Chapter 21 – Atmospheric Pollution
1) Give three examples each of natural and anthropogenic air pollutants.
First, volcanoes, fires and dust storms are natural polluters. The major constituents of the atmosphere are Nitrogen, Oxygen, Argon, Carbon Dioxide and water vapor (page 544).
Anthropogenic air pollutants- Carbon monoxide, nitrogen oxides, sulfur oxides. Sources include combustion of fuels, from nitrogen gas due to high combustion temperatures when burning fuels, combustion of leaded fuels and solid wastes (page 547).
2) What naturally occurring cleanser helps to remove pollutants from the atmosphere? Where does it come from?
Hydroxyl radical (OH) is a natural pollutant and a naturally occurring cleanser, which oxidizes many gaseous pollutants to products that are harmless or that can be brought down to the ground or water by precipitation. Sea salts picked up from sea spray as air masses move over the oceans are a second cleansing agent. These sea salts, now aerosols, act as excellent nuclei for the formation of rain drops. The rain then brings down many particulate pollutants (other aerosols) from the atmosphere to the ocean, cleansing pollutant laden air coming from the land. Third, sunlight breaks organic molecules apart. These three processes hold natural pollutants below toxic levels (except in the immediate area of a source, such as around an erupting volcano)- page 544.
3) Describe the origin of industrial smog and photochemical smog. What are the differences in the cause and appearance of each?
The Industrial Revolution introduced smog into urbanizing areas and emerging cities. Smog and haze shrouded and covered cities almost entirely. This shrouding haze became known as industrial smog (a combination of smoke and fog), an irritating, grayish mixture of soot, sulfurous compounds, and water vapor. This kind of smog continues to be found wherever industries are concentrated and where coal is the primary energy source. Photochemical smog is produced when several pollutants from automobile exhausts, nitrogen oxides, and volatile organic carbon compounds, are acted on by sunlight. Industrial smog is grayish black and photochemical smog is brownish and hovers over a city for longer periods during the day (page 545).
4) What are the major primary pollutants and their sources?
Suspended particulate matter: soot smoke, metals and carbon from combustion; dust, salts, metal, and dirt from wind erosion; atmospheric reactions of gases.
Volatile organic compounds: Incomplete combustion of fossil fuels; evaporation of solvents and gasoline; emission from plants.
Carbon monoxide: incomplete combustion of fuels.
Nitrogen oxides: from nitrogen gas due to high combustion temperatures when burning fuels.
Sulfur oxides: combustion of sulfur-containing fuels, especially coal.
Lead: combustion of leaded fuels and solid wastes.
Air toxics: industry and transportation
Radon: rocks and soil, natural breakdown of radium and uranium, (page 547).
5) What are secondary pollutants and how are they formed?
Ozone is one, which is produced from photochemical reactions between VOCs (volatile organic carbons) and NOx. The second is Peroxyacetyl nitrates which derive from the same source as ozone. Ozone formation occurs when Nitrogen dioxide absorbs light energy and splits to form nitric oxide and atomic oxygen, which rapidly combines with oxygen gas.
If other factors are not involved, ozone and nitric oxide then react to form nitrogen dioxide and oxygen gas. A steady-state concentration of ozone results, and there is no appreciable accumulation of the gas. When VOCs are present, however, the nitric oxide reacts with them instead of with the ozone, causing several serious problems. The reaction of nitric oxides and the VOCs leads to highly reactive and damaging compounds known as peroxyacetyl nitrates, or PANs, (pages 549-550).
6) Distinguish between emissions and ambient concentrations. How are they measured?
The EPA Office of Air and Radiation measure and track both emissions and ambient concentrations. Emissions are the result of primary pollutants from all sources. Ambient concentrations have to do with air quality, (page 549).
7) What is the difference between an acid and a base? What is the pH scale?
Acidic properties are due to the presence of hydrogen ions (H+, a hydrogen atom without its electron), which are highly reactive. An acid is any chemical that releases hydrogen ions when dissolved in water. The chemical formulas of a few common acids are shown in table 21-2. All acids ionize, their components separate, to hydrogen ions plus a negative ion. A base is any chemical that releases hydroxide ions when dissolved in water. pH reflects the concentration of hydrogen ions. The pH scale goes from 0 (highly acidic) to 7 (neutral) to 14 (highly basic). Each of the numbers on the scale represents the negative logarithm (power of 10) of the hydrogen ion concentration., expressed in grams per liter (g/L). One ion concentration is added as the numbers on the scale go up from 0 – 14. But they also represent an increase hydroxide ion concentration. pH scales measure the acidity and/or base levels of things, (pages 553-554).
8) What two major acids are involved in acid deposition? Where does each come from?
Sulfuric acid (H2SO4) and nitric acid (HNO3) in a ratio of about 2 to 1. They come form what is know as tail pipe emissions. Burning fuels produce sulfur dioxide and nitrogen oxides, so the source of the acid deposition problem is evident. These oxides enter the troposphere in large quantities from both anthropogenic and natural sources. Once in the troposphere, they are oxidized by hydroxyl radicals to sulfuric and nitric acids, which dissolve readily in water or absorb to particles and are brought down to Earth in acid deposition. This usually occurs within a week of the oxides’ entering the atmosphere. Natural sources include volcanoes, sea spray, and microbial processes (for sulfuric acid), and lightning, burning of biomass, and microbial processes (nitrogen oxide). Anthropogenic sources include heavily industrialized areas which tend to be concentrated in certain areas whereas natural sources are spread out through the world, (page 555).
