Air Pollution: A 20Th-Century Concern

Air pollution has been a concern for thousands of years, but the Industrial Revolution of the mid-19th century introduced new sources of air pollution, and by the middle of the 20th century, the effects of these changes were being felt worldwide. In the 1960s, an environmental movement emerged, leading to the Clean Air Act of 1970, which has since resulted in 62% less pollution in the US. However, in the second half of the 20th century, Europe and North America, the continents that first experienced rapid industrial growth, were the most impacted by emissions, responsible for over 80% of global sulphur dioxide emissions until 1970.

Industrial Revolution and coal-burning

The Industrial Revolution of the mid-19th century introduced new sources of air pollution, with far-reaching consequences. By the middle of the 20th century, the world began to experience the effects of these changes. The burning of coal, in particular, contributed significantly to air pollution during this period. Coal-fired power plants emitted harmful pollutants, including sulphur dioxide and nitrogen oxides, which had detrimental effects on the environment and human health.

Coal-burning played a crucial role in powering the Industrial Revolution, but it left a legacy of environmental degradation. Acid rain, caused by sulphur dioxide emissions, damaged lakes and forests, especially in the Eastern United States. The Clean Air Act Amendments of 1990 addressed this issue, significantly reducing sulphur dioxide emissions from coal-fired power plants. However, the damage to soils and vegetation, such as the iconic sugar maple, persists, and the recovery process is challenging and prolonged.

Coal ash, a byproduct of coal combustion, contains toxic contaminants like mercury, cadmium, and arsenic. It has contaminated groundwater, polluted lakes, and caused fish deformities. Despite growing awareness of the hazards of coal ash, regulatory responses have been inadequate. In 2015, the EPA declined to classify coal-burning wastes as hazardous, opting for less stringent solid waste regulations. This decision has led to inconsistent and ineffective enforcement, leaving citizens and states to bear the burden of addressing coal ash-related issues.

The burning of coal also contributed to air pollution in cities, with London experiencing one of its most severe air pollution events in December 1952, known as the Great Smog. This event highlighted the urgent need to address air quality issues. Motor vehicles, first mass-produced in the US in the early 20th century, also played a significant role in air pollution, particularly in the US, where they are the leading cause of air pollution today.

Automobiles and emissions

The link between air pollution and cars was first established in the early 1950s. A California researcher found that pollutants from traffic were responsible for the smoggy skies over Los Angeles. Typical new cars at the time emitted high levels of pollutants, including 13 grams per mile of hydrocarbons, 3.6 grams per mile of nitrogen oxides, and 87 grams per mile of carbon monoxide.

In the 1950s and 1960s, air pollution was a significant problem in the United States, with notable incidents in Donora, Pennsylvania, and on the Cuyahoga River in Cleveland, Ohio. These incidents led to the creation of the Air Pollution Control Act of 1955 and the Clean Water Act of 1972, marking the first federal attempts to control air and water pollution.

The Clean Air Act of 1970 set the first fuel economy goals and established the Environmental Protection Agency (EPA), which was tasked with regulating motor vehicle pollution. The EPA began to phase out lead in gasoline in the 1970s, and by 1995, leaded gasoline was fully prohibited. As a result, lead levels in the air decreased by 94% between 1980 and 1999. The EPA also set standards for emissions of nitrogen oxides from heavy-duty engines and particulate matter from heavy-duty diesel-powered trucks and buses.

The Clean Air Act was amended over time to require further reductions in hydrocarbon, carbon monoxide, nitrogen oxide, and particulate matter emissions. These amendments introduced lower tailpipe standards, more stringent emission testing procedures, and expanded inspection and maintenance programs. The 1990 Clean Air Act set limits on the discharge of air pollutants from industrial facilities and motor vehicles, addressing acid rain and ozone depletion.

Overall, efforts to reduce air pollution from transportation have been successful and cost-effective. New passenger vehicles are 98-99% cleaner for most tailpipe pollutants compared to the 1960s. Despite these improvements, the transportation sector remains one of the largest sources of carbon pollution in the United States, and the EPA continues to work on developing standards and technologies to reduce emissions further.

Scientific discoveries and research

The Industrial Revolution and its Impact: The Industrial Revolution of the 19th century introduced new sources of air pollution, and by the mid-20th century, its effects were being felt worldwide. Europe and North America, the first continents to experience rapid industrial growth, bore the brunt of emissions, particularly during the second half of the 20th century.

The Great Smog of London (1952): In December 1952, London experienced one of its most severe air pollution events, known as the Great Smog. This event highlighted the deadly consequences of air pollution and sparked increased concern and action.

The Keeling Curve (Late 1950s): Geochemist Charles Keeling's development of the Keeling Curve revealed a steady rise in CO2 levels, demonstrating the link between human activities and climate change. This discovery provided crucial scientific evidence for the growing awareness of global warming and the need to reduce air pollution.

