When residents of Centre County, Pennsylvania, opened their doors and windows in June 2023, they were greeted by the faint smell of woodsmoke and a haziness in the air.
In what may have been a first for many, they were experiencing smoke from massive Canadian wildfires burning hundreds of miles to the north.
Skies turned orange in cities like Philadelphia and officials in Pennsylvania ordered a Code Red, meaning air pollution concentrations reached unhealthy levels for the general public for outdoor activities.
Under the changing climate, these massive Canadian wildfires sending smoke long distances to the Eastern United States may become the norm, said Manzhu Yu, assistant professor of geography.
Yu is working on ways to better model pollution from smoke, potentially helping public health officials in urban and rural areas better warn high risk populations when air quality is especially harmful.
Her latest work examines the impact of wildfire smoke combined with other air pollution that already negatively affects air quality – like ozone pollution.
“As climate change continues to cause ecological changes and challenges, it is likely that wildfire activities will continue to rise,” Yu said. “Because of this, it is an urgent research priority to accurately predict air pollutant concentrations induced by wildfire smoke, especially in wildfire-prone areas.”
A perfect storm
It rained for days in Western North Carolina, and streams and rivers were already high just as Hurricane Helene was preparing to make landfall in Florida. Then the hurricane dropped another foot of rain on the already saturated ground and brought unprecedented devastation to the state, leading to more than 100 deaths and billions of dollars in damage.
This was an example of a co-occurring or compound weather event. When multiple weather or climate hazards happen simultaneously, their combined impact is greater than the sum of the individual effects.
“Recently, I’ve been studying co-occurring weather because with the changing climate that’s what we are often seeing right now,” Yu said. “It’s not just the intensification of one type of extreme weather event. It’s the compounding of them. For hurricanes, it might be storm surge and heavy precipitation creating coastal flooding. For wildfires, it can be compounded with drought, creating ideal conditions for a severe blaze.”
Yu’s latest research focuses on compounding impacts of air pollution from wildfire smoke and from ozone pollution, a type of air pollution formed primarily from photochemical reactions between two major classes of air pollutants, volatile organic compounds and nitrogen oxides.
Smoke and other sources of air pollution contain tiny particles, called fine particulate matter (PM 2.5). These tiny particles can reach the lungs and trigger respiratory health issues like asthma, especially for people with pre-existing heart and lung conditions.
Since ozone pollution can trigger asthma, it is important to study both and not just one source of air pollution, Yu said.
“What if fire-induced PM 2.5 and ozone are both peaking in his particular area after one of these wildfire smoke events,” Yu asked. “Then the coexistence becomes very hard for people to cope with because they’re used to one of them being very high but the other being very low.”
Yu is analyzing a health outcome dataset from the Hershey region from the time of the wildfire smoke intrusion in June 2023 to study whether peaks in both types of air pollution triggered more reports of child asthma.
“PM 2.5 and ozone both have potential to trigger asthma, and we want to see if this is making a difference in health outcomes,” she said. “One part that I think is lacking in this research area is underling health outcomes. It is actually the end point of our research studying air pollution—it is always connected to people’s health.”
Using models to improve warnings
Yu and her team developed a model that combines wildfire smoke forecasts and data from ground-based sensors to improve smoke forecasts.
The team found that the refined forecasting model better estimated the magnitude and timing of PM 2.5 spikes and that urban and rural communities already burdened by existing environmental pollution face higher air pollution levels during unexpected smoke events than other areas.
They also used anonymized mobility data from devices like smartphones to see how people changed their travel activities during the smoke events. Their findings suggest that their model can help decision makers find ways to better warn people who may be at high risk to stay home when air quality reaches dangerous levels.
“The good news, according to our findings, is that when people hear about wildfire smoke, they tend to reduce their mobility,” Yu said. “But we found that during these smoke events, cities like New York City and Philadelphia and the surrounding counties still showed high mobility activities. We probably need to think about targeted interventions in urban areas because with so many people living in the area, exposure rates to unhealthy air are very high.”
Yu said future work may involve wildfires in South America that are having a large impact on the Global South.
Massive fires have burned in the Amazon Basin, sometimes set to clear land for agricultural uses or logging. And Yu said the smoke from these fires is blowing over the Atlantic Ocean and reaching West Africa, where it poses potential health impacts.
“September was the worst on record in the Amazon Basin, particularly in Bolivia and Brazil,” she said. “Both countries are having huge burns, and their wildfire smoke is trans-boundary. It is passing to West Africa. So, we are starting to look into that, especially for fire sensitive areas.”