Facts about UV radiation

Most parts of NSW experience high levels of UV radiation, especially from October to March. However UV levels are affected by a number of different factors including geographic location, time of day and cloud cover. This means that UV levels are higher in some parts of NSW than in others – even on the same day.

 

Geographic location

There is more UV radiation in sunlight in the north than in the south of NSW. In regions closer to the equator the sun is higher in the sky. The sun’s rays have a more direct pathway to earth (straight down, not angled) and pass through less atmosphere which acts to absorb UV radiation.

Altitude

UV radiation is stronger at high altitudes (i.e. in the mountains) because the air is cleaner and the thinner atmosphere absorbs less UV radiation. UV levels increase by 10%-12% with every 1000 metres increase in altitude.

Time of year or season

The angle of the sun varies depending on the time of year. UV radiation is greatest in summer because the sun is high in the sky and its rays pass through less atmosphere before reaching the earth’s surface. In winter the sun is lower in the sky and its rays have a longer course through the atmosphere; more UV radiation is absorbed and UV levels are lower.

Time of day

UV radiation levels change throughout the day – lower in the morning, peaking in the middle part of the day (when the sun is overhead) and gradually dropping again throughout the afternoon as the sun moves lower in the sky.

Cloud clover

Thick cloud provides a good filter for UV radiation. However in areas that experience clear, cloud free skies UV levels are likely to be high – even on cool or cold days. Thin and scattered cloud does little to reduce UV levels.

Reflection

Surfaces such as snow, water and sand reflect UV radiation. For example, snow reflects between 50 and 88% of UV radiation, sea surf (white foam) reflects 25 to 30% and dry beach sand reflects 15 to 18%. This means that not only is UV radiation present overhead directly from the sun but also indirectly, reflected back from different surfaces.

Solariums

UV radiation is also available from artificial sources such as solaria (solariums, sun lamps, tanning booths). UV radiation in solariums is a significant risk factor for melanoma and other skin cancers.

 

 

 

 

 

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