Ultraviolet radiation tends to present high points throughout the year in Quito due to its altitude and latitude. However, during March and September, the sensation of the intensity of the rays is greater. On March 21 of each year the equinox occurs, the date that marks the change from cold to warm seasons in the Northern Hemisphere.
“The country is more aligned with the sun on the dates of the equinoxes,” confirms Valeria Díaz, a technician from the Secretariat of Environment of Quito. This phenomenon is known by the Andean world as the date of the straight sun, since it is completely zenith and this causes the shadow not to be projected.
The rays, when falling perpendicular, have less travel distance to the surface than when the relationship with the sun is diagonal. Then, the rays have to cross by less amount of atmosphere, where the ozone layer is located and, therefore, more UV rays reach the surface.
In the last three years, the highest points of radiation in Quito occurred in March 2016 with 17.01 points, in January 2017 with 15.85, in October of the same year with 15.75, and in February 2018 with 15.14 points.
The World Health Organization (WHO) reports that altitude is a factor that affects the increase in radiation and its intensity increases by 20% for every 1 000 m of altitude.
Additionally, there are three other factors that determine how much ultraviolet radiation reaches the Earth’s surface: clouds, the ozone layer and reflectivity.
Cusco is the city with the most radiation in the world
The places with the most radiation in the world are in South America, according to the National Institute of Aquifer and Atmospheric Research of New Zealand. This is due to the Earth’s elliptical orbit, ozone and altitude.
The place with the highest radiation is Cusco, which is 3 360 meters above sea level and is close by in Tropic of Capricorn. The highest registered value of the UV index is 25, according to the New Zealand Institute. This number is 6 points higher than the highest registered in Quito since March 2016: 17 points. The peaks, as indicated in the infographic, occurred on dates close to the perihelion and the equinoxes.
In 2009, Quito hosted the International Meeting on monitoring and public dissemination of ultraviolet radiation levels in Latin America. The conclusion of this meeting was to propose a more extensive range for the values of the UV index, than that of the WHO.
The WHO manages a code in which the high range is 6 and 7 points; very high, between 8 and 10, and extreme is from 11. Meanwhile, the Municipality of Quito uses a scale in which the high range is between 8 and 10 points; very high, between 11 and 15, and extreme, more than 16.
The objective, according to Díaz, is that the population can distinguish when to avoid exposing themselves to the Sun and when to do it with protection. (I)