What Is Smog, and What Have We Done to Improve Air Quality?

Centuries before the term was even coined, scientists have known what causes smog. But deciding how to reduce air pollution — and then actually doing it — took a lot longer.

By Stephen C. George
May 13, 2023 3:00 PMOct 6, 2023 12:59 PM
Los Angeles smog
(Credit: Cate Frost/Shutterstock)


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Smoke and fog: Put them together and you get smog. It’s a short word for a long-standing problem, one that humanity has inflicted on itself for hundreds of years.

Simply put, smog is the generic term for certain types of air pollution, particularly very visible, thick air pollution associated with large cities and industrial zones.

Credit for the word usually goes to a doctor in Britain, Henry Des Voeux, who in 1905 used “smog” in a widely disseminated scientific paper, aptly titled “Fog and Smoke.” (However, some evidence suggests the term appeared as early as the 1880s.) It couldn’t have been a difficult word to come up with, especially for anyone familiar with the air quality of Britain’s major cities in the 19th and early 20th centuries.

Back then, coal-fueled fires burned in most homes and nearly all factories, of which there were many — never forget that Britain was an industrial colossus at the time. London in particular was famous for its pea-soupers, periods of dense haze so enveloping that it all but obliterated daylight.

What Causes Smog?

(Credit: testing/Shutterstock)

The recipe for smog is pretty basic: Start by burning a lot of fossil fuels — coal-fired factories and gas-powered vehicles are unfortunately all too effective at doing this. The resulting smoke and emissions, which are full of irritating and toxic airborne particles, mix with moisture in the air or react to sunlight, creating a thick haze that can make it hard to see, and hard to breathe.

That’s because smog is more than just a nuisance — it’s a killer. Many of the chemicals that are found in it are nothing we should be inhaling. For people with respiratory issues, especially children and seniors, it can increase risk of asthma, heart attack, stroke and more.

Read More: Fine Particle Pollution is Down, But Still Killing People

Types of Smog

Although all smog is bad for you, there are different types of it, depending on how it’s formed, what chemicals it contains or how it reacts with the environment.

Photochemical Smog

(Credit: Javier Garcia/Shutterstock)

This type of smog is created when nitrogen oxides and volatile organic compounds, generated largely by vehicle exhaust, but also by factory emissions, are released into the air and react to sunlight. The photochemical reaction creates a secondary pollutant — ozone, a major irritant when inhaled, which only adds to the respiratory woes of anyone who breathes it in.

As if that wasn’t bad enough, ozone also counts as a greenhouse gas. Photochemical smog tends to be more common in summer and in warmer, sunnier climates, which is why cities like Los Angeles, Mexico City and others tend to be literal hotbeds for this kind of pollution.

Industrial Smog

(Credit: TR STOK/Shutterstock)

Historically, industrial smog is what most people think of when they think of smog. Emissions from urban and industrial areas lead to smoke and particles that can mix with moisture in the air (especially fog) to create a dense and low-lying haze. 

Sulfurous Smog

Nelson's Column during the deadly Great Smog of 1952. (Credit: NTStobbs/CC-BY-SA-2.0/ Wikimedia Commons)

As the name suggests, sulfurous smog is a type of industrial smog that contains troublesome and even dangerous levels of sulfur dioxide, typically the result of burning high levels of coal. This has also sometimes been referred to as “London smog,” and with good reason, since the city was for decades a conspicuous consumer of coal for both home and industrial use.

The Great Smog of London

In 1952, one the most dramatic examples of smog’s deadly potential occurred when a catastrophic combination of weather conditions and rampant air pollution led to the so-called Great Smog of London.

The city was plunged into a noxious near-darkness that lasted several days and is said to have contributed to the deaths of as many as 12,000 people, both from respiratory-related health issues and from pedestrian, automobile and other accidents blamed on conditions of supremely poor visibility.

As terrible as the event was, it would come to have a galvanizing effect on the population and the government, as people finally took steps to create more effective regulations to curb air pollution and safeguard public health.

Read More: We Can See Disparities in Air Quality from Space

How Can We Reduce Air Pollution and Smog?

(Credit: Cate Frost/Shutterstock)

While attempts at creating some form of environmental regulation date back to the 1600s, it wasn’t until the mid-1950s that humanity began to see some watershed moments in environmental law. For example, in 1955, the U.S. passed the Air Pollution Control Act, the first federal law addressing air pollution.

Meanwhile, after the trauma of London’s Great Smog, Britain passed the Clean Air Act in 1956. Among other things, the act reduced the once-rampant burning of coal in both homes and factories. It also created zones where smoke and emissions could be banned outright.

By 1963, the U.S. had a Clean Air Act of its own, which enabled research into more effective methods to monitor and control forms of air pollution. Subsequent amendments to the act in the 1970s and 1990s would continue to set more stringent standards and control areas for emissions of air pollutants, as well as the ability to enforce the law with penalties.

Even so, smog in its various forms remains a problem for many cities around the world. In the U.S. alone, nearly 70 million tons of pollution per year continue to be emitted into the atmosphere. While it’s true that the numbers of most major air pollutants have been trending downward since the turn of the millennium, it’s clear that environmental experts — and the rest of us — can’t breathe easy just yet.

Read more: How to Save Planet Earth

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