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Other Major Specific Sources of Air Pollution (Including Toxic Air Pollutants)

1. Agriculture (See endnote 45) (See the section on “Greenhouse Gases” later in this chapter)

Agricultural sources contributing to air pollution problems include: concentrated animal feeding operations where a large number of animals are confined and fed or maintained for extended periods of time in small areas; production of considerable amounts of manure from the concentration of animals; improper application of fertilizers, herbicides, and pesticides; water pollutants that become airborne; gaseous emissions from the decomposition of manure; and particulate matter from soil erosion, unpaved roadways and other areas, agricultural equipment, fire and smoke, and bulk materials handling.

Worldwide, cattle, sheep, buffalo, and goats produce about 80 million tons of methane a year, which is about 22% of all the methane from human activities. Their digestive systems can use unusable plant materials for food and fiber, but also produce methane. The livestock production system can also produce nitrous oxide, ammonia, hydrogen sulfide, and particulate matter. Besides lowering air quality in the area of these factory farms and producing substantial amounts of methane (a greenhouse gas), nitrous oxide, which is also a powerful greenhouse gas, is also produced. Odors also reduce the quality of the air.

The animal feeding operations and especially concentrated animal feeding operations (factory farms) increase the level of asthma and bronchitis in neighboring communities, especially in children. The ammonia produced is rapidly absorbed in the body and can cause severe coughing, buildup of mucus, and scarring of the airways.

Best Practices for Agriculture (See endnote 46) (See the “Particulate Matter” section)

  • • When the land is prepared for growing crops (tillage), use techniques that reduce the intensity of the work and therefore retain the residue on the surface of the soil.
  • • Use as little vehicular traffic on fields as possible.
  • • Use mulching material when possible to retain the soil cover.
  • • Reduce agricultural field operations of tilling, planning, weeding, fertilizing, etc., to the minimum amount necessary to reduce dust.
  • • Reduce the amount of engine emissions through proper maintenance of motorized equipment.
  • • Modify the timing of operations where possible to achieve maximum productive effort with minimum soil removal as dust.
  • • Observe the level of air quality and take into account weather conditions when performing agricultural work.
  • • Use dust suppressants where possible on dirt roads.
  • • Use vegetative and artificial barriers to retard the flow of wind over unprotected surfaces.
  • • Retrofit existing equipment to prevent or reduce the emissions of particulate matter, VOCs, and nitrogen oxides.
  • • Use fire with great care and take meteorological conditions into account when controlling undesirable vegetation and plant disease, reducing fuel hazards, and improving plant productivity.
  • • Reduce the amount of methane produced by herds by improving grazing, supplementing diets with nutrients, and improving genetics and reproductive efficiency. These techniques allow for improved management of livestock with lower numbers needed to produce the same amount of meat and milk.
  • • Use an anaerobic manure digester (AgSTAR Program) to convert the manure into energy.
  • • Turn large quantities of manure in the form of methane found in biogas into renewable energy which can be used on the farm and/or be sold to electric utilities. (See endnote 47.)
  • • Evaluate the potential health effects of individuals who are close to large animal feed- lots and provide necessary medical care for them.
  • 2. Aluminum Industry (Primary and Secondary) (See endnote 68)

The primary aluminum industry produces molten aluminum from ore and then the metal is used in a variety of products such as automobiles, trucks and other vehicles, packaging containers and foil, residential, industrial, commercial and farm structures, electrical appliances, etc. The ore called bauxite is refined into alumina, a feedstock. The alumina and electricity are then combined in a cell with a molten electrolyte called cryolite, which produces molten aluminum metal and carbon dioxide. This process uses a substantial amount of electricity with the attendant air pollution problems based on the fuels being consumed. Other potential emissions to the air are: dust at the various production facilities from dryers, materials handling equipment, movement of trucks, and blasting; smoke; metal compounds; and VOCs including dioxins, carbon monoxide, nitrogen oxides, sulfur dioxide, chlorides, hydrogen chloride, and hydrogen fluoride. The process also produces perfluorocarbons, which are very long-lasting in the atmosphere and significant contributors to climate change.

The secondary aluminum industry recovers aluminum cans, foundry returns, and scrap. Toxics are released during the processing of the scrap through shredding, melting, and removing the coating on the material. The toxics include metals, organic compounds, hydrogen chloride, fluorine compounds, chlorine, chlorinated benzenes, dioxins, and furans.

Best Practices for the Aluminum Industry (Primary and Secondary)

  • • At the site of the bauxite mine wash, the ore to remove contaminants that can go into the air.
  • • Use dry scrubbers after the smelting systems with aluminum oxide as the adsorbent to capture gases containing fluorides and recycle the fluorides.
  • • Use low sulfur tars for helping to control sulfur dioxide emissions.
  • • Reduce the emissions of organic compounds from secondary aluminum production by removing coatings, paint, oils, and greases in a very efficient manner.
  • • Use electrostatic precipitators and baghouse dust collectors to remove the dust from the emissions from the dryers.
  • • Use hoods and enclosures at the site of conveyors and material transfer points to minimize dust which has been created by stockpiled materials.
  • • Use baghouses at the production plants and lime kilns to control bauxite and limestone dust.
  • 3. Cement Kilns

