PHOTOCHEMICAL SMOG & OZONE

1. PHOTOCHEMICAL SMOG & OZONE Ground Level Ozone

2. Primary Pollutant • Dangerous substance when emitted into the atmosphere • Directly cause lung damage and respiratory distress • NOx • VOCs • PM2.5 • PM10 Ground Level Ozone

3. Secondary Pollutant • Chemical that is not emitted per se, but forms from chemical interactions between or among primary pollutants in the atmosphere • PM2.5 • Photochemical Smog • Ozone Ground Level Ozone

4. London-type smog • caused mainly by air pollution due to combustion of coal and emission of sulfur dioxide (SO2) and dust • Such pollution mixed with fog can produce droplets of sulfuric acid (H2SO4) suspended in the air Ground Level Ozone

5. Photochemical Smog • the dominant pollutant in most of the big cities of the world  • main component is ozone (O3), which in high concentrations can cause breathing problems and burning eyes • Primary Pollutants involved in ozone formation are: • NOx • VOCs Ground Level Ozone

6. 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). Ground Level Ozone

7. 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.  Ground Level Ozone

8. Ozone Formation Cycle • Ozone in small amounts is a normal part of the atmosphere • NO is oxidized by ozone and forms nitrogen dioxide NO2 • NO + O3 NO2 + O2 • 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.O2 ) • R.OH + O2 R.O2 Ground Level Ozone

9. Ozone Formation Cycle • Nitrogen dioxide NO2 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 (O3). • NO2 + O2 NO + O3 • Nitrogen oxide NO reacts with peroxy-radicals R.O2 and forms NO2 again. • NO + R.O2 NO2 + R.O Ground Level Ozone

10. Ozone Formation Cycle • Some ozone is consumed by NO depending on the competing concentration of peroxy-radicals R.O2. • The peroxy-radicals are consumed and ozone is formed while the nitrogen oxides are always recycled. Ground Level Ozone

11. 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. Ground Level Ozone

12. 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." Ground Level Ozone

13. 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. Ground Level Ozone

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