Chapter 14: Atmospheric Science and Air Pollution

The Atmosphere and Weather

  • Atmosphere - Thin layer of gases that surrounds a planet or moon
  • Retained by gravity
  • Earth’s atmosphere - 78% N, 21% O, 1% other

Earth’s Atmosphere

  • Absorbs radiation and moderates climate
  • Transports/recycles water, heat, pollutants, nutrients
  • Vertical differences in temperature, density, and composition
  • Human activity is changing the composition of the atmosphere

The Atmosphere is Layered

  • The atmosphere consists of four layers, they all have differences in properties: temperature, pressure and humidity

1. Troposphere

  • 80% of all gases: As altitude increases, temp decreases (gets colder)
  • Bottommost layer. Blankets earth’s surface and provides us with the air we need to live
  • 80% mass, 99% aerosols and water vapor; “tropos” - change; well mixed; atmosphere is thick at equator and thin at poles
  • In troposphere, all 3 properties decline with an increasing altitude (As altitude increases there are fewer air molecules
  • Temperature - Lower atmosphere is warmed by conductance of earth and as air moves up it expands and loses energy
  • Humidity - Amount of vapor air can hold depends on temp. Saturated cold air has much less water than saturated warm air
  • Limits mixing with stratosphere

2. Stratosphere

  • 11-50 km above sea level
  • Dry, thin, little mixing
  • Temp. increases due to upward absorption of solar energy by ozone layer (gets warmer). Max temp of -3
  • These 4 zones are created because of the ozone

3. Mesosphere

  • 50-80 km above sea level
  • Extremely low air pressure, temperatures decrease with altitude; reaching their lowest point at the top of the mesosphere

4. Thermosphere

  • Up to 500 km - Warmed from above solar radiation

Properties of Atmosphere

  • Atmosphere Pressure - Force per unit of area produced by a column of air. Decreases with high altitude as fewer molecules are pulled down by gravity
  • Relative Humidity - The ratio of water vapour a given volume of air contains to the maximum amount it could contain at a given temperature.
  • Temperature - Varies with location and time. Global scale: Temp varies because sun rays strike some areas of earth more directly than others. Local scale: Temp varies because of topography - plant cover, proximity of land and water, etc.

Auroras are Phenomena in the Upper Atmosphere (Northern Lights)

  • Result from emissions of photons in the Earth's upper atmosphere
  • Nitrogen & oxygen atoms are ionized by colliding with particles; lose energy by emitting a photon

Solar energy heats the atmosphere

  • Heats and moves the air
  • Causes evaporation
  • Creates seasons
  • Influences weather and climate
  • Drives photosynthesis
  • Unequal distribution of solar energy

Effect of Axial Tilt

  • Because the earth is tilted on its axis by about 23.5 degrees, the northern and southern hemispheres each tilt towards the sun for half the year, resulting in the change of seasons
  • Changes in day length and altitude of the sun at noon
  • Axial tilt is the reason for the season

Climate and Weather

  • Weather can change quickly when air masses with different physical properties meet.
  • Weather - Atmospheric conditions over short time periods and small geographic areas
  • Climate - Patterns of average atmospheric conditions across large geographic regions and long periods of time
  • “Climate is what we expect; weather is what we get.” – Mark Twain

Air Masses Interact to Produce Weather

  • Air Mass - A large volume of air that is relatively homogeneous in temperature and humidity
  • Front - Boundary between air masses that differ in temperature, moisture, and density
  • Warm Front - Warm, moist air moves in to replace colder, dry air that is moving away. May produce light rain.
  • Cold Front - Where cold, dry air is pushing into warmer, moister air. Makes clouds that cause thunderstorms and tornados. Once a cold front passes sky becomes clear, and temp/ humidity drop. Cold front is steeper
  • High Pressure System - Contains air that moves outward away from a centre of high pressure as it descends. Bring fair weather
  • Low Pressure System - Air moves towards the low atmosphere pressure at the centre of the system and spirals upward. Clouds and precipitation occurs.
  • Thermal Inversion - When cool air occurs beneath a layer of warmer air at the top. (Figure 14.8, page 413)

What causes wind to blow?

