Key takeaways
- During the June 6–8, 2023, smoke wave, fine-particle pollution in New York City averaged about 11 times its usual level, by our math, and the city’s emergency rooms saw about 261 asthma visits a day instead of about 1821.
- In the rest of New York State, asthma emergency visits rose 82% on June 7, the worst day, and nearly tripled among people ages 10 to 2923.
- In EPA chamber tests, a box fan fitted with four MERV 13 filters and a cardboard shroud delivered about 3.6 times as much clean air as a fan with one filter, by our math7.
- A 2024 Stanford model linked nitrogen dioxide from gas and propane stoves to about 50,000 current cases of childhood asthma, an estimate the gas utilities’ trade group calls misleading89.
- California has capped ozone from indoor air cleaners since 2010, and EPA says no federal agency has approved ozone generators for rooms where people are1314.
In early June 2023, smoke from Canadian wildfires drifted south and settled over New York City. For three days, from June 6 to 8, the city breathed it1.
Fine particles in the city’s air averaged about 101 micrograms per cubic meter, compared with about 9 in comparison periods1. That’s roughly 11 times the usual level, by our math.
Asthma visits to the city’s emergency rooms climbed to about 261 a day, up from about 182, a team led by Kai Chen of the Yale School of Public Health reported in JAMA1. That’s about 79 extra visits a day, by our math.
Outside the city, asthma emergency visits jumped 82% on June 723. Nationally, CDC researchers found these visits ran 17% above normal on 19 smoke days between late April and early August 20234.
You can’t choose the air outside. You can choose when to go out, what you breathe indoors, and which “air-cleaning” gadgets to skip.
Smoke sent older kids and young adults to the ER in surprising numbers
The state report, published by CDC in August 2023, tracked asthma emergency visits across New York outside the city2. On an average day in early June, there were about 81. On June 7, there were 1472.
The biggest jump came in people ages 10 to 29, whose visits rose from about 17 a day to 502. Adults 50 to 69 rose 89%, and adults 70 and older about 77%2. Children under 10 were the exception: their visits dipped slightly2.
In the city study, adults ages 18 to 64 were the most likely to go to the ER1. Smoke isn’t only a worry for toddlers and the very old.
Federal air officials list children, older adults and anyone living with heart or lung disease as most sensitive to particle pollution5. For ozone, another pollutant the index tracks, the list includes people with lung disease such as asthma and anyone, young or old, who is active outdoors5. New York’s health department adds pregnant people to its at-risk list3.
The report’s authors noted that children and Black New Yorkers bear more than their share of asthma attacks, and urged doctors to warn asthma patients before smoke arrives2. They also flagged limits, including one air monitor per region2.
The Air Quality Index is a breathing forecast in six colors
The Air Quality Index, or AQI, turns pollution readings into one number from 0 to 5005. Higher means dirtier air. A reading of 101 means the air has crossed a national health standard5.
You’ll find it on AirNow.gov and in many weather apps. AirNow turns hourly monitor readings into a near-real-time figure called the NowCast6. So the morning forecast and the afternoon reading can differ. Check both before outdoor work or exercise.
Here is how the colors line up with the advice New York’s health department gave during the 2023 smoke35.
| AQI | Color and label | What New York’s health department advised |
|---|---|---|
| 0–50 | Green, Good | No smoke precautions listed |
| 51–100 | Yellow, Moderate | No smoke precautions listed |
| 101–150 | Orange, Unhealthy for Sensitive Groups | People at higher risk should avoid outdoor exertion |
| 151–200 | Red, Unhealthy | Everyone should skip strenuous exercise outside; higher-risk people should stay in |
| 201–300 | Purple, Very Unhealthy | Higher-risk people should skip any outdoor exercise; others should skip long or hard effort |
| 301–500 | Maroon, Hazardous | Everyone should skip exercise and exertion outdoors |
The particle scale got stricter on May 6, 2024, when EPA tightened several of the cutoffs between colors6. EPA said the change reflects newer health science, not dirtier air, and that some wildfire days may now land in a higher category6. The new cutoff between Good and Moderate is tied to the 2024 annual particle standard6, and our article on that standard explains the numbers.
That standard is now in legal limbo. In November 2025, EPA asked a federal appeals court to throw it out. The court refused and upheld the standard in June 2026, and in October 2026 the federal government asked the Supreme Court to review it15. If the standard changes, the AQI cutoffs tied to it could change too, so read the colors on AirNow rather than memorizing numbers.
On smoke days, filtered indoor air is your best refuge
When smoke rolls in, the advice flips. Outdoor air becomes the problem, and filtered indoor air becomes the fix.
