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ED visits for asthma increase in New York City during Canadian wildfires

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  • Poor air quality peaked in New York City on June 7 with excess PM2.5 levels reaching 146.1 µg/m3.
  • Daily ED visits for asthma also peaked on June 7 at 335, compared with an average of 188.

Canadian wildfire smoke led to a slight increase in ED visits for asthma in New York City in June compared with days with high pollen counts, according to a study published in the American Journal of Respiratory and Critical Care Medicine.

However, other potential effects on health such as heart attacks and stroke due to the smoke still need investigation, George Thurston, ScD, professor, departments of medicine and population health, NYU Langone, and colleagues wrote.

New York City during the Canadian wildfires

When smoke from Canadian wildfires blew into New York City in June, ED visits for asthma increased by 10% compared with days that had high pollen counts. Image: Adobe Stock

The researchers conducted the study due to the “widespread public concerns over possible adverse health effects from breathing the wildfire pollution,” Thurston told Healio.

Particulate matter pollution at the 2.5 µg/m3 scale (PM2.5) counts peaked in New York City on June 7, greatly exceeding daily ambient air quality standards in the United States, the researchers said.

George Thurston

Using data from the NYC Department of Health, the researchers tallied ED visits for asthma and other respiratory causes for the first 6 months of 2023. The 335 visits for asthma on June 7 was 10% higher than the 302 visits on April 6, which was considered a day with high pollen counts.

When the skies were clear of wildfire smoke earlier in the year, the researchers said, the daily average for asthma visits was 188.

The researchers also collected data for PM2.5 for the first 6 months of 2023 from monitoring stations in north Manhattan, the Bronx, and north and south Brooklyn and computed composite citywide daily averages.

Specifically, data from Jan. 1 through June 4 indicated expected background levels of PM2.5 pollution. By subtracting background PM2.5 from monitored PM2.5, the researchers estimated excess PM2.5 due to wildfire smoke, which reached 146.1 µg/m3 on June 7.

From June 6 to June 9, the researchers said, PM2.5 from the wildfires was associated with visits to the ED for asthma (incidence rate ratio [IRR] = 1.03; 95% CI, 1.02-1.04) but background PM2.5 was not (IRR = 1.01; 95% CI, 0.97-1.05) per 10 µg/m3 increment.

The researchers also said they found an association between daily pollen counts per cubic meter (PCM) and ED visits for asthma (IRR = 1.02; 95% CI, 1.01-1.04), but these pollen counts were uncorrelated with PM2.5, and they did not change the estimated effect of wildfire PM2.5.

Adults aged 18 to 64 years experienced more pronounced effects on their asthma from the wildfire PM2.5 compared with adults aged 65 years and older and with children and adolescents younger than age 18 years.

ED visits due to other respiratory issues were associated with same-day ambient background PM2.5 (IRR = 1.03; 95% CI, 1.01-1.05) but not with wildfire PM2.5 (IRR = 1; 95% CI, 0.99-1.01) per 10 µg/m3 increment.

“Given the ominous appearance of the wildfire pollution, it was somewhat surprising that the increase in asthma and COPD emergency room visits were only slightly more than occurred early this year in New York City on a high pollen day in April,” Thurston said.

Using a distributed lag model, the researchers additionally found that wildfire PM2.5 had no impact on asthma beyond same-day effects.

Although the researchers called the impact of wildfire PM2.5 on asthma ED visits significant, they noted that it was lower per µg/m3 than previous studies on wildfire PM2.5. The effect of PM2.5 on asthma per unit mass indicated in this study was similar to previous studies of non-wildfire ambient PM2.5 mass as well, the researchers continued.

Between June 7 and June 8, the researchers also collected a sample of PM2.5 at their lab on 25th Street in Manhattan and compared it with annual average PM2.5 trace element data from 2019 obtained from the EPA Chemical Speciation Network.

The wildfire PM2.5 had much lower percentages of oxidative stress-inducing metals, the researchers said. For example, the wildfire copper per µg was 12% of usual PM2.5 content in New York City, and the wildfire sulfur was only 26% of the usual PM2.5 content.

“It is significant that the samples of the wildfire particle pollution that we collected and then analyzed indicated the pollution’s particles had relatively low enrichments in many of the most toxic constituents usually found in New York City air pollution, like transition metals and sulfur,” Thurston said.

