Wildfire Smoke in the San Juans

Health Effects, Mitigation Measures, and Personal Monitoring

APART FROM A MAJOR EARTHQUAKE ON THE CASCADIA FAULT, wildfire is arguably the greatest threat to property and lives in the San Juan Islands.  Fortunately, fires of serious magnitude have been limited in our islands, and with an increasing focus on wise fire-prevention practices there is reason to hope this will continue to be the case.  But wildfires elsewhere in the United States, particularly in the Pacific Northwest, have increased substantially in recent decades. This increase has been most dramatic in the last five years, creating trends of larger areas burned, greater fire-season length and higher sustained wildfire-related smoke and air-pollutant impacts.

The reasons for these increasing trends include decades of fire suppression, episodic drought conditions in areas of western North America, forest pest infestations, and warming atmospheric temperatures.  These factors have culminated in widespread wildfires in the Pacific Northwest, resulting in serious smoke impacts in the San Juan Islands.  Such episodes have lasted for as long as two weeks, with concentrations of fine smoke particles reaching levels hazardous even for healthy individuals.

Because our islands experience winds and air movements from both north and south, we can be impacted by distant wildfires, especially occurring east of the Cascades.  For example, smoke from inland British Columbia and eastern Washington wildfires can pour through the Fraser River Gap on winds from the northeast, strongly affecting the San Juan islands, while intense smoke can arrive from Oregon and northern California on southerly winds. 

This article examines the potential health effects associated with wildfire-smoke exposures in the San Juan Islands. It offers measures to reduce personal exposures and health impacts from future wildfire smoke episodes affecting our communities.

Health Effects of Wildfire Smoke

Hospitalizations and emergency-room visits for respiratory diseases have consistently increased with wildfire-smoke exposures in adults and children.  Of the numerous air pollutants that occur in wildfire smoke, breatheable particles less than 2.5 microns in diameter (PM2.5) — roughly 50 times smaller than a human hair — are of greatest concern.  These “fine” particles can penetrate into the deepest part of the lungs and cause a range of illnesses and even death. 

Fine smoke particles can penetrate into the deepest parts of the lungs and cause illness and even death.

Health effects specifically associated with exposure to smoke include cardiovascular and respiratory morbidity and mortality, wheezing, coughing, eye irritation, neurodegenerative disease and adverse reproductive effects.  People at highest risk for wildfire-smoke exposures include those with respiratory diseases such as asthma and bronchitis, individuals with cardiovascular disease, children, the elderly, and pregnant women and their fetuses.  

Children are especially vulnerable because they typically have more outdoor exposure, they breathe more air relative to their body weight, and they have less deposition of particles in the larynx and trachea, allowing a higher proportion of particles to penetrate into their lungs. [1] More than 25 years of research has demonstrated that pediatric asthma visits increase in association with wildfire events.    

Health-based indices have been created for the key pollutants in wildfire smoke, for which the official National Ambient Air Quality Standards are set by the Environmental Protection Agency.  The EPA’s Air Quality Index (AQI) runs from 0 to 500 and is divided into six levels of concern from Good to Hazardous as shown in the table below.  Higher AQI levels correspond to greater concentrations of PM2.5 particles in the air we breathe.

Environmental Protection Agency chart of Air Quality Index (AQI)

In recent years, numerous wildfire-smoke episodes in north Puget Sound locations surrounding the San Juan Islands have sent the AQI into the Hazardous level.  It’s highly likely hazardous air-quality conditions also existed in San Juan County during those episodes, although no agency monitoring data are available to confirm that for reasons to be discussed.

Washington State created the Washington Air Quality Advisory index [2], similar to the EPA’s AQI but based on lower levels of fine-particle pollution, with the intent to provide earlier alerts of potential health impacts.  This index is available as a free, mobile-friendly application.

