The Atmosphere

Chapter 3

* Note that you may be using one of two editions of Geosystems:  for convenience I will use abbreviations:

    – if you have Geosystems, 4th Canadian edition 2016, I will use the abbreviation:  4CE (most of you will have this one)

    – if you have Geosystems, 3rd Canadian edition 2013, I will use the abbreviation:  3CE

The heavens tell of the glory of God.
The skies display his marvelous craftsmanship.
Day after day they continue to speak;
night after night they make him known.
They speak without a sound or a word;
their voice is silent in the skies;
yet their message has gone out to all the earth,
and their words to all the world.
The sun lives in the heavens
where God placed it.
It bursts forth like a radiant bridegroom
after his wedding.
It rejoices like a great athlete
eager to run the race.
The sun rises at one end of the heavens
and follows its course to the other end.
Nothing can hide from its heat.

Psalm 19:1-6 (NLT)

**There is a video version of this lecture here:

**The exam is based on the content in these notes, so please print them off to study from.

The thin shell of gases surrounding the Earth is called the atmosphere.  Life as we know it would be impossible without the atmosphere (like the moon, which has virtually no atmosphere) or with a different kind of atmosphere (Venus, Mars).  For practical purposes, we tend to think of the atmosphere extending up to 480 kms above the earth’s surface.

There is a gradually thinning layer of gases beyond this, referred to as the exosphere, but we won’t worry about it.

Air is a mixture of many different gases that is so thoroughly mixed together it behaves as if it were a single gas.  It is naturally odourless, colourless, tasteless, and formless.

I.  Atmospheric Composition

Study Figure 3.1, ”Profile of the modern atmosphere,” p.67 4CE (p.63 3CE) and Figure 3.3, “Temperature profile of the atmosphere…” p. 70 4CE, (p.63 3CE). Know these! (HINT! some good exam questions here!)

* Use these figures as a reference as you read through this section. *

The atmosphere can be subdivided according to:

  1. chemical composition, or
  2. temperature, or
  3. function
A.  Chemical Composition

Considering the chemical composition of the atmosphere there are two distinct layers, or “spheres”:

  1. Heterosphere (outer atmosphere, 80-480 km above the surface)

In this layer, gases are not evenly mixed in a uniform (homogenous) layer.  They are separated into distinct (heterogeneous) layers, by gravity, according to atomic weight.  The lightest gases (hydrogen, helium) are at the top; heavier gases (oxygen) near bottom.  This layer, although very thick (83% of the atmospheric depth), includes only 0.001% of the atmospheric mass.

  1. Homosphere (inner atmosphere, surface up to 80 km)

In this layer, gases are blended in a relatively uniform (homogenous) way.  The gases are not sorted.  At certain elevations there are specific additions to the uniform mix – like the “ozone layer,” 19-50 km, and variations in water vapor and pollutants – but, in general, the composition is uniform.

Note that although the homosphere is not that thick (only the lowest 80 km (17%) of the entire atmosphere, which is 480 km thick), it includes 99.999% of the atmospheric mass.

The homosphere is composed of a blend of gases that include:

  • Nitrogen – 78%
  • Oxygen – 21%
  • Everything else – 1% (including consistent amounts of gases like argon, neon, and helium, AND variable amounts of water vapour, carbon dioxide, methane, hydrogen, and nitrous oxide)

See Table 3.1 “Composition of the Modern Homosphere” p.68 4CE (p.65 3CE)

Note that the majority of the air we breathe – because we live in the homosphere – is actually nitrogen.  Read the paragraphs on “nitrogen” and “oxygen” in your text, p.68 4CE (p.65 3CE).

Carbon dioxide is a natural byproduct of life processes, but is also a major byproduct of human activities including burning fossil fuels and deforestation.  Since the mid-19th century, the amount of CO2 in the atmosphere has increased dramatically because of human industrial and deforestation activity, which profoundly affects global climate, weather, ice melt, sea level, and habitat for species (more about this in Chapter 11).

