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Tiny Particles, Big Storms

Natural aerosols such as mineral dust from deserts and sea salt have always served as nuclei where water vapor condenses to form clouds.

Since the Industrial Revolution however, human-created sources of aerosols have made their way into the atmosphere. Why does this matter? Two reasons related to the total amount of aerosols and the type of aerosols in our atmosphere.

The number of aerosols in the air is one of the most important factors for cloud formation. Imagine there is a set amount of condensed water in the atmosphere. If there are fewer numbers of aerosols present, larger water drops form… allowing precipitation to form more easily.

When aerosols are present in very large numbers, as in polluted environments, that same amount of water gets spread over a greater number of drops. As a result, the drops may not get big enough to rain out and precipitation formation may be suppressed. Therefore, polluted air can lead to suppressed or decreased rainfall amounts in a given location, or even shifting precipitation patterns elsewhere.

Or, depending on aerosol type, the opposite can occur. High amounts of human-made aerosols in the atmosphere can also lead to heavier rainfall. Why? Because clouds with high levels of human-made aerosols can lead to delayed rainfall, making clouds grow larger, taller, and live longer. When they finally shed their water, the clouds can release their water through stronger storms.