Air pollution and air pollution control

An air pollutant is any substance added to the atmosphere by human activities that affects humans, animals, or the environment adversely. Many pollutants are toxic, while seemingly benign emissions such as carbon dioxide, a major contributor to global warming, and chlorofluorocarbons, which decimate the stratospheric ozone layer, are dangerous in less obvious ways. Significant worldwide resources have been committed to reducing all such hazardous emissions.

Background

Air pollution, occurring in gaseous, particulate, or aerosol form, has been problematic since humans began living in large cities and burning carbon-based fuels. The first known air pollution ordinance was passed in London in 1273, in an attempt to alleviate the soot-blackened skies from excessive combustion of wood. From the mid-eighteenth century through the mid-twentieth century, the increasingly heavy use of coal for heat, electricity, and transportation resulted in filthy air and an escalation of respiratory diseases. In the latter half of the twentieth century and the beginning of the twenty-first century, governments began attacking the problem with legislation to control noxious emissions at their source.

Earth’s atmosphere consists primarily of nitrogen, oxygen, water vapor, and trace amounts of many other substances. Emissions from human activities can alter the concentrations of these substances or release noxious chemicals with serious implications—including smog, acid rain, the greenhouse effect, and holes in the ozone layer—for both human and planetary health.

The major air pollutants are carbon oxides, sulfur oxides, nitrogen oxides, hydrocarbons, and particulate matter. According to a 2022 estimate, the United States adds around 5 million metric tons of carbon dioxide (CO₂) to the air; China adds approximately 10.5 million metric tons. Worldwide, the amount of CO₂ inserted into the atmosphere reached a new record high in 2022 at 417.06 parts per million, composed of various proportions of fossil-fuel electric power plants, industry, transportation, and homes and businesses.

Air Pollutants

CO₂ results whenever a carbon-containing fuel—such as coal, oil, or gasoline—is burned. When combustion is incomplete carbon monoxide (CO) is also produced. Although CO₂ is a relatively benign compound, the vast amount of fossil fuels (coal, oil, and natural gas) burned since the Industrial Revolution increased the atmospheric amount by more than 50 percent by 2023 and continued to increase at an escalating rate. Carbon dioxide molecules, while transparent in visible light from the Sun, reflect infrared radiation emitted by Earth and reradiate it as heat. Eventually, this will likely raise Earth’s average temperature in proportion to the amount of atmospheric CO₂. This “greenhouse effect” poses a long-term risk because a warming trend could increase sea levels, change rainfall patterns, disrupt grain belts, cause storms of greater intensity, and shift zones. Carbon monoxide is a toxic compound that causes death by suffocation by replacing oxygen in the bloodstream, thus depriving cells of their necessary oxygen.

Sulfur oxides are created whenever fossil fuels, particularly coal containing sulfur, are burned. Inhaling even relatively small concentrations of these gases can damage the upper respiratory tract and lung tissue. Another problem is that they react with water vapor in the atmosphere to produce sulfuric acid, a major component in acid rain.

Nitrogen oxides are synthesized whenever air is rapidly heated under pressure, followed by quick cooling, such as occurs in internal combustion engines and thermoelectric power plants. These compounds play a major role in the formation of acid rain, photochemical smog, and ozone (O₃), a potent reactive compound that attacks the lungs. Combustion-caused ozone is dangerous to living organisms near Earth’s surface, but in the stratosphere it occurs naturally. This “ozone layer” prevents most of the Sun’s ultraviolet light from reaching Earth’s surface. Therefore, it can cause skin cancer in humans as well as affect plants and wildlife adversely.

Particulates are minuscule solid or liquid particles suspended in the air. They occur from combustion, dry grinding processes, and spraying. The human respiratory system has evolved a mechanism to prevent certain sizes of particulates from reaching the lungs, but there is no protection against the smaller particles of coal dust and the larger particulates in tobacco smoke. Coal dust settling in the lungs leads to black lung disease, while the particulates from tobacco smoke are a leading cause of lung cancer.

The United States emits millions of metric tons of suspended particulate matter each year, chiefly from fossil-fuel electric power plants and industrial smelting plants. Even particulates that do not reach the lower regions of the respiratory tract can affect breathing, cause emphysema, aggravate an existing cardiovascular disorder, or damage the immune system.