B.  Temperature

Considering the temperatures throughout the atmosphere there are four distinct layers:

  1. Thermosphere (outer atmosphere, equivalent to the heterosphere)

The thermosphere corresponds with the heterosphere.  Temperatures rise sharply from -90°C at the mesopause (top of mesosphere) to over 1200°C at the thermopause (top of thermosphere).  Despite such high temperatures, the thermosphere doesn’t feel hot.  Temperature and heat are different concepts.  Temperature refers to the kinetic energy, or energy of motion of a particle.  In the upper atmosphere, insolation is very intense and excites individual gas molecules so they vibrate intensely (they have a high temperature).

Heat is created when kinetic energy is transferred between molecules.  Heat is the flow of kinetic energy from one molecule to another molecule because of the difference in temperature between them.  Therefore, in order for heat to be generated, molecules have to collide with one another.  In a very low density environment, like the upper atmosphere, where there are very FEW molecules, there is little interaction and thus very little heat.  In the lower atmosphere, with a much higher density of molecules, there is more heat generated.

In the thermosphere, intense insolation excites/heats individual gas molecules so that individual particles have a high temperature (high kinetic energy).  But they are so spread apart (remember, the atmosphere at this altitude has only 0.001% of all atmospheric mass – spread out over 83% of the atmosphere’s depth!) that it doesn’t feel hot!  In order to feel heat, a particle has to collide with you and transfer its heat to you.  Because of such low densities, in the thermosphere the chances of collision are so few and collisions so isolated, that you would not feel the heat that the individual particles have!

To feel heat, you also need high densities (molecules collide with you, transferring their heat energy).

  1. Mesosphere

This is the upper portion of the homosphere, 50-80 km above the surface.  It is very cold, and has low densities.  Temperatures drop from 0°C at the stratopause (50 km) to -90°C at the mesopause (85 km).

  1. Stratosphere

This is the middle portion of the homosphere, from 18-50 km above the surface.  This layer warms from the tropopause (18 km, -57°C) to the stratopause (50 km, 0°C), because of the presence of atmospheric ozone.  Ozone effectively traps insolation.  Stratospheric ozone has been decreasing since the 1970s due to human-generated pollutants, which is creating serious health risks (below).

  1. Troposphere

This is the lowest level of the homosphere, from the surface to 18 km (the tropopause).  This is the layer in which we live and fly!  All weather (water vapour, clouds, storms, pollution, etc.) is in this layer.  It is dense, containing 90% of atmosphere’s total mass.  Temperatures cool with elevation at a normal lapse rate of 6.4°C/1000 metres.

Thus, for every 1000 m you go up in elevation, on average, the temperature will drop 6.4°C.  This is why the tops of mountains are usually much colder than the valley bottoms, below.

Lapse rate vary depending on weather conditions.  We’ll discuss this in Chapters 7 & 8.

C. Function

Considering the function of various components of the atmosphere, there are two distinct layers:

  1. Ionosphere

This includes all the heterosphere and the upper homosphere (the mesosphere):  50-480 km above the surface.  The ionosphere absorbs much short-wave insolation (gamma rays, x-rays, ultraviolet radiation).  This absorption results in changing atoms in the atmosphere to be positively charged ions (thus the name – “ion”-osphere).  This is where auroras occur (interaction between the ions in the solar wind and the Earth’s magnetic field).

  1. Ozonosphere

The stratosphere is where atmospheric ozone is located, thus it may be called the ozonosphere. Ozone is a highly reactive oxygen molecule  made up of three oxygen molecules (O3) rather than the usual two in oxygen gas (O2).  Ozone absorbs much ultraviolet (UV) radiation and converts it to heat energy.  Thus ozone “protects” the earth’s surface by absorbing 95% of UV radiation.

Ozone is concentrated near the equator and is less dense toward the poles (where solar radiation is less intense and it cannot be formed as readily).  “Holes” in the ozone are located over the poles where ozone levels are least.  These occur naturally, but have been exacerbated by human pollutants.

This reaction also produces heat — which is why the stratosphere warms with altitude.

