The weather is getting warmer. The days are getting longer. Some stores are reopening. And California is slowly easing up on the sheltering restrictions placed on us during this pandemic. In other words, we’re getting out of our homes a little more after weeks of a statewide shutdown.

But this isn’t the same world we remember from before. There are new questions about personal contact and social distancing. There are fresh concerns about infection in the environment around us. The Chronicle talked to some health experts about how we can best navigate the Bay Area without contracting the coronavirus.

Q: What are the transmission rates for people who are outside? Are they higher than being inside?

A: Outside exercise lowers the chance of spreading the virus by a magnitude of 10 compared with the same level of exertion indoors, said Dr. Gary Green, medical director of infection control at Sutter Santa Rosa Regional Hospital. The main danger is in exercising outdoors with others because the tendency is to pile into a car to get to the trailhead and then bunch up once you are there: “People are used to congregating before and after exercising and you want to be careful.”

Dr. Peter Chin-Hong, an infectious disease specialist at the UCSF School of Medicine, said that in all circumstances the outdoors are safer than indoors. It is easier to maintain social distancing and the virus does not have as many opportunities to spread. That’s why tuberculosis patients were always placed out in the fresh air. “If you want to meet people, meet them outside,” he said. “It is all about risk reduction.”

Q: Are there places outside that are worse for virus transmission? Like, is the beach better than a park?

A: It is not the setting that matters, it is the crowding. When the sun is out people tend to set up umbrellas for shade and crowd under them. That is to be avoided. The coronavirus “likes cold weather more than it likes hot weather, and it likes low altitude more than it likes high altitude,” said Chin-Hong. “But it likes people more than it likes hot or cold.”

Q: How long does the virus live on grass or trees? Is it safe to sit on grass at a park?

A: Unless you immediately occupy a patch of grass that someone else has been sitting on or touch the exact same spot on a tree that someone else touched, it is highly unlikely that the living virus is there. Guardrails and public restrooms are much more dangerous.

The virus “doesn’t love grass or trees or clothing,” Chin-Hong said. “I would rate these as low-risk surfaces.”

People walk and run around Lake Merritt in Oakland this month. Lake Merritt has been a popular destination during the coronavirus pandemic despite shelter-in-place orders.

Q: Will the sunlight cleanse a surface that has the virus on it?

A: Yes. “On a warm day in the outside air the virus will only survive for minutes under sunlight,” Green said. “The warmer the day, the quicker the virus dries out.”

Q: Does a runner exhaling while exercising potentially spread the virus greater than someone who is simply walking? And should we be worried about people running past us on sidewalks or trails?

A: There are no scientific data to suggest that a runner has more viral spread than a walker, according to Green. “If everyone is wearing a mask, and practicing social distancing, the brief time a runner goes by a walker is a minimal risk of exposure.”

Singing and loud talking, however, have emerged as activities that could produce significantly more exhalations of viral droplets than normal activity and thus spread the virus. So watch for the noisy walkers, not the silent runners.

Chin-Hong recommends a simple solution. “If you can’t control your environment, wear a mask.”

Q: Do people running or biking create “slipstreams” that could potentially push the virus toward you?

A: There are no data about this scenario, which has caused some online discussion. If everyone wears a mask, there is little or no danger.

Q: Are there masks that allow you to breathe better while exercising?

A: Doctors agree that the standard surgical mask is the best for exercise and the N95 mask — commonly worn by house painters, and more recently during wildfires — is the worst because it becomes uncomfortable when exercising and breathing heavily. “The N95 mask is more like a respirator,” Dr. Green said. He also recommends against anything that has a button on it. “That button opens and it allows breath to go out the vent,” he said. “These vented masks are not protective for the community. That’s why we never use them in the hospital.”

Double cloth masks are effective but can be difficult to draw breath through during a vigorous workout.

Chin-Hong advises runners and walkers to wear a cloth mask around the neck that can easily be pulled up when passing other people.

Q: Does sweat make it easier to transfer the virus? If you bump into a sweaty person, is that cause for concern?

A: Not really because COVID-19 is caused by a respiratory virus. “We are really only interested in mouth secretions and nose secretions,” Green said.

“The risk of random sweat vaporizing on you is very small,” Chin-Hong said, “unless the person runs around you in circles and creates a COVID sauna.”

Q: Does the wind affect transmission of the virus? Can it blow the virus onto me?

A: Wind is your friend in defending against the virus. “It disperses the virus much more rapidly and thins it out, which lowers the risk of infection,” Chin-Hong said. “The virus is trying to jump from someone who is infected, the wind creates turbulence and disrupts the path of the virus,” he added.

Q: Does chlorine kill the virus in a swimming pool?

A: “Disinfectant is a good thing for the virus in general and chlorine is a disinfectant, so that is good,” Chin-Hong said. “You don’t need to wear a mask while swimming. Just maintain 6 feet of distance and if you are doing laps with others, swim in alternate lanes.” Keeping your distance in locker rooms is more the problem.

Sammy Consani and Nutella (left) sits with Hannah Suh at Lake Merritt in Oakland this month. Oakland city officials are strongly discouraging gatherings at the lake and at parks and are reminding people to maintain social distancing during the coronavirus shelter in place orders.

Q: How long does coronavirus stay in the air?

A: The virus can linger as droplets in the air for up to three hours, according to the New England Journal of Medicine, and it can travel at least 13 feet by aerosols that are emitted by breathing or speaking — twice as far as established physical distancing guidelines, based on a report by the CDC.

Talking can release thousands of fluid droplets per second that can remain suspended in the air for eight to 14 minutes, according to a study conducted under experimental conditions by the Proceedings of the National Academy of Sciences.

Masks are effective in blocking, or at least limiting, your exposure to these contagious viral droplets and aerosol particles.

Q: Can the virus travel on your shoes?

A: Yes. Samples taken from the soles of the medical staff working in intensive care units at a hospital in Wuhan, China, where the coronavirus outbreak started, tested positive for coronavirus on the soles of their shoes.

“Therefore, the soles of medical staff shoes might function as carriers,” according to the study, which was published in the CDC’s Emerging Infectious Diseases journal.

Outside a hospital setting, the CDC does not offer advice on handling footwear but some good general guidelines to follow are to leave your shoes at the door when entering your home, minimize handling them and be sure to thoroughly wash your hands and disinfect any surfaces they come into contact with after touching them.

If your shoes are machine-washable, follow the laundry guidelines below to sanitize them.

Still, Chin-Hong cautions against the scenario of being infected from your shoes tracking in the virus. “I don’t know of any data that supports that someone has got it from the pavement. The probability is extremely small. You would have to rub your hands on the pavement and then put your fist in your mouth.”

Q: How long can the virus live on outdoor surfaces like, say, a basketball hoop structure?

A: “We know the virus loves cold and hard more than warm and soft surfaces and poles are good for that,” Chin-Hong said. “But if you don’t touch your face, and wash your hands, it doesn’t matter where you find it.”

San Francisco Chronicle reporter Aidin Vaziri contributed to this report.

Sam Whiting is a San Francisco Chronicle staff writer. Email: swhiting@sfchronicle.com Twitter: @samwhitingsf

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