Good 0–50
Everyone: Enjoy being active outside. EPA
Sensitive groups: The same. The air carries little or no risk. AirNow
Breathe
Breathing easier on bad-air days
What to change when the air index climbs, from your morning run to the air in one room. Agency advice, in plain words.
What to do at each level
The Air Quality Index (AQI) has six color-coded categories. Up to 100 is generally satisfactory. Above 100, the air is unhealthy, first for sensitive groups and then for everyone. AirNow
Most lines on the cards paraphrase the cautionary statements EPA gives agencies for each level in its May 2026 AQI guidance. EPA For your county's number right now, see Today on the home page.
Two pollutants, two patterns. Ozone is a gas that forms in sunlight. It is worst on summer afternoons and early evenings, so morning is usually the easy fix. EPA
PM2.5 means fine particles. Here they build up under winter inversions and ride in with wildfire smoke. Utah DEQ inversions Utah DEQ smoke They can be high at any hour, and inside as well as out, so the fix is filtered indoor air. EPA schools EPA particles
Moderate 51–100
Everyone: Being active outside is still fine. EPA
Sensitive groups: Only people who are unusually sensitive may want to adjust, by keeping outdoor activity shorter and easier. A cough or shortness of breath means ease off (ozone) or go inside (PM2.5). EPA
Unhealthy for Sensitive Groups 101–150
Everyone: Most people are less likely to be affected. AirNow On ozone days, EPA suggests everyone consider going shorter and easier. EPA
Sensitive groups: Keep outdoor activity shorter and lighter, take more breaks, and watch for coughing or shortness of breath. On ozone days, plan outdoor time for the morning. EPA
Unhealthy 151–200
Everyone: Cut back on long or hard outdoor activity, take more breaks, and head indoors if symptoms start. On ozone days, move it to the morning. EPA
Sensitive groups: Skip long or intense outdoor activity. Think about moving it indoors or to another day. EPA
Very Unhealthy 201–300
Everyone: Limit outdoor activity and head indoors if symptoms start. With ozone, avoid long or hard exertion and favor the morning. EPA
Sensitive groups: Skip all outdoor physical activity. Move it inside or wait for better air. EPA
Hazardous 301+
Everyone: Skip all outdoor physical activity. EPA
Sensitive groups: Stay indoors, keep activity light, and keep indoor particle levels low, as in the clean-air room below. EPA
From Unhealthy for Sensitive Groups up: if you have asthma, follow your action plan and keep your quick-relief medicine close by. EPA Heart symptoms to watch for are under When to get care.
Who counts as sensitive
"Sensitive groups" means different people for different pollutants, so EPA keeps a list for each. EPA
PM2.5 (fine particles)
- People with heart or lung disease
- Older adults
- Children, including teenagers
EPA adds that some minority groups, people with lower incomes and outdoor workers may face higher exposure that can worsen conditions they already have. During wildfire smoke, it also counts pregnant people as at risk. EPA
Ozone
- People with lung disease, such as asthma
- Children, including teenagers
- People who are active outdoors
- Older adults
Utah's ozone-season guidance also names people with heart conditions, people with allergies and people who work outdoors. Utah DHHS
Not being on a list doesn't rule you out. At Unhealthy, some people in the general public may feel effects too. AirNow
Make one clean-air room
A clean-air room is one room you set up to hold smoke and other fine particles to a minimum. EPA writes its steps for wildfire smoke. EPA EPA's particle guide gives the same core advice for any high-particle day: filter the air and don't add smoke. EPA
- Pick the room. One big enough for the household and comfortable for long stretches. A bedroom with its own bathroom works well. EPA
- Close it up. Shut the windows and doors, but keep a way out. Use a bath fan or range hood only briefly. EPA