A decrease in ozone has been observed since the 1970’s due to ozone-depleting substances (ODS), especially manufactured chemicals, including refrigerants, solvents, propellants, and chlorofluorocarbons.  Decrease in stratospheric ozone has been most intense at the poles, resulting in growing “ozone holes” at polar latitudes (up to a 67% decrease in ozone levels).  Chloroflourocarbons (CFCs, found in old aerosol cans and refrigerators) are broken down in the upper atmosphere and the free chlorine gases destroys ozone, thus allowing more UV radiation to reach the earth.  Because the ozone layer does block out UV radiation, it is important for the health of biological organisms (like us!).

This ozone depletion, and the resultant increase in UV radiation reaching the earth’s surface – has serious consequences:

  • The most basic impact for humans is the increase in skin cancers.
  • Over-exposure to the sun’s UV rays can also cause eye damage, including cataracts, and may even weaken the immune system.
  • Increased UV levels will also have an impact on agriculture, including many of the world’s major food crops. It has been observed that some crops, such as barley and oats, have shown decreased growth as a result of exposure to increased UV radiation.
  • In marine ecosystems, UV can damage the tiny single-celled plants, known as phytoplankton, which form the base of the food chain.  Decreases in the food source at this early stage, may have effects throughout the entire system, and could ultimately affect fish populations.
  • Increased UV levels also reduce the lifetime of construction materials used outdoors, particularly the plastics that are prevalent in our homes, playgrounds, and other structures.

Learn more about How UV radiation affects life on Earth (NASA)

For more on ozone balance (why ozone is important and how it is being destroyed) )and ozone depletion (current trends), check out these highlighted links.

Arctic ozone depletion hit record levels:  BBC News – Arctic ozone loss at record level.

In 1992 Environment Canada developed the UV Index.  Canada was the first country in the world to issue nation-wide daily forecasts of UV radiation. The Index changes slightly with day-to-day changes in the ozone layer. Much larger variations can be seen as UV changes with the seasons, the time of day and the amount of cloud cover.  UV is measured on a scale of 0 to 10, with 10 being a typical midday value for a summer day in the tropics – where UV is at its highest on earth.  The higher the number on the UV index, the more UV you will get, and the faster you’ll sunburn.

What does the UV Index mean to you?

UV Index Category Sunburn Time
over 9 extreme less than 15 minutes
7-9 high about 20 minutes
4-7 medium about 30 minutes
0-4 low more than 1 hour
When the UV index is over 9, UV-B is extremely strong, and you will burn in less than 15 minutes. (Sunburn times are for light untanned skin, the times would be somewhat longer for those with darker skin.) Even if you do not get a burn, you may still be damaging your skin.

The UV Index: Typical summer midday values

UV Index
Tropics 10 (extreme)
Washington, D.C. 8.8 (high)
Toronto 8.0 (high)
Halifax 7.5 (high)
Edmonton 7.0 (high)
Yellowknife 6.0 (moderate)
Iqaluit, NWT 4.8 (moderate)
North Pole 2.3 (low)
The farther south you go, the higher the UV index. This is why you burn so quickly on a southern vacation.

The ozone layer could/should recover, if ozone-depleting substances are eliminated. Under the Montreal Protocol, an international agreement to protect the ozone layer, action has been taken to reduce ozone-depleting substances. The build-up of the most significant CFCs in the lower atmosphere has slowed considerably, and one of the key chemicals, CFC-11, is now decreasing.

Because of the time it takes for these chemicals to move from ground level to the stratosphere, the impact of the Montreal Protocol will not be felt for many years. It is estimated that the ozone layer should recover by about 2050 – providing that all human-made ozone-depleting substances are eliminated. However, long-term predictions are uncertain because the processes of ozone depletion are not all understood.  Global warming and the exhaust from high-flying aircraft may significantly affect the recovery of the ozone layer.

The challenge, too, is that the replacement for zone-depleting Chlorofluorocarbons (CFCs) and hydrofluorochlorocarbons (HCFCs)  – HFCs (Hydrofluorocarbons) — are now dramatically increasing in the atmosphere — and are potent greenhouse gases .(BBC News – Climate concerns as ‘ozone-friendly’ HFCs use grows)

READ:  Focus Study 3.1 p.74 4CE (p.70 3CE).