Smog

The word “smog” is a melding of “smoke” and “fog” to describe fog polluted by smoke. When a local atmosphere becomes stagnant, smog pollution levels can create “killer fogs.” Three times in recent history these killer fogs have caused statistically significant increases in the death rate, particularly among those with respiratory problems. The first instance occurred in 1948 in Donora, Pennsylvania, when a stagnated fog became progressively more contaminated with the smoky effluents from local steel mills. The second case occurred in 1952 in London when a stagnant fog mixed with the smoke from thousands of coal-burning homes caused many with respiratory ailments to die. Finally, during Thanksgiving of 1966, New York City experienced an increased death rate because of choking smog.

A second, completely different type of smog is “photochemical smog,” a noxious mixture of reactive chemicals created when sunlight catalyzes reactions of residual hydrocarbons and nitrogen oxides from automotive exhaust. The first occurrence of such was in the late 1940s in Los Angeles, where the abundant sunlight and the dramatic increase of vehicular traffic created ideal conditions for photochemical smog. This smog contains, among other things, powerful eye irritants, noisome odors, and dangerous reactive compounds. Although first observed in Los Angeles, in the twenty-first century, photochemical smog maintained prevalence in most other large, densely populated cities with automobiles.

Chlorofluorocarbons

When first synthesized in the 1930s, chlorofluorocarbon (CFC) was hailed as an ideal refrigerant (Freon) because it was nontoxic, non-corrosive, nonflammable, and inexpensive to produce. Later, pressurized CFCs were used as aerosol propellants and as the working fluid for air conditioners and refrigerators. By 1970, scientists realized that the huge quantities of CFCs released into the atmosphere from aerosol cans and discarded refrigerant units were migrating to the stratosphere, where they were decomposed by highly energetic ultraviolet radiation from the Sun, releasing large quantities of ozone-destroying chlorine. The reduction of ozone was most pronounced over Antarctica, where an “ozone hole,” first detected in the early 1970s, was increasing in size annually. In 1978, pressured by environmentalists and consumer boycotts, the US government banned aerosol cans and refrigeration units utilizing CFC propellant, forcing the chemical industry to develop alternatives. By 1987, the depletion of the ozone layer had become so problematic that most industrial nations met in Montreal to ratify an international treaty calling for immediate reductions in all CFC use with a complete phase-out by the year 2000. By 2001, the Montreal Protocol had limited the damage to the ozone layer to about 10 percent of what it would have been had the agreement not been ratified. From its original 46 signatories, the protocol was eventually signed by around 200 countries with goals to eliminate all ozone depleting chemicals by 2040. In 2018, the ozone showed its first signs of recovery, with the potential to recover fully by 2050, according to some estimates.

Air Pollution Control in the United States

In the United States, the first attempts to control the smog or black smoke prevalent in industrial cities were the Clean Air Act of 1963 and the Motor Vehicle Pollution Act of 1965. The 1963 act was too weak to be effective; in 1967, the stronger Air Quality Act was enacted. The Clean Air Act Amendments of 1970 mandated national air quality standards set by the Environmental Protection Agency (EPA) to be met by 1975. Standards for six major air pollutants (sulfur oxides, nitrogen oxides, particulates, ozone, carbon monoxide, and lead) were legislated. When the pollution concentration exceeded these limits, control devices were obligatory, regardless of the cost.

Although most forms of air pollution were reduced after enactment of the Clean Air Act Amendments, mounting public concern over the continuing deterioration of air quality in major cities resulted in several important revisions in 1990. New legislation mandated that coal-burning power plants reduce sulfur oxide emissions by 9 million metric tons per year from 1980 levels by the year 2000. The revisions also required that industry reduce several hundred carcinogenic airborne substances by up to 90 percent by the year 2000. Because of its smog problem, California set even more stringent standards by legislating that 2 percent of all new vehicles must emit zero emissions by 1998, a rate that was to increase to 10 percent by 2003. In October 2006, the EPA’s scientific advisers recommended that the allowable levels of surface ozone be substantially reduced, but industrial lobbying and the conservative political climate prevented any substantial change.

