Module 6: Air Pollution

Air Pollution

• Means any alteration of the physical, chemical, and biological properties of the atmospheric air, or any discharge thereto to any liquid, gaseous or solid substances that will or is likely to create or to render the air resources of the country harmful, detrimental or injurious to public health, safety or welfare or which will adversely affect their utilization for domestic, commercial, industrial, agricultural, recreational, or other legitimate purposes. (RA 8749, 1999)

• Estimated to contribute to over 3 million deaths per year.

Air Pollutant

Any matter found in the atmosphere other than oxygen, nitrogen, water vapor, carbon dioxide, and the inert gases in their natural or normal concentrations, that is detrimental to health or the environment.

Ambient Air Quality

The general amount of pollution present in a broad area; and refers to the atmosphere’s average purity as distinguished from discharged measurements taken as the source of pollution.

Ambient Air

The air around us.

Primary Pollutants

Released directly from the source into the air in a harmful form

Secondary Pollutants

Converted to a hazardous form after they enter the air or are formed by chemical reactions as components of the air mix and interact.

Fugitive Emissions

• Those do not go through a smoke stack

• The most massive of this category is dust from soil erosion, strip mining, rock crushing, and building constructions.

• Hard to monitor but they are extremely important sources of air pollution.

Sulfur Dioxide

• Natural Sources of sulfur in the atmosphere include evaporation of sea spray, erosion of sulfate-containing dust from arid soils, fumes from volcanoes.

• Total yearly emissions of sulfur from all sources amount to some 114 million metric tons.

• Worldwide, anthropogenic sources represent about 2/3 of the all airborne sulfur, but in most urban areas they contribute as much as 90% of the sulfur in the air.

• China and the United States are the largest sources of anthropogenic sulfur, primarily from coal burning and smelting.

• Colorless corrosive gas, directly damaging to both plants and animals.

Nitrogen Oxides (NOx)

• Highly reactive gases formed when nitrogen in fuel or in air is heated (during combustion) to temperatures above 650°C in the presence of oxygen.

• Bacteria can also form NO as they oxidize nitrogen-containing compounds in soil or water.

• In addition, nitrous oxide (N2O) is an intermediate form that results from soil denitrification. Nitrous oxide absorbs ultraviolet light and is an important greenhouse gas.

• Because nitrogen readily changes from one of these forms to another by gaining or losing O atoms, the general term NOx is used to describe these gases.

• Nitrogen oxides combine with water to make nitric acid (HNO3), a major component of acid rain

Carbon Monoxide (CO)

• Colorless, odorless, nonirritating, but highly toxic gas.

• Produced mainly by incomplete combustion of fuel (coal, oil, charcoal, or gas), as in furnaces, incinerators, engines, or fires, as well as in decomposition of organic matter.

• CO blocks oxygen uptake in blood by binding irreversibly to hemoglobin (the protein that carries oxygen in our blood), making hemoglobin unable to hold oxygen and deliver it to cells.

• Human activities produce about half of the 1 billion metric tons of CO released to the atmosphere each year.

• About 90% of the CO in the air is converted to CO2 in photochemical reactions that produce ozone.

• Catalytic converters on vehicles are one of the important methods to reduce CO production by ensuring complete oxidation of carbon to carbon dioxide (CO2).

• Carbon dioxide is the predominant form of carbon in the air.

Ozone (O3) and Photochemical Oxidants

• Ground level O3 is a product of photochemical reactions (reactions initiated by sunlight) between other pollutants, such as NOx or volatile organic compounds. A general term for products of these reactions is photochemical oxidants.

• One of the most important of these reactions involves splitting nitrogen dioxide (NO2) into nitrous oxide (NO) and Oxygen (O). This single O atom is then available to combine with a molecule of O2 to make ozone (O3).

• A general term for organic chemicals that evaporate easily or exist as gases in the air is Volatile Organic Compounds (VOCs).

• Plants are the largest source of VOCs, releasing an estimated 350 million tons of isoprene (C5H8) and 450 million tons of terpenes (C10H15) each year. Isoprene is emitted by trees like oaks and eucalyptus and is used as raw material for polymeric products (Britannica, 2020) while terpene is released by trees in warm weather (Adam, 2008).

Lead

• Most abundantly produced metal air pollutant

• Lead is toxic to our nervous systems and other critical functions. Lead binds to enzymes and to components of our cell, such as brain cells, which then cannot function normally.

