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Earth Notes: Dust and Pollen Bring On the Rain

For allergy sufferers, dust and pollen are an irritating part of life in the Southwest. Yet recent research reveals that these tiny particles are crucial to the formation of life-giving rains, both here and around the world. 

In order for atmospheric water vapor to become a granule of ice that can fall as precipitation, it needs a microscopic building block around which to form. Scientists have known for decades that airborne particles are crucial to forming rain and snow. Yet only recently have they been able to identify the precise characteristics of these particles.

Atmospheric chemist Kimberly Prather of the University of California San Diego has developed techniques to decode the chemical makeup of clouds. Her studies reveal that much of the rain and snow that fall in the American West form around ultra-fine dust particles from Asian deserts 8,000 miles to the west.

In separate studies, a research team led by University of Michigan scientist Allison Steiner explored the role of pollen in producing precipitation.

Because only particles smaller than 200 nanometers will prompt ice formation, pollen initially seemed far too big for the task. But Steiner’s team discovered that when pollen gets wet, it breaks into tiny fragments—small enough to trigger the ice-making process.

These ongoing studies will help scientists predict and respond to changes in global weather patterns caused by climate change. And they might even remind us to be thankful for the dust and pollen that help water our drought-prone region.

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