Smoke billows from a mountainside east of Mariposa as the Oak Fire rages on Saturday, July 23, 2022. Credit: CRAIG KOHLRUSS

What's at stake:

Breathing in wildfire smoke can damage your health, but experts agree that taking some steps can limit impact. In short: buy filters, N95 masks, and follow PurpleAir.

This summer’s stretch of low-intensity wildfires that did not significantly degrade the Valley’s air quality ended with the explosive growth of Mariposa County’s Oak Fire. 

Wildfire forecasts and climate models show increasing temperatures and dry forests in the Sierra Nevada in the coming weeks, which means a higher likelihood of large wildfires and heavy smoke impacts on Valley air quality in the next several months. 

People under the age of 18 and pregnant women are especially vulnerable to the side effects of wildfire smoke exposure. Experts say breathing in wildfire smoke can lead to health emergencies and premature death. 

Fresnoland has compiled everything you need to know about wildfire smoke and how to protect your health during this wildfire season. 

What Are the Health Impacts of Wildfire Smoke?

Wildfire smoke contains PM2.5 particles, which include chemicals that cause damage to every organ in the human body. Breathing PM2.5 pollution is linked to brain inflammation, impaired cognitive functioning, emergency-room visits, early-onset Alzheimer’s and premature death

A study estimated that wildfire pollution is 10 times more toxic than regular air pollution, and even short-term exposure to smoke was found to cause hard-to-reverse changes to how DNA is expressed in young adults. 

Breathing in wildfire smoke can also make you more vulnerable to other ailments and diseases. For example, a recent study from Science, one of the world’s top science journals, estimates that 2020’s Creek fire caused a 45% increase in COVID deaths in Fresno because wildfire smoke stresses and weakens the body’s immune system. 

Pregnant women and children are especially sensitive to the toxic effects of wildfire smoke and should take protective measures whenever possible. 

Due to their higher exposures and developing bodies, children suffer lifelong consequences from PM2.5 pollution, including altered brain structure, increased risk for autism, depression, schizophrenia and suicide later in life, obesity, and asthma. Even small increases in PM2.5 exposure can increase children’s risk for self-harm by 42% later in life.

Brain health is probably even more impacted by wildfire smoke than regular air pollution. A study by the California Air Resources Board also found that in addition to PM2.5, wildfire smoke contains other toxic chemicals such as high levels of lead, which is catastrophic for the brain development of babies and children. 

Pregnant women benefit from every protective measure against wildfire smoke exposure. Maternal exposure to toxic air has serious health impacts on the fetus. The tiny particles in PM2.5 pollution have been found to sediment in the placenta and increase the risk for fetal death.

Women who breathe high pollution levels during pregnancy give birth to children with higher rates of health problems like pediatric leukemia, kidney cancer, eye tumors, and heart malformations.

Each increase of 1 µg/m3 in the trimester-average wildfire smoke PM2.5 over the second trimester is associated with a 13.2% increase in odds of preterm birth. A study from 2017 found that high pollution levels in the year a baby is born create detriments for a child’s ability to earn high wages when they reach adulthood.

How To Protect Yourself From Wildfire Smoke

Reducing the amount of smoke you breathe is the main goal of any protective measure. This can be done through three actions: 

1. Indoor Air Filters

Air filters are rated by so-called MERV levels. A MERV-13 filter, for instance, captures more pollutants than a MERV-11.

According to experiments conducted over the last year by the Central California Asthma Collaborative, your filter should be rated at least a MERV-11. “Any filter rated under a MERV-11 is simply not going to keep you safe from wildfire smoke in your home,” said Kevin Hamilton, co-director of the Central California Asthma Collaborative.

While MERV-11 filters are OK at filtering wildfire smoke, Hamilton says MERV-13/14 filters offer superior protection.

Replace these filters once a month during wildfire season.

  • If your AC motor is older than 10-15 years old, buy a MERV-11 filter
  • If your AC motor is less than 10 years old, buy a MERV-13/14 filter.

Adding a HEPA filter to your car can be helpful too. Replace every three months. Run AC on recirculate.

2. N95 Masks

When you have to go outside when smoke is in the air, wearing a well-fitting N95 mask is essential.

Fresnoland recommends N95 masks that cost between 70 cents and $1.10 per mask. Replace your N95 mask once a week during wildfire season. 

To make sure the mask is sealed on your face, see here.

3. Outdoor Activity

Avoid outdoor activity when the AQI is greater than 80-100 or when the PM2.5 concentration is over 25. People under the age of 18 should avoid sports and recess when the AQI is over 80.

Check PurpleAir (AQI) or SJVAir (PM2.5 concentration) for real-time air quality information in Fresno before going outside. 

Family Buying Guide

Assuming wildfire season goes from August to November, keeping your family safe from wildfire smoke will cost between $160 and $240 for N95 masks and AC filters. Add an additional $100-600 if you want the extra protection of a HEPA filter. 

$ — $40/month + $100 upfront 

Adult Mask: 3M vFlex $6/month (assumes two adults, using one mask each per week)

Child Mask: Savewo Small KN94 (2-6), Dr. Puri Sm. KN94 (6-9), Savewo Lrg KN94 (7-13) $19 / month (assumes two kids, using two masks each per week.)

AC Filter: MERV-11 filter 1 / month $15/month

HEPA for bedroom/living room: Medify Air or Dreo Air.

$$ — $50/month + $200 upfront 

Adult Mask: 3M Aura $9/month (assumes two adults, using one mask each per week)

Child Mask: Savewo Small KN94 (2-6), Dr. Puri Sm. KN94 (6-9), Savewo Lrg KN94 (7-13) $19 / month (assumes two kids, using two masks each per week)

AC Filter: MERV-13 filter: 1x month $20/month

HEPA filter for living room: Winnix 5500-2 

$$$ — $60/month + $800 upfront 

Adult Masks: Flomask $180 upfront, $8/month for filters

Child Masks: Savewo Small KN94 (2-6), Dr. Puri Sm. KN94 (6-9), Savewo Lrg KN94 (7-13) $19 / month (assumes two kids, using two masks each per week.)

AC Filter: MERV-14 filter 1 / month $30/month

HEPA filter for living room: Medify air MA-112 or BlueAir 680i 

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Gregory Weaver is a staff writer for Fresnoland who covers the environment, air quality, and development.