Steps You Can Take to Mitigate Smoke Exposures

The Washington State Department of Health has useful resources concerning exposures to wildfire smoke, including steps that can be taken to protect family members. [3] Here are some of their most important recommendations, paraphrased:

  • Avoid physical exertion outdoors during wildfire-smoke episodes.
  • Stay indoors and keep windows and doors closed. This will reduce indoor fine-particle concentrations to approximately one half to two thirds of the outdoor concentrations, depending on the building quality.  The tighter the seal of windows and doors, the more readily one can protect the indoor environment from outdoor smoke.
  • An air purifier with a HEPA filter will reduce the number of particles inside.  But air purifiers that produce ozone should be avoided.
  • Correctly worn respirator masks may provide some protection against fine particles in wildfire smoke.  N95 respirators are relatively inexpensive and widely available but must be properly fitted to provide protection.  Men with ample facial hair are generally not well protected by masks.
  • If you belong to one of the vulnerable populations discussed above, you might consider leaving the area temporarily if it’s not possible to reduce indoor air pollution adequately.

A recent paper evaluating the impact of wildfire smoke events on indoor air quality evaluated a low-cost filtration method that might be an alternative to a HEPA filter. [4]

Measurements of Fine Particles in Wildfire Smoke

Factors that influence the specific composition and exposures of wildfire smoke include the type of combustion (flaming versus smoldering), atmospheric conditions and the composition of the fuel being burned.  As fine particles are the most important exposure from wildfire smoke, the most valuable data to evaluate risks are therefore the PM2.5 concentrations. Because fine particles scatter visible light efficiently, instruments for measuring PM2.5 concentrations are generally based on light-scattering measurements.  

The most reliable PM2.5 instruments are sophisticated devices employed by local, state and federal air agencies, which are regularly calibrated.  Unfortunately, San Juan County withdrew from the Northwest Clean Air Agency years ago, and at present there are no such monitoring stations measuring air quality in our islands.  That has forced us to interpolate measurements made by air agencies elsewhere around north Puget Sound — in Anacortes, Bellingham, Oak Harbor and on Vancouver Island — to try to estimate levels of PM2.5 experienced during severe smoke episodes in the San Juan Islands.  

During the 2019 fire season, for example, PM2.5 concentrations in Bellingham reached more than five times higher than the 24-hour health-based EPA air-quality standard and more than ten times higher than the annual-average standard.  These fine-particle concentrations corresponded to the Hazardous health-index level, potentially affecting the health of all individuals.  Given the regional nature of smoke impacts during these episodes, it’s likely that PM2.5 concentrations in the San Juan Islands were roughly comparable to those measured in Anacortes, Bellingham, Oak Harbor and other surrounding areas. But with no Northwest Clean Air Agency monitors in our islands, it’s impossible to quantify accurately the exposures we experienced.

Visual-Range Estimating and Personal Monitoring

Visual range is a relatively crude — but in some circumstances useful — approach to estimating fine-particle concentrations, especially when these concentrations are extraordinarily high and no official local monitoring data are available. Based on scattering of visible light by fine particles, the progressive disappearance of distant and closer objects can be used to estimate roughly the seriousness of particulate exposures. For example, the US Forest Service uses photos such as those shown below to aid firefighters in estimating exposures to fine particles in areas where air-monitoring data are unavailable.

Typical visibility under conditions of “Good” AQI (Credit: US Forest Service)
Typical visibility under conditions of “Unhealthy” AQI.
Typical visibility at the borderline between “Very Unhealthy” and “Hazardous” AQI.

Islanders could use this approach by obtaining the distance to fixed visible features that range from 1 to 15 miles from their homes and roughly estimating unhealthy exposures from the disappearance of these objects.  When the visibility drops below 2 miles, you can be fairly certain that the air quality is becoming hazardous.

In addition to depending on subjective visualization, however, visual range is also dependent on humidity and smoke composition — and will vary with these factors.  For these reasons, visual range is only a qualitative indicator at best, and not a substitute for air-agency or personal monitoring data.  

 As noted earlier, PM2.5 measurements and Washington Air Quality Advisory health status indications at Anacortes, Oak Harbor and Bellingham can provide a rough sense of the smoke impacts in our islands. Air quality measured at these locations by the Department of Ecology can be accessed on-line at https://enviwa.ecology.wa.gov/home/map.  

