> the clusters in nursing homes and indoor parties also indicate there is some mechanisms in play when indoor
One know mechanic is the virus's half life when airborne. We know that the airborne virus can be killed/filtered when there is enough UV light and/or a fine enough particulate air filter in place. In other words, indoor safety can be improved with better filters. Without the proper filtration, HVAC circulation can help circulate the virus, which could be the problem in nursing homes and at parties.
Meanwhile, outdoor air is relatively safe when there is enough distancing as sunlight will take the virus's half life down to 90 seconds at 20% humidity and 70-75 degrees [1]. 20% humidity is pretty low, but the good news is that half life gets even shorter as humidity goes up. Sunlight doesn't even contain the best frequency of UV light to kill the virus, but it's intense enough that it still works fairly well.
One know mechanic is the virus's half life when airborne. We know that the airborne virus can be killed/filtered when there is enough UV light and/or a fine enough particulate air filter in place. In other words, indoor safety can be improved with better filters. Without the proper filtration, HVAC circulation can help circulate the virus, which could be the problem in nursing homes and at parties.
Meanwhile, outdoor air is relatively safe when there is enough distancing as sunlight will take the virus's half life down to 90 seconds at 20% humidity and 70-75 degrees [1]. 20% humidity is pretty low, but the good news is that half life gets even shorter as humidity goes up. Sunlight doesn't even contain the best frequency of UV light to kill the virus, but it's intense enough that it still works fairly well.
1) https://medicalxpress.com/news/2020-04-sunlight-coronavirus-...