Excellent websites on global ozone issues include:

II. Air pressure

The atmosphere is “held” to the Earth by the force of the Earth’s gravity.  Like any other object held to the Earth by gravity, the atmosphere has a certain amount of “weight” and exerts “pressure” on the surface.  The weight of the atmosphere, called air pressure, pushes on earth’s surface, and on us.  Because that same pressure is also inside us – pushing outwards – we do not feel it.

Air pressure, at sea level, is normally 1012.3 mb (millibars). This can also be expressed as 101.23 kPa (kilopascals).  In the U.S. this is often expressed as 29.92 inches of mercury.

Air pressure diminishes with altitude.  The force of gravity is greatest closest to the Earth’s surface, so the majority of the atmosphere is held close to the surface.  See Figure 3.2a “Density decreases with altitude” p.68 4CE (p.64 3CE).

Note that density (how many gas molecules there are in a given volume of atmosphere) is directly linked to air pressure:

Higher altitude = lower density = lower air pressure

Lower altitude = higher density = higher air pressure

Look at Figure 3.2b .  Note the “Measurement equivalents” section.

  • The atmosphere is approximately 480 km thick.
  • But 90% of its mass is below 16 km!
  • 99.9% of its mass is below 50 km.
  • And 99.999% of its mass below 80 km (the bottom 17% of the atmosphere’s depth)
  • Thus, only 0.001% of the atmosphere’s mass is from 80-480 km, the upper 83% of the atmosphere’s depth!  The air is VERY, VERY THIN out there!

Your text notes that when a jet airplane travels at an altitude of 11,000 m (36,000 ft), you are traveling above 80% of the earth’s atmospheric mass!

Why do your ears “pop”? If you’ve ever been to the top of a tall mountain, you may have noticed that your ears pop and you need to breathe more often than when you’re at sea level. As the number of molecules of air around you decreases, the air pressure decreases. This causes your ears to pop in order to balance the pressure between the outside and inside of your ear. Since you are breathing fewer molecules of oxygen, you need to breathe faster to bring the few molecules there are into your lungs to make up for the deficit.

Remember, because air is so much less dense at higher altitudes, it does not “FEEL” hot, even though it is at a high temperature (kinetic energy).

III. Pollution

Pollution, small particles or aerosols, from both natural and human sources is always present in the air (including dust, salt from ocean, soot from fires, industrial and automobile emissions, pollens, microorganisms, volcanic dust).

Large particles settle out quickly.  Fine particles remain suspended for long periods.  When Krakatoa, a huge volcano in Indonesia, erupted in 1883, particles suspended in the atmosphere circled the globe for more than two years.  These resulted in haze and colourful sunsets all around the earth, and possibly produced one of the coolest summers and periods of greatest glacial advance ever in Europe.  The huge eruption of Mt. Pinatubo in the Philippines (1991) and wildfires have also launched pollutants into the atmosphere that have been suspended for months or years (See Figure 6.1, “Atmospheric effects of the Mount Pinatubo volcanic eruption …” p.144 4CE (p.134 3CE)).

In recent decades, pollution is increasing associated with human activity (for instance, Los Angeles receives the equivalent fallout of 17 tonnes per square kilometre a month — mostly auto related).

 A.   “Natural” Pollution

A variety of natural sources produce air pollution … volcanoes, forest fires, living and decaying plants, soil, oceans (Table 3.3 “Sources of Natural Pollutants” p.73 4CE (p.72 3CE).

B.     “Anthropogenic” (human-caused) Pollution

Virtually every human activity produces pollutants.  Thus, where this activity is concentrated — cities, industrial regions — produce largest amounts of pollutants.  Cars and trucks produce 50-60% of human-caused air pollution, especially carbon monoxide (CO) and nitrogen oxides (NO, NO2), caused by incomplete combustion of fuels.