• Airborne lead is produced by a wide range of industrial and mining processes.

• The main sources are smelting of metal ores, mining, and burning of coal and municipal waste, in which lead is a trace element and burning of gasoline to which lead has been added.

• Leaded gasoline was the main source of lead in the United States, but leaded gas was phased out in the 1980s. Banning leaded gasoline in the US was one of the most successful pollution-control measures in American history.

• Worldwide atmospheric lead emissions amount to about 2 million metric tons per year, or 2/3 of all metallic air pollution. Globally, most of this lead is still from leaded gasoline, as well as metal ore smelting and coal burning.

Particulate Matter

• Includes solid particles or liquid droplets suspended in a gaseous medium.

• Very fine solid or liquid particulates suspended in the atmosphere are aerosols. These include dust, ash, soot, lint, smoke, pollen, spores, algal cells, and many other suspended materials.

• Particles smaller than 2.5 micrometers in diameter, such as those found in smoke and haze, and produced by fires, power plants, or vehicle exhaust, are among the most dangerous particulates because they can be drawn into the lungs , where they damage respiratory tissues. Asbestos fibers and cigarette smoke are among these dangerous fine particles. This fine particulate matter is referred to as PM2.5, in reference to its size. Reducing sulfur in coal and diesel fuel, which produces aerosol droplets of sulfuric acid, is one important strategy for controlling PM2.5 particulates.

• Coarse inhalable particles are larger than 2.5 micrometers but less than 10 micrometers in diameter. These are known as PM10, and they are typically found near roads or other visible dust sources. The “dust bowl” of the 1930s involved mainly this kind of particulates. At that time, farmland soils were often left bare, especially during severe drought, and billions of tons of topsoil blew away from farmlands. Soil conservation on farmlands is one strategy for reducing PM10; another strategy is better management of dust at construction sites.

• Aspergillus sydowii, a soil fungus from Africa, has been shown to be causing death of corals and sea fans in remote reefs in the Caribbean.

• In the Philippines, a study of Simpas, et al. (2014) showed that traffic is the main contributor to PM2.5 at all sites in Metro Manila while biomass burning appeared to be the highest contributor in the areas outside NCR.

Mercury (Hg)

• Mercury has become regulated relatively recently (in Philippines, DAO 1997-38)

• Volcanoes and rock weathering can produce mercury, but 70% of airborne mercury derives from coal-burning power plants, metal processing (smelting), waste incineration, and other industrial combustion.

• About 75% of human exposure to mercury comes from eating fish. This is because aquatic bacteria are mainly responsible for converting airborne mercury into methyl mercury, a form that accumulates in living animal tissues.

• Much of our understanding of mercury poisoning comes from a disastrous case in Minamata, Japan, in the 1950s, where a chemical factory regularly discharged mercury-laden waste into Minamata Bay. Babies whose mothers ate mercury-contaminated fish suffered profound neurological disabilities, including deafness, blindness, mental retardation, and cerebral palsy. In adults, mercury poisoning caused numbness, loss of muscle control, and dementia. The connection between “Minamata disease” and mercury was established in the 1950s, but waste dumping didn’t end for another ten years.

Carbon Dioxide

• Some 370 billion tons of CO2 are emitted each year from respiration (oxidation of organic compounds by plant and animal cells). These releases are usually balanced by an equal uptake by photosynthesis in green plants.

• At normal concentrations, CO2 is nontoxic and innocuous, but atmospheric levels are steadily increasing (about 0.5 percent per year) due to human activities and are now causing global climate change, with serious implications for both human and natural communities.

Halogens

• The EPA is charged with regulating six greenhouse gases: carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride. These are gases whose emissions have grown dramatically in recent decades.

• Three of these six greenhouse gases contain halogens, a group of lightweight, highly reactive elements (fluorine, chlorine, bromine and iodine). Because they are generally toxic in their elemental form, they are commonly used as fumigants and disinfectants, but they also have hundreds of uses in industrial and commercial products.

• Chlorofluorocarbons (CFCs) have been banned for most uses in industrialized countries, but about 600 million tons of these compounds are used annually worldwide in spray propellants and refrigeration compressors and for foam blowing. They diffuse into the stratosphere, where they release chlorine and fluorine atoms that destroy ozone molecules that protect the earth from ultraviolet radiation.

Hazardous Air Pollutants (HAPs)

• These chemicals include carcinogens, neurotoxins, mutagens, teratogens, endocrine system disrupters, and other highly toxic compounds.