- Run a portable air cleaner sized for the room. EPA's rule of thumb is a smoke CADR (clean air delivery rate) of at least two-thirds of the floor area in square feet, so a 12-by-15-foot bedroom (180 square feet) needs at least 120. Run it all the time on its highest setting. EPA The sizing assumes 8-foot ceilings, so size up for higher ones. EPA
- Upgrade the furnace filter. With central air or a forced-air furnace, use a snug MERV 13 or higher filter and switch the thermostat fan from Auto to On. Ask an HVAC technician if you're not sure your system can take it. EPA During heavy smoke, change it more often than the label says. EPA
- Skip anything that makes ozone. Buy an air cleaner certified by the California Air Resources Board (CARB), which means it gives off little or no ozone. EPA does not recommend ionizers or other electronic cleaners for smoke. EPA No federal agency has approved ozone generators for rooms people are in. EPA
- Don't add to it. Hold off on high-heat or long cooking, candles, gas, propane and wood stoves, fireplaces, aerosol sprays, smoking and vaping, and vacuuming without a HEPA filter. EPA AirNow names frying in particular. AirNow
- Air it out when the air clears. When outdoor air improves, even briefly, open the windows and run the kitchen and bath fans. EPA
Swamp coolers and window units
A swamp cooler pulls outdoor air, smoke and all, into the house. On smoky days, Utah DHHS suggests skipping it if you can. Otherwise cover the outside intakes completely with 4-inch MERV 13 filters, or run it only when you need to. Utah DHHS
Close a window unit's outdoor-air damper if it has one, and seal the gap around it. Avoid single-hose portable units if you can. Set a central system to recirculate, or close its fresh-air intake. Utah DHHS
Stay inside, but stay cool
Without air conditioning, staying shut in during extreme heat may be dangerous. If you get too hot, go somewhere with air conditioning or to a cooling center. EPA
If you can't stay cool, the power goes out or smoke keeps getting in, it may be best to go elsewhere: friends or family away from the smoke, a public clean-air shelter, or a big air-conditioned building with good filtration, like a mall. EPA
Salt Lake County keeps a Cool Zones list of public buildings where you can cool off, such as senior and recreation centers. Each building's hours and eligibility rules still apply. Salt Lake County Elsewhere, ask your city or county.
A box-fan filter in a pinch
EPA treats a box fan with a furnace filter strapped to it as a stopgap air cleaner: fine when a store-bought one isn't available or affordable, but not a permanent substitute. EPA
In EPA's lab tests with simulated wildfire smoke, design mattered. A cardboard shroud, which covers the outer corners of the fan's face, raised the smoke CADR by about 40% at no cost. EPA research EPA clean room
| Design | Smoke CADR (cubic feet per minute) | Room it could serve (our estimate) |
|---|---|---|
| DesignOne 1-inch filter | Smoke CADR (cubic feet per minute)111 | Room it could serve (our estimate)About 165 sq ft |
| DesignOne 1-inch filter and a shroud | Smoke CADR (cubic feet per minute)156 | Room it could serve (our estimate)About 235 sq ft |
| DesignOne 4-inch filter and a shroud | Smoke CADR (cubic feet per minute)248 | Room it could serve (our estimate)About 370 sq ft |
| DesignTwo 1-inch filters and a shroud | Smoke CADR (cubic feet per minute)263 | Room it could serve (our estimate)About 395 sq ft |
| DesignFour 1-inch filters and a shroud (Corsi-Rosenthal box) | Smoke CADR (cubic feet per minute)401 | Room it could serve (our estimate)About 600 sq ft |
CADR values are EPA lab results. EPA Room sizes are our arithmetic from EPA's two-thirds rule and 8-foot ceilings, not measurements. The same EPA page cites a stricter rule from appliance makers, a CADR equal to the room's square feet, which would make each room about a third smaller. EPA
- Use a newer fan. Build on a box fan made in 2012 or later with a UL or ETL safety mark. Newer fans have fused plugs and thermal cutoffs. EPA
- Retire the old one. EPA does not recommend fans made before 2012. If you use one anyway, never leave it running unattended or while you sleep. EPA
