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Smoke from nearby wildfires enveloping East Oakland, Aug. 19, 2020 Credit: Jacob Simas

What do wildfires have to do with air pollution, and how do distant fires cause pollution in the Bay Area?

Topography and weather patterns play a large role in why wildfire smoke from hundreds of miles away lingers in the Bay Area, affecting health. 

Also affecting how smoke travels in and around the Bay Area are the Diablo winds — the strong, hot winds that usually blow for at least a few days, usually in the fall. 

A high-pressure system will develop inland as a jetstream sends hot and dry air down the side of the Sierras and across the Central Valley. The winds typically pick up speed as they whip through coastal mountains. 

The hot and powerful winds have toppled power lines and started fires and created wildfire smoke in the process. That wildfire smoke needs a place to go and for inland areas, that’s typically through the Bay Area and out to sea. 

The smoke can linger in the Bay Area if winds from the Pacific meet Diablo winds.

Otherwise, the smoke can travel inland, like in 2020 when California’s wildfire smoke could be seen and felt as far as the East Coast. 

How bad is wildfire smoke for my health?

Wildfire smoke is especially damaging to the human body because it contains tiny bits of aerosolized particulate matter that the lungs can’t filter out, so it goes directly into a person’s bloodstream. 

“That’s why it’s so dangerous,” said Thomas Dailey, a pulmonary and critical care specialist with Kaiser Permanente Santa Clara who served three terms as chair of the Bay Area Air Quality Management District’s hearing board, a state agency that helps enforce air quality rules.

Wildfire smoke can trigger a slew of health risks, especially for older people, children, and those with respiratory disorders. Dailey said the Bay Area sees an increase in heart attacks and strokes during Spare the Air days. Spare the Air alerts are triggered when the air quality index rises above 100.

A team of researchers from University of California San Diego looked at data from wildfires in Southern California from 1999 to 2012, specifically the impacts on human health from smoke, ash, and dust. Their findings, published in March in the journal Nature Communications, concluded that the particulate matter generated during a wildfire “is up to 10 times more harmful on human health” than particulate matter from other sources. 

A more recent study from the California Air Resources Board found that wildfire smoke may contain dangerous levels of toxic metals that can cause lead poisoning.

Some people are more likely to be impacted by wildfire smoke. According to the U.S. Environmental Protection Agency, that includes children and teenagers because they breathe more per pound of body weight. It also includes older adults, those who are pregnant, people with asthma and other upper respiratory conditions and people with diabetes, because they’re more likely to have underlying cardiovascular or lung diseases. 

I’ve had COVID-19. What do I need to know about wildfire smoke? 

If you have or are recovering from COVID-19, you may be at greater risk from wildfire smoke, according to the Centers for Disease Control (CDC), because the virus affects the heart and lungs. 

The CDC recommends that anyone with the virus, or who is still experiencing symptoms, make an extra effort to avoid smoke exposure. 

The best protection against the risks of mixing wildfire smoke and COVID-19 is to get vaccinated against the virus. (This is the best way to protect yourself from the virus, smoke or not.)

Some of the symptoms of wildfire smoke inhalation and of COVID-19 are similar, including dry cough, sore throat and difficulty breathing. But other common symptoms of the virus aren’t associated with smoke exposure, such as fever, body aches and diarrhea.

If conditions are smoky and you have COVID-19 or are recovering, talk with your health care provider. 

If you’re unsure what’s going on but have some of these symptoms, the CDC recommends you take its COVID-19 symptom checker or get tested. 

Call 911 if your symptoms are severe. 

How can I protect myself from wildfire smoke? When do I need to wear a mask or stay indoors? 

The public health message during bad air days is the same one heard during the worst of the pandemic: stay home. 

Thomas Dailey, the former chair of the BAAQMD’s hearing board, said it’s best to remain indoors as much as possible, as an N95 or KN95 mask only blocks 95% of the particles that can become lodged deep in your lungs and enter the bloodstream. “That means 5% is still getting through,” he said.

Experts recommend sealing up your living space as best as possible to keep smoke from getting in, as well as using air filters to cleanse your indoor air. If you can’t smoke-proof your whole house, create a “clean room” to hang out in, or a room protected as much as possible from the outside air.

But staying home is not always a viable option if you are unhoused, if your work or daily life requires you to be outside, or if your home can’t protect you from the smoke.

When exposed to smoke, you should wear N95 or KN95 respirator masks, ensuring the mask has a tight seal around your nose and mouth.

