mixture. For example, 21% of the atmosphere is made of the gas oxygen, or O2. Atmospheric composition is also expressed in the number of parts per a certain amount. The term “ppt” for example, means “parts per thousand”, while “ppm” refers to parts per million. Many of the atmosphere’s gases are in the ppm, ppb (parts per billion), and ppt (parts per trillion).

The relative amounts of some gases are more or less fixed, while the relative concentration of other gases varies. The amount of water vapor in the atmosphere, for example, is influenced by factors such as the amount of evaporation and precipitation. Table 1, below, lists the gaseous composition of the atmosphere, as well as indicates whether the concentrations are variable.

The breath you just took also contains solid material in addition to the gases listed in Table 1. This solid material is very small, between .1 and 25 thousandths of a millimeter, or micrometer and is known as particulates. To give you some idea how small particulates are, a single grain of table salt is about 100 micrometers in size, and so we are talking about a mass of material that is 1/1000 to ¼ the size of a grain of table salt. Because the limit of visibility of the naked eye is around 40 micrometers, particulates can’t be seen and float around in the atmosphere behaving more like gases than solids.

Table One - Gaseous Composition of the Atmosphere by Volume & Number of Parts, 2001

Full Name	Formula	% Volume	# Of Parts	Unit	Variable?	Cumulative Volume
Nitrogen	N2	78.1%	78 parts per	Hundred		78.10%
Oxygen	O2	20.9%	21 parts per	Hundred		99.00%
Argon	Ar	0.934%	9 parts per	Thousand		99.93%
Water Vapor	H20	0.04%	400 parts per	million	variable	99.97%
Carbon Dioxide	CO2	0.0369%	369 parts per	million		99.99%
Neon	Ne	0.00182%	18 parts per	Million		100.00%
Helium	He	0.000524%	5 parts per	Million		100.00%
Methane	CH4	0.0001839%	2 parts per	Million		100.00%
Krypton	Kr	0.000114%	1 part per	Million		100.00%
Hydrogen	H2	0.0001%	1 part per	million	variable	100.00%
Nitrous Oxide	N20	0.0000315%	315 parts per	billion		100.00%
Carbon Monoxide	CO	0.00002%	200 parts per	billion	variable	100.00%
Xenon	Xe	0.0000087%	87 parts per	billion		100.00%
Ozone	O3	0.000005%	50 parts per	billion	variable	100.00%
Sulphur Dioxide	SO2	0.000002%	20 parts per	billion	variable	100.00%
Ammonia	NH3	0.000002%	20 parts per	billion	variable	100.00%
Formaldehyde	CH20	0.000001%	10 parts per	billion	variable	100.00%
Nitrogen Dioxide	NO2	0.0000003%	3 parts per	billion	variable	100.00%
Nitric Oxide	NO	0.0000003%	3 parts per	billion	variable	100.00%
Hydrogen Sulfide	H2S	0.0000002%	2 parts per	billion	variable	100.00%
Hydrochloric Acid	HCl	0.00000015%	2 parts per	billion	variable	100.00%
Nitric Acid	HNO3	0.0000001%	1 part per	billion	variable	100.00%
Methyl Chloride	CH3Cl	0.00000006%	600 parts per	trillion		100.00%
Freon-12	CF2Cl2	0.0000000544%	544 parts per	trillion		100.00%
Carbonyl Sulfide	COS	0.00000005%	500 parts per	trillion		100.00%
Freon-11	CFCl3F	0.0000000263%	263 parts per	trillion		100.00%
Carbon Tetrachloride	CCl4	0.000000098%	98 parts per	trillion		100.00%
Freon-113	C2F3Cl3	0.000000082%	82 parts per	trillion		100.00%
Methyl Chloroform	CH3CCl3	0.000000056%	56 parts per	trillion		100.00%
HCFC-22	CHClF2	0.0000001525%	153 parts per	trillion		100.00%
HFC-23	CHF3	0.0000000011%	11 parts per	trillion		100.00%
Sulphur Hexaflouride	SF6	0.000000004%	4 parts per	trillion		100.00%
Perfluoroethane	C2F6	0.000000004%	4 parts per	trillion		100.00%
Triflouromethyl Sulphur Pentaflouride	SF5CF3	0.00000000012%	.12 parts per	trillion		100.00%
Sources
1. McGraw-Hill Encyclopedia of Science and Technology, 1987, McGraw-Hill, Inc.
2. Carbon Dioxide Information Analysis Center

IV. We Are All “Airheads”

Okay, you’ve taken that deep breath and you’re hopefully ready to continue. That breath you took, as you now know, is composed of a mixture of gases and particulates. Except for certain microorganisms, all living things require oxygen to live. The process by which humans and animals get and use oxygen is known as respiration. When we breathe, we inhale oxygen and exhale carbon dioxide. This exchange of gases is the respiratory system's means of getting oxygen to the blood. Without air, a person will die faster than if they were deprived of any other human need, such as food, water, cable television, and the Internet.

