Long-term impact of wildfire smoke pollution

Welcome to Science Sessions, the podcast of the proceedings of the National Academy of Sciences, where we connect you with Academy members, researchers, and policymakers. Join us as we explore the stories behind the science. I'm Paul Gabrielson. During the summer, the arrival of wildfire smoke from regional fires is a common occurrence in the Western United States. In 2023, however, smoke from wildfires in Canada poured into major cities on the U.S. East Coast. This showed that wildfire smoke and the health risks associated with smoke-related air pollution is a widespread issue. In a recent PNAS article, Kai Chen of the Yale School of Public Health and Colleagues examined the effects of smoke-related fine particulate matter air pollution, or PM 2.5, on health in every county in the contiguous United States between 2007 and 2020. The health burden of wildfire smoke they found is significant and widespread, with more than 11,000 deaths per year attributable to wildfire smoke PM 2.5. Kai, what is PM 2.5 and how does it affect human health? PM 2.5 is called fine particulate matter. So because it's so small, it can get inhaled, go deeper into our lungs, and penetrate to the bloodstream, to trigger oxidative stress and inflammation that leads to a lot of health problems. And over the decades of research on air pollution in the health, we have known from the avidus that this particular matter pollution can adverse impact almost all the organ systems. So think about respiratory illness like asthma, like lung cancer, to cardiovascular system diseases like heart attack, stroke, even to renal system disease, even to diabetes, to adverse burst outcomes like low burst weight, preterm burst, and recently evidence showing that they can even affect Alzheimer's disease and cognitive kinds, and also leads to adverse impacts on mental health. Why did you decide to look at the nationwide health impact of wildfire smoke? When we do air pollution in the health study, we have seen over the past few decades that because of the Clean Air Act, the PM 2.5 level in the US has actually been declining over the past few decades. And that's a good story and a remarkable success. However, if you look at the recent years, the annual average PM 2.5 level is not a continue to decline, even in some areas, began to rebound. One of the reasons behind this is actually the increasing contributions from these Wi-Fi smoke PM 2.5. And unfortunately, with the warming climate, we actually see more and more of these Wi-Fi events happening and the weather happens, it tends to be more intense. But most of the previous studies degenerate focus on the western part of the US. But we actually know that Wi-Fi smoke can travel hundreds to thousands of miles away from a source so that they can impact human health, even hundreds to thousands of miles away. And if you remember last June, the sky on New York City turned to orange. And that is because the extremely high level of Wi-Fi smoke from the Canadian Wi-Fi. So that was a kind of weak article for everyone knows that Wi-Fi smoke pollution is not a regional problem, it's not a western problem, it's the national problem. And this problem is also a nationwide health problem. So that's why we started looking at this nationwide health impact. What did you find? How widespread are health impacts due to smoke? We found that the long-term exposure to these Wi-Fi smoke actually associated with increased mortality from a variety of health conditions, with majority from the cardiovascular system disease, mental health, mortality, endocrine disease, and digestive disorders. And if those associations we found are causal, we asked that more than a level of 1,000 deaths per year in the US could be attributed to this Wi-Fi smoke, PM-25. And if you consider the total all-source PM-25, this mortality attribution could account from about 16% of the total PM-25 from all the different sources. Interestingly, another thing we found actually looks kind of intuitive, that actually people leaving far away from the Wi-Fi sources that are 150 km away, they actually have much larger mortality risk from the Wi-Fi smoke compared with people leaving nearby where the Wi-Fi are happening. They've been thinking about it when there's a major Wi-Fi events happening, the smoke plume can be hundreds to thousands of meters high. And not everyone leaving nearby the fire will actually experience the high air-perch episode on the ground. Compared to there were larger number of people, they are leaving on the downwind but far away from the fire because of the long-range transport of Wi-Fi smoke, their impact. So that's why we actually see this important phenomenon that it's not only people leaving nearby the Wi-Fi impacted, but also folks leaving far away from the Wi-Fi can also be impacted by this long-term Wi-Fi exposure. What conditions exacerbated the effect of the smoke-related PM-2.5? So when we look at the subgroups, what's consistent in finding is that older adults, compared to younger adults, they are actually more vulnerable to these mortality impacts from the Wi-Fi smoke-pume-2.5. So we know for a lot of reasons both their physical responses but also social and living conditions are combined making them more vulnerable to the Wi-Fi smoke-pume-2.5. Another issue that exacerbated the effects of Wi-Fi smoke-pume-2.5 is the heat exposed. So during amounts of when we have a larger number of extreme heat days, the heat exposure actually would make the house risks of Wi-Fi smoke-pume-2.5 even worse. So this is important because with the warming climate, we are actually going to see more of these extreme heat days in the future. So what we show here is really the compounding risk from heat and Wi-Fi smoke could be much larger than the individual event. What are the caveats or limitations of the study? The first one is when we look at the Wi-Fi smoke exposure, we're not using the direct environment although Wi-Fi smoke because that is challenging and not available right now, nationwide. So we have to rely on motor estimates and despite the model has good performance, it also brings uncertainty and a measurement error. So there's an inherent limitation of any kind of this study using the motor estimates of Wi-Fi smoke. The second challenge in doing this study is we only look at the annual average exposure matrix for the long term P-25. But this does not capture very well about the frequency and duration of some high intensity Wi-Fi episode. For example, even with the same annual average constriction only the long term P-25 from smoke, we do not know where well what's the difference between if you only experience a few days of the extreme high Wi-Fi smoke episode like the New York City has experience versus if you just experience amounts of low exposure Wi-Fi smoke by the continued persistence. So that remains an open question for researchers to tackle. And the third one I want to mention is in this study we look at a county level population. So that brings us a klot of bias and also the issue that we could not exceed within each county where there are certain communities have high exposure or they have high risks from the Wi-Fi smoke. I think that these questions need to be answered in the future studies. What are the implications for policymakers and the public? So first of all, Wi-Fi smoke is a national problem. It's not just a western problem and it can affect the entire country. And when it impacts our house, it goes beyond respiratory illness. It impacts cardiovascular system, endocrine disease, and mental disorders. And when we look at the impacts of Wi-Fi smoke, it's more than just a few days short term exposure. The long term exposure to Wi-Fi smoke P-25 contributes substantial mortality burden in the US per year. And unfortunately with the warming climate, these mortality burden expect it to be even larger with more intense, more frequent and more prolonged Wi-Fi seasons. So what that means, that means we need to take more effective public health actions to better protect the populations with the Wi-Fi smoke. And also we need to better communicate with people so that when they see Wi-Fi happening, they have the knowledge to protect themselves, not only for the short few days exposure to Wi-Fi, but also for the long term right with low-level exposure to Wi-Fi smoke. for all across the region, not just in areas near by the but also for people outside of the region. So I think this is an important week of a call for us to reconsider how to better protect the public house from this ongoing and increasing Wi-Fi smoke pollution. Thanks for tuning in to Science Sessions. You can subscribe to Science Sessions on iTunes, Spotify, or wherever you get your podcasts. If you like this episode, please consider leaving a review and helping us spread the word. [Music]