Consider:  Table 3.4, “Major Pollutants over Urban Areas” p.77 4CE (p.75 3CE).  Notice the top major pollutants are all related to fossil fuel combustion, especially by cars/trucks/etc.

Please also read “Geosystems in Action 3:  Air Pollution”  (Figures 3.1-3.3 p.82-83 4CE (p.77 3CE)):  Industrial Smog, Photochemical Smog, and Air Pollution: A Global Problem.

Major human produced pollutants include:

  1. Carbon Monoxide (CO) is a by-product of incomplete fuel combustion or decaying organic material.  CO is produced naturally by rotting organic matter and forest fires (90% of global CO production).  Humans release CO when fossil fuels (oil, gas, coal, etc.) are burned, directly from transportation systems (combustion of fossil fuels to power vehicles and engines  – cars and trucks; large trucks and buses; recreational vehicles; lawn and gardening equipment; farming and construction; rail and marine), to produce electricity (coal, natural gas generating stations), to heat buildings (natural gas, oil, or electricity from coal/gas generating stations), and by burning wood or other organic matter.

CO is odourless, colourless, tasteless … and lethal!  CO reduces oxygen in the blood.   Persons with heart disease are especially sensitive to CO poisoning. Infants, elderly persons, and individuals with respiratory diseases are also particularly sensitive. CO may affect healthy individuals resulting in headaches, dizziness,  impairing exercise capacity, visual perception, manual dexterity, learning functions, and ability to perform complex tasks.  In extreme amounts it can result in death.

  1. Carbon dioxide (CO2) is produced when vegetation (wood, etc) is burned.  This happens in two major ways:
  • when land is cleared and vegetation burned (90% of biomass burning is human caused)
  • residential wood heating, even from tobacco smoke (a total of 10% of global CO2 production).
  1. Photochemical smog is the result of UV rays in sunlight reacting with automobile exhaust to create a dirty haze composed of ozone, nitric acid, and other nitrates. (Figure 3.2. p.83 4CE (p.77 3CE)).   Ozone in the troposphere, at ground level, can irritate the eyes, nose, throat, cause fatigue, and other health problems.  Ozone is another byproduct of automobile emissions.  This smog damages biological tissues, potentially impacting human health (especially children) in urban areas.
  1.  Industrial smog, (Figure 3.1, p. 82).  Industrial coal burning activities produce a dirt smudge, Sulphur dioxide (SO2).  SO2, combined with water in the atmosphere, forms sulphuric acid (H2SO4).  Nitrous oxides (and nitric acid) are also produced as a pollutant from industrial activity.  Fuel combustion (primarily to produce electricity in coal-fired generating stations) is the leading sources of human-induced NO and SO2 production.

One of the by-products of these emissions is acid rain Read Focus Study 3.2 “Acid Deposition …” p.78-79 4CE (p.78-79 3CE). When these pollutants are released into the atmosphere they react with water vapour to become sulphuric and nitric acids.  When washed out of the air by rain, snow or fog, the acid changes the pH factor of soil and water.

(NOTE: pH of 0-7 is acidic; from 7-14 is alkaline. pH is measured on a logarithmic scale; a pH of 4 is 10 times as acidic as a pH of 5 and 100 times as acidic as a pH of 6).

Rainfall is normally a little bit acidic (pH 5.6) because of the presence of natural pollutants.  However human activity can result in rainfall with a pH as low as 2.1 (equivalent to vinegar or lemon juice).  Lowering soil and water pH makes it difficult for vegetation to absorb nutrients from the soil, resulting in large-scale environmental degradation.  Acid rain also coats the ground with particles of aluminum and toxic heavy metals such as cadmium and lead, which can be fatal if ingested by biota (living organisms).

Acid rain is a particularly serious problem in eastern Canada because many of the water and soil systems in this region lack natural alkalinity – such as a lime base – and therefore cannot neutralize acid naturally.  Provinces that are part of the Canadian Shield, like Ontario, Quebec, New Brunswick and Nova Scotia, are hardest hit because their water and soil systems cannot fight the damaging consequences of acid rain.