Most people can only hold their breath for about a minute. After 30 seconds, it begins to get uncomfortable. After 3 to 5 minutes, hypoxia, or oxygen deprivation sets in, brain cells begin to die and you’re on your way to being dead. So, if you hold your breath you deprive your body of oxygen. If your body is deprived of oxygen, even for a short time -- 3 minutes is a short time -- you die. But what happens if you don’t hold your breath but, rather, change the concentration of gases a little? How does that affect things? The human lung is a complex physiological system that has evolved over millions of years to need and “expect”, if you will, the concentration of gases listed in Table 1. If the concentration changes even slightly for a short period of time, our breathing and physiology are greatly affected.

Let’s look at how changing the chemical composition of air, even a little, can cause a large effect. To do this, let’s take the phenomenon known as carbon monoxide poisoning, from which thousands of people across the world die each year. Carbon monoxide, or CO, is a colorless, odorless gas that results from incomplete combustion or burning. As you can see from Table 1, the atmosphere contains 200 parts per billion (ppb) of carbon monoxide, which converts to .02 parts per million (ppm). If the concentration of carbon monoxide in the air you breathe increases slightly to 9 parts per million, you may begin to have difficulty breathing. A healthy person may be just barely affected by CO exposure of 9ppm, but older individuals and asthmatics, whose lung function may be already compromised, are likely to feel a greater level of effect.

An increase from .02 ppb to 9 ppm may seem like a large relative increase, but a change of this magnitude is a change of only 0.000088% in the total concentration of gases in the air you breathe. Several fuel burning or combustion devices commonly found around our houses can increase the amount of carbon monoxide by amounts much greater than 9 ppm. For example, CO levels in a room with unvented kerosene space heaters will vary between 0.5 and 50 ppm. Chimney smoke from a woodstove contains 5,000 ppm of CO. Undiluted warm car exhaust contains about 7,000 ppm of CO, and undiluted cigarette smoke about 30,000 ppm of CO.

This small magnitude change of 9 ppm also drives the federal regulations for air pollution. The USEPA Clean Air Regulations, for example, define a locality as being out of compliance with clean air standards if the average CO concentration over any one-hour period during an entire year exceeds 35 ppm or if it exceeds 9 ppm over an eight-hour average. So, you see that even small amount of gas, in this case 9-ppm; can have a huge impact on human physiology.

V. Structure of the Atmosphere

Of all the earth's abiotic spheres, the atmosphere is the most dynamic and changing. Every day, in every town, city and village around the world, the light, clouds, and energy in the atmosphere go through a million variations. The elements of the atmosphere affect daily life in thousands of subtle and direct ways and, for generations, humans have been fascinated by the atmosphere's many changes.

The atmosphere is a blanket of gases, suspended liquids, and solids that entirely surrounds the solid and liquid earth. The earth's gravity pulls these gases toward the surface. Not surprisingly, there are more gases closer to the surface and fewer as you move away. Therefore, the earth's atmosphere is denser at the surface and gradually thins as altitude increases.

The earth's atmosphere begins at sea level, (and in some places on land that are just below sea level) and extends outward some 6,000 miles (10,000 km) into space. From the earth's surface to an altitude of 50 miles (80 km) the chemical composition of the atmosphere is highly uniform. Due to this uniformity, this section of atmosphere is known as the homosphere or lower atmosphere. Fifty miles equals 264,000 feet and since most human activities take place from sea level to around 10,000 feet or 2 miles, conditions in homosphere or lower atmosphere are what really affect us day to day.

The homosphere is also subdivided into various sublayers. The troposphere is the layer closest to the surface and it extends outward an average of 11 miles (18 km) though it is thicker at the equator and thinner at the poles. Beyond the troposphere is the stratosphere, which extends from 11 to around 30 miles from the surface. The mesosphere starts at around 30 miles and extends outward to 50 miles from the surface.

Above 50 miles, the chemical composition of the atmosphere changes with altitude. This layer is known as the upper atmosphere or heterosphere. This upper layer is also known as the thermosphere and it extends outward several thousand miles with no real boundary between the upper atmosphere and space.

Though the atmosphere extends vertically several thousand miles, one half of the gas molecules that comprise the atmosphere are located within the first 3.5 miles (5.6 km), or 18,840 feet. Fully 90% of the molecules are within the first 10 miles (16 kilometers), or 52,580 feet, and some 97% of gas molecules are packed within the first 18 miles (30 km). Gravity, therefore, keeps the atmosphere very close to the earth's surface.

VI. Important Trace Gases

1. Carbon dioxide (CO2) - Carbon dioxide is both an important input to photosynthesis and helps to keep the atmosphere warm.

