Some wear masks on the trail, others don't. Who is right?

I was walking my dog on the LoBo Trail through Niwot, wearing a homemade blue-cotton mask, when a group of three runners came toward me. None wore masks. One coughed about 25 feet in front of me. I hoped my mask gave me some protection, but I wasn't sure. I heard that wearing a mask was mostly to keep my germs out of someone else's lungs.

The cough set me off. I felt like I was put in danger by someone who carelessly spewed his viral or non-viral particles (I'll never know) and I was walking right into his cloud. I couldn't help but say something. The first time I have ever done that.

"Why aren't you wearing a mask?" I asked in a statement-like way. "You just coughed right in front of me and I don't appreciate it." One of the non-coughing members in the group said, "Oh well."

Errrr! Why should I have to remind her of what we've been hearing for months? "Some of us have vulnerable people in our lives!" I said, which I do, and I also don't know if I may have pulled the short-straw in the life and death game of COVID-19. None of us knows.

For the rest of my walk I played back the image of the coughing runner and tried to remember if there was a breeze and whether I was upwind or down, whether I was far enough away, whether it was a COVID cough or just an exercise reflex, whether it was right for me to say something or if I had overreacted. I briefly wondered if I should have sicced my dog on him, but that would have ended in an embarrassing flurry of wags and sniffs.

It's upsetting that we don't know more about the virus and the granular details of when we're at risk. But it's called a novel coronavirus for a reason. We haven't seen anything exactly like this. Literally. Our bare eyes can't see it and the rest of our senses are useless. It's why horror films are so disturbing. The killer is lurking and we don't know where.

Thank goodness there are smart people working hard to inform us where it might be hiding and others who are developing weapons to slay it. For now, we have to rely on those who inform us. Unfortunately, they aren't in perfect agreement.

But there is information we can use to make decisions based on our conscience and our risk tolerance.

I spoke with Dr. Payal Kohli, a Harvard-trained cardiologist and disease prevention specialist who is steeped in the latest information about COVID-19 as the medical expert for 9News in Denver. She explained the origin of the six-foot distancing rule.

It is based on a hypothesis that came out of tuberculosis studies from the 1930s. That model of disease transmission looked at the size and behavior of particles that are released when a person exhales. It categorized respiratory emissions as large and small droplets with the large ones falling to the ground and small ones evaporating upward, all within a few feet of the individual, but, she added, "This is oversimplified and isn't true with COVID."

Newer research from MIT cited in an article by Lydia Bourouiba, Ph.D., showed that respiratory emissions can travel much further as a cloud of gas, like a puff of smoke. An infected person can exhale fine particles of virus, called aerosols, that can remain suspended in the gas cloud for up to three hours depending on wind, temperature and humidity.

Add force, like a cough or sneeze, and those aerosols travel well beyond six feet, she said. A high velocity sneeze can launch a gas cloud up to 27 feet. Coughing, laughing and hard breathing from exercise all add velocity and increase the distance that respiratory particles travel.

There is no telling whose gas cloud is infectious since some people don't present symptoms of COVID-19. "The only way to keep the virus particles from getting out is to wear a mask," said Kohli, who shared a link to a video that demonstrates how particles spread without a mask and how they are corralled with one.

Gov. Jared Polis issued an executive order requiring that masks be worn by employees of essential businesses and government services. He strongly recommends that everyone wear them anytime they leave home. That would include trails.

As someone who walks and bikes the trails, I know that masks make it harder to breathe. That's probably a big reason why the runners I encountered weren't wearing them. Perhaps they were also thinking that being outdoors makes a difference in the chance of transmitting or catching the virus.

There is more fresh air and air movement outdoors than indoors and, in some situations, there is more space to avoid people. Those considerations factor into the opinion of Dr. John Zhai, a building systems engineer from the University of Colorado at Boulder who earned his Ph.D. from MIT. His research is on air quality and ventilation, indoors and out.

Zhai wrote an article in early March for a trade publication in which he encouraged people to wear masks. "I was worried," he said. At the time, the CDC, Centers for Disease Control, wasn't even recommending masks. "It was totally against what I learned," he said.

But his opinion isn't as cut and dried when it comes to being outdoors. According to Zhai, there are several factors that can influence whether a person contracts the virus outside--the concentration of the virus, the quantity that is inhaled and the exposure time.

The concentration depends on the amount of virus released by the infected person and how much it is diluted by environmental factors such as wind, temperature and humidity.

The next variable is how much of the virus is actually inhaled by a healthy person. Being closer to the sick person increases the potential amount.

Duration of exposure is the third consideration. It could be just a couple of seconds while people pass one another or it could be longer if people are walking, running or riding side by side.

"The three variables together make the chance you'll be infected very low," Zhai said. He doesn't think masks are necessary when outdoors with few people around, but he thinks people should stay as far apart as possible. More than six feet, if there is space.

Dr. Kohli has a more cautious outlook. She said that scientists are still trying to understand how much virus it takes to get sick and whether the quantity affects the severity of the illness.

"Health care workers have had worse outcomes with COVID because they have a higher viral load," Kohli said. "Other respiratory illnesses, we've seen that happen as well. The viral load may be tied to the risk of getting sick and for how sick you get. We don't really know what the truth is. Some people get really sick and some don't have symptoms. It may be based on our own susceptibility."

The stay-at-home order has slowed transmission of the virus, but the virus is still around. As restrictions loosen, it's possible that infections will go up. "I'm worried that people will get the idea that life is getting back to normal," said Kohli. "This is the time to double down. We are taking off the parachute that's slowing us down, which is staying at home. So we need to do the same with masks that we did with staying at home. We all have to do it to get it to work. The more people that do this, it's like social distancing, we all have to do it to get it to work."

Kohli wants people to keep a mask on when on the trails. She even recommends wearing it when you think you're alone so you don't leave a gas cloud in your wake.

Wearing a mask is a proven way to trap respiratory particles before they are unleashed into the world. Unfortunately, Kohli and other experts say wearing a mask doesn't necessarily protect you. That's still an open question.

As of now, the main benefit of a mask is to keep our germs to ourselves, a sacrifice that isn't easy. "It's uncomfortable. I hate it too, but you have to assume everyone has the virus," said Kohli.

I don't like wearing a mask either. I've been guilty of loosening my mask around the nose or letting it hang off one ear when I'm alone on an empty stretch of trail or a street. I understand that wearing a mask is really hard to get used to and everyone has to do what they feel is right.

For my part, I won't sic my friendly dog on any maskless, coughing runners, but I will continue to appreciate people who wear masks and/or give me a wide berth. Oddly enough, the distancing makes me feel more connected to others. I'm reminded that we're on this winding path together and we're not out of the cottonwoods yet.