Smoke changes over time and distance, but health risks remain

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A study of air quality in New York City while it was heavily affected by Canadian wildfire smoke revealed that multi-day transport to the New York region significantly transformed the smoke, but serious health risks remained. The results are published in Environmental Science and Technology Letters.

One key takeaway of the study, led by Prof. Drew Gentner, is how critical it is to fully understand the full extent of wildfire smoke's effects not just on immediate communities, but on those far downwind from the fires. This is especially true as wildfires will likely continue to increase due to climate change. The study further demonstrates that the chemical reactions of the smoke may actually amplify some of the smoke's health risks.

For the study, the researchers used the Aerosol Chemical Speciation Network (ASCENT), a recently deployed system of instrumentation that was installed in 12 U.S. locations. Specifically, they used the ASCENT site in Queens, New York, which Gentner's team installed and maintains. As part of a project, they are analyzing air quality in New York City since summer 2022, including from June 6 to June 9, 2023 during the peak of the large Quebec wildfire's effects on New York City.

"With this ASCENT instrumentation, we can now consistently capture changes in air quality using advanced techniques that we wouldn't have previously had with routine measurements," Gentner said. "So when the big Quebec wildfire transport events happened, we were able to monitor it in real-time across several advanced instruments with chemical detail that would not have been typically available."

One of the insights they were able to glean with this technology was just how much the smoke, which contained particulate matter, transformed chemically after traveling hundreds to thousands of miles over several days.

"Because of particulate matters' major health risks, we were really interested to connect our observations during these wildfire smoke episodes with public health research," Gentner said. Gentner's lab teamed up with Prof. Michelle Bell at the School of the Environment, who conducted a chemically-specific epidemiological analysis in May and June of last year. The analysis specifically looked at asthma-related emergency department visits, which showed a significant increase associated with the sum of wildfire-related particulate matter during the study period.

In the case of several smoke episodes during this time, the researchers saw that the chemical makeup had been oxidized so much over the period that it no longer resembled typical wildfire smoke or any kind of biomass burning. Because of this transformation, previous studies have misidentified low-level wildfire smoke as other forms of air pollution, and underestimated the role of wildfire smoke in contributing to the amount of particulate matter in the air.

One of the instruments they used at the Queens site can measure trace elements in the smoke, including potassium, which is abundant in biomass burning emissions and is not changed by photochemical oxidation. That proved particularly helpful in identifying the chemical makeup as wildfire smoke.

"We hope this work demonstrates the utility of using potassium to identify, validate, and quantify the influence of biomass burning emissions on air quality," said Mitchell Rogers, a Yale graduate student and a co-author of the study.

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Gentner noted that the level of detail they were able to get from the instrumentation clearly showed that the air was affected by smaller wildfire smoke episodes in addition to the one from Quebec. This expands the capabilities to readily detect and quantify the effects of smaller smoke episodes that would not be immediately obvious from routine data.

The findings are all the more significant, Gentner said, since a number of studies indicate that wildfires will increase due to climate change. So, it's important to understand how far-ranging the air quality and health effects of these wildfires can be.

"Understanding the extent of their influence on downwind populations, and how the health risks of particulate matter change with downwind transport is really important," he said, "which is one of the things that we were interested to investigate with this multidisciplinary research."

More information: Taekyu Joo et al, Aged and Obscured Wildfire Smoke Associated with Downwind Health Risks, Environmental Science & Technology Letters (2024). DOI: 10.1021/acs.estlett.4c00785

Journal information: Environmental Science & Technology Letters

Provided by Yale University