The production of cement, called Portland cement, utilizes a substantial amount of electricity and produces about 22% of the carbon dioxide emitted by industries throughout the world. Cement is made commercially in over 120 countries and in every state in the United States and therefore contributes substantially to local air pollution. Cement is made by grinding and heating a mixture of materials such as limestone, clay, marl (an easily breakable earth deposit containing clay and calcium carbonate), iron ore, fly ash, slag from blast furnaces used by steel mills, etc., in a rotary kiln, which uses as its energy source coal, oil, gas, coke, or a variety of waste materials which may be the cheapest to buy and use but also produce the most pollutants. The product, which is called clinker, is cooled, mixed with a small amount of gypsum and then ground into a fine powder to produce cement. Concrete is then made by adding cement (about 10-15% of the concrete mix by volume) and water to sand, gravel or crushed stone and allowing the mixture to cure, thereby increasing its strength and durability. (See endnote 61.) Several harmful air pollutants are produced from making cement including air toxics especially mercury, hydrochloric acid, particulate matter, total hydrocarbons, carbon dioxide, nitrogen oxides, and sulfur dioxide. Many of these pollutants come from the firing of the substances and the materials used for heating, and are affected by the temperature of the flue gases. Mercury is found in small amounts especially in the raw materials and also in the fuels used in the cement industry, and the amount present varies widely from one place to another and from one country to another.

Best Practices for Cement Kilns

  • • Use high-efficiency fabric filters to control emissions of particulate matter from cement kilns, clinker coolers, material handling, product bagging, etc.
  • • Use continuous emission monitoring systems to record and report emissions from cement companies to meet US EPA regulations.
  • • Especially in older cement plants, check the accuracy of the bag leak detection system that is used to measure particulate matter loading in the exhaust of a fabric filter.
  • • Use a regenerative thermal oxidizer to destroy hazardous air pollutants by breaking the bonds of the hydrocarbon at high temperatures and then recombining the carbon and oxygen to form carbon dioxide and the hydrogen and oxygen to form water.
  • • Use powdered activated carbon injection technology for controlling mercury from cement plants.
  • • Reduce the amount of nitrogen oxides emissions through: control of temperature in the combustion zone, control of excess air through the process, use of low nitrogen oxide burners in the kiln, and use of efficient cooler systems.
  • • Use lime to help capture sulfur dioxide in the cement manufacturing process.
  • • Use a fuel that has particles that are small enough to burn quickly and easily.
  • • At the cement plant, put the cement kiln dust in enclosed, covered vehicles and conveyance systems.
  • • Compact the dust from the cement kilns and periodically wet it down at the disposal site in the landfills.
  • • Store cement kiln dust in enclosed tanks, containers, and buildings when preparing it for disposal or sale.
  • • Use a dry kiln instead of the wet process because it requires about a third less energy and therefore reduces greenhouse gas emissions.
  • 4. Chemical Industry (See endnote 27)

The major industries engaged in chemical manufacturing transform inorganic and organic raw materials into finished products. They manufacture:

  • • Basic chemicals
  • • Resin, synthetic rubber, and artificial fibers
  • • Pesticide, fertilizer, and agricultural chemicals
  • • Pharmaceuticals
  • • Paint, coating, and adhesives
  • • Soap and other cleaning compounds
  • • Miscellaneous chemical products

There are five major steps in chemical manufacturing and each one may create contamination of the air, water, and land. They are:

  • 1. Purification of the raw materials
  • 2. Chemical reactions when the raw materials are converted into other products
  • 3. Finishing operations such as purification of the products
  • 4. Handling, storage, transport, and equipment cleaning
  • 5. Disposal of unusable waste

Besides the inherent toxicity of the chemicals being produced by the manufacturing process, there are numerous highly significant heavy metals, VOCs, nitrate compounds, sulfur oxides, carbon monoxide, carbon dioxide, and particulate matter of all sizes produced and potentially released to the air. As an example, there are at least 131 organic air toxics found in the chemical manufacturing of synthetic organic chemicals. These toxics are emitted to the air from process vents, storage vessels, transfer racks and equipment leaks, and from wastewater treatment systems which have processed waste from the chemicals. Organic chemicals stay in the environment for long periods of time. They are deposited in water from the air and then bioaccumulate (the uptake, retention, and concentration of environmental substances by an organism) from low concentrations in water to high concentrations in animal tissue, and are highly toxic at low levels.

The chemical industry is responsible for releasing primary air pollutants into the air and creating secondary air pollutants which are formed from reactions between the air pollutants and atmospheric conditions. Particulate matter may either come from primary sources or be created by secondary sources. Organic chlorine compounds are of particular concern. They are found in large numbers of products including solvents, pesticides, plastics, disinfectants, etc., and may exist in the environment for long periods of time. Highly toxic byproducts are formed during the production of organic chlorine compounds. The burning of trash creates dioxins which may accumulate in the body fat and in the environment. Compounding the problem are temperature inversions which occur when the atmosphere is warmer as the altitude increases from the Earth. The temperature inversion creates a lid or blanket which forms over the area and the pollutants increase in concentration, thereby creating greater opportunities for illness among the residents as well as decreased visibility and deterioration of materials.

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