Major Air Pollutants: Part 2 Nitrogen Oxides, Volatile Organic Compounds, Ozone, and Heavy Metals

Where do the air pollutants come from?

Major Air Pollutants Nitrogen oxides and nitric acid: Nitrogen oxide (NO) forms when nitrogen and oxygen gas in air react at the high-combustion temperatures in automobile engines and coal-burning plants. NO can also form from lightening and certain soil bacteria. NO reacts with air to form NO2. NO2 reacts with water vapor in the air to form nitric acid (HNO3) and nitrate salts (NO3-) which are components of acid deposition.

Major Air Pollutants Volatile organic compounds (VOCs): Most are hydorcarbons emitted by the leaves of many plants and methane. About two thirds of global methane emissions comes from human sources. Other VOCs include industrial solvents such as trichlorethylene (TCE), benzene, gasoline, paint thinner, and vinyl chloride. Long-term exposure to benzene can cause cancer, blood disorders, and immune system damage.

Sunlight plus Cars Equals Photochemical Smog Mexico City is one of the many cities in sunny, warm, dry climates with many motor vehicles that suffer from photochemical smog. Figure 19-4

17_16b.JPG Figure 17-16b Title: Photochemical smog. Caption: Mexico City (b) is one city that frequently experiences photochemical smog. Notes: Keywords: atmosphere, air pollution, pollutants, photochemical smog, nitrogen dioxide, nitric acid, ozone, acid precipitation, rain, energy resources, fossil fuels, nonrenewable, oil, petroleum, transportation, temperatures, thermal, inversions, layers

Sunlight plus Cars Equals Photochemical Smog Photochemical smog is a mixture of air pollutants formed by the reaction of nitrogen oxides and volatile organic hydrocarbons under the influence of sunlight.

17_16a.jpg Figure 17-16a Title: Photochemical smog. Caption: Nitric oxide, a key element of photochemical smog, can start a chemical chain reaction (a) that results in the production of other compounds, including nitrogen dioxide, nitric acid, ozone, and peroxyacyl nitrates (PANs). PANs can induce further reactions that damage living tissues in animals and plants. Nitric acid contributes to acidic deposition as well as photochemical smog. Photochemical smog is common today over many urban areas, especially those with hilly topography or frequent inversion layers. Notes: Keywords: atmosphere, air pollution, pollutants, photochemical smog, nitrogen dioxide, nitric acid, ozone, acid precipitation, rain, energy resources, fossil fuels, nonrenewable, oil, petroleum, transportation

Major Air Pollutants Ozone (O3): Is a highly reactive gas that is a major component of photochemical smog. It is a secondary air pollutant It can Cause and aggravate respiratory illness. Can aggravate heart disease. Damage plants, rubber in tires, fabrics, and paints.

Ozone Formation Formation of Ozone When NO2 gets struck by UV radiation an oxygen atom is knocked off: NO + O Normally the oxygen atom would recombine forming NO2 again, but when there are VOC’s present they will combine with the NO, preventing the oxygen from rejoining the NO. The free oxygen atom then joins a O2 molecule to form O3

17_08a.jpg Figure 17-08a Title: A thermal inversion is a natural atmospheric occurrence that can worsen air pollution locally. Caption: Under normal conditions (a), tropospheric temperature decreases with altitude, and air of different altitudes mixes, dispersing pollutants upward and outward from their sources. Notes: Keywords: atmosphere, temperatures, thermal, inversions, air pollution, layers

17_08b.jpg Figure 17-08b Title: A thermal inversion is a natural atmospheric occurrence that can worsen air pollution locally. Caption: During a thermal inversion (b), cool air remains near the ground underneath an 'inversion layer' of air that warms with altitude. Little mixing occurs, and pollutants are trapped near the surface. Notes: Keywords: atmosphere, temperatures, thermal, inversions, air pollution, layers

Temperature Inversions Cold, cloudy weather in a valley surrounded by mountains can trap air pollutants (left). Areas with sunny climate, light winds, mountains on three sides and an ocean on the other (right) are susceptible to inversions. Figure 19-5

Descending warm air mass Warmer air Inversion layer Inversion layer Sea breeze Figure 19.5 Natural capital degradation: two sets of topography and weather conditions that lead to prolonged temperature inversions, in which a warm air layer sits atop a cooler air layer. Air pollutants can build to harmful levels during an inversion. A temperature inversion can occur during cold, cloudy weather in a valley surrounded by mountains (left). Frequent and prolonged temperature inversions can also occur in an area with a sunny climate, light winds, mountains on three sides, and the ocean on the other (right). A layer of descending warm air from a high-pressure system prevents ocean-cooled air near the ground from ascending enough to disperse and dilute pollutants. Because of their topography, Los Angeles, California and Mexico City, Mexico (Figure 19-4) have frequent temperature inversions, many of them prolonged during the summer. QUESTION: Do you live in an area that suffers from fairly frequent thermal inversions? Increasing altitude Decreasing temperature Fig. 19-5, p. 447

Major Air Pollutants Lead Is a powerful neurotoxin. Was removed from gasoline over three decades ago Concentrations in the air have declined precipitously Mercury from coal fired power plants is now of greater concern than lead