During the 2023 smoke, New York’s health department told people to stay inside more and run the air conditioner on hot days3. It advised setting central fans to “on” instead of “auto,” so air keeps passing through the filter3. Outdoors, it recommended a well-fitting N95 or KN95 mask3.
EPA suggests a furnace filter rated MERV 13, or the highest your system can handle, changed every 60 to 90 days13. MERV rates how well a filter catches particles.
A portable air cleaner adds a second layer. Size it by its clean air delivery rate, or CADR. EPA’s chart suggests at least 130 for a 200-square-foot room and 195 for 300 square feet, with 8-foot ceilings13. For smoke, use the tobacco-smoke CADR, which reflects the smallest particles13.
One caution: commercial CADR ratings are usually tested with tobacco smoke, pollen and dust, not wildfire smoke7. And one verification program California lists for shoppers is run by the Association of Home Appliance Manufacturers, which, as the name says, speaks for the makers themselves14.
A box fan can do surprising work. EPA researchers smoldered pine needles in a room-sized chamber in North Carolina and tested homemade air cleaners against the smoke7. Here is each design’s clean air delivery rate for smoke7:
- A box fan with one MERV 13 filter: 111
- Adding a cardboard shroud around the fan: 156, a 40% gain
- Two filters with a shroud: 263
- Four filters with a shroud, a design called the Corsi-Rosenthal box: 401
The shrouded multi-filter designs removed particles better than a commercial air cleaner that cost more7. But a dirty filter left a homemade cleaner almost useless, so check filters daily during smoke and swap them when they look dark or smell smoky7.
Use fans safely. In testing for EPA, Underwriters Laboratories saw no fires, but internal parts heated up by nearly 60°C with a dusty filter7. EPA advises a fan made in 2012 or later with a UL or ETL safety mark, no extension cord, and never leaving an older fan running unattended or while you sleep7. Real-world data on homemade units are limited7.
If your home gets too hot to keep closed, EPA says to find a cooler place7. Our smoky-day and bedroom-air articles explain how to set up a clean room.
A gas burner makes its own pollution, and the science is contested
Smoke days are rare. Cooking happens every day.
More than 40 million U.S. homes cook with gas or propane9. Burning that fuel releases nitrogen dioxide, or NO2. Electric stoves release none8.
In 2024, a Stanford team led by Yannai Kashtan and Rob Jackson measured NO2 in more than 100 homes and built a national model8. Average stove use added about 4 parts per billion of NO2 to a person’s exposure over a year89. The World Health Organization’s annual guideline is about 5.3 parts per billion, for indoor and outdoor air combined9.
Some findings stood out:
- Bedrooms weren’t spared. Less than an hour after the burners came on, NO2 there could cross health benchmarks, and it lingered for hours8.
- A big house and an outdoor-vented hood didn’t guarantee safety. Levels still spiked into unhealthy territory during and after cooking8.
- Homes under 800 square feet had four times the long-term exposure of homes over 3,000 square feet89.
- American Indian and Alaska Native households had 60% more exposure than average, and Black and Hispanic households 20% more89.
The team’s models linked NO2 from stoves to about 50,000 current cases of childhood asthma, and the stoves’ full pollutant mix to as many as four times that number89. They also suggested stove NO2 might contribute to as many as 19,000 deaths a year8.
Those are model estimates, not counted cases. The work was funded by HT, LLC, a company the release doesn’t describe8.
An earlier 2022 paper estimated that 12.7% of U.S. childhood asthma, roughly 650,000 children, could be traced to gas stoves10. One co-author works on carbon-free buildings at RMI, and the authors said their assumptions could push the estimate too high or too low10.
The gas industry pushes back hard. The American Gas Association, a trade group for companies that deliver natural gas9, called the 2022 paper a “headline-grabbing approach”10. Its chief executive, Karen Harbert, called the Stanford conclusions “misleading and unsupported”9.
The group pointed to a review that found only a small rise in childhood asthma with gas cooking, one that wasn’t statistically significant9. NBC News noted that the same review found a significant rise in pneumonia and chronic lung disease with gas compared with electric cooking9.
The fair reading: a gas flame measurably raises NO2 indoors, while the number of asthma cases it causes is still argued. Either way, you can cut your exposure. Run a range hood that vents outside, open a window or use a fan while you cook, and never heat your home with a gas oven811. An electric stove makes no NO28.
Candles, incense and radon deserve a look, too
Most people spend more than 90% of their time indoors, EPA notes, so indoor sources matter12.