The Alameda County Health Department will also open clean air facilities to the public where you can go to breathe clean air indoors as well as cool off from any heat. When those shelters are open, they’ll be listed on the county’s Open Clean Air Facilities page.

Which masks best protect against wildfire smoke?

Masks are among the least expensive forms of protection against smoke and fallen ash, especially outdoors. But many kinds of masks, including many types popular for COVID-19 protection — disposable paper masks, cloth masks, etc. — are ineffective at blocking out the fine particulate matter contained in wildfire smoke. 

To filter out smoke, the Environmental Protection Agency recommends you use an N95 respirator mask — the highly sought-after face coverings most needed by frontline health care workers during the pandemic. They are available at local hardware stores, but local retailers say 3M — the manufacturer of most N95 masks — has instituted a three-per-customer limit.

In the past, it’s been difficult to get N95s both online and in-person, especially once the smoke has arrived, so experts recommend stocking up early.

Recommendations for N95 masks can be contradictory even among experts. The Centers for Disease Control, for example, states they’re the best choice for fire smoke, but also says they should be saved for health care providers, given the pandemic. 

The course of COVID-19 and the course of wildfire smoke can’t be predicted. On days with unhealthy smoke, look for the latest information on N95 mask needs and availability to help you with differing opinions and advice. 

N95 masks will have straps meant to go around the back of your head to create a tighter seal around the nose and mouth, which can be difficult if you have facial hair. Double masking, or using a cloth mask over an N95, can help create a tighter seal. The same is true with a KN95 mask or N95 equivalents made in other countries that meet China’s standards but not those of the U.S. National Institute for Occupational Safety and Health (NIOSH). KN95 masks will most likely be easier to find. 

Both the N95s with and without valves provide adequate protection against smoke. The valves help keep the mask from overheating, but they don’t prevent a person from potentially spreading COVID-19 when they exhale.

Neetu Balram, the spokesperson for the Alameda County Public Health Department, said N95 masks may make it difficult for you to breathe and may be dangerous if you have certain lung and heart conditions. 

There aren’t any N95s certified for children because all are too big to fit snugly over smaller faces.  

How can I reduce the impact of wildfire smoke inside of my home? 

The key to living indoors during fire season is to keep smoke out, especially if you have or live with someone who has underlying conditions such as asthma or heart issues. 

The California Air Resources Board recommends you consider permanently installing a ventilation system that filters outdoor air before it enters your home to protect against long-term or recurring episodes of air pollution, like seasonal wildfire smoke. For many — such as renters — that’s not feasible. 

Purifying indoor air requires a filter — whether for a home’s HVAC system or a portable air purifier — with a Minimum Efficiency Reporting Value (MERV) of 13 or above. Thirteen is the lowest-rated filter used in smoking lounges, but anything rated 16 or higher does a good job filtering wildfire smoke, according to CARB ratings

Experts recommend investing in a good portable air purifier before California’s wildfire season begins. 

The cheapest model on Consumer Reports’ best air purifiers for wildfire smoke is $220, though they’ve put their stamp of approval on models as cheap as $60. Other models are available at local hardware stores and big-box retailers, though all are susceptible to supply chain issues during an emergency. 

One low-cost upgrade that can be used in a pinch is affixing a MERV 13 filter (less than $55 for a six-pack) to a standard box fan.

Other ways to help keep wildfire smoke out of your home include sealing up any drafty areas, such as around older windows or underneath doors. Foam tapes can help create a better seal at the bottom of a door or window. For larger, more problematic areas, consider using a window insulator kit that is installed with tape and a hairdryer.

How can I monitor air quality in my neighborhood?

During wildfire season, it’s important to monitor the AQI, or air quality index, frequently, as levels can change by the hour. You should start getting concerned when the AQI reaches above 100.

There are a growing number of options for monitoring air quality. The trend is toward neighborhood-level monitoring, made possible by crowdsourced data from private sensors. There can be discrepancies and glitches in all systems, but quality control is a big part of the effort. 

Here are a few of the most popular options for checking air quality near you: 

Each of the above options displays AQI readings as a number and a color, most of which appear on maps updated dozens of times a day. The East Bay remains green for most of the year, meaning the concentration of pollutants is scored below 50. That means the air is safe outside.

When the AQI rises above 100, entering the orange stage, it triggers a Spare the Air alert, encouraging you to drive less and use combustible sources of fuel as little as possible. The BAAQMD, which issues those alerts, says particulate matter is the most common form of pollutant between November and February. It issued more alerts in 2020 than ever before.