Chapter 12: Air Pollution A brief history of air pollution A brief history of air pollution Types and sources of air pollutants Types and sources of air pollutants Factors that affect air pollution Factors that affect air pollution Air pollution and the urban environment Air pollution and the urban environment Acid deposition Acid deposition

A Brief History of Air Pollution disastrous London smog event of 1952 disastrous London smog event of 1952 smog: smoke and fog; smog: smoke and fog; 5 days, nearly 4000 deaths; 5 days, nearly 4000 deaths; Clean Air Act in 1956 Clean Air Act in 1956 Los Angeles: photochemical smog Los Angeles: photochemical smog forms in sunny weather and irritates the eyes forms in sunny weather and irritates the eyes U.S. Clean Air Act, 1970, 1990 U.S. Clean Air Act, 1970, 1990 set federal emission standards for states to implement set federal emission standards for states to implement and enforce and enforce

Types and Sources of Air Pollutants Air pollutants are airborne substances (either solids, liquids, or gases) that occur in concentrations high enough to threaten the health of people and animals, to harm vegetation and structures, or to toxify a given environment. They come from natural sources and human activities: Natural: dust, volcano, forest fire, ocean waves, … Human: fixed sources (power plants, homes, …) mobile sources (cars, ships, …)

Principal Air Pollutants primary and secondary pollutants primary and secondary pollutants particulate matter: a group of solid particles and liquid droplets that are small enough to remain suspended in the air particulate matter: a group of solid particles and liquid droplets that are small enough to remain suspended in the air PM10, PM2.5: <10 or 2.5 micrometer in diameter PM10, PM2.5: <10 or 2.5 micrometer in diameter Carbon monoxide: colorless, odorless, poisonous Carbon monoxide: colorless, odorless, poisonous Globally, a large percentage of air pollution sources are natural. Within localized areas, however, human- caused sources are often the largest contributors.Globally, a large percentage of air pollution sources are natural. Within localized areas, however, human- caused sources are often the largest contributors.

Over U.S.

Principal Air Pollutants Volatile organic compounds (VOCs): represent a class of organic compounds that are mainly hydrocarbons – individual organic compounds composed of hydrogen and carbon Volatile organic compounds (VOCs): represent a class of organic compounds that are mainly hydrocarbons – individual organic compounds composed of hydrogen and carbon nitrogen oxides: nitrogen dioxide (NO 2 ) and nitric oxide (NO), together called NO x nitrogen oxides: nitrogen dioxide (NO 2 ) and nitric oxide (NO), together called NO x Along with ozone, VOCs and NOx are major components of photochemical smog.Along with ozone, VOCs and NOx are major components of photochemical smog. Photochemical smog is a problem on most Photochemical smog is a problem on most major cities of the world. major cities of the world.

Ozone in the Troposphere Photochemical smog: in the presence of sunlight Photochemical smog: in the presence of sunlight Ozone: unpleasant odor, irritates eyes and hurt human health, reduce crop yield Ozone: unpleasant odor, irritates eyes and hurt human health, reduce crop yield

Ozone in the Stratosphere relationship to ultraviolet radiation relationship to ultraviolet radiation chlorine compounds chlorine compounds chlorofluorocarbons (CFCs); a single chlorofluorocarbons (CFCs); a single chlorine removes as many as 100,000 chlorine removes as many as 100,000 ozone molecules ozone molecules Montreal Protocol Montreal Protocol When scientists first measured extremely low ozone values in the Antarctic stratosphere, they thought the instruments were malfunctioning.When scientists first measured extremely low ozone values in the Antarctic stratosphere, they thought the instruments were malfunctioning.

Figure 1, p. 337 Ozone hole in 2006; mainly due to changes in polar stratospheric temperatures

Air Pollution: Trends and Patterns Air Quality Index (AQI): includes the pollutants CO, SO 2, NO 2, particulate matter, and O 3 Air Quality Index (AQI): includes the pollutants CO, SO 2, NO 2, particulate matter, and O 3 Secondary air pollutants (e.g., O 3 )Secondary air pollutants (e.g., O 3 ) are particularly difficult to control, are particularly difficult to control, because they are not emitted because they are not emitted directly into the atmosphere. directly into the atmosphere.

Fig , p. 338

Factors affecting air pollution dilution dilution turbulence turbulence mixing mixing “Dilution is the solution to pollution” - in the 1950s this motto led to the construction of tall smokestacks for large factories. Pollution was released higher in the atmosphere where winds were stronger. Air quality improved locally but suffered downwind.“Dilution is the solution to pollution” - in the 1950s this motto led to the construction of tall smokestacks for large factories. Pollution was released higher in the atmosphere where winds were stronger. Air quality improved locally but suffered downwind. The role of the wind

The Role of Stability and Inversions temperature lapse rates temperature lapse rates inversions inversions mixing depth mixing depth The mixing layer can often beThe mixing layer can often be easily seen from an airplane. easily seen from an airplane.

The Role of Topography cold air drainage cold air drainage air blockage by mountain ranges air blockage by mountain ranges

Severe Air Pollution Potential Sources (clustered close together) Sources (clustered close together) high pressure (for inversion and weak wind) high pressure (for inversion and weak wind) Inversions Inversions Stagnation (unable to disperse pollutants) Stagnation (unable to disperse pollutants) A valley (for accumulation of pollutants) A valley (for accumulation of pollutants) Some locations, like Los Angeles and Mexico City, have an unfortunate combination of surrounding topography, frequent inversions, abundant emissions and plentiful sunlight - perfect conditions for photochemical smog.Some locations, like Los Angeles and Mexico City, have an unfortunate combination of surrounding topography, frequent inversions, abundant emissions and plentiful sunlight - perfect conditions for photochemical smog.

Air Pollution and the Urban Environment urban heat island urban heat island country breeze country breeze

Acid Deposition pH pH wet deposition wet deposition dry deposition dry deposition acid fog: SO 2 and NO x acid fog: SO 2 and NO x acid rain effects acid rain effects Precipitation pH values