“This could explain the moderate health impacts found to date for such high PM2.5 exposures, recorded to be more than 10 times typical NYC concentrations of fine particulate mass,” he continued.

Potassium, which the researchers said usually is enriched in biomass combustion particles, was 64% higher per unit mass in the wildfire PM2.5 than in usual PM2.5 content. The wildfire plume also had significant entrained soil PM2.5, with higher percentages of silicon and calcium compared with usual PM2.5 content as well.

Based on these findings, the researchers called the increase in same-day asthma ED visits associated with wildfire PM2.5 statistically significant. The researchers attributed this association potentially to allergenic material also present in the smoke, lung irritation and inflammation from the particulate matter, or a combination of these factors.

The lack of an association between wildfire PM2.5 and other respiratory visits may indicate the dominant role of allergic reactions in these visits, which the researchers called an opposite situation compared with usual PM2.5 in New York City.

However, the researchers cautioned that unmeasured factors such as avoided exposure to PM2.5 due to air quality warnings and other components in the particulate matter such as secondary organic aerosol may have modified these overall effects.

The researchers also speculated that the limited transition metal content of the wildfire PM2.5 reduced its oxidative potential and may indicate a diminished association with impacts on cardiovascular health compared with usual PM2.5 content in New York City, although they advised that these and other health outcomes still need to be evaluated.

Meanwhile, these findings provide a scientific basis for physicians who want to advise their asthma and COPD patients to take care to avoid exposure, just as they would when there is a high pollen day, Thurston said.

The researchers also plan on continuing their studies.

“We plan to obtain more daily New York City health outcome data for the wildfire period, such as daily respiratory and cardiac hospital admission counts, cardiovascular ED visit counts, and daily by-cause mortality counts once they are available,” Thurston said.

“This will allow us to more extensively assess the range of health effects by the wildfire pollution event in June 2023,” he said.


For more information:

George Thurston, ScD, can be reached at

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Albert Rizzo, MD, FACP)

Albert Rizzo, MD, FACP

These findings are significant, but not surprising. Although PM2.5 is measured by cubic meter and levels may be similar on different days, the actual makeup of the particles can vary based on what the cause or source of the PM is — wildfire, mainly organic material vs. urban fossil fuel sources such as cars or trucks, mainly containing other metals and toxins different from wildfires.

This means the effect on the body can vary a bit. The bottom line is that any level of PM2.5 is small enough to enter deep into the lungs and cause airway inflammation, triggering cough, wheezing and flares in asthma and COPD. PM2.5 also often carries with it smaller, ultrafine particles 0.1 µg in size that can even get into the body’s circulation and may be a key factor in other health consequences outside of the lung such as cardiovascular events.

Other factors such as humidity, prevailing winds and heat may play a role in altering or determining the makeup of the PM2.5 particles as well. Also, the time of the year will play a role, as PM2.5 during pollen season may represent more allergens and trigger more allergic-type symptoms.

Patients, especially those with chronic lung conditions such as asthma or COPD, should get in the habit of assessing daily air quality by checking such sites as This information can help them plan their day regarding the need to be outdoors vs. trying to stay inside. Bad outside air should be kept out by closing doors and windows and using the recirculation setting of indoor air on air conditioner units and employing HEPA filters if possible.

If patients do need to go outdoors, they should consider wearing masks, specifically the N95 type, which can filter out the PM2.5. Standard cloth, bandana or surgical masks will not be as effective.

These patients should also keep their asthma or COPD action plans up-to-date with instructions from their health care provider on what to do if symptoms start to flare and should be sure they have adequate medications available, especially rescue-type inhalers. Having a level of good, ongoing communication with their health care provider is key, especially during these circumstances.

But because the social determinants of health are not equitable in our society, not all individuals at risk will have the ability to stay out of the bad outdoor air during these times, and not all will be able to use air conditioners or HEPA filters.

Just as facilities are made available during severe cold spells during the winter, communities should be able to provide safe zones for severe heat days and severe air quality days. Also, hospital EDs and urgent care centers should be able to ramp up staffing when they know these bad air quality days are ahead or occurring to help prevent long, potentially life-altering wait times for patients to be seen as well as prevent burnout of physicians overwhelmed by the number of patients seeking help.

Albert Rizzo, MD, FACP

Chief Medical Officer for the American Lung Association

Disclosures: Rizzo reports no relevant financial disclosures.


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