The Clean Air Acts: In 1956, England passed the Clean Air Act to address the issues highlighted by the Great Smog. Subsequently, in 1963, the United States Congress passed its own Clean Air Act, which has since been amended and strengthened. These legislative victories were milestones in the global effort to combat air pollution.

The Environmental Movement (1960s): The 1960s witnessed the emergence of an environmental movement aimed at curbing the tide of pollutants affecting the planet's ecosystems. This movement led to significant events like Earth Day and legislative changes, including the Clean Water Act of 1972.

Understanding Ozone and Nitrogen Oxide (Second Half of the 20th Century): During this period, scientists discovered ground-level ozone, a highly polluting secondary gas formed from nitrogen oxide and volatile organic compounds. This discovery led to ground-level ozone being listed as a dangerous pollutant in the Clean Air Act, as it was linked to premature mortality and respiratory issues.

Forest Loss and Eutrophication (1980s): In the 1980s, scientists noticed accelerated forest loss in several European countries, linking it to deteriorating air quality. Additionally, eutrophication, caused by high concentrations of phosphorus and nitrogen in bodies of water, became a growing concern, impacting the health of grasslands and other ecosystems.

Particulate Matter Research (1990s): The 1990s saw continued research into air quality issues, with the Harvard Six Cities study in 1993 linking particulate matter to reduced life expectancy. This research contributed to a growing body of knowledge on the health impacts of air pollution, particularly the effects of atmospheric particulate matter with a diameter of less than 2.5 micrometers (PM2.5).

The 20th century was a pivotal period in the scientific understanding and mitigation of air pollution, setting the stage for ongoing efforts to address this global challenge.

Clean Air Acts

The Clean Air Act (CAA) is the primary federal air quality law in the United States, aimed at reducing and controlling air pollution nationwide. The Act was initially enacted in 1963 and has been amended several times since, becoming one of the country's first and most influential modern environmental laws.

The 1963 Clean Air Act was the first federal legislation regarding air pollution control, establishing a federal program within the U.S. Public Health Service and authorizing research into techniques for monitoring and controlling air pollution. This was followed by the Air Quality Act of 1967, which expanded studies of air pollutant emissions and control techniques.

The Clean Air Act of 1970 marked a significant shift in the federal government's role in air pollution control, authorizing comprehensive federal and state regulations to limit emissions from both stationary and mobile sources. This legislation established the National Ambient Air Quality Standards (NAAQS), setting maximum allowable concentrations of particulate matter and other pollutants. It also required each state government to devise its own plan for achieving and sustaining compliance with the standards.

The Clean Air Act has been amended multiple times to reflect technological advancements and an evolving understanding of safe pollutant levels. Major amendments were made in 1977, focusing on the Prevention of Significant Deterioration (PSD) of air quality in areas attaining NAAQS, and in 1990, which substantially increased the authority and responsibility of the federal government. The 1990 amendments also addressed the issue of acid rain, particularly targeting nitrogen oxides and sulfur dioxide emissions from fossil fuel power plants and other industrial sources.

The Environmental Protection Agency (EPA), formed in 1970, is responsible for administering the Clean Air Act in partnership with state, local, and tribal governments. The EPA develops extensive administrative regulations and associated regulatory programs to implement the law's mandates. The National Emissions Standards for Hazardous Air Pollutants, for example, sets standards for emissions of specific hazardous pollutants from particular sources.

The Clean Air Act has substantially reduced air pollution and improved US air quality, leading to significant health and economic benefits. Reductions in particulate air pollution alone have added up to 1.5 years to the life expectancy of Americans since 1970.

Global warming and climate change

The Keeling Curve, developed in the late 1950s, revealed a steady and concerning rise in CO2 levels, indicating the potential for climate change. This was further supported by computer models in the 1980s, which predicted a doubling of CO2 could cause a significant rise in global temperatures within a century. The Clean Air Act, passed in 1963 and amended over time, aimed to address air pollution, and the environmental movement of the 1960s led to Earth Day and the Clean Water Act of 1972.

The 20th century, particularly the first half, witnessed the Early Twentieth Century Warming (ETCW). This period of global warming was characterised by multidecadal phases of accelerated warming and slowed warming. The warming was more pronounced at higher latitudes of the Northern Hemisphere. Detection and attribution studies have indicated that external forcings, such as increasing greenhouse gas concentrations, changing solar and volcanic activity, and internal variability, contributed to the observed warming.

The understanding and management of air pollution evolved significantly in the 20th century. Ground-level ozone, a highly polluting secondary gas formed from primary pollutants like nitrogen oxide, was discovered in the second half of the century. The link between air pollution and deforestation was also established during this time, with experts noticing accelerated forest loss across Europe. These insights led to increased efforts to control and reduce air pollution, particularly in Europe and North America, the continents most impacted by emissions during the second half of the century.

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