9) What impact does air pollution have on human health? Give the three categories of impact and distinguish among them.
Too much sulfur dioxide inhalation can lead to bronchitis. Chronic ozone inhalation can lead to fibrosis of the lungs. Carbon monoxide reduces the capacity of blood to carry oxygen and can also cause heart disease. Nitrogen oxides can cause immune diseases and impairs lungs from functioning properly. Any of the combination of exposures can lead to Chronic Obstructive Pulmonary Disease and asthma. This category of problems or effects is known as Chronic Effects. Next, Acute effects, are levels of pollution that can lead to human deaths. Gases in high concentrations can be lethal. These cases occur when there is an accidental poisoning or explosion. Last, Carcinogenic effects are caused by heavy metal smelting and are identified as the organic constituents of air pollution which include many chemicals known to be carcinogenic in high doses. The presence of trace amounts of these chemicals in air may by responsible for a significant portion of the cancer observed in humans, (pages 557-558).
10) Describe the negative effects of pollutants on crops, forests, and other materials. Which pollutants are mainly responsible for these effects?
Crops- Ozone and photochemical oxidants damage crops, orchards, forests downwind of urban centers. Grains, soybeans, corn and wheat all suffer millions of dollars annually due to crop damage caused by pollution.
Forests- damage on forests is worse than in crops. Forests under stress from pollution are more susceptible to damage from insects and other pathogens. Trees die at a rapid rate from acid rain for instance.
Other materials- Walls, windows, and other exposed surfaces turn gray and dingy as particulates settle on them. Paints and fabrics deteriorate more rapidly. Car tires become hard and crack because of oxidation by ozone. Metal corrosion increases due to sulfur dioxide and acids derived from sulfur and nitrogen oxides, as are weathering and deterioration of stonework. The cleaning of these things costs millions of dollars. Sometimes, objects become irreplaceable.
Ozone and sulfuric acid are the main culprits to the damage listed above, (pages 558-559).
11) How can a shift in environmental pH affect aquatic ecosystems? In what other ecosystems can acid deposition be observed? What are its effects?
pH of an environment is extremely critical, because it affects the functions of virtually all enzymes, hormones and other proteins in the bodies of all organisms living in that environment. A consistently low environmental pH level can overwhelm the regulatory mechanisms in many life-forms, thus weakening or killing them. Most freshwater lakes, ponds and streams have a natural pH in the range of 6 to 8. The eggs and sperm and developing young of organisms are extremely sensitive to pH levels. Acid deposition can also occur in lakes, forests, mountains and other environments. Increased acidity can also kill organisms in lakes. Acid precipitation may leach aluminum and various heavy metals from the soil as the water percolates through it. Mercury tends to accumulate in ponds as acidity increases, affecting the reproductive organs of many aquatic and land animals that drink water from the lake, pond or river. Acidification is also a visual effect as well, making an environment look lifeless, (page 559).
12) What are the National Ambient Air Quality Standards and how are they used?
These standards cover criteria pollutants. They cover primary standards that must be upheld according to what humans can tolerate. Each pollutant is based on the presumed highest level that can be tolerated without noticeable effects, minus a 10% to 50% margin of safety. For many of the pollutants, long term and short term levels are set. The short term are designed to protect against acute effects while the long term are to protect against chronic effects, (page 561).
13) Discuss ways in which the Clean Air Act Amendments of 1990 address the failures of previous legislation.
This targets specific pollutants more directly and enforces compliance more aggressively, through such means as the imposition of sanctions. Each US state must develop a State Implementation Plan that is required to go through a process of public comment before being submitted to the EPA for approval. One major change is a permit application process (already in place for the release of pollutants in water ways. The amendments also afford more flexibility than the earlier command-and-control approach, by allowing polluters to choose the most cost effective way to accomplish the goals. In addition, the legislation uses a different market system to allocate pollution among different utilities. Under the CAAA, regions under the US that have failed to attain the required levels must submit attainment plans, based on reasonably available control technology (RACT) measures. Offending regions must convince the EPA that the standards will be reached within a certain timeframe, (page 562).
14) What technological and political changes are taking place in the United States to reduce acid deposition?
Politically, power plant emissions have been put in check. Also, since 70% of Canada’s acid deposition problem came from the US, diplomatic pressure toward a resolution was applied. Then came the passage of Title IV of the CAAA of 1990, which mandated reductions in both sulfur-dioxide and nitrogen oxide levels. By the year 2010, total SO2 emissions must be reduced 10 million tons below 1980 levels. This is the 50% reduction called for by scientists and it involves the setting of a permanent cap of 8.9 million tons on such emissions. The reduction will be implemented in phases. Also, nitrogen oxide emissions from power plants were to be reduced by 2 million tons by the year 2001, (pages 565-566).
Technology: One of the main culprits of pollution is the automotive industry. A new technology that is already on the market and is increasing in sales is the hybrid electric vehicle. This technology combines a conventional gasoline engine and a battery-powered electric motor to achieve substantial improvements on fuel economy, (page 569).
15) What are some recent air pollution programs that deserve our attention?
CAIR, Clean Air Interstate Rule, sets new lower caps on SO2, and NOx in 28 eastern states.
CAFE, Corporate Average Fuel Economy, addresses the dependence on foreign oil, all the health issues from smog and particulates, and carbon dioxide emissions that are bringing on global climate change, (pages 567, 568, 569).