Image provided by Anna Yablonskaya via Unsplash.

TL;DR: Historical records from ancient civilizations to early modern cities show that people have long contributed to air pollution through activities like wood burning, smelting, and coal use. The Industrial Revolution intensified the problem with large-scale fossil fuel combustion, producing dangerous city smogs. Modern sources, from vehicles and industry to wildfires, continue to affect air quality today. While some countries have made progress through regulation, air pollution remains a widespread public health concern. Addressing it requires both local action and broader policy efforts.

Air pollution causes roughly 6.7 million deaths every year, affecting communities worldwide and impacting the environment and global public health. But how did it get to this point, and has there been any improvement? Although air pollution has been around for thousands of years, its severity and main emission sources have changed throughout the centuries. 

Pre-industrial revolution air pollution sources 

At least 5,000 years ago, people began clearing forests for agriculture, producing smoke through the burning of wood. Livestock and human waste added methane to the air. Early societies developed metal smelting, which emitted sulfur, nitrogen oxides, and heavy metals. 

By the Middle Ages, people in some European populations became more aware of air pollution, particularly from human waste and butchering in cities. Smoke from the burning of wood and coal was also a concern. The development of the chimney, which was first adopted in the twelfth century, was a key milestone in indoor air quality. Before that, fires inside confined structures exposed inhabitants to toxic gases and particles. 

The chimney was a milestone in improving indoor air quality. This image is provided by Sandra Grünewald via Unsplash. 

Although other authors, from 400 BC Greece to Song Dynasty China, documented air pollution, John Evelyn published a particularly notable document describing air pollution in London in the 17th century. Even if Evelyn’s proposals to solve the problem were largely ignored, his work proves the existence and recognition of air pollution long before the Industrial Revolution. 

Early Industrial Revolution air pollution sources 

The Industrial Revolution began in Britain in the 18th century, and soon spread to other European countries, the United States, and Japan. This movement featured a rise in factory production, chemical manufacturing, iron production, and steam power.

The Industrial Revolution saw an explosion in the use of coal and steam power. This image of a train, taken around 1914, is provided by Museums Victoria via Unsplash. 

During this time period, air pollution significantly worsened, especially in European and American cities where industry and populations were exploding. Factory emissions, as well as domestic heating and cooking, produced unprecedented amounts of air pollution. The Industrial Revolution included a drastic increase in fossil fuel consumption, especially coal, resulting in sulfur dioxide (SO2), nitrogen dioxide (NO2), ammonia (NH3), and smoke emissions. 

For their intense sulfurous smogs, which were a combination of sulfur oxide emissions, including sulfur dioxide, and water vapor, London was colloquially known as “the Smoke,” and Edinburgh was referred to as the “Auld Reekie.” Yet, their conditions were not unique among large European cities in the late nineteenth century. 

Ammonia was also released by poor sewage treatment and dung from horses, which were commonly used for transportation. In the late 19th century, New York’s horses, for instance, produced as much as 1000 tonnes of manure daily, which understandably did not improve air quality. 

20th-century air pollution and progress

Poor air quality conditions continued in Industrialized areas well into the 1900s. In October of 1948, the sulfurous Donora Smog killed at least 20 people in Pennsylvania and affected an additional 5900 individuals. In London, the Great Smog of 1952 caused up to 12,000 deaths. 

Fortunately, this century also saw legislation and policy aimed at promoting clean air. Following the Donora Smog, the United States passed its first legislation addressing air pollution in 1955. Around 1970, the US established the Environmental Protection Agency (EPA) and passed the Clean Air Act, which made significant strides in reducing air pollution within the country. The United Kingdom passed the Clean Air Act of 1956, which, along with subsequent legislation, improved the air quality in London and other British cities. 

Through responsible public policy, many parts of Europe and North America made significant progress in addressing air pollution in the 1900s. This image is provided by VD Photography via Unsplash. 