During the decades following the Clean Air Act Amendments, particulate emissions decreased by 80 percent, carbon monoxide by 55 percent, hydrocarbon emissions by 40 percent, sulfur oxides by 27 percent, and atmospheric lead by 98 percent. The particulate emission reduction is attributed to control equipment installed on utility plant and industrial smokestacks, a decreased use of coal, and less burning of solid wastes. Carbon monoxide and hydrocarbon emissions have decreased, despite an increase in automotive traffic, because of federal automotive emission standards. The drop in sulfur oxides is directly attributable to a switch to low-sulfur coal and the removal of sulfur from the discharged gases at electric power plants. The drastic drop of lead compounds in the atmosphere resulted from the switch to unleaded gasoline during the 1970s.

During the first decade of the twenty-first century, concern about global warming caused by CO₂ created a consensus that drastic action was needed to reduce this threat. Early in 2009, the EPA declared CO₂ an air pollutant, thus empowering the Clean Air Act to establish national emission standards for new automobiles and new coal-fired electric power plants, the two largest contributors to global warming emissions. In December 2022, the EPA implemented the Control of Air Pollution for New Motor Vehicles: Heavy-Duty Engine and Vehicle Standards, which will take effect in 2027 to limit the emissions allowed from new vehicles.

In 2024, the United States Supreme Court blocked the EPA's "good neighbor" plan, which would have mandated that Western States cut polluting emissions from power plants and factories that travel into Eastern states. Previously, the Supreme Court determined in 2022 that the EPA could not regulate power plant emissions as Congress had not given the agency the ability to regulate the energy industry.

Global Air Quality Control

Air pollution, an ongoing problem in industrialized nations, has also become problematic in virtually all undeveloped countries undergoing rapid industrialization. The countries of the European Union have taken collective action because pollution generated in one country affects air quality in neighboring countries. Because road transportation is Europe’s largest air polluter, beginning in the 1970s motor vehicles manufactured on the continent have had required exhaust-emission controls. Fossil-fuel emissions from power plants and factories are also stringently regulated. In the United Kingdom, national air quality objectives were instituted in 2000 in association with an air quality network to monitor levels of major pollutants in various locations and a daily warning system to indicate potentially dangerous air pollution levels. In the summer of 2006, a directive on emission ceilings for cleaner air in Europe was passed by the European Parliament. In March 2021, the EU Ambient Air Quality Directives were strengthened by the European Parliament by increasing the number of pollutants included in European regulations and laws. These directives were merged in 2022, introducing a zero-pollution objective with an aim to improve EU air quality to that of WHO guidelines by 2050. This directive was set to be revisited every five years to ensure standards remain consistent with global needs.

The environmental crisis in the former Soviet republics of Eastern Europe is a direct result of the policies pursued under the communist regime when rapid industrialization ignored local conditions. Air pollution controls were deemed unnecessary because the biosphere was assumed to be self-purifying. With the advent of glasnost, a state committee on environmental protection was instituted in 1988; this became a state ministry in 1991 but was abolished nine years later. No significant change in ecological concerns occurred after the fall of the communist regime and the transition to capitalism. Because agencies responsible for environmental matters were either nonexistent or severely underfunded, internationally funded pollution abatement projects were abandoned when the funds expired. According to the European Environment Agency’s 2022 air quality status report, Central-eastern European countries and the Po Valley region in northern Italy ranked highest on the continent for benzopyrene and particulate matter because of high industry prevalence and reliance on solid fuel heating. However, in the same year, 96 percent of the urban areas in Europe tested above the WHO’s health-based guidelines.

In India, rapid industrialization and urbanization combined with unregulated vehicular emissions and uncontrolled industrial effluents have exacerbated a pre-existing problem. Legislation to alleviate the crisis in cities such as New Delhi, one of the top-ten most polluted cities in the world, has been extremely difficult to implement. Auto emissions account for approximately 70 percent of urban air pollution, and regulations required all public transportation vehicles in New Delhi to switch to compressed natural gas engines by April 1, 2001. However, the statute had to be rescinded when it removed about fifteen thousand taxis and ten thousand buses from service, creating commuter chaos and public riots. India’s high air pollution has not happened because of a lack of legislation but because of insufficient enforcement at the local level. According to a study conducted by Lancet, 2.3 million Indians died because of pollution in 2019, with 1.6 million of these deaths the result of air pollution.

