New! Sign up for our free email newsletter.
Reference Terms
from Wikipedia, the free encyclopedia

Smog

Smog is a kind of air pollution, originally named for the mixture of smoke and fog in the air. Classic smog results from large amounts of coal burning in an area and is caused by a mixture of smoke and sulfur dioxide. In the 1950s a new type of smog, known as Photochemical Smog, was first described.

Smog is a problem in a number of cities and continues to harm human health. Ground-level ozone, sulfur dioxide, nitrogen dioxide carbon monoxide are especially harmful for senior citizens, children, and people with heart and lung conditions such as emphysema, bronchitis, and asthma. It can inflame breathing passages, decreasing the lungs' working capacity, and causing shortness of breath, pain when inhaling deeply, wheezing, and coughing. It can cause eye and nose irritation and it dries out the protective membranes of the nose and throat and interferes with the body's ability to fight infection, increasing susceptibility to illness. Hospital admissions and respiratory deaths often increase during periods when ozone levels are high.

The U.S. EPA has developed an Air Quality index to help explain air pollution levels to the general public. 8 hour average ozone concentrations of 85 to 104 ppbv are described as "Unhealthy for Sensitive Groups", 105 ppbv to 124 ppbv as "unhealthy" and 125 ppb to 404 ppb as "very unhealthy."

Smog can form in almost any climate where industries or cities release large amounts of air pollution. However, it is worse during periods of warmer, sunnier weather when the upper air is warm enough to inhibit vertical circulation. It is especially prevalent in geologic basins encircled by hills or mountains. It often stays for an extended period of time over densely populated cities or urban areas, such as London, New York, Los Angeles, Mexico City, Houston, Toronto, Athens, Beijing, Hong Kong, the Randstad or Ruhr Area and can build up to dangerous levels.

Related Stories
 


Earth & Climate News

October 8, 2025

The Amazon has suffered its most destructive fire season in more than two decades, releasing a staggering 791 million tons of carbon dioxide—on par with Germany’s annual emissions. Scientists found that for the first time, fire-driven ...
Researchers at KAUST have confirmed that the Red Sea once vanished entirely, turning into a barren salt desert before being suddenly flooded by waters from the Indian Ocean. The flood carved deep channels and restored marine life in less than ...
Marine heatwaves can jam the ocean’s natural carbon conveyor belt, preventing carbon from reaching the deep sea. Researchers studying two major heatwaves in the Gulf of Alaska found that plankton shifts caused carbon to build up near the surface ...
Solar energy is now the cheapest source of power worldwide, driving a massive shift toward renewables. Falling battery prices and innovations in solar materials are making clean energy more reliable than ever. Yet, grid congestion and integration ...
New research reveals that deep-sea mining could dramatically threaten 30 species of sharks, rays, and ghost sharks whose habitats overlap with proposed mining zones. Many of these species, already at risk of extinction, could face increased dangers ...
Billions of years ago, Earth’s atmosphere was hostile, with barely any oxygen and toxic conditions for life. Researchers from the Earth-Life Science Institute studied Japan’s iron-rich hot springs, which mimic the ancient oceans, to uncover how ...
In 2020, California’s Creek Fire became so intense that it generated its own thunderstorm, a phenomenon called a pyrocumulonimbus cloud. For years, scientists struggled to replicate these explosive fire-born storms in climate models, leaving major ...
Swiss glaciers lost nearly 3% of their volume in 2025, following a snow-poor winter and scorching summer heatwaves. The melt has been so extreme that some glaciers lost more than two meters of ice thickness in a single season. Scientists caution ...
Fungi may have shaped Earth’s landscapes long before plants appeared. By combining rare gene transfers with fossil evidence, researchers have traced fungal origins back nearly a billion years earlier than expected. These ancient fungi may have ...
Scientists have uncovered an unexpected witness to Earth’s distant past: tiny iron oxide stones called ooids. These mineral snowballs lock away traces of ancient carbon, revealing that oceans between 1,000 and 541 million years ago held far less ...
Scientists found that biochar doesn’t just capture pollutants, it actively destroys them using direct electron transfer. This newly recognized ability accounts for up to 40% of its cleaning power and remains effective through repeated use. The ...
Bio-tar, once seen as a toxic waste, can be transformed into bio-carbon with applications in clean energy and environmental protection. This innovation could reduce emissions, create profits, and solve a major bioenergy industry ...

Latest Headlines

updated 12:56 pm ET