Pediatric environmental health specialists at the University of California, San Francisco, advise against burning anything indoors, including incense, candles and wood, and against air fresheners11. EPA lists scented candles among household sources of volatile organic compounds, gases released into indoor air12. Our article on household flames covers what each one gives off.
Radon is a radioactive gas that seeps into homes from the soil, and you can’t see or smell it. EPA calls it the second leading cause of lung cancer after smoking, and inexpensive kits can test for it12. Our radon article explains testing and fixes.
Portable purifiers help a little, but ozone machines can hurt
EPA’s guide to home air cleaners puts them third in line. The most effective steps are cutting pollution at the source and bringing in clean outdoor air; filtration supplements both13.
EPA describes studies of portable HEPA units, which use high-efficiency filters, as showing small gains in heart and lung measures, often too small for people to notice13. In allergy and asthma studies, people improved on one or more symptoms, but not across the board13. A purifier earns its keep on smoke days, not as a treatment.
Some devices add a pollutant. Ozone generators make ozone on purpose, and no federal agency has approved them for rooms where people are, EPA says13. Ionizers and some ultraviolet and plasma units may also give off ozone13.
California sets its own limit. Since 2010, every indoor air cleaner sold in or shipped to the state must emit less than 0.050 parts per million of ozone and carry a certification label14. The state’s air board strongly advises against ozone generators and uncertified cleaners in homes14. It also found harmful ozone from some refrigerator air purifiers and sanitizing wands14.
Ozone works fast. Within a few hours it can irritate the lining of your airways, and you may cough, feel your chest tighten or get short of breath14. Mixed with terpenes, the chemicals behind many fragrances, it can produce formaldehyde14. It also numbs your sense of smell, so your nose is a poor alarm14.
Watch for sales terms like “activated oxygen,” “energized oxygen” and “super-oxygenated air”14. Houseplants, another popular fix, are covered in our bedroom-air article; they are a pleasure, not an air-cleaning plan.
Your clean-air action plan
Use this plan to match the day to the step. The ratings use our four-level scale.
| Situation | What to do | Evidence behind it |
|---|---|---|
| AQI orange and you’re in a higher-risk group | Skip outdoor exertion; recheck the AQI later in the day36 | that smoke days raise asthma emergencies124; the advice itself is agency guidance |
| AQI red or worse | Everyone cuts hard outdoor activity; higher-risk people stay in; wear a well-fitting N95 or KN95 if you must go out3 | of harm from smoke; mask advice is agency guidance |
| Smoke is getting indoors | Close up, set the system fan to “on,” use MERV 13 and run a sized purifier or a watched box-fan filter3713 | that filtration cuts indoor particles in tests7; for symptom relief13 |
| Cooking on gas | Vent the hood outdoors, open a window or run a fan; never heat the home with the oven811 | that burners raise NO28; , and disputed, for asthma effects8910 |
| Shopping for an air cleaner | Choose a filter-based unit with a CARB certified label; skip “activated oxygen” claims1314 | for ozone generators1314 |
| Any home, once | Test for radon; skip candles and incense indoors1112 | Agency guidance; radon is a leading cause of lung cancer12 |
What the evidence shows
| Claim | Evidence level | What it rests on |
|---|---|---|
| Wildfire smoke days send more people with asthma to the ER | City, state and national counts from 2023 agree124 | |
| HEPA and MERV 13 filtration lowers indoor smoke particles | EPA chamber tests and long-standing EPA guidance713 | |
| Homemade box-fan filters work in real homes | Strong chamber results, little real-world data7 | |
| Portable purifiers ease asthma or allergy symptoms | Small, mixed gains in studies EPA reviewed13 | |
| Gas-stove pollution adds to childhood asthma | NO2 rises are measured; asthma counts come from models, and a review the industry cites found only a small, nonsignificant rise8910 | |
| Ozone generators safely clean the air | Ozone irritates airways; no federal approval for occupied rooms1314 |
Fresh air is an old remedy, and smoke days rewrite the rules
Many natural-health traditions prize fresh air: open windows, time outdoors, a walk to clear your head. That instinct holds up most days. EPA’s air cleaner guide still ranks clean outdoor air among the two best tools you have13.
Smoke days are the exception. Then the natural move is to treat outdoor air like any exposure you’d limit. Wanting fewer pollutants in your body is a reasonable goal, and the steps that reach it remove the source or filter the air.
When to get help. New York’s health department advised anyone with symptoms during smoke events to contact a health care provider3. If you have asthma, the CDC report’s authors urged doctors to talk with patients before smoke arrives, so ask now about your plan for smoke days2. Our upcoming article on serious respiratory symptoms covers when breathing trouble is an emergency.
