Dust Particles

The atmosphere is not just a mixture of gases — it also holds a vast number of tiny solid particles suspended within it. These are called dust particles, and though they are small, they play an outsized role in weather and climate. The atmosphere has a sufficient capacity to keep these particles aloft, and they come from a wide range of sources, both natural and human-made.

Dust particles originate from several distinct places. Sea salts are thrown into the air by breaking waves and ocean spray. Fine soil is lifted by winds from dry, bare land. Smoke, soot and ash pour out of fires, volcanoes and industrial activity. Pollen comes from plants, while ordinary dust is stirred up from the ground by moving air. On top of all this, the atmosphere also receives disintegrated particles of meteors — fragments of space rock that burn up and break apart as they enter the atmosphere. Each of these sources contributes to the constant, invisible load of solids floating around us.

These particles are not spread evenly through the atmosphere. They are generally concentrated in the lower layers, close to the Earth's surface, where their sources lie and where winds are less able to lift them high. Yet this is not a fixed rule — convectional air currents, the rising columns of warm air that form on heated ground, can transport dust particles to great heights. A strong updraft can carry them far above their usual zone, so dust is found even in the upper atmosphere, though in far smaller amounts.

The distribution across the globe is also uneven. The higher concentration of dust particles is found in subtropical and temperate regions, and the reason is dry winds. These regions have extensive arid and semi-arid belts where loose soil is easily picked up and carried, so the air there is dustier. In contrast, equatorial and polar regions have a lower concentration — the equator because heavy rainfall and lush vegetation keep the soil anchored and wash the air clean, and the poles because they are covered in ice and snow, with little exposed soil to lift. …