- Follow the fan's own rules. No extension cord, no damaged fan, no children left alone with it running, and working smoke detectors in the home. EPA
- Change filters often. With dirty filters, the units barely worked in EPA's tests. During smoke, check the filter daily and replace it when it turns dark gray or brown or smells like smoke. EPA
Masks
A mask is the last step, not the first. In smoke, limiting your time outside protects you most. Taking it easy and running an air cleaner indoors also help, and a respirator is for when you have to go out. EPA
- What works. A NIOSH-approved N95 or P100 respirator, with "NIOSH" and the rating printed on it, two straps that go around your head, and a size that seals over your nose and under your chin. EPA Utah DEQ says a correctly worn N95 can filter winter PM2.5 too. Utah DEQ
- Seal it every time. One strap above your ears and one below, press the nose clip with both hands, and do the seal check on the package. Facial hair under the edge keeps it from sealing. EPA
- What leaks. Masks with ear loops or only one strap aren't made to seal, and air that leaks around the edge is breathed in unfiltered. EPA says they won't protect your lungs from smoke. EPA Utah DHHS says to skip surgical masks too. Utah DHHS
- What doesn't protect. Cloth masks won't protect you from smoke, and EPA says not to rely on dust masks or bandanas either. AirNow EPA A wet towel might catch big particles, but the fine ones that get deep into the lungs pass through. Utah DHHS
- Not for gases. Masks don't filter the gases in smoke. Utah DHHS Ozone is a gas, and EPA's and Utah's advice for high-ozone days is about timing and effort, not masks. EPA Utah DHHS
- Know the trade-offs. A respirator can make breathing harder, and in heat or during exercise it raises the risk of heat illness. If you feel dizzy or short of breath, move to cleaner air and take it off. Get medical care if the symptoms are severe or don't get better. EPA
Children. EPA says children 2 and older can wear respirators, but NIOSH-approved respirators aren't made in sizes for young children. Pick one that covers the nose and chin, doesn't block vision and stays comfortable, and watch your child while it's on. EPA Some older children may be able to wear an adult small, and children under 2 should not wear a respirator. EPA Ask your child's clinician what makes sense for your family.
Heart or lung disease, or pregnancy. Ask your doctor before you use a respirator. EPA
- Utah DHHS: Protect your health from wildfire smokehttps://appletree.utah.gov/wp-content/uploads/Wildfire-smoke-and-health-FAQ-1.pdf
- Protege tu salud del humo de los incendios forestales (Spanish)https://appletree.utah.gov/wp-content/uploads/Espanol-Wildfire-smoke-and-health-FAQ.pdf
Timing, cars and pets
Ozone: go early or late
Ozone is worst in the afternoon and early evening, so EPA says to plan outdoor activity for the morning. EPA
Utah's ozone-season advice (May through September) is more specific: the best time for outdoor exercise is before noon or after 6 pm. Between noon and 6, consider lighter activity, such as walking instead of running, or an indoor workout. Utah DHHS
With the windows closed, indoor ozone should be much lower. EPA
Particles and smoke: check the hour
Particle pollution can be high at any time of day. EPA In winter, the Utah Division of Air Quality (DAQ) notes, it builds until a storm or weather system clears the valley. Utah DAQ
Even on a bad forecast day, some hours may be fine for being outside, so check current readings first. EPA Today on the home page has them. When you go, stay away from busy roads. EPA
In the car
On smoky days, close the windows and vents and run the air conditioning on recirculate. Utah DEQ Slow down when smoke cuts visibility. EPA
Pets
If smoke bothers you, it probably bothers your pets. Keep them inside as much as you can while staying cool, keep bathroom breaks short, and skip the run. Keep a closer eye on pets that are older, very young or pregnant, or that have heart or lung disease. Short-nosed dogs like pugs and bulldogs, and pet birds, need extra care too. EPA
