SCOTT SIMON, HOST:
And across the country, cities are opening up. People are heading outside. Parents are eager to get their children back in school. At the same time, coronavirus cases are spiking, making many traditional Fourth of July plans riskier than usual. Linsey Marr is a professor of engineering at Virginia Tech and an expert in aerosol science. She joins us now. Dr. Marr, thanks so much.
LINSEY MARR: Thank you for having me.
SIMON: What do we currently know about airborne transmission? Can we contract coronavirus through the air or not?
MARR: It seems that we can. There's more and more evidence suggesting that when people talk or breathe - obviously, we know that coughing and sneezes release droplets. But we know that when people just talk or breathe, they're also releasing droplets into the air. Some of these are large enough to see. But for every one that's large enough to see, there's hundreds more that are too small to see. And those can contain virus that can remain floating around in the air for a while. And then other people could breathe those in.
SIMON: A lot of us have seen studies recently contending that air conditioning can actually circulate the virus and accelerate the spread.
MARR: I think that is possible, especially because air conditioners often use a large fraction of recirculated air. So if your building doesn't have the air conditioning on and you have kind of natural ventilation with windows open and maybe some doors open, then you're getting a lot of fresh air or outdoor air into the space and removing any virus and helping reduce the amount that might build up in the air. But as soon as you close up the building and turn on the air conditioner, you know, any virus that builds up in the air isn't being removed. Rather it's being recirculated through the air conditioning system. There are filters that can remove virus-sized particles and droplets from the air, but those are not typically installed in HVAC systems.
SIMON: Today's the Fourth of July. People want to get outside, do something that they recognize as, you know, something from their former normal lives, but does doing that just mean risking reinfecting ourselves again so we have to do the lockdown all over?
MARR: Going outside to celebrate the Fourth is a great idea if you observe certain precautions. So going to a big party with lots of people, talking and hanging out, is not a good idea. If it's your household and maybe a small group of people where you strictly observe distancing, then I think it can be a great way to celebrate the Fourth. But you have to really pay attention to the distancing and, especially if you're in a vulnerable population, to wear a mask. I know that talking at a 6-foot distance is unnatural. It's almost like you have to talk louder. But that's what we need to do to keep ourselves safer.
SIMON: And what about masks? I mean, it's hard to wear a mask at a barbecue, isn't it?
MARR: Masks I think are - especially if you're in a crowded outdoor area, masks are really important. Obviously, you need to take it off when you're eating. When you do have it off, maybe cut down on the talking. But if you are talking and it's in a crowded area, I think people should definitely be wearing masks.
SIMON: Dr. Marr, it's personal, but what are you going to do this Fourth of July?
MARR: I'm in the San Francisco Bay Area right now, and we're planning to get together with some family members. We will stay distanced. It will be outdoors. We're thinking of going out towards the beach for a hike early in the morning before it gets crowded and then also walking across the Golden Gate Bridge if it's not crowded. And then my kids want to see Lombard Street. So it's all outdoor activities. We're not hanging out at a barbecue talking in large groups of people.
SIMON: Professor Linsey Marr of Virginia Tech, thanks so much for being with us.
MARR: Thank you. Transcript provided by NPR, Copyright NPR.