Beginning in the 1980s, the growth of China’s economy removed millions of people from poverty, but at a great cost to the environment. The increase of urban automotive traffic, the dependence on coal, and a weak environmental protection system have left China with sixteen of the world’s twenty most polluted cities. Both urban and rural dwellers suffer from air pollution, which annually causes approximately 1 million premature deaths, according to the WHO in 2016 (2 million on average by the early 2000s). In 2005, to help alleviate the problem, the government proposed that strict fuel efficiency standards and emission controls be required on all vehicles. Efforts to clean up the air in Beijing for the 2008 Summer Olympics were successful, but after the event, air pollution in the city quickly reverted to previous levels. China’s excessive air pollution is not contained within its borders. Unregulated airborne effluents from the numerous coal-burning plants reach Japan and become a major contributor to acid rain. In addition, sulfate-encrusted dust, carbon particulates, and nitrates cross the Pacific Ocean, where they are responsible for almost one-third of the polluted air over Los Angeles and San Francisco. Though air quality is said to have improved from 2012 to 2022, thanks to the Ambient Air Quality Standards, most cities in the country still failed to meet these set standards in 2023. Additionally, most scientists in the United States call for standards to be more stringent for most pollutants.

Arguably, Japan is the Asian country that has taken air pollution abatement and control most seriously. Laws regulating the emission of sulfur dioxide and nitrogen oxides are among the strictest in the world, but polluted air from China keeps the rain acidic. The huge increase in automotive traffic in the twentieth and twenty-first centuries is a major contributor to urban air pollution as well as severe congestion. Several stringent laws regulate automotive emissions in an attempt to control these related problems. In addition, the Japanese Ministry of the Environment promotes low-emission vehicles and continues to strengthen measures to reduce factory emissions. In June 2001, the Japanese legislature passed a law strengthening controls on diesel vehicle emissions; two years later, diesel-powered commercial vehicles were banned from Tokyo if these limits were exceeded. However, due to increased industrialization, sixty thousand individuals died prematurely in 2019 as a result of air pollution in Japan, and despite domestic efforts to reduce emissions, the country also struggled with cross-border pollution. In 2021, Japan ranked seventh in the world for pollution rates.

Context

According to a 2022 report from the World Health Organization (WHO), approximately 6.7 million premature deaths in the world occur annually because of air pollution, many of them in India and China. In both developed and developing nations in the twenty-first century, air pollution from the escalating number of vehicles, as well as consumer preference for larger, more powerful vehicles, continues as a major challenge despite gains since the 1980s. By early 2024, the WHO reported that only seven countries (Australia, Estonia, Finland, Grenada, Iceland, Mauritius, and New Zealand) met the organization’s air quality guidelines for particulate matter, the inhalation of which had previously been linked by the EPA to a number of health problems mostly pertaining to the heart and lungs.

However, controlling air pollution is not inexpensive. Pollution control devices increase costs to factories and to automobiles, costs that are passed to the consumer. Unless a radical change away from conspicuous consumption and the overreliance on fossil fuels occurs, air quality will not improve substantially.

The issue of whether global warming is caused by humans may not be completely resolved, but strong measures to control carbon dioxide as well as noxious gaseous and particulate air pollutants began during the last decades of the twentieth century. Because the preponderance of scientific evidence suggests that global warming is due to humanity’s excessive use of fossil fuels, it would seem prudent to curtail the disproportionate dependence on nonrenewable resources. When it was discovered in 1985 that the ozone layer was being depleted by CFCs, the Montreal Protocol was ratified by most industrial nations. This precedent indicates that strong, effective action and international cooperation are possible when the threat to the environment are grave enough. In 2023, the UN reported tremendous success of the protocol, with 99 percent of ozone-depleting substances phased out of use in only thirty-five years. At the 2023 rate, the ozone was on track to recover within four decades, and the efforts were estimated to have avoided around 0.5 degrees Celsius.

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