With Los Angeles County currently fighting some of its most damaging wildfires ever, recent research indicates that U.S. policies should focus on promoting equity and educating the public on how to shield themselves from the dangers posed by wildfire smoke pollutants.
According to a recent study led by the Boston University School of Public Health (BUSPH), individuals with limited access to air conditioning are more likely to seek emergency medical care for health issues linked to wildfire smoke exposure.
This study, which will be published in the journal Environmental Research: Health, reveals that inhaling fine particulate matter (PM2.5) from California wildfires corresponds with increased emergency department visits for various health issues, including respiratory ailments and non-accidental causes. The risk levels varied among different age groups and racial demographics, with those living in areas with fewer air conditioning resources being particularly affected.
These findings are especially timely as firefighters in Southern California combat multiple wildfires that have been raging around Los Angeles County since January 7, including the Palisades fire, which is anticipated to be one of the largest and most devastating in the county’s history. Health experts are advising residents—who have not been ordered to evacuate—to use air conditioning and/or air purifiers if available to protect themselves.
Even with this advice and the increasing threat of intense wildfires due to climate change, research on how health impacts from wildfire smoke exposure differ based on air conditioning access is scarce. Understanding this connection can guide policies and interventions that address barriers to gaining access to air conditioning, ultimately helping to protect at-risk communities from the harmful effects of PM2.5 and other dangerous pollutants that can travel long distances in the air.
Dr. Jennifer Stowell, the lead researcher and corresponding author, emphasized that “the effectiveness of air conditioning in lessening health risks from smoke exposure can depend on the type of system and filter used.” She indicated that their analysis focused on access to air conditioning in general, rather than the specific types of systems or their actual use. “Research like this will be increasingly important as wildfire occurrences rise. California serves as a prime example, facing larger wildfires and prolonged fire seasons. A crucial next step is to find more precise ways to define access to air conditioning.”
For their research, Dr. Stowell and her BUSPH colleagues, along with those from the Boston University College of Arts & Sciences (CAS) and the Health Effects Institute, analyzed a national database of healthcare claims to evaluate over 50,000 emergency department visits during California’s wildfire seasons from 2012 to 2019, which lasted from May to November each year. They assessed the negative health outcomes related to PM2.5 exposure among all participants and various subgroup categories.
Similar to prior studies, exposure to wildfire smoke primarily correlated with emergency visits for respiratory problems, while cardiovascular issues were less common. These emergency visits were particularly more frequent among children under 10 years old and adults aged 20 to 74, as well as among the Black population, although elevated visits were also observed in White, Hispanic, and Asian/Pacific Islander groups.
Individuals living in areas with limited air conditioning access faced a 22% greater risk of emergency department visits due to respiratory issues linked to wildfire smoke. Gaining a clearer understanding of how residents use air conditioning as a tool for filtering pollutants—along with the challenges different populations encounter in accessing such systems—is essential. Wildfires are predicted to become more common in the Wildland-Urban Interface (WUI) areas, where human development intersects with potential fuel sources, as currently evidenced in LA County by the devastation caused to homes and businesses near vegetation.
Dr. Stowell noted, “WUI fires are particularly alarming because they involve the burning of human-made structures and the accompanying release of harmful chemicals and particles in the smoke.” She mentioned that the current fires in LA occur out of the typical season due to intense Santa Ana winds originating from the mountains. As climate change progresses, the temperature differences between land and sea are expected to intensify, potentially resulting in more powerful late-season winds.
How do residential air conditioning units help filter PM2.5 from homes? The filters in these systems can eliminate particulate matter, but some filters are significantly better than others. “HEPA filters can capture most particles larger than 0.3 µm but are much pricier than fiberglass filters, which may not effectively block fine particulate matter and allow considerable amounts inside,” explained Dr. Stowell. “Standard pleated air filters are also relatively effective at removing the majority of particulate matter.”
Air conditioning units that come with a Minimum Efficiency Reporting Value (MERV) rating of seven or above are believed to be the best at filtering particulate matter from outside air but also tend to be more costly.
The results of the study underscore a pressing need for enhanced policy measures aimed at mitigating the health risks posed by wildfire smoke exposure.
Dr. Stowell remarked, “Many homeowners are unaware of the differences in MERV ratings and how these variations could impact their health. Policymakers should work to provide better information regarding filter types and ratings, which perform more effectively—especially for residents of smoke-affected areas.”
Considering the disproportionate health impacts on marginalized communities from wildfire smoke exposure, she also suggests that economic support should be evaluated, specifically aimed at low-income residents in high-risk areas. “In light of the current wildfires in California, local and state officials should enhance their response strategies and develop plans and policies to lower exposure risks before fires strike,” asserted Dr. Stowell.
Dr. Gregory Wellenius, professor of environmental health and director of the Center for Climate and Health at BUSPH, served as the senior author of the study, with contributions from Dr. Ian Sue Wing, a professor of earth and environment at CAS; Dr. Yasmin Romitti, a staff scientist at the Health Effects Institute; and Dr. Patrick Kinney, Beverly Brown Professor of Urban Health at BUSPH.
