1. Lecture 33: Air Pollution & The Ozone Hole

2. Air Pollution and The Ozone Hole We will discuss: 1.Air pollution types, sources, and trends 2.Tropospheric and stratospheric ozone 3.Pollution in the urban environment

3. Types & Sources of Air Pollution Primary air pollutants enter the atmosphere directly, while secondary pollutants form by chemical reaction. Pollutant sources are both natural, such as volcanoes and forest fires, and human caused, such as cars and industry.

4. Emission inventories On-road and non-road mobile sources Point sources Area sources Biogenic emissions

5. Principal Air Pollutants Carbon monoxide, sulfur oxides, nitrogen oxides, volatile organic compounds, and particulate matter are the most prevalent primary pollutants, and transportation and power generation are the primary sources for these pollutants. SO X NO X VOC

6. Definitions: NO x oxides of nitrogen (NO + NO 2 ) NO colorless, odorless, nonflammable NO 2 orange, toxic, corrosive, sharp odor Emitted by combustion processes National emission inventory (18,690 tons N/day)

7. Definitions: Volatile Organic Compounds, VOCs VOCs are a group of compounds, characterized by their ability to evaporate and their reactivity in the atmosphere National emission inventory (133,200 tons C/day) Emitted by combustion processes (especially vehicles), fuel and solvent evaporation

8. Particulate Matter Pollution Particulates (particles or droplets) are classified as having diameters less than 10 μm (PM 10 ) and less than 2.5 μm (PM 2.5 ). 1 inch = 25,000 microns (μm). One larger PM 2.5 particle width=30 times smaller than that of a human hair. PM 10 pollutants settle out of the atmosphere relatively quickly compared with the lingering PM 2.5. Both can adversely affect human health and reduce visibility.

9. Visible & Invisible Pollutants Suspended hygroscopic particles may scatter light and create a white wet-haze, while carbon monoxide and sulfur dioxide are not visible. The reaction of nitrogen dioxide and hydrocarbons in the presence of sunlight may generate unsightly photochemical smog.

10. Ozone in the Troposphere Human health is compromised by exposure to ozone and photochemical smog, which is formed when on a daily cycle when sunlight dissociates NO 2. The product O reacts with atmospheric O 2 to create O 3. Usually, the product NO would then react with and destroy the O 3. Excessive hydrocarbons, often from automobile exhaust, react with the product NO and O 3 concentrations increase to harmful levels. OZONE = Volatile Organic Compounds * Oxides of Nitrogen * Sunlight * Stagnant Air

11. Ozone in the Stratosphere UV radiation has enough energy to adversely impact the health of plants and animals, including humans. Naturally occurring O 3 in the stratosphere can block the most harmful UV radiation from entering the troposphere.

12. Stratospheric Ozone Destruction Naturally destructive agents of ozone include NO and NO 2, or oxides of nitrogen, which largely originate from bacterial activity at the earth's surface. Human released chlorofluorocarbons (CFCs) have upset the balance of O 3 production and destruction, and have caused formation of ozone holes and an increase in human UV exposure.

13. 90% of ozone in atmosphere occurs in a ‘layer’ between 19 and 48 km altitude in stratosphere. CFCs and Ozone DepletionOzone Depletion Stratospheric ozone protects life on Earth from harmful UV radiation CFC’s destroy ozone: CFC’s + UV  Cl O 3 + Cl  ClO + O 2 No loose O to make O 3 Natural production and destruction O 2 + O + UV  O 3 O 3 + UV  O 2 + O One Cl atom in a CFC molecule can destroy thousands of O 3 molecules

14. Evidence of Ozone Depletion

15. 1995: Crutzen, Molina and Rowland share Nobel Prize. Short history of discovery of ozone problem 1985: Ozone "hole" above Antarctica discovered 1976: M. Molina and F. Rowland theorized that chlorine in chlorofluorocarbons (CFCs: e.g., CH 3 Cl) also help destroy the ozone layer. Cl + O 3  ClO + O 2 1970: P. Crutzen showed that nitrogen oxides are involved in reactions that destroy ozone. NO + O 3  NO 2 + O 2 1987: Montreal Protocol signed to restrict CFCs emissionsMontreal Protocol

18. Ozone depletion is a global problem! Ozone depletion is not just confined to the stratospheric Arctic and Antarctic. Over the United States in March, 1994, ozone levels fell between 8 and 16% below the values observed during March, 1979.

19. Decline of CFCs 1987: Montreal Protocol signed to restrict CFCs emissionsMontreal Protocol 1992: more than half the world’s nations called for a quicker-phase out 1996: NOAA reported a 1% decline around the world from ground stations 1997: stratospheric chlorine concentrations peaked about 1997

20. Air Pollution Patterns & Trends Air quality in the U.S. may have been at its worst in the 1970s, but programs implemented by the Clean Air Act have helped the U.S. move toward primary ambient air quality standards. Regional Air Quality Indices may identify certain non- attainment areas, which are then targeted by the Environmental Protection Agency for improvement.

21. Trends in Tropospheric Ozone Yearly ozone trends are influenced by hot sunny weather and light surface winds, but many cities have demonstrated an overall decline in harmful ozone levels during the 1980s.

22. Air pollutants of concern in Texas PM 10 and PM 2.5 - Fine particulate matter suspended in the atmosphere degrades visibility and has been associated with increased rates of mortality O 3 - Ozone at ground level is an irritant, and is associated with increased incidence of respiratory disease and decreased respiratory function Hazardous air pollutants – A variety of health impacts associated with exposure to HAPs

23. Air Quality in Texas cities Houston, Dallas/Fort Worth Beaumont/Port Arthur and El Paso violate the current ozone standard and Austin, San Antonio and Longview would violate the new ozone standard. El Paso violates the current particulate matter standard. Houston and possibly DFW would likely violate the new particulate matter standard.

24. 32-Hour back trajectories for days with peak 8-hour ozone levels over 75 ppb in Austin (1993-1999)