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It takes three to ten hours for solar ultraviolet (UV) radiation to remove the new coronavirus from outdoor surfaces in summer and more than 20 hours in winter in cities located on the latitude of Lisbon, according to a study by Portuguese researchers.
The work, to which the Lusa agency had access, managed to demonstrate the effectiveness of UV radiation in eliminating the new coronavirus on surfaces in various latitudes, defining values for cities such as Lisbon, São Paulo (Brazil) or Vienna (Austria).
The investigation, which began during the confinement, resulted from the cooperation between the Portuguese Institute of the Sea and the Atmosphere (IPMA), the University of Veterinary Medicine of Vienna (Austria) and the Center for Research in Health Technologies and Services of the University from Porto. and it aims to help define and adjust public policies.
“We build maps of the solar ultraviolet radiation reaching the Earth’s surface, which is effective in inactivating the virus. Although the germicidal effect of UVC radiation had been known for a long time, it remained to be seen to what extent UV solar radiation reaching the surface of the globe (UVA and UVB) could inactivate SARS-CoV-2. It was a suspicion, but we had never anticipated to check it, ”explains IPMA researcher Fernanda Carvalho to Lusa.
“When we said that ultraviolet radiation could play an important role in inactivation, it was thought that it was only ultraviolet C, used in the laboratory to sterilize surfaces, but we concluded that solar radiation that reaches the earth’s surface also performs this task” , He explained.
This was the first work of the Portuguese Institute of the Sea and Atmosphere (IPMA) published in an international scientific journal (a Photochemistry and photobiology) on the relationship between SARS-CoV-2 and a meteorological element, in this case solar radiation.
Fernanda Carvalho explained the path followed by the researchers in this work, exemplifying: “We have a period between March and October, which generally coincides on the mainland and the islands, and in which the ultraviolet index is equal to or greater than six (High ). In Lisbon, for example, in summer, in three to ten hours the virus is eliminated by ultraviolet radiation ”.
“In winter, we have sterilization times greater than 20 hours. One day is not enough to sterilize surfaces outside ”, said the expert.
Fernanda Carvalho gives two other examples: “In São Paulo, in summer, ultraviolet radiation takes between half an hour and eight hours to eliminate the virus. In winter, it may take a little longer, around ten hours, but their winter reaches the upper limit of our summer.
In other latitudes, the effect of solar UV radiation on the elimination of the coronavirus is different. According to the conclusions reached by the researchers, in Vienna (Austria) – one of the authors of the study is Austrian – sterilization takes between three and 30 hours and, in winter, the period of time is longer than 100 hours.
The intention of this work is to help define public policies, adjusting them to the time: “Perhaps, it would not be interesting to worry a lot in summer about disinfecting surfaces exposed to the sun on the beach, such as terrace furniture, because UV solar radiation does the job , but it would be important to concentrate efforts in the period after sunset ”, explained the expert.
“Perhaps it makes more sense to have a more restrictive policy when there is no sunlight, both in summer and winter, since now we are moving very quickly towards decreasing both the intensity and the number of hours with solar radiation; therefore, the number of hours required for the virus to inactivate increases, “he added.
Fernanda Carvalho says that, with this study, it was shown that, of all the work done on the influence of meteorological factors on the new coronavirus, solar UV radiation is the most effective in inactivating the virus. “Humidity and temperature condition the virus, but through people’s behavior, because when it is colder, people are further inside and, therefore, there is greater contagion.”
