1. 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 Air pollution and the urban environment urban environment Acid deposition Acid deposition

2. A Brief History of Air Pollution disastrous London smog event in December 1952 disastrous London smog event in December 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

3. 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. Q1: What are the natural sources of air pollutants? A: dust, volcano, forest fire, ocean waves, vegetation, … Q2: What are the anthropogenic sources? A: fixed sources (power plants, homes, …) mobile sources (cars, ships, …)

4. Principal Air Pollutants Primary pollutants: from direct emission (next slide) Primary pollutants: from direct emission (next slide) secondary pollutants: from chemical reaction secondary pollutants: from chemical reaction 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 PM2.5 is especially dangerous to health (e.g., lung) PM2.5 is especially dangerous to health (e.g., lung) Globally, a large percentage of air pollution sources are natural.Globally, a large percentage of air pollution sources are natural. Within localized areas, however, human-caused sources are often the largest contributors.Within localized areas, however, human-caused sources are often the largest contributors.

5. Over U.S. Q3: Is CO 2 a pollutant? a) yes; b) no Q4: What do air pollutants include? a) gases; b) liquids; c) solids; d) all of them

6. Principal Air Pollutants Carbon monoxide (CO): colorless, odorless, poisonous; primarily from incomplete combustion of fuels (e.g., cars) Carbon monoxide (CO): colorless, odorless, poisonous; primarily from incomplete combustion of fuels (e.g., cars) That is why we need to have CO detector at home! That is why we need to have CO detector at home! Sulfur dioxide (SO 2 ): colorless; primarily from the burning of fossil fuels (such as coal and oil) and from volcano and ocean spray Sulfur dioxide (SO 2 ): colorless; primarily from the burning of fossil fuels (such as coal and oil) and from volcano and ocean spray Volatile organic compounds (VOCs): represent a class of organic compounds that are mainly hydrocarbons – individual organic compounds composed of hydrogen and carbon, such as methane; primarily from industrial processes, transportation, and vegetation Volatile organic compounds (VOCs): represent a class of organic compounds that are mainly hydrocarbons – individual organic compounds composed of hydrogen and carbon, such as methane; primarily from industrial processes, transportation, and vegetation Nitrogen oxides: nitrogen dioxide (NO 2 ) and nitric oxide (NO), together called NO x; primarily from motor vehicles, power plants, and waste disposal systems. Nitrogen oxides: nitrogen dioxide (NO 2 ) and nitric oxide (NO), together called NO x; primarily from motor vehicles, power plants, and waste disposal systems. Dust: PM10 and PM2.5; from dust storm and agricultural and industrial activities Dust: PM10 and PM2.5; from dust storm and agricultural and industrial activities

7. Q5: What do automobiles emit? A: CO, NO x, VOCs, particulate matter, … Q6: Do automobiles emit O 3 ? a) yes; b) no Q7: What do power plants (using coal) emit? A: SO x, NO x, ash Q8: What do vegetation emit? A: VOC s, pollen Q9: Can the dust from Asia travel across the Pacific to reach Tucson? a) yes; b) no

8. Ozone in the Troposphere Photochemical smog: smog in the presence of sunlight Photochemical smog: 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 (tropospheric) O 3 forms as a secondary pollutant from a complex series of chemical reactions involving NO x and VOC s in the presence of sunlight. (tropospheric) O 3 forms as a secondary pollutant from a complex series of chemical reactions involving NO x and VOC s in the presence of sunlight. Q10: does Tucson have O 3 problem? a) yes, b) no Q11: does Tucson have particulate matter problem? a) yes, b) no

9. Ozone in the Stratosphere Stratosphere O 3 absorbs ultra-violet radiation to reduce human skin cancer; its concentration is highest at ~25 km altitude Stratosphere O 3 absorbs ultra-violet radiation to reduce human skin cancer; its concentration is highest at ~25 km altitude chlorine compounds such as chlorofluorocarbons (CFCs) are widely used as refrigerants, propellants (e.g., in hairspray) and solvents; chlorine compounds such as chlorofluorocarbons (CFCs) are widely used as refrigerants, propellants (e.g., in hairspray) and solvents; these gases are safe in the these gases are safe in the troposphere but destroy O 3 in the troposphere but destroy O 3 in the stratosphere: a single chlorine stratosphere: a single chlorine removes as many as 100,000 ozone removes as many as 100,000 ozone molecules molecules Montreal Protocol in 1987 Montreal Protocol in 1987

10. Ozone hole in 2006 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. Q12: why are there still ozone holes when chlorine is decreasing? A: there are still CFCs in the stratospphere; mainly due to changes in polar stratospheric temperatures

11. 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 ; on any day the pollutant measuring the highest value is the one used in the index on any day the pollutant measuring the highest value is the one used in the index 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. Higher emission standards along with cleaner fuels (such as natural gas) have made the air over our large cities cleaner than it was years agoHigher emission standards along with cleaner fuels (such as natural gas) have made the air over our large cities cleaner than it was years ago

12. Q13: why was the lead emission reduced to zero in 1980s? a) federal regulation; b) new technology; c) voluntary industrial decision Q14: Why did the emission peak for CO, SO 2, VOC s occur in early 1970s? Q15: What are the main air quality concerns in Tucson? a) PM2.5 and O 3 b) CO and SO 2 c) SO 2 and O 3 d) CO and PM2.5

13. Fig. 12-11, p. 338 Results based on AQI in 2003 Q16: Why is air in California not as good as rest of the U.S.? A: higher anthropogenic emission; dust; weather pattern; topography

14. Factors affecting air pollution “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. Role of the wind: dilution by advection and turbulent mixing

15. The Role of Stability and Inversions Inversions: temperature increases with height (i.e., very stable) Inversions: temperature increases with height (i.e., very stable) mixing layer: from surface to inversion base where air is unstable and hence well mixed mixing layer: from surface to inversion base where air is unstable and hence well mixed Q17: if air temperature decreases with height, what is the air stability? a) stable, b) unstable, c) undecided Q18: if air temperature increases with height, what is the air stability? a) stable, b) unstable, c) undecided Q19: is the layer below inversion in the figure a mixing layer? a) yes, b) no

16. The Role of Topography Nighttime drainage flow Nighttime drainage flow air blockage by mountain ranges air blockage by mountain ranges Los Angeles

17. 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 (weak wind; unable to disperse pollutants) Stagnation (weak wind; 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.

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

19. Acid Deposition pH: measure of the acidity or basicity of a solution pH: measure of the acidity or basicity of a solution Acid deposition: wet and dry deposition Acid deposition: wet and dry deposition wet deposition: removal of pollutants by precipitation wet deposition: removal of pollutants by precipitation dry deposition: by gravity dry deposition: by gravity acid rain or fog: SO 2 and NO x acid rain or fog: SO 2 and NO x Q20: why is natural rain somewhat acidic? Because of a) CO 2 dissolution b) SO 2 dissolution c) NO x dissolution

20. Acid Rain acid rain effects: damaging forest; eroding the foundations of structures; polluting lakes acid rain effects: damaging forest; eroding the foundations of structures; polluting lakes Control of acid rain is an international issue due to long- distance transport of pollutants Control of acid rain is an international issue due to long- distance transport of pollutants Precipitation pH values in 2005