What Affects UV Level?

The UV level or its intensity is affected by several factors such as:

• sun height:the higher the sun in the sky, the higher the UV radiation level. So the radiation intensity varies depending on the time of the day. In general the sun is at the highest elevation at midday and hence the intensity is at its highest.
• latitude:the closer to the equator, the higher the UV radiation level
• altitude:at higher altitudes, a thinner atmosphere filters less UV radiation. With every 100 meters increase in altitude, the level increase by 10-12%. So when you go mountain climbing take note of this.
• ground reflection:UV radiation is reflected or scattered to varying extents by different surface, eg. snow can reflect as much as 80% of UV radiation, dry beach sand about 15% and sea foam about 25%.
• cloud cover:obviously radiation levels are highest whenever there is a cloudless skies.
• ozone layer:ozone absorbs certain amount of UV radiation that would otherwise get to the Earth's surface. Ozone level fluctuate over the year and even across the day.

So it all depends on where you are on the Earth surface. Very obviously when you are up on a high mountain the UV intensity increases. Also at midday the intensity is at the highest. A rule of thumb, if your shadow is shorter than you are, then the sun is high in the sky, and the UV radiation is the most intense.

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