05-14-2020, 01:15 PM
I still haven't seen even a preprint of the sunlight (etc) study that was highlighted in an April 23 White House press briefing. Has anyone else?
I remember being furious at the idiocy of presenting half life information to the 144-character public. This was just begging to get misunderstood. Indeed, a friend later said about their cloth mask that they could just put it on their car dashboard for 3 minutes in the sunlight. Amongst the things I informed her of was that the windshield filters out the UV that probably does most of the inactivation. And, oh yes, the time of day matters. And 3 minutes is nowhere near long enough.
There were some posters presented that I haven't seen in an easy-to-read format. Indeed, I tried some Google searches and didn't find the contents of the posters, so I'm going to put them here.
Hmmmm... I wonder why they didn't put up 50-55 F and 30-35 F?
From a scientific viewpoint, this chart is quite simplistic. Only 2 points are listed on each of the 3 variables. I guess you're supposed to believe these are monotonic at least (which other studies have shown isn't true for humidity). They also showed half-life times and didn't show something like to get rid of 99.9% of the virus particles, you need 10 half-lives, and that leaves alive a billion particles from a cough.
Then there's the matter of summer sunlight. Noon? Latitude? Altitude? It all makes a difference. The above half-life of 2 minutes suggests a 1 log (10x) reduction inn 6.6 minutes. That's a good bit less than the >= 20 minutes (to 100 minutes) for a different virus in this earlier study, which gives some indication of how the duration for a 1 log reduction at different places at different times.
If a surface is at 30 degrees from horizontal (for noon sun) it will get cos(30) = 87% as much sunlight (so to get as much, it has to go (100-87)/87 longer = 15% longer, so 2.3 minutes.
If at 45 degrees, 71%, so 29/71 =41% longer, or 2.82 minutes.
If at 60 degrees, 50% so 50/50 = 100% longer or 4 minutes
90 degrees gets no benefit from the sun.
And no shadows. The strap of a mask casts a shadow that gets NO benefit of the sun, so it is as strong as ever. No overhead clouds. No window in the way
The underside of the mask would seem to get no benefit.
I remember being furious at the idiocy of presenting half life information to the 144-character public. This was just begging to get misunderstood. Indeed, a friend later said about their cloth mask that they could just put it on their car dashboard for 3 minutes in the sunlight. Amongst the things I informed her of was that the windshield filters out the UV that probably does most of the inactivation. And, oh yes, the time of day matters. And 3 minutes is nowhere near long enough.
There were some posters presented that I haven't seen in an easy-to-read format. Indeed, I tried some Google searches and didn't find the contents of the posters, so I'm going to put them here.
Quote:Increased temperature, humidity, and sunlight
are detrimental to SARS-CoV-2 in saliva droplets
on surfaces and in the air
CONDITION Temp Humidity Solar HALF LIFE Surface 70-75 F 20% None 18 hours Surface 70-75 F 80% None 6 hours Surface 95 F 80% None 1 hour Surface 70-75 F 80% Summer 2 minutes Aerosol 70-75 F 20% None ~60 minutes Aerosol 70-75 F 20% Summer ~1.5 minutes
Hmmmm... I wonder why they didn't put up 50-55 F and 30-35 F?
From a scientific viewpoint, this chart is quite simplistic. Only 2 points are listed on each of the 3 variables. I guess you're supposed to believe these are monotonic at least (which other studies have shown isn't true for humidity). They also showed half-life times and didn't show something like to get rid of 99.9% of the virus particles, you need 10 half-lives, and that leaves alive a billion particles from a cough.
Then there's the matter of summer sunlight. Noon? Latitude? Altitude? It all makes a difference. The above half-life of 2 minutes suggests a 1 log (10x) reduction inn 6.6 minutes. That's a good bit less than the >= 20 minutes (to 100 minutes) for a different virus in this earlier study, which gives some indication of how the duration for a 1 log reduction at different places at different times.
If a surface is at 30 degrees from horizontal (for noon sun) it will get cos(30) = 87% as much sunlight (so to get as much, it has to go (100-87)/87 longer = 15% longer, so 2.3 minutes.
If at 45 degrees, 71%, so 29/71 =41% longer, or 2.82 minutes.
If at 60 degrees, 50% so 50/50 = 100% longer or 4 minutes
90 degrees gets no benefit from the sun.
And no shadows. The strap of a mask casts a shadow that gets NO benefit of the sun, so it is as strong as ever. No overhead clouds. No window in the way
The underside of the mask would seem to get no benefit.