2. Ozone (O3) - Despite its' small quantity, ozone is significant because it absorbs most of the sun's ultraviolet radiation, much of which is harmful to plants, humans and animals.

3. Water (H20) - Water exists in the atmosphere as a gas (water vapor), solid (ice & snow), and liquid, and helps to retain heat and scatter solar radiation.

4. Particulates - The atmosphere contains many types of small, airborne particles.

Carbon dioxide, or CO2, is the gas, which is principally responsible for warming the troposphere, or lower atmosphere. How CO2 helps warm the atmosphere is not immediately intuitive or apparent. The energy in the atmosphere comes from the sun. The sun is a tremendous source of energy. It generates about 5.6 x 1027 calories every minute. The sun's energy transmitted from the sun in the form of waves and this energy travels at the speed of light, which is 186,000 miles per second or 11,160,000 miles per minute. Since the distance between earth and sun ranges from 91,500,000 to 94,500,000 million miles and averages 93,000,000, it takes about 8½ minutes for the sun's energy to reach earth.

The earth intercepts only one part in two billion of the total amount of energy released by the sun, yet this is a tremendous amount, some 173,000 x 1015 watts per year. To provide some perspective on this amount, it is roughly 30,000 times the energy used by all humans on the planet.

The sun's energy, called insolation, for incoming solar radiation, travels to the earth in relatively short wavelengths. About ½ of the insolation that reaches the earth's atmosphere is reflected immediately back out into space and is not available for heating the planet. The other ½ reaches the surface either directly or indirectly as scattered light. Once the sun's energy reaches the earth's surface, it is absorbed and the temperature of the surface increases. The surface begins to emit radiation in the form of heat, which has a longer wavelength than light energy. The atmosphere, and particularly carbon dioxide, traps or absorbs this reradiated, long wave, heat energy and the atmosphere warms.

The ability of the earth's atmosphere to allow the passage of shortwave radiation, but trap reradiated long wave heat radiation emitted from the earth's surface is known as the Greenhouse Effect. Eventually this heat is returned to space. We know this because the earth's atmosphere would continue to heat if this energy was not released back into space.

Ozone (O3) molecules form in the stratosphere atmosphere when oxygen molecules (O2) are split by ultraviolet radiation. The two free oxygen atoms quickly combine with other oxygen molecules to form O3. The creation of ozone in the stratosphere is a naturally occurring process. There is a very small amount of ozone in the atmosphere. If all the ozone in the atmosphere were brought down to sea level pressure and temperature, it would form a layer only 2.5 mm thick.

Ozone is important because it absorbs ultraviolet radiation from sun. Because of the absorption capacity of ozone, only a small percentage of ultraviolet, or UV, radiation reaches the earth's surface.

Water is also an important component of the atmosphere. As a gas, it is referred to as water vapor. When it is in liquid form, we call it rain, clouds, or fog. Water also exists as a solid in the atmosphere as snow, sleet, or hail.

Water gets into the atmosphere via two processes. Liquid water from the oceans or the surface of the continents is converted into water vapor by evaporation. Heat, sunlight, and wind are the agents of evaporation and convert water from a liquid to a gas. The second mechanism by which water gets into the atmosphere is transpiration. Transpiration occurs when plants take in liquid water in their roots and release the water as gas or vapor. Large, mature trees, such as oaks, can transpire as much as 100 gallons of water daily.

Once water vapor is up into the atmosphere, it often is carried great distances by wind currents. At some point, condensation may occur, which transforms the vapor back into a liquid. If the droplets of water remain airborne for any time, they form a cloud. On the other hand, if the droplets are heavy enough then they fall towards the earth's surface as precipitation.

The general effect of water in the atmosphere is moderate temperature. Water both scatters and blocks incoming solar radiation and traps outgoing heat energy released from the earth's surface. So, on a cloudy day, the high temperature is likely to be less than it would be if it were a clear day. At night, the low temperature is likely to remain higher than it might be if it was clear. This is also why places with very little water in the atmosphere, such as deserts, are often scorching hot during the day and freezing cold at night and why the coldest night in the winter is usually occurs when the sky is crystal clear.

The final important trace element in the atmosphere to be mentioned here are solid particles. There are many different types of solid particles in the atmosphere, some which are visible and some which are too small to be seen by the naked eye. These include dust, soot from grass and forest fires, pollen, microorganisms, meteoric dust, salt from the oceans, and volcanic ash.

These particles perform an important role in condensation. The transformation of water from a vapor to a liquid state occurs around these atmospheric particles. Atmospheric particles, therefore, enable condensation to occur. These airborne particles also scatter sunlight. The greater the amount of sunlight that is scattered in the atmosphere, the less sunlight that reaches the earth's surface which is why a global cooling usually occurs after large volcanic eruptions.

Lastly, atmospheric particles can also affect human health. The more particles that are in the air, generally, the harder it is to breathe, especially for the elderly and for folks with asthma.