• The most persistent compounds require special reporting and management because they remain in ecosystem for long periods of time and accumulate in animal and human tissues.

• Most of these chemicals are either metal compounds, chlorinated hydrocarbons, or volatile organic compounds.

• Gasoline vapors, solvents, and components of plastics are all HAPs that you may encounter on a daily basis.

Aesthetic Degradations

• Any undesirable change in the physical characteristics or chemistry of the atmosphere, such as noise, odors, and light pollution.

• These factors rarely threaten life or health directly, but they can strongly impact our quality of life.

• They also increase stress, which affects health.

• Factories that emit noxious chemicals sometimes spray “odor maskants” or perfumes into smokestacks to cover up objectionable odors.

• Light pollution also is a concern in most urban areas, where ambient light confuses birds and hides the stars.

Temperature Inversions

• Can greatly concentrate air pollutants.

• Inversions occur when a stable layer of warmer air lies above cooler air.

• The normal conditions, where temperatures decline with increasing height, are inverted, and these stable conditions prevent convection currents from dispersing pollutants.

• Inversions might last from a few hours to a few days.

• The most stable inversion conditions are usually created by rapid nighttime cooling in a valley or basin where air movement is restricted.

Bronchitis

A persistent inflammation of bronchi and bronchioles (large and small airways in the lung) that causes mucus buildup, a painful cough, and involuntary muscle spasms that constrict airways.

Emphysema

Severe bronchitis, an irreversible chronic obstructive lung disease in which airways become permanently constricted and alveoli are damaged or even destroyed.

Acid Precipitation

• The deposition of wet acidic solutions or dry acidic particles from the air.

• English Scientist Robert Angus Smith coined the term “acid rain” in his studies of air chemistry in Manchester, England, in the 1850s.

• By the 1940s it was known that pollutants, including atmospheric acids, could be transported long distances by wind currents. This was thought to be only an academic curiosity until it was shown that precipitation of these acids can have far reaching ecological effects.

• Unpolluted rain generally has a pH of about 5.6 due to carbonic acid created by CO2 in air. Sulfur, chlorine, and other elements also form acidic compounds as they are released in sea spray, volcanic emissions, and biological decomposition. These sources can lower the pH of rain well below 5.6. Other factors, such as alkaline dust can raise it above 7.

Air Pollution Control Facilities (APCF)

• General term for structure or installation controlling the quality of emissions of air pollution source equipment (APSE).

• Examples are filters, scrubbers and dust collectors

Particulate Removal

Involves filtering air emissions. Filters trap particulates in a mesh of cotton cloth, spun glass fibers, or asbestos-cellulose. Industrial air filters are generally giant bags 10 to 15 m long and 2 to 3 m wide. Effluent gas is blown through the bag, much like the bag on a vacuum cleaner. Every few days or weeks the bags are opened to remove the dust cake. Electrostatic precipitators are the most common particulate controls in power plants.

Sulfur Removal

• Important because sulfur oxides are among the most damaging of all air pollutants in terms of human health and ecosystem viability.

• Switching from soft coal with a high sulfur content to low sulfur coal is the surest way to reduce sulfur emissions.

• Switching to cleaner oil or gas would eliminate metal effluents as well as sulfur.

• Cleaning fuels is an alternative to switching. Coal can be crushed, washed, and gasified to remove sulfur and metals before combustion. This improves heat content and firing properties, but may replace air pollution with solid-waste and water pollution problems; furthermore, these steps are expensive.

Nitrogen Oxides (NOx)

• Can be reduced in both internal combustion engines and industrial boilers by as much as 50 percent by carefully controlling the flow of air and fuel.

• Staged burners, for example, control burning temperatures and oxygen flow to prevent formation of NOx.

• The catalytic converter on your car uses platinum-palladium and rhodium catalysts to remove up to 90% of NOx, hydrocarbons and carbon monoxide at the same time.

Hydrocarbon Controls

• Mainly involve complete combustion or controlling evaporation.

• Hydrocarbons and VOCs are produced by incomplete combustion of fuels or by solvent evaporation from chemical factories, paints, dry cleaning, plastic manufacturing, printing, and other industrial processed. Closed systems that prevent escape of fugitive gases can reduce many of these emissions.

• In automobiles, for instance, positive crankcase ventilation (PCV) systems collect oil that escapes from around the pistons and unburned fuel and channels them back to the engine for combustion.