Call your veterinarian for trouble breathing, red or watery eyes, a runny nose, unusual tiredness, weakness or stumbling. EPA
Kids, schools and coaches
Utah's recess guidance for elementary schools was last updated in July 2016. It covers PM2.5 only, works from the current reading on air.utah.gov, and is built for a 20- to 30-minute recess, which is why it differs from EPA's adult, 24-hour advice. Utah DHHS Utah DHHS PDF
| PM2.5 now | Recess | Same edges as |
|---|---|---|
| PM2.5 nowUp to 35.4 | RecessAll students go outside. | Same edges asGood and Moderate |
| PM2.5 now35.5–55.4 | RecessStudents with breathing symptoms and sensitive students stay in. | Same edges asUnhealthy for Sensitive Groups |
| PM2.5 now55.5 and up | RecessAll students stay in. | Same edges asUnhealthy and above |
Recess levels from Utah's guidance. Utah DHHS Its 35.5 and 55.5 cut points still match the edges of EPA's PM2.5 categories as of May 2026. EPA EPA's categories are for 24-hour averages, though, so only the numbers line up, not the time span.
"Sensitive" here can include asthma, cystic fibrosis, chronic lung disease, congenital heart disease, a weakened immune system and other breathing problems. Parents, with their clinician's advice, should tell the school if their child is in that group. The school makes the final call. Utah DHHS
- Recess Guidance for Schools (English, PDF)https://asthma.utah.gov/wp-content/uploads/recessguidance.pdf
- Guía del Receso para las Escuelas (Spanish, PDF)https://asthma.utah.gov/wp-content/uploads/RGSpanish.pdf
For ozone, and for longer activities such as practices and games, EPA's school guidance fills the gap. At Unhealthy for Sensitive Groups, recess and PE are fine, but longer sessions need more breaks and less intensity. At Unhealthy, every activity gets more breaks, and longer or harder ones may move indoors or to another time. At Very Unhealthy, move everything inside or reschedule. EPA
- Cut the hard breathing, not the practice. Rotate players often and swap running for walking. On ozone days, practice in the morning. EPA
- Mind the pickup line. Keep active play away from idling cars and buses and from busy roads, especially at rush hour. EPA
SmokeReadyUtah, a project of DAQ and partners including Utah DHHS and the University of Utah, says it will supply air cleaners and filters to public schools and preschools in smoke-affected communities. Households in eligible zip codes can also request one of its free air cleaners while the limited supply lasts. As of October 2026, the project runs through March 2027. Utah DEQ
When to get care
Ahead of smoke season, talk with your health care provider if you have heart or lung disease. If you have asthma, have an asthma action plan. EPA
Slow down, then call your clinician
A cough or shortness of breath is a signal to take it easier or go inside. EPA
With heart disease, palpitations, shortness of breath or unusual tiredness may signal something serious. Call your health care provider. EPA
If smoke makes you feel sick, cut your exposure and contact your provider. EPA Ozone symptoms can show up right away or a day or more later. Utah DHHS
Call 911
During an asthma attack, if your medicines aren't relieving your symptoms or breathing is still very hard. NHLBI
For a young child with asthma who seems drowsy, confused or troubled, has a bluish tint to the skin and lips, or has a fast heartbeat. NHLBI
For possible heart attack signs, such as chest pain, heaviness or discomfort, pain in an arm, the back, neck or jaw, or shortness of breath at rest or with light activity. Call even if you're not sure, and let an ambulance take you rather than driving. NHLBI
For stroke signs: one side of the face droops, one arm drifts down, or speech is slurred or strange. NHLBI
For the household side, including furnace filters, a bedroom air cleaner and an action plan for inversion season, see our sister site.
- Prepare Utah: Winter inversions and air qualityhttps://prepareutah.com/hazards/air.html
Checked October 24, 2026.