To obtain local or personal air quality data, however, relatively inexpensive personal PM2.5 monitors are available, and their measurements can be integrated into island and regional monitoring networks. Such monitors provide spatially resolved air quality at relatively low cost (generally around $300 each). Examples of widely used personal monitors include the PurpleAir and IQAir instruments that allow measurement of local indoor and outdoor air quality in real time. And online comparisons can be made with personal measurements made by other islanders using these monitors.* (See Appendix for additional information on these personal monitors.)

In lieu of the more sophisticated and accurate monitoring instruments employed by the Northwest Clean Air Agency, San Juan County has installed PurpleAir monitors on Orcas, Lopez and San Juan Islands to provide data that can be used in conjunction with the Department of Ecology network to make local public-health recommendations. The monitor on Orcas Island, for example, is located at the Senior Center in Eastsound.

A Model Community Air-Monitoring Network

In response to long-standing air-quality impacts associated with agricultural burning and woodstove use, and more recently wildfire smoke, the rural Methow Valley community in Washington’s Okanagan County established a community air-monitoring network called Clean Air Methow. [5] In partnership with University of Washington’s Department of Environmental and Occupational Health Sciences, the program recruited 18 citizen volunteers who employed PurpleAir monitors in their homes or places of business in the summer of 2018. Data generated from this cooperative effort provided spatially resolved air-quality information in the valley. Methow’s program is a possible model for the San Juan Islands if interest exists in establishing a citizen-scientist volunteer community air-monitoring network on individual islands or across the county. More information about Clean Air Methow can be found at www.cleanairmethow.org.


GIVEN THE TRENDS OF THE LAST FIVE YEARS in the factors leading to wildfires, it seems likely the San Juan Islands will continue to experience serious smoke episodes, and that the frequency, intensity and duration of such episodes may continue to increase public-health concerns for our communities. This article has summarized key information that should be useful in understanding the health impacts of wildfire smoke, how to minimize exposures, and approaches to individual and community monitoring.  Additional useful information can be found in the references below and appendix.


*Dozens of different personal air monitors are available; the PurpleAir and IQ Air monitors are cited only for illustrative purposes and do not indicate endorsement of these products.

Top photo credit: Oregon Occupational Safety and Health Administration.

References and Resources

[1] “Health Effects of Wildfire Smoke in Children and Public Health Tools: A Narrative View,” J. Exp. Sci & Env. Epi., Holm et. al., Nature, 2021, 31: 1-20. https://pubmed.ncbi.nlm.nih.gov/32952154/

[2] Washington Air Quality Advisory index, available online at: https://ecology.wa.gov/Research-Data/Monitoring-assessment/Washington-Air-Quality-Advisory

[3] www.doh.wa.gov/CommunityandEnvironment/AirQuality/SmokeFromFires

[4] “Impact of Wildfire Smoke Events on Indoor Air Quality and Evaluation of a Low-costFiltration Method,” May, et. al., Aerosol and Air Quality Research, 2021, 21: 1-11. http://doi.org/10.4209/aaqr.210046

[5] “Establishing a Community Air Monitoring Network in a Wildfire Smoke-Prone Rural Community: The Motivations, Experiences, Challenges, and Ideas of Clean Air Methow’s Clean Air Ambassadors,” Durkin, et.al. Int. J. Environ. Res. Public Health 2020, 17: 8393. https://pubmed.ncbi.nlm.nih.gov/33202742/

A good fact-sheet on use of face masks for wildfire smoke is: https://clark.wa.gov/sites/default/files/dept/files/public-health/wildfire%20smoke/DOH_Wildfire_Smoke_Face_Masks_Factsheet.pdf


Appendix: Additional Information about Personal Air-Quality Monitors

Both the US Environmental Protection Agency and the California South Coast Air Quality Management District (AQMD) have shown that the accuracy and precision of personal monitors varies between manufacturers.  The AQMD Air Quality Sensor Evaluation Center website (http://www.aqmd.gov/aq-spec) presents data collected from testing more than two dozen different personal monitors.  They found, for example, that the IQAir personal monitor showed good accuracy at all but the highest PM2.5 concentrations (that is, greater than 300 micrograms/cubic meter).  The original PurpleAir PA-I monitor showed lower accuracy but high precision over all concentration ranges, and it’s likely the new generation of PA-II monitors, with a double sensor, gives improved performance.