The Canadian Department of the Environment estimates acid rain has already damaged 14,000 Canadian lakes (they are fish-less); 150,000 others are in danger.  In Europe, acid rain has “killed” more 20% of Sweden’s lakes and over 50% of Norway’s lakes. On coastlines, the ocean diminishes the effect of acidity (it gets diluted), but the influx of extra nitrogen seems to stimulate the growth of algae (it acts as a fertilizer).  The algae consume oxygen in the water and reduce the ability of sunlight to penetrate the water, causing cooler temperatures: both of these tend to inhibit fish life.

Acid rain harms soil and vegetation by introducing toxic heavy metals and aluminum (inhibiting regeneration), and by poisoning microorganisms that decompose organic matter.  Consequently forests become “sick” — susceptible to temperature extremes, droughts, high winds and insects.  In 1983, over one-third of West German forests showed visible acid rain damage.

Urban areas see the effects in increased weathering of stone (especially limestone and marble), iron and bronze features as they are repeatedly “washed” by acid precipitation.  (Check out “environmental tales from the tomb”!)

There is concern that human health is affected by acid deposition. The 1994 Canada – United States Air Quality Agreement  reported that long-term exposures to acid aerosols have been linked to lung problems in children. Acid aerosols are very tiny particles (less than 2.5 micrometres in size) which can enter the respiratory system.  because of their size they may filter through natural bodily defences.  Short-term exposure to poor air quality episodes may also cause breathing difficulties amongst for example asthmatics. These conditions may occur during summer months, particularly in cities where car pollution is the main source of nitrogen oxides.

   (U.S. Environmental Protection Agency; check out “acid rain” links)

  1. Particulate Matter (PM). Humans produce a variety of other pollutant particles such as dust and smoke – more visible examples of air pollution.

For a thorough discussion of various pollution sources in Canada, check out:

Pollution is problematic because it can cause respiratory and other health problems in living organisms (like humans).

Pollution also can change the earth’s albedo (how much energy the earth absorbs or reflects).  Particles of black soot have been discovered in the Arctic air (during winter and spring approaching levels in major cities), and then are deposited in the Arctic environment.  While white snow reflects insolation (resulting in little surface heating), dark particles absorb insolation, resulting in much heating..  Because they absorb insolation effectively are producing a heating effect, this particulate matter is causing substantial warming of Arctic environments.

Do you want to know how industries in your community are contributing to air pollution?

Environment Canada’s National Pollutant Release Inventory (NPRI)  is searchable by Canadian community over 10,000 — it gives you the exact tonnage of emissions by company/plant).  If there is a particularly noxious industry in your community, what can you do about it?  Take action!  Write a letter!  Challenge them to “clean up their act”! — it’s your health (and your neighbour’s, and your kids’ [eventually, maybe, if not yet], and your grandparents’ …)!

    Canada’s Air Pollution

Canada is one of the world’s leading air polluters — as a whole and per capita.  For (relatively unbiased) data, check out the Environment Canada website.

There are a variety of serious effects associated with air pollution:

Environment Canada also has an Air Quality Health Index (AHQI) for many communities across Canada.  The Air Quality Health Index or “AQHI” is a scale designed to help you understand what the air quality around you means to your health.  It is a health protection tool that is designed to help you make decisions to protect your health by limiting short-term exposure to air pollution and adjusting your activity levels during increased levels of air pollution. It also provides advice on how you can improve the quality of the air you breathe.

The AQHI communicates four primary things;

  1. It measures the air quality in relation to your health on a scale from 1 to 10. The higher the number, the greater the health risk associated with the air quality. When the amount of air pollution is very high, the number will be reported as 10+.
  2. A category that describes the level of health risk associated with the index reading (e.g. Low, Moderate, High, or Very High Health Risk).
  3. Health messages customized to each category for both the general population and the ‘at risk’ population.
  4. Current hourly AQHI readings and maximum forecast values for today, tonight and tomorrow.

“No borders”

Part of the problem with air pollution is that it does not stay in the source area.  Winds move natural and human-produced components around the globe.  This has serious political implications!  Once pollutants are airborne, winds can carry them hundreds of kilometers, depositing them far from their source.

