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The UV Index: Definition, Distribution and Factors Affecting It

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Abstract

The UV Index was introduced in Canada in 1992 in response to growing concerns about the potential increase of ultraviolet (UV) radiation due to ozone depletion. The index was adopted as a standard indicator of UV levels by the World Meteorological Organization and World Health Organization in 1994. This survey article gives an overview of the UV Index and the main features of its geographical distribution.

UV index values are determined from measurements made by ground-based spectrometers, broad-band filter radiometers and multi-filter radiometers. Radiative transfer models are used to estimate UV Index values from other types of geophysical observations, primarily column ozone and cloud thickness. UV Index values can also be retrieved from satellite measurements of atmospheric ozone and cloud cover. Forecasts of UV Index values are now widely available and are intended to be used by the public as a guide to avoid excessive exposure to UV radiation.

Over the UV and Canada, mean noontime UV Index values in summer range from 1.5 in the Arctic to 11.5 over southern Texas and can be as high as 20 at high elevations in Hawaii. The UV Index is also often used to quantify UV levels in studies investigating the impact of UV on other biological and photochemical processes. Factors affecting the UV Index, such as the sun elevation, total amount of ozone in the atmosphere, cloud cover, reflection from snow and local pollution, are also discussed.

Since its introduction in 1992, the UV Index has become a widely used parameter to characterize solar UV. Information about it can be useful for helping people avoid excessive levels of UV radiation.

Résumé

L’indice UV (ultraviolet) a été institué au Canada en 1992 en réponse aux préoccupations croissantes suscitée par l’augmentation possible des rayons ultraviolets avec l’amincissement de la couche d’ozone. Cet indice a été adopté par l’Organisation météorologique mondiale et l’Organisation mondiale de la santé en 1994 comme indicateur standard des niveaux de rayons UV. Notre article donne un aperçu de l’indice UV et des principaux attributs de sa répartition géographique.

Les valeurs de l’indice UV sont déterminées à partir des mesures prises par des spectromètres au sol, des radiomètres à large bande et des radiomètres multifiltres. Au moyen de modèles de transfert radiatif, on estime ces valeurs à partir d’autres types d’observations géophysiques, principalement la colonne d’ozone et l’épaisseur des nuages. On peut aussi les obtenir à partir des mesures satellitaires de l’ozone atmosphérique et de la couverture nuageuse. Les prévisions de l’indice UV sont maintenant largement diffusées; on veut que le public s’en serve pour éviter les expositions excessives aux rayons ultraviolets.

Pour les États-Unis et le Canada, l’indice UV moyen à midi en été varie entre 1,5 dans l’Arctique et 11,5 pour le Sud du Texas et peut atteindre 20 dans les hauteurs d’Hawaï. L’indice UV sert aussi souvent à chiffrer les niveaux de rayonnement ultraviolet dans les études portant sur l’incidence des rayons UV sur d’autres processus biologiques et photochimiques. Les facteurs qui influent sur l’indice UV, comme la hauteur du soleil, la quantité totale d’ozone dans l’atmosphère, la couverture nuageuse, la réflexion des rayons sur la neige et la pollution locale, sont également abordés.

Depuis son adoption en 1992, l’indice UV est devenu un paramètre très utilisé pour caractériser les ultraviolets solaires. L’information à ce sujet peut être utile pour aider les gens à éviter les niveaux d’exposition excessifs aux rayons ultraviolets.

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Authors and Affiliations

  1. Science and Technology Branch, Environment Canada, 4905 Dufferin St., Toronto, ON, Canada, M3H 5T4

    Vitali Fioletov PhD, James B. Kerr PhD & Angus Fergusson MSc

Authors
  1. Vitali Fioletov PhD
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  2. James B. Kerr PhD
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  3. Angus Fergusson MSc
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Correspondence to Vitali Fioletov PhD.

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Acknowledgements: The publication of this manuscript was supported by funds from the Canadian Partnership Against Cancer.

Conflict of Interest: None to declare.

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Fioletov, V., Kerr, J.B. & Fergusson, A. The UV Index: Definition, Distribution and Factors Affecting It. Can J Public Health 101, I5–I9 (2010). https://doi.org/10.1007/BF03405303

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