Access to air-conditioning may affect wildfire-related health outcomes
Since 7 January, Southern California wildfires have burned tens of thousands of acres and displaced even greater numbers of people. Still more have been affected by the resulting poor air quality: Particles in wildfire smoke that are smaller than 2.5 micrometers across, known as PM2.5, cardiovascular and pulmonary diseases when inhaled.
The suggests that to mitigate potential health effects, people facing poor air quality who are not under evacuation orders stay indoors when possible.
"Depending on the type of building you live in, how old it is, the windows, all those kinds of things, there's always going to be transfer from outdoor pollution to indoor," explained , a geohealth scientist at Boston University.
Because of this, EPA also suggests using air cleaners or high-efficiency heating, ventilation, and air-conditioning (HVAC) filters with a (MERV) of 13 or higher. However, little research has been done on the effectiveness of running air conditioning (AC) to mitigate the health effects of wildfire smoke.
In a published in Environmental Research: Health, researchers sifted through data on more than 50 million emergency department visits during California wildfire seasons from 2012 to 2019. Overlaying residential data on maps of wildfire-related PM2.5, they found that people living in areas with low availability of residential air-conditioning had a 22% greater risk of visiting an emergency department for a respiratory problem caused by wildfire smoke-related PM2.5 exposure.
Access to AC is a factor, regardless of socioeconomics
The researchers used data from a national demographic survey and a predictive model that calculated the probability of residential AC ownership on the basis of demographic, socioeconomic, housing, and climate characteristics.
"It's not a perfect proxy, but it's the best that we have right now," Stowell said. She noted that one important limitation of their study is that it did not include data on what kinds of AC units people were most likely to have. This information would be helpful in future research because recommendations for AC usage during wildfires vary on the basis of system type. Many portable AC units bring outside air into a home, so they should be used sparingly, whereas a central HVAC system that can be set to recirculate air within a house can both filter air and help residents stay cool.
The team examined emergency department visits associated with wildfire smoke within subgroups classified by race, age, and . They found that the people most likely to face health effects lived in zip codes with lower access to AC, regardless of socioeconomic status.
Stowell noted that the correlation between socioeconomic status and access to AC was weaker than the researchers initially expected. The reason could be that some areas of California have high socioeconomic status but a moderate climate that doesn't require AC, she said.
A choice between heat and smoke
, an atmospheric scientist at the University of California, Davis, who was not involved in the research, said he thought the study did a good job validating something that many researchers already assumed to be true.
When used in a well-sealed home, a high-powered HVAC system equipped with high-efficiency filters "would have a significant impact on the intrusion of outdoor air to the inside of your home," he said.
In addition to acting as a filter, an AC unit can allow people to stay cool without opening windows and letting in smoky air.
"Since wildfire season is usually during the hottest time of the year, people without ACs can be forced to choose between cooling down their homes by leaving their windows open or closing their windows to keep out smoke," wrote , an environmental health scientist at the University of California, Los Angeles, in an email to Eos. Schollaert, who was not involved in the study, is based in Seattle, where air-conditioning is relatively uncommon. "We've experienced simultaneous smoke and heat wave events in recent years, when I've had to make this choice in my own household," she said.
Stowell said she hopes the work will help people living in fire-prone areas better understand what steps they can take to protect their respiratory health during a fire, such as by using HVAC filters with high MERV ratings. She also hopes it makes policymakers more aware of the importance of AC access and perhaps consider initiatives like reimbursing residents for high-quality HVAC filters.