What causes haze?

Around large urban areas, you may have noticed the existence of dusty-looking clouds blocking a clear view of the city skyline at times. This is usually not fog or clouds, rather something known as haze.

Haze forms when weather conditions remain stagnant for a considerable length of time. This enables the dust, smoke and other pollutants to loiter between the sky and ground and collect in a small area. Inhabitants often rejoice when a rainstorm arrives, because it can disperse the haze with windy conditions. Rain and clouds can also clean particles from the air because water vapor tends to condense into liquid drops on aerosols in the air (known as condensation nuclei).

Specific weather patterns can cause haze to form in areas somewhat far away from the origination point of the dust, smoke or pollutant particles. For example, dust that originates in African dust storms can be transported across the Atlantic Ocean and have a hazy impact on locations in the Caribbean. Haze isn’t always bad, though. At low levels it has little impact on health, and it can create beautiful red and orange sunsets. The size of the particles means that the wavelengths of light that appear red and orange to humans can be selectively scattered, creating a romantic evening in the Caribbean, courtesy of Sub-Saharan dust.

The Environmental Protection Agency (EPA) issued the Clean Air Act in 1963 to protect the population of the United States from air pollution, and the EPA has made several amendments since then, implementing new programs and technologies to reduce the effect of acid rain, toxic air pollution and smog.

Quick facts about haze:

  • Haze can linger in the Arctic for months due to stagnate conditions.
  • The layer of haze/smog caused by air pollution and fires near South Asia and the Indian Ocean is visible on satellite imagery and is known as an Atmospheric Brown Cloud.
  • Dust transported from the Sahara has been found to have an impact on the content of soils in places such as Hawaii, so scientists are aware this transport has been going on for a long time.


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