1. November 2004 - Siebert Ground Level Ozone1 PHOTOCHEMICAL SMOG & OZONE

2. November 2004 - Siebert Ground Level Ozone2 Primary Pollutant Dangerous substance when emitted into the atmosphere Directly cause lung damage and respiratory distress –NOx –VOCs –PM 2.5 –PM 10

3. November 2004 - Siebert Ground Level Ozone3 Secondary Pollutant Chemical that is not emitted per se, but forms from chemical interactions between or among primary pollutants in the atmosphere –PM 2.5 –Photochemical Smog –Ozone

4. November 2004 - Siebert Ground Level Ozone4 London-type smog caused mainly by air pollution due to combustion of coal and emission of sulfur dioxide (SO 2 ) and dust Such pollution mixed with fog can produce droplets of sulfuric acid (H 2 SO 4 ) suspended in the air

5. November 2004 - Siebert Ground Level Ozone5 Photochemical Smog the dominant pollutant in most of the big cities of the world main component is ozone (O 3 ), which in high concentrations can cause breathing problems and burning eyes Primary Pollutants involved in ozone formation are: –NOx –VOCs

6. November 2004 - Siebert Ground Level Ozone6 Los Angeles-type smog (photochemical smog) Occurs on sunny days due to intense traffic. Oxides of nitrogen and hydrocarbons react in the presence of sunlight to produce a mixture of aerosols and gases. Photochemical smog contains ozone, ketones, formaldehyde, and PAN (peroxyacetyl nitrates).

7. November 2004 - Siebert Ground Level Ozone7 Ozone Formation Summary VOC + NOx + Heat + Sunlight = Ozone Motor vehicle exhaust and industrial emissions, gasoline vapors, and chemical solvents are some of the major sources of NOx and VOC that help to form ozone.

8. November 2004 - Siebert Ground Level Ozone8 Ozone Formation Cycle Ozone in small amounts is a normal part of the atmosphere NO is oxidized by ozone and forms nitrogen dioxide NO 2 –NO + O 3  NO 2 + O 2 Hydroxy-radicals (R.OH) are results of VOCs In the presence of sunlight the hydroxy-radical reacts with an oxygen molecule. The result is a peroxy-radical (R.O 2 ) –R.OH + O 2  R.O 2

9. November 2004 - Siebert Ground Level Ozone9 Ozone Formation Cycle Nitrogen dioxide NO 2 is split by the sun and forms O-atoms and nitrogen oxide NO. O-atoms react with the molecular oxygen in the air and form ozone (O 3 ). –NO 2 + O 2  NO + O 3 Nitrogen oxide NO reacts with peroxy- radicals R.O 2 and forms NO 2 again. –NO + R.O 2  NO 2 + R.O

10. November 2004 - Siebert Ground Level Ozone10 Ozone Formation Cycle Some ozone is consumed by NO depending on the competing concentration of peroxy-radicals R.O 2. The peroxy-radicals are consumed and ozone is formed while the nitrogen oxides are always recycled.

11. November 2004 - Siebert Ground Level Ozone11 Ozone Formation Cycle This can only happen if –enough sunlight is available for efficient photolysis (hot sunny days) –the mixture of peroxy-radicals and nitrogen oxides favors the ozone formation.

12. November 2004 - Siebert Ground Level Ozone12 Good and Bad Ozone Ozone has the same chemical structure whether it occurs miles above the earth or at ground level "Good" ozone occurs naturally in the stratosphere approximately 10 to 30 miles above the earth's surface and forms a layer that protects life on earth from the sun's harmful rays. In the earth's lower atmosphere, ground-level ozone is considered "bad."

13. November 2004 - Siebert Ground Level Ozone13 The summertime pollutant Peak ozone levels typically occur during hot, dry, stagnant summertime conditions. The length of the ozone season varies from one area of the United States to another. Southern and Southwestern states may have an ozone season that lasts nearly the entire year.

14. November 2004 - Siebert Ground Level Ozone14 Not Just a Local Problem Ozone and the pollutants that form it can cause air quality problems hundreds of miles away.