Scientific experiments showed that the activity of Covid-19 reduces when it is exposed to sunlight, high temperatures, high humidity and alcohol. Bill Bryan, head of science and technology at the Department of Homeland Security said so as quoted by CNN in their story.
“Our most striking observation to date is the powerful effect that solar light appears to have on killing the virus — both surfaces and in the air. We’ve seen a similar effect with both temperature and humidity as well, where increasing the temperature and humidity or both is generally less favorable to the virus,” Bryan told reporters. "The virus is dying at a much more rapid pace just from exposure to higher temperatures and just with exposure to humidity. … You inject sunlight into that, you inject UV rays into that, … the half-life goes from six hours to two minutes".
According to the official, the virus that is contained in saliva has best chances to survive in dry places and closed environment.
Bryan added that the bleacher would kill the virus in five minutes, while it would take only thirty seconds for the isopropyl alcohol to do so.