During the past month, the fear of coronavirus had spurred political leaders to close parks and nature areas throughout the country.

In Washington State, all state parks and state lands managed by the Department of Natural Resources are closed through at least May 4.  Here in Seattle, all major city parks were closed last weekend and parking lots for city parks are still shuttered.  Picnicking, barbecuing, and any sports are illegal in Seattle parks.  In California, hundreds of state parks, including many major beach areas, have been closed, and parking has been blocked off for all state recreation facilities.

All of these closures are predicated upon the assumption that coronavirus infection is a serious threat in outside air and that virus spread is significant outdoors.  As documented in this blog, such an assumption is not consistent with the best science.  Furthermore,  there is strong evidence that restriction of public access to parks and natural areas threatens both the physical and mental well being of the population and thus is counterproductive.  Many politicians claim that parks must be closed to prevent large groups from gathering and spreading the virus.  As we will see, such worries appear to have little basis in fact.

Torrey Pine Beach north of San Diego Is closed 

Is Outside Air Safe?


After searching through the literature and talking to a number of doctors and researchers, I could not find a single paper suggesting significant outdoor transmission of COVID-19 or any coronavirus. But there is a huge literature and long historical experience suggesting that outside air is immensely safer than indoor air within constrained spaces.  Here are a few examples and some quotes from medical experts on this point:

  • Nishiura et al., 2020:  Transmission of COVID-19 in a closed environment was 18.7 times greater compared to an open-air environment (95% confidence interval).
  • Lidia Morawska, professor and director of the International Laboratory for Air Quality and Health at Queensland University of Technology in Brisbane, Australia.”: Outdoors is safe, and there is certainly no cloud of virus-laden droplets hanging around… Firstly, any infectious droplets exhaled outside would be quickly diluted in outdoor air, so their concentrations would quickly become insignificant. “In addition, the stability of the virus outside is significantly shorter than inside. So outside is not really a problem…It is safe to go for a walk and jog and not to worry about the virus in the air”

Influenza patients were moved into the sunny, outside air to promote recovery during the 1918-1919 pandemic.

  • There is deep experience during other pandemics that placing patients outdoors greatly enhanced their recoveries and lessened spread to others.  In fact, during some pandemics (like 1918-1919) open-air hospitals were built and patients were moved outside into the sun, with very positive impacts.  To quote one paper on the subject (“The Open Air Treatment of Pandemic Influenza”, which documented the reduction of mortality and morbidity in the open air: “more might be gained by introducing high levels of natural ventilation or, indeed, by encouraging the public to spend as much time outdoors as possible.” 
  • There is an extensive literature that ultraviolet radiation from the sun can quickly degrade the viability of viruses in the air (e.g., Schuit et al. 2020: The Influence of Simulated Sunlight on the Inactivation of Influenza Virus in Aerosols).  As noted by Lytle et al., 2005: “Sunlight or, more specifically, solar UV radiation (UV) acts as the principal natural virucide in the environment.” Duan et. al. 2003 found that “UV irradiation can efficiently eliminate the viral infectivity”
  • A fascinating study of virus transmission in dorms at the University of Maryland compared students in rooms with poor ventilation, with those who kept their windows open all the time (Zhu et al., 2020).  Those with open windows had one-fourth the rate of respiratory infections. Some did complain of being cold, though.
  • Virus particles rapidly disperse in the open air as noted by Case Western Reserve University Hospitals infectious disease specialist Dr. Amy Edwards: “When someone coughs or sneezes, most of the virus drops to the ground within 6 feet pretty quickly. That’s why doctors recommend social distancing. If a few particles remained in the air, they would be killed off by UV light in the sun, or blown away by the wind”

I could quote a lot more literature and from additional specialists, but you get the point.  Being in fresh, outside air, particularly when the sun is out, is clearly a good place to lessen one’s exposure to COVID-19.

The risk of transmission of COVID-19 is extraordinarily less in outside air compared to within buildings.   There is essentially no background concentrations of the virus in outside air.  Ultraviolet radiation from the sun is destructive to the virus.  They is rapid dispersion of any source of virus (e.g., an infected coughing individual) by the wind in the vast outside volume of air.  And there is a substantial literature that concentration matters:  the more exposure to viral particles the greater the chance of infection. Viral concentrations will be very low outside, if they are measurable at all.


Another issue is humidity.   Viral transmission is degraded by high humidities and enhanced by lower humidities (check out this excellent recent review article: Moriyama et al. 2020);several papers suggest that relative humidities above 40% degrade transmission.   During the cool season, humidity inside building tends to be very low (check my earlier blog for an explanation), but outside humidities are generally much higher.  For example, below is a plot of the relative humidity in Seattle over the three years.  Outside relative humidity only rarely drops below 40% around here.  Inside RH is often below 40% during the cool season.

