Clouds, air pollution, haze and elevation all impact the amount of ultraviolet (UV) radiation that reaches Earth’s surface. These factors help to scatter or reduce the intensity of UV exposure as it works through the troposphere, the lowest region of the atmosphere that extends from the surface to about 3.7 to 6.2 miles.

Air molecules and dust increase as the UV radiation travels from higher elevations to lower elevations. The further down into the atmosphere UV radiation travels, the more UV radiation is scattered or weakened. As more UV radiation is scattered, less UV reaches the surface. As a result, there is more UV radiation at higher elevations than at lower elevations.

According to the National Oceanic and Atmospheric Administration (NOAA), UV exposure increases 4 to 5 percent for every 1,000 feet of elevation. For example, the amount of UV exposure you would experience in Truckee is roughly 25 percent greater than in Bay Area due to about 6,000 feet in elevation difference.

Intense UV exposure at elevation impacts everything from how careful to be when outdoors to how long paint and stain will last on your home.

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