1. Convection moves air (hot air rises, cool air sinks)

  • Warm, less dense air rises, creating vertical currents
  • Rising air expands, cools
  • Moisture condenses, precipitation falls
  • Cool, dry air descends and compresses, becoming warmer
  • Rising air - Warm, moist. Low-pressure zone leads to convergence at the surface; divergence aloft. Cloudy, rainy conditions. <- ->
  • Falling air - Cool, dry. High-pressure zone leads to divergence at the surface; convergence aloft. Fair, dry conditions. -> <-

2. Pressure gradient force affects wind speed (variations in atmospheric pressure)

  • Horizontal variations in atmospheric pressure
  • Air moves from areas of high to low pressure

3. Coriolis force (influences the direction of movement of air)

  • Apparent deflection of moving objects when viewed from a rotating frame of reference
  • A “fictitious” force that affects any freely-moving object on Earth’s surface (including air and ocean water — also planes and rockets!!)
  • Only discernible in motions over long distances and times
  • Because the Earth is a sphere, the equator spins faster than the poles

Wind direction is the result of a balance between the pressure gradient and Coriolis forces

  • Around a low pressure region winds circulate in the counter clockwise (cyclonic) direction (NORTHERN HEMISPHERE)
  • Around a high pressure region winds circulate in the clockwise (anticyclonic) direction (SOUTHERN HEMISPHERE)
  • Winds circulates around low pressure systems in the opposite sense in the two hemispheres

Large-scale air movements drive global circulation, influence weather and climate

  • Air moves from the equator to the poles
  • Transports heat and moisture
  • Keeps Earth’s temperature and climate in balance
  • Broken up by the Coriolis force

Convection is broken up into a series of circulation cells

  • Hadley cells form near the Equator where surface air warms, rises, and expands
  • Ferrel cells and polar cells lift air and create precipitation at 60 degrees latitude north and south
  • Trade Winds - Between equator and 30° latitude = Easterlies
  • Westerlies - From 30 ° to 60 ° latitude
  • Doldrums - Near the equator (few winds; no Coriolis force right at equator)

Outdoor Air Pollution

  • Air Pollution - Refers to the release of air pollutants
  • Outdoor air pollution affects climate and harms people and ecosystems
  • Air Pollutants - Gases and particulate material added to the atmosphere
  • Outdoor (Ambient) Air Pollution - Has decreased in recent decades due to government policy and improved technologies in developed countries - Developing countries and urban areas still have significant problems
  • Many pollutants are aerosols, which vary in both time and space Atmospheric aerosol profile:

Natural Sources can Pollute

  • Dust Storms - 100s of millions of tonnes of dust are blown westward across the Atlantic Ocean by trade winds every year and across the Pacific Ocean by jet stream
  • Waves Breaking - Major source of salt moving from ocean to land-based reservoirs
  • Fires - Pollutes atmosphere with soot (tiny particles) and gases
  • Over 60 million hectares of forests and grasslands burn each year
  • Fires are made more severe by human action - Decades of fire suppression - Fires from “slash-and-burn” clearing of forests
  • Volcanic Eruptions - Large quantities of particulate matter (ash), aerosols, sulphur dioxide and other volcanic gases
  • Can remain in the atmosphere for months or years - Aerosols = reflect sunlight back into space and cool the atmosphere and surface
  • Aerosols enhance cloud formation

Types and Sources of Outdoor Air Pollution

  • Point sources (e.g., factories)
  • Non-point sources (e.g., automobiles)
  • Primary Pollutants - Directly harmful, and/or react to form harmful substances (e.g., soot; carbon dioxide)
  • Secondary Pollutants - Form when primary pollutants react with other constituents of the atmosphere Identifies Harmful Airborne Substances

  • 1999 - Canadian Environmental Protection Act*
  • Environment Canada groups pollutants of greatest concern into four (overlapping) categories:
  • Criteria air contaminants
  • Persistent organic pollutants (e.g., DDT, TCE)
  • Heavy metals (e.g., lead, mercury)
  • Other toxic air pollutants (e.g., radon, asbestos)
  • *CEPA still exists but has been impacted by Bill C-38

Criteria air contaminants pose the biggest threats to human health

  • Both common and harmful
  • Sulphur dioxide (SO2 or SOX or TRS)
  • Nitrogen dioxide (NO2 or NOX)
  • Particulate matter (PM by particle size)
  • Volatile organic compound (VOC or VOX)
  • Carbon monoxide (CO)
  • Ammonia (NH3 )
  • Tropospheric ozone (O3)
  • Other things are monitored less frequently
  • Lead, mercury, POPs, etc.

