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 29, 2025

Global scientists warn that humanity is on the verge of crossing irreversible climate thresholds, with coral reefs already at their tipping point and polar ice sheets possibly beyond recovery. The Global Tipping Points Report 2025 reveals how rising ...
Researchers at QUT uncovered how corals reattach to reefs through a three-phase process involving tissue transformation, anchoring, and skeleton formation. Differences among species reveal why some corals grow and attach faster than others. ...
Beneath the ice of Antarctica’s Weddell Sea, scientists discovered a vast, organized city of fish nests revealed after the colossal A68 iceberg broke away. Using robotic explorers, they found over ...
Extinction rates are not spiraling upward as many believe, according to a large-scale study analyzing 500 years of data. Researchers found that species losses peaked about a century ago and have decreased since, with different drivers shaping past ...
The Southern Ocean absorbs nearly half of all ocean-stored human CO2, but its future role is uncertain. Despite models predicting a decline, researchers found that freshening surface waters are currently keeping deep CO2 trapped below. This ...
A team of researchers has developed a floral-scented fungus that tricks mosquitoes into approaching and dying. The fungus emits longifolene, a natural scent that irresistibly draws them in. It’s harmless to humans, inexpensive to produce, and ...
New research shows that hippos lived in central Europe tens of thousands of years longer than previously thought. Ancient DNA and radiocarbon dating confirm they survived in Germany’s Upper Rhine Graben during a milder Ice Age phase. Closely ...
Scientists have uncovered that glaciers can temporarily cool the air around them, delaying some effects of global warming. This self-cooling, driven by katabatic winds, is nearing its peak and will likely reverse in the next two decades. Once ...
For the first time, scientists have seen a subduction zone actively breaking apart beneath the Pacific Northwest. Seismic data show the oceanic plate tearing into fragments, forming microplates in a slow, step-by-step collapse. This process, once ...
Scientists have discovered that El Niño and La Niña could become far more powerful and predictable as the planet warms. By 2050, the tropical Pacific may hit a tipping point, locking ENSO into strong, rhythmic oscillations that synchronize with ...
In the mist-shrouded mountains of New Guinea, a Czech researcher has achieved a world-first — capturing photos, video, and data of the elusive Subalpine Woolly Rat, Mallomys istapantap. Once known only from museum specimens, this giant, shaggy ...
Sea levels are rising faster than at any time in 4,000 years, scientists report, with China’s major coastal cities at particular risk. The rapid increase is driven by warming oceans and melting ice, while human activities like groundwater pumping ...

Latest Headlines

updated 12:56 pm ET