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Image courtesy of Cathy Russell.
Sea Salt Aerosols
If you've ever been to the ocean, you know that ocean water contains salt. But did you know that air also has salt in it? Many types of tiny particles waft around in our atmosphere. Scientists call these particles "aerosols". Wind-blown dust and small soot particles from fires and smokestacks are two types of aerosols you may be familiar with. Salt from the sea also gets into the air to form aerosol particles. In fact, sea salt is one of the largest sources of aerosols on Earth.
On windy days waves form "whitecaps" as they break, creating millions of little bubbles. As these bubbles burst, tiny amounts of salt get tossed into the air, forming aerosols. Most of the salt in sea water is simple sodium chloride (NaCl), like our familiar table salt. Sea salt also contains smaller quantities of other salts, so sea salt aerosols also have chemicals like magnesium, sulfate, calcium, and potassium in them. Salt aerosols can even have organic materials mixed in. The overall chemical makeup of these aerosols determines how they react with other materials once they are in the atmosphere.
Aerosols of many types, including sea salt, influence Earth's climate. Salt aerosols scatter sunlight, reducing the amount of energy that reaches Earth's surface and thus exerting a cooling influence on climate. Sea salt aerosols also interact with clouds. They can act as the seeds, technically known as "cloud condensation nuclei" (CCN), around which cloud droplets grow. More clouds lead to a whiter, brighter Earth as seen from space. This further reduces the amount of sunlight that reaches the ground, again producing a net cooling effect on global climate.
In ocean areas that are far from land and where winds are high, sea salt is by far the largest source of aerosols. Since oceans cover more than 70% of Earth's surface, these particles can play a large role in climate. Climate scientists are therefore very interested in studying sea salt aerosols. So, the next time you're at the beach on a windy day and your skin feels sticky with salt even before you go for a swim... impress your friends by telling them about sea salt aerosols!