Many forms of air pollution have decreased over the past few decades

  • Sulphur Dioxide
  • Lead

Other pollutants show little to no improvement

  • Nitrous oxide
  • Tropospheric ozone
  • Particulates

Reasons for the decline in some pollutants

  • Cleaner - Burning vehicles and catalytic converters decrease carbon monoxide
  • Permit-trading programs and clean coal technologies reduce SO2 emissions
  • Scrubbers - Technologies that chemically convert or physically remove pollutants before they leave the smokestacks
  • Phaseout of leaded gasoline
  • Improved technologies and federal policies

Smog is the most common, widespread air quality problem

  • Industrial smog (aka “grey air”)
  • Primary air pollutants from industrial sources combine chemically to form harmful compounds
  • Mainly in and downwind of industrial areas
  • Government regulations in developed countries have reduced smog
  • Coal-burning industrializing countries face significant health risks

Photochemical smog is produced by a complex series of reactions

  • Photochemical smog (aka “brown” air)
  • Light-driven reactions of primary pollutants and normal atmospheric compounds
  • Morning traffic exhaust releases pollutants
  • Most problematic in cities - Irritates eyes, nose, throat
  • Vehicle inspection programs

Thermal inversions can worsen air pollution

  • Normally there is vertical mixing – Warm air rises
  • Thermal Inversion - Layer of cool air trapped beneath a layer of warmer air - Denser, cooler air at the bottom of the inversion layer resists mixing

Ontario AQI was replaced by the Air Quality Health Index in 2015

  • Describes health risks associated with air pollution
  • Better harmonization with other jurisdictions
  • Based on three contaminants:
  • Ground-level Ozone (O3 )
  • Fine Particulate Matter (PM2.5)
  • Nitrogen Dioxide (NO2 )
  • AQHI for any given day is based on whichever pollutant is the worst – usually ozone, in Southern Ontario deposition is a transboundary pollution problem

  • Acidic Deposition - Acid or acid-forming pollutants moving from atmosphere to surface
  • Deposition - Wet or dry fallout
  • Acid Rain - Wet deposition of acid
  • Primary pollutants originate mainly from burning of fossil fuels
  • Releases sulphur dioxide and nitrogen oxides
  • Reacts with water to form sulphuric and nitric acids

Sources of Acid Deposition - NOx and SOx

  • Acid deposition affects ecosystems
  • Accelerates leaching of base cations from soil
  • Causes accumulation of Sulphur and nitrogen in soil
  • Hinders plant uptake of water and nutrients
  • Causes calcium to leach from needles of red spruce
  • Increases tree mortality
  • Acidifies lakes
  • Lowers lakes’ capacity to neutralize further acids
  • Elevates aluminium levels in surface waters
  • Negatively affects entire food webs deposition has not been reduced as much as scientists had hoped

  • New technologies such as scrubbers have helped
  • SO2 emissions are lower
  • NOx emissions are higher
  • Acid deposition’s effects are worse than predicted

Synthetic chemicals deplete stratospheric ozone

  • Ozone is an important trace chemical in the atmosphere
  • Tropospheric ozone - “ground-level ozone”
  • A major component of photochemical smog
  • Causes eye irritation and respiratory problems
  • A greenhouse gas
  • Stratospheric ozone = “ozone layer”
  • 25-35 km above the surface
  • 90% of O3 in the atmosphere is stratosphere

The ozone layer protects life on Earth

  • Ozone is destroyed and created naturally
  • Steady state among O, O2 , and O3 •
  • Stratospheric ozone acts as an atmospheric “blind”
  • “Blind” or filter = radiation is absorbed - e.g., greenhouse gases strongly absorb in the IR wavelengths - “Window” = radiation is transmitted - e.g., visible light passes easily through the atmosphere
  • Ozone strongly absorbs radiation in the shortest ultraviolet wavelengths - almost all UV-C & most UV-B rays absorbed.

There are several ways to measure O3

  • How much ozone is in the stratosphere?
  • Ground-based: absorption spectroscopy
  • Satellite-based: Total Ozone Mapping Spectrometer (TOMS) on Nimbus 7 spacecraft - Measures total ozone in a column of air - 100 Dobson Units (DU) = 1-mm-thick layer of pure ozone at surface temperature and pressure
  • Average ozone worldwide = 300 DU
  • Ozone “hole” has been as depleted as 90 DU

Ozone depletion is most severe over the South Pole

  • Ozone depletion is facilitated by the presence of catalysts and certain conditions
  • Ozone depletion most severe over South Pole
  • Antarctic ozone hole reappears every austral spring
  • Growing in both intensity and area of depletion
  • 1993 ozone was particularly depleted \approx 90 DU; intensified by the eruption of Mt. Pinatubo
  • Arctic and mid-latitude ozone depletion not as severe
  • Global average decreasing by \approx 0.5%/yr since 1978