Fifty per cent of acid deposition in eastern Canada is estimated to originate from sources in the USA. Because of prevailing southerly winds during summer months, much of the pollution from the USA is exported to Canada. Some pollutants from Canada are transported to the US but on balance, Canada receives much more pollution than it exports. The import / export of pollutants across the border has therefore made acid rain a serious diplomatic issue between the US and Canada. The problem is compounded by the fact that the states in the US that are most heavily populated and have high air pollution emissions are located south of the sensitive eastern regions of Canada.  Click here for a discussion of this issue.

Most of the pollutants causing severe acid deposition problems in Scandinavia did not originate in these countries, but came from the United Kingdom, France, and Germany.

International agreements on air quality and air pollution have made news recently.  However the political will to implement them – given the high financial and human cost involved – has often been lacking.  Enforcement methods – if present at all – are weak.

This can introduce you to a whole sub discipline in geography — geopolitics — how do we deal with global issues like acid rain when they involve many different local, provincial, and national governments and laws, and international bodies like the U.N.  (‘Geopolitics” is the the study of the relationships between a nation and the rest of the world – each nation has a sphere of influence it exerts over surrounding nations in areas such as trade, economic aid, military intervention, and pollution!)

Temperature inversions

In the troposphere, temperature normally decreases with altitude.  Warm air rises, removing pollution from the surface.

A temperature inversion occurs when this normal pattern is reversed.  Warmer air is over top of cooler air.  The air cannot rise.  It is trapped at the surface.  Therefore, during a temperature inversion, air pollution released into the atmosphere’s lowest layer is trapped there.  Pollutants are trapped at the surface.  They can be removed only by strong horizontal winds. Because high-pressure systems often combine temperature inversion conditions and low wind speeds, when they stay over an industrial area for a prolonged time, the result is severe smog.

3 wintersmg

Winter smog trapped at the surface by a temperature inversion, Montreal, QC

See Figure 3.7, “Normal and inverted temperature profiles” p.84 4CE (p.74 3CE).

Temperature inversions often happen at night and in coastal areas (Los Angeles, Vancouver).  The surface air cools because of proximity to the ocean.  During the day, the surface air warms as the land heats up, but a layer of cooler air may be present several hundreds of meters above the surface.  The surface air (complete with all its pollutants from automobile and industrial exhaust) is trapped.

In Los Angeles and Vancouver the problem is further exacerbated because the mountains to the east of the cities prevent lateral (horizontal) movement of the pollutants out of the region.  The air and its pollution are trapped over the city.

Canada also has “winter smog” problems associated with temperature inversions and residential (and commercial) heating exhaust.

Local and regional landscapes

 A location surrounded by mountains or hills can naturally “trap” pollutants because they cannot easily be blown away.  Locations that are in open countryside tend to have higher air quality.

Some locations have major natural polluters – like volcanoes or frequent dust storms.  These decrease air quality in the region.


Winds can gather and move pollutants.  Sometimes this results in decreasing the concentration of pollutants.  Or winds may result in the concentration of pollutants.  Winds, of course, know no boundaries, and so have been particularly implicated in increased air pollution and acid rain in eastern Canada, with much of the pollution originating in the U.S.  One example of winds transferring pollution is an “Arctic haze” that exists over much of the Arctic region.  Since this region has no industrial activity, the pollutants all originate in other areas and are blown, by wind, into the Arctic environment.

Worth Reflecting on …

Prof. John Houghton reflects on the problem of evil and suffering, particularly as brought about by natural disasters. He says that in part, we must take part of the blame for suffering brought about by natural disasters because although we have the ability to put preventative and life-saving measures in place, often we do not.  Why do ‘Natural disasters’ happen? – YouTube.  What do you think?

To review …

Check out the resources at

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Scripture quotations marked (NLT) are taken from the Holy Bible, New Living Translation, copyright © 1996. Used by permission of Tyndale House Publishers, Inc., Wheaton, Illinois 60189. All rights reserved