Questions readers ask
Is a cloth or surgical mask enough on a smoke day?
New York’s health department recommended a well-fitting N95 or KN95 for outdoor time during the 2023 smoke3. Staying indoors in filtered air remains the bigger step37.
Should I open my windows to air out the house?
On clean-air days, yes. EPA counts ventilation with clean outdoor air among the most effective steps13. When the AQI is high, keep windows shut, as UCSF’s pediatric specialists advise11.
Do I have to replace my gas stove?
That’s your call. Gas burners do raise indoor NO2, and venting and fans help, though spikes can persist even with a vented hood8. If you’re replacing a stove anyway, electric models make no NO28.
My purifier has an ionizer setting. Is that a problem?
It can be. EPA says ionizers may give off ozone13. Check whether your model carries a CARB certified label, which caps ozone output14.
The bottom line
The 2023 smoke showed how fast dirty air reaches people’s lungs, with asthma emergencies climbing in New York and around the country. The AQI’s six colors give you warning, and filtered indoor air gives you shelter.
Indoors, vent your stove, skip indoor flames, test for radon, size filters to the room and leave ozone machines in the store. Clean air comes from removing pollution, not from a product that claims to purify it.
Keep exploring: detox immune boost.
Related reading
About this article
This article was researched using CDC, EPA and California Air Resources Board documents, state health department data, university research summaries and news reports on peer-reviewed studies, all listed below. It was reviewed in October 2026 and is general education, not medical, legal or financial advice..
Sources
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- Meek HC, Aydin-Ghormoz H, Bush K, et al. “Asthma-Associated Emergency Department Visits During a Wildfire Smoke Event — New York, June 2023.” Morbidity and Mortality Weekly Report, 2023;72(34):933–935. cdc.gov
- New York State Department of Health. “New York State Department of Health Publishes Study on Asthma-Related Emergency Visits During June Wildfire Smoke Event.” Press release, August 24, 2023. healthweb-back.health.ny.gov
- WHYY. “Canadian Wildfires Led to Spike in Asthma ER Visits, Especially in the Northeast” (on CDC MMWR national analysis). August 25, 2023. whyy.org
- AirNow (EPA and partner agencies). “Air Quality 101.” AirNow API documentation, accessed October 2026. docs.airnowapi.org
- U.S. Environmental Protection Agency. “Final Updates to the Air Quality Index (AQI) for Particulate Matter: Fact Sheet.” EPA, February 2024. epa.gov
- U.S. Environmental Protection Agency. “Research on DIY Air Cleaners to Reduce Wildfire Smoke Indoors.” EPA, published August 19, 2021, updated July 6, 2026. epa.gov
- Stanford University news release (via ScienceDaily) on Kashtan Y, Jackson RB, et al., “Nitrogen Dioxide Exposure, Health Outcomes, and Associated Demographic Disparities Due to Gas and Propane Combustion by U.S. Stoves,” Science Advances, 2024;10(18). May 3, 2024. sciencedaily.com
- NBC News. “Gas and Propane Stoves Linked to 50,000 Cases of Childhood Asthma, Study Finds.” May 2024. nbcnews.com
- Popular Science. “Gas Stoves Could Be Making Thousands of Children in America Sick” (on Gruenwald T, et al., International Journal of Environmental Research and Public Health, 2022/2023). January 2023. popsci.com
- UCSF Western States Pediatric Environmental Health Specialty Unit. “Prescriptions for Prevention: Indoor Air.” University of California, San Francisco, 2026. wspehsu.ucsf.edu
- U.S. Environmental Protection Agency, Region 9. “A Healthy Home & More Environmentally-Friendly, Too!” EPA-908-K-10-001, January 2012. epa.gov
- U.S. Environmental Protection Agency. “Guide to Air Cleaners in the Home,” 2nd edition. EPA, 2018. epa.gov
- California Air Resources Board. “California’s Regulation to Limit Ozone Emissions from Indoor Air Cleaning Devices” (fact sheet) and “Air Cleaner Information for Consumers.” CARB, both accessed October 2026. ww2.arb.ca.gov and ww2.arb.ca.gov
- U.S. Environmental Protection Agency. “EPA Notifies States of Potential Designations for the Biden EPA’s Flawed 2024 Air Quality Standard Following Appealed Court Order.” News release, October 2, 2026, updated October 22, 2026; and Vargas G. “PM2.5 NAAQS Quick Take.” Harvard Law School Environmental & Energy Law Program, July 8, 2026. epa.gov and eelp.law.harvard.edu