Chlorofluorocarbons facilitate ozone depletion

  • Transported quickly to the stratosphere
  • Break down in the presence of sunlight, releasing chlorine
  • A single chlorine atom can recycle to break down many 1000s of ozone molecules

Conditions at the South Pole facilitate ozone depletion

  • Polar Vortex - Unimpeded circulation of very cold air
  • Tiny ice crystals in stratospheric clouds provide sites for ozone-destroying reactions
  • Arctic ozone depletion is not as severe - Not as cold - Polar vortex not as well defined

Ozone-depleting substances come from many sources

  • CFCs come from many industrial processes: - Refrigerants (Freon), aerosol propellants, cleaning solvents, Styrofoam, etc. - (CFCs are also greenhouse gases)
  • Other halogens also facilitate ozone depletion, especially bromine - Many sources – fire retardants, pesticides, dyes, etc.
  • Nitrous oxide and other chemicals also facilitate ozone depletion

Experts agree that ozone depletion

  • Allows more UV radiation to reach the surface
  • Has occurred over the South Pole
  • Is increasing in intensity
  • Is increasing in geographic area
  • Is facilitated by conditions in the polar vortex
  • Is facilitated by the presence of catalysts (including CFCs)

Experts do not completely agree on…

  • The significance of changes in a long-term context - There are no tools that allow scientists to measure changes in atmospheric ozone over geologic time.
  • The exact mechanisms of ozone depletion
  • The importance of CFCs relative to other causes • the environmental impacts of CFC replacements

Ozone depletion could have serious impacts

  • Increase in UV radiation flux may lead to…
  • Increased incidence of skin cancers
  • More rapid deterioration of materials
  • Damage to oceanic phytoplankton productivity and hence to the rest of the food chain
  • Decline in crop yields (maybe)
  • Harm to human immune system (maybe)
  • Related socioeconomic impacts

It is challenging to respond to international problems like this


  • Very long time scale
  • Built-in delay
  • CFCs now in the atmosphere will stay for many years
  • Lack of replacement technologies
  • Assigning responsibilities and costs


  • Limit emissions of CFCs
  • Monitor and control atmospheric changes
  • Develop CFC free technologies

The Montreal Protocol may be a success

  • Montreal Protocol (1987)
  • International agreement to phase out production of ODS
  • Use of precautionary principle
  • Collaborative approach
  • Built-in checks and updates
  • Covers CFCs and other halogens
  • Common-but-differentiated responsibility
  • Today: 95% drop in production of ODS
  • Ozone hole record size (2000), intensity (1993, 2006)
  • By 2050 the ozone hole may disappear

There are still many questions to be resolved about ozone depletion

  • Will ozone depletion spread from the Polar Regions to encompass mid-latitude regions?
  • What is the actual relationship between ozone depletion and human health impacts?
  • What are the other potential impacts of ozone depletion (e.g., on ecosystems)?
  • Are the substitute chemicals that are being proposed in international agreements definitely less damaging to the stratospheric ozone layer?
  • Is there any way to measure stratospheric ozone levels back through geologic time?

Indoor air pollution can also be problematic

  • Indoor air contains higher concentrations of pollutants than outdoor air - 6,000 people die each day from indoor air pollution
  • Average person in North America indoors 90% of the time - Exposed to synthetic materials (insecticides, cleaning fluids, plastics, chemically treated wood)
  • “Sick building” syndrome = produced by indoor pollution - Solved by using low-toxicity building materials and good ventilation
  • 1970s: ventilation systems sealed off, non-opening windows installed for energy efficiency, trapping pollutants inside

Many VOCs pollute indoor air

  • VOCs - Volatile organic compounds
  • Released by everything from plastics and oils to perfumes and paints, new furniture and rugs, etc. - Burning releases dioxins and furans
  • Formaldehyde from pressed wood and insulation, irritates mucous membranes and induces skin allergies - Includes pesticides, which are found indoors more often than outdoors
  • Most VOCs are released in very small amounts - Unclear health implications due to low concentrations

Indoor air pollution in the developing world arises from fuel wood burning

  • Burning wood, charcoal, crop and animal wastes for cooking fuel
  • Kills 1.6 million people each year
  • Causes pneumonia, bronchitis, allergies, cataracts, asthma, heart disease, cancer and premature death

Tobacco smoke and radon are the most dangerous indoor pollutants in the developed world

  • Second hand smoke from cigarettes is especially dangerous
  • Contains over 4000 dangerous chemicals
  • Causes eye, nose, and throat irritation
  • Radon gas is the second-leading cause of lung cancer in the developed world - Colourless, odourless gas that can seep into buildings
  • Tiny living organisms can also pollute

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