Falling temperatures forcing more people inside and the reopening of schools, gyms and restaurants across the country have highlighted the need for proper indoor ventilation to help stop the spread of the coronavirus.
NBC News investigative and consumer correspondent Vicky Nguyen consulted with experts about how to lessen the risks of getting and spreading COVID-19 indoors and what products may be helpful in determining airflow at indoor public places as well as your home.
Health experts have stressed that close contact indoors without masks and proper ventilation is one of the primary ways that coronavirus spreads.
A simulation created by Rainald Lohner, who runs the Center for Computational Fluid Dynamics at George Mason University, showed on TODAY Friday how droplets from a sneeze can linger in a classroom with poor ventilation. The risks shown in the simulation may also apply to dining indoors, exercising at the gym and working at an office.
In a room with poor ventilation, enough droplets from a sneeze could linger in a cloud of particles even five minutes afterwards. However, with a ventilation system, the particles thin out quickly and within a minute, a majority of them are sucked up into the air intake vents in the ceiling, with some blown back down.
The simulation also showed that wearing a mask makes a crucial difference, allowing fewer particles to escape into the air after a sneeze.
Opening windows and doors to allow fresh air also helps dilute the number of droplets within two minutes, making the invisible cloud less infectious.
"The probability of infection increases with the time that particles remain in the room," Lohner told Nguyen on TODAY. "And it also increases with the number of particles that you inhale. Ventilation is very important."
For those looking to test the air quality of an indoor public space, experts say there are some simple precautions you can take as well as a handheld product you can use.
Shelly Miller, an expert in indoor air quality at the University of Colorado Boulder, says two easy steps are looking for open windows to see if there is some air coming from outside, as well as sensing whether you feel hot or stuffy, because that's a sign there is not enough ventilation.
People should also remember to make sure others are wearing masks and are not tightly crowded together. Miller suggested keeping your mask on until you have to eat at a restaurant, and restricting your meal to about 60 minutes.
Another option to determine air quality at public indoor spaces is a carbon dioxide meter, a handheld device that costs about $200 and can determine how much carbon dioxide is in a room. Anything above 800 parts per million could be a red flag that not enough outdoor air is mixing with indoor air. The average outdoor air reading is 400 parts per million.
One effective option to improve air quality in indoor spaces like classrooms with older ventilation systems or windows that don't open is using a room air cleaner, which recycles and filters the air.
Experts say to make sure to check the box to see what size room the air cleaner is designed to accommodate and to ensure it has a certified room air cleaning rate, with higher numbers being better. You should also check to see that it has a high-efficiency filter, or HEPA.
Air cleaners are mainly meant for public indoor areas, as the risks of contracting COVID-19 at your home are low as long as you don't have strangers coming and going. Scientists say there have been no known cases of coronavirus spreading through shared ventilation in multiple apartment units or between college dormitories.
The only potential use for an air cleaner at home would be if you have a family member who contracts COVID-19. Experts recommend putting the air cleaner in their quarantine room in addition to opening windows if possible in order to decrease the chance of the virus spreading outside the room or to anyone who has to enter the room.