Recently, there has been a lot of media attention regarding a simulation of particle dispersion from a coughing runner, with recommendations not to run directly behind him/her and particularly in the wake region behind the runner. There was some dramatic imagery (see below), but the risk from sick runners is really quite small.

First, there are not many runners coughing and sneezing while running–when someone is sick with the virus they have great fatigue and if they were asymptomatic carriers they would not be coughing! (Note:  there are some folks that cough after intense exercise).  Furthermore, the large virus-laden droplets tend to fall quickly and the smaller particles/droplets tend to follow the streamflow around an obstacle (that’s you).  Most importantly, the droplets ejected from a sick runner would rapidly disperse in the free atmosphere and the UV radiation would work to lessen the viability of a virus.   Yes, there is a slipstream of air immediately behind a runner in which concentrations could be greater….but how many people are running immediately behind a sick runner? Even in the video, little of the particles reach the face of the runner following immediately behind.   Folks, this is a very small risk.

So let’s get back to the policy decision to ban folks from parks and why it is illogical and contrary to common sense.

Hopefully, you are convinced that outside air is immensely more healthful with far less COVID-19 risk than the air we breathe inside of buildings.  You really want folks outside for that reason alone.

But what about social distancing?  If that is good, you want folks to spread out as much as possible. Thus, they should be ENCOURAGED to get their fresh air in vast open public spaces and particularly ones with lots of air motion (i.e. wind).

But yet that is exactly the opposite of what our political leadership is doing.  Here in Seattle, the Parks Department closed the largest parks in the city (like Magnuson, Lincoln and Discovery) last weekend, parks that afford great opportunities for social distancing (see map).  Many of these large parks (red X in the above figure) are near the water and experience stronger winds that are  particularly favorable for virus dispersal.  In contrast, the city left the smaller parks open, concentrating folks in small areas.  Just is bad is the closing of park parking lots, which forced folks to leave their cars outside of parks and to walk in narrow corridors (less social distancing) to enter the parks.

Magnuson Park was closed and everyone is forced to walk on the crowded path to the left.

In California, vast beach areas are closed, again forcing folks to stay indoors or crowd onto limited walkways.

All these park closures are based on fears of transmission within groups enjoying the parks.  But such closures do not make sense.   First, there is little evidence of viral spread in outdoor spaces, even when crowded.  Second, there is little evidence for such crowding in Washington State and California parks in other than the most isolated incidents.  I have been to several Seattle parks during the past weeks– folks are generally careful and respectful, without large collections of folks in close proximity.  Obviously, park officials can make it clear that closely packed large crowds are not appropriate and that there will be giving warnings and citations if such crowds occur.   To put it succinctly, park closure is a solution in search of a problem that has never been shown to exist.  And it hurts exactly the people it is meant to help.

More Issues


Going to parks is extraordinarily good for physical and mental health.  Being outside exposes folks to the sun’s UV rays that facilitate production of vitamin D, which bolsters the immune system and reduces the chance of infection by COVID-10 and other pathogens.  Recently, I got a call from a UW professor of medicine who is working on exactly this important relationship with COVID (he needed global UV/solar radiation data), confirming the above.   Vigorous exercise and even walking enhance the immune system, reducing chances of infection.  And exercise and fresh air have a very positive effect on mood, reducing stress and anxiety–both of which weaken the immune system,

And in a progressive city like Seattle, or in the progressive states of Washington or California, there are simple equity ideas that should be compelling.  Closing parks or making entry difficult hurts low income people the most.  Folks that live in small apartments or in crowded environments greatly enjoy the physical and emotional release of our wonderful large parks.  They are the ones who are most deprived by the park closings, both mentally and physically, in comparison to those with large homes and extensive garden areas.  And the closing of parking lots deprives the elderly and physically handicapped from the healthful conditions in our parks and the emotion salve of enjoying the outdoors.  I have noted the demographic shift in the park when the parking lots were closed.

In some ways, this is all about risk.  There is an extraordinarily small risk of catching COVID-19 while enjoying parks and natural areas.  I mean really, really small.   But park closures provide substantial risks that clearly threaten one’s physical and mental health.  Our society is not particularly good in qualifying and acting upon risks, and the park closures are a prime example of this failure.

Sunset at Shoreline’s Richmond Beach Park. 

Parking is closed and many cannot enjoy this view anymore

Governors Inslee, Cuomo, and Newsom have all stated that in dealing with the COVID-19 crisis it is essential to “follow the science.”   It is time that they follow their own advice, reopening all the parks and nature areas, including the restoration of all parking facilities and access.



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