Online map of PurpleAir monitor AQI readings in north Puget Sound on 14 July 2021 (Source: PurpleAir web site).

Corrections can be made to PurpleAir monitors to improve their accuracy using data from a variety of on-line sources.  A PurpleAir instrument includes built-in WiFi capability to upload data automatically for display on the PurpleAir Monitoring website (https://www2.purpleair.com/).  Similarly, IQAir data are reported to a global network (https://www.iqair.com/). 

Author Profile

A resident of Orcas Island, Arthur Winer is Distinguished Professor Emeritus of Environmental Health Sciences in the UCLA Fielding School of Public Health and served for nine years as Director of the UCLA Environmental Science and Engineering Program. During a forty-year career he has published nearly 200 peer-reviewed articles on a wide range of atmospheric chemistry and air-pollution topics, including exposures to — and health impacts of — wildfire smoke. In addition to his research contributions, he has worked at state and national levels to promote legislation and public policies designed to address key air pollution, environmental-justice, and public-health concerns.

10 thoughts on “Wildfire Smoke in the San Juans”

  1. Great article. I appreciate the explanation and directions on how we all can monitor air quality and contribute to an important data base. Thanks Authur.

  2. San Juan County’s three PurpleAir monitors on Lopez, Orcas and San Juan Islands are a welcome addition. But it should rejoin the Northwest Clean Air Agency, which costs only a paltry $6,000 or so a year. We are the only county in the entire Puget Sound region that is not a member of such an agency. Go figure.

  3. Thanks for your incisive review of this vital topic, Arthur. The smoke a couple years ago was so dense that visibility was in the low hundreds of yards. Our county would surely benefit from rejoining the Northwest Clean Air Agency aas Michael Riordan has suggested, though until that happens I’ll post interesting readings from my handheld particulate monitor to Facebook… though that platform has not proven to be the most reliable aggregator of useful data.

  4. Michael Riordan

    The credit all belongs to Dr. Winer, Michael. I’m just the editor who, knowing of his expertise, suggested he write this article — and added a few improvements.

  5. Last week’s smoke-intrusion event began on Thursday morning, August 12, as NE winds began to pour through the Fraser River Gap, carrying wildfire smoke from inland BC with them. It struck Orcas Island first. At about 7:30 am, I noticed PurpleAir monitors around Olga turning yellow to orange and showing readings from 60 to over 80 (especially at higher elevations), while most of the rest of the islands were all bright green — indicative of good air quality. But the smoke began spreading to most of the remainder of San Juan County that morning and then to parts south, including Anacortes and Mount Vernon. PurpleAir monitors began turning red and even purple, indicative of unhealthy and potentially dangerous air conditions.

    In part because they are members of the Northwest Clean Air Agency (NWCAA), Skagit, Island and Whatcom Counties issued air-quality alerts that Thursday. So did Clallam and Jefferson Counties, members of the Olympic Clean Air Agency. But San Juan County did not issue any such alert until Friday morning, despite the fact that the wildfire-smoke problem had first appeared hereabouts. One can attribute such a lapse to the fact that the County is not a member of any of the regional clean-air agencies and therefore does not have their professionals to analyze the data and advise us when the monitors began to indicate air-quality problems.

    Fortunately, westerly winds coming down the Strait of Juan de Fuca began to hit the islands and alleviate the problems late Friday afternoon and that evening — although at least one PurpleAir monitor on Orcas Island remained above 200. By Saturday morning, the wildfire smoke had largely cleared in the County.

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