In 1979, the Convention on Long-Range Transboundary Air Pollution (LRTAP) was established, addressing transboundary air pollution throughout much of Europe and North America. LRTAP has dramatically reduced sulfur emissions, which, in turn, has mitigated acid rain and improved soil health. Over time, the convention’s scope and protocols have expanded to include other pollutants such as ground-level ozone (O3), heavy metals, and particulate matter (PM). 

Although policy has made great strides in addressing air pollution, we still have a long way to go in improving air quality and protecting public health.

Today’s air pollution sources 

Fossil fuel combustion, including the combustion of oil, gasoline, diesel, and natural gas, makes up the majority of air pollution today. In 2011, fossil fuels represented 82% of the total primary energy supply worldwide. Fossil fuel combustion emissions are the leading environmental threat to child health and a major contributor to global inequality. 

The fossil fuel combustion process results in many air pollutants, including carbon dioxide (CO2), carbon monoxide (CO), sulfur dioxide, black carbon (BC), particulate matter (PM), nitrogen oxides (NOx), and Volatile Organic Compounds (VOCs).

Clarity Movement’s flagship Node-S air quality sensor measures fine particulate matter (PM2.5) and nitrogen dioxide (NO2). We offer additional modules that measure ozone (O3), black carbon (BC), carbon monoxide (CO), nitric oxide (NO), and nitrogen oxides (NOx). 

Sulfurous smog continues to this day, produced by coal-burning power plants and factories. However, it has now been eclipsed by photochemical smog, which is composed of ground-level ozone, nitrogen oxides, VOCs, and particulate matter. Photochemical smog forms when sunlight triggers chemical reactions between pollutants released by vehicles, industry, and other urban sources. 

Photochemical smog was first discovered in Los Angeles in the 1950s. This image of LA is provided by Joel Mott via Unsplash. 

Although wildfires have always been a source of air pollution, new attention has been directed towards this emission source due to climate change. Increased heat and drought have been driving more intense wildfire activity in many parts of the world. 

Wildfire smoke contains air pollutants such as ozone, carbon monoxide, and particulate matter. There is even some evidence to suggest that fine particulate matter from wildfires is more harmful to humans than particulate matter from other sources. Clarity is currently offering a discount for the 2025 wildfire season.

On a more positive note, indoor air pollution has been on the decline. This is due to a decline in the use of solid fuels for cooking. In 1980, 60% of homes engaged in this practice, whereas only 42% did so in 2012. 

Geographic changes in air pollution 

Over the past fifty years, the regions where most air pollution originates have shifted. Up until 1970, Europe and North America combined were responsible for more than 80% of the global sulfur dioxide emissions. Yet, by the mid-20th century, the Industrial Revolution spread into more parts of Asia, causing emissions to rise in places like China and India. 

Rapid economic expansion in Central, East, and South Asia caused increased combustion of oil and coal in these regions. Rapid industrialization led to poor air quality in cities in India and Pakistan. While legislation led to a sharp decline in sulfur dioxide emissions in Europe and North America from their peak in the 1970s, other countries have unfortunately seen a significant rise in air pollution.

This graph illustrates the global sulfur dioxide emissions for different world regions between 1850 and 2010. While some parts of the world show a sharp decrease in emissions in recent decades, Asian emissions are on the rise. 

Low- and middle-income countries are disproportionately exposed to harmful levels of air pollution. In 2019, roughly 89% of premature deaths caused by ambient air pollution occurred in low- and middle-income countries, with the greatest number in the WHO South-East Asia and Western Pacific regions. 

However, as much as 99% of the global population breathes air that exceeds World Health Organization (WHO) guideline limits. While exposure and impact are not equal, poor air quality affects nearly everyone. 

Looking forward

While air pollution is a serious threat to public health, there are steps you can take to protect yourself and your community from unsafe air. Check your local Air Quality Index (AQI) for current conditions. Clarity’s OpenMap and AirNow’s Fire and Smoke Map both show local AQI. Be sure to take proper precautions if your local air quality is poor. 

Advocate for responsible air pollution legislation and safe industry practices. Invest in air quality monitoring to better understand and address air quality challenges. Clarity can help you build a solution to ensure public health and environmental justice.