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Wildfire smoke infiltrates homes: More than 1 billion people faced high indoor exposure from 2003 to 2022, study finds

A small team of architects and environmental scientists from Tsinghua University and the Chinese Academy of Sciences, both in China, has estimated that more than 1 billion people worldwide were exposed to wildfire particulate matter while indoors at least one day each year over the years 2003 to 2022.

In their study in the journal Science Advances, the group created models to show particulate concentrations for people around the globe and to show disparities in air purifier use by people of different economic levels. Jing Li and Yifan Zhu have published a in the same journal issue outlining the work done by the team.

Prior research has shown that breathing fine particulate matter generated by fires can be extremely harmful, resulting in a wide variety of health problems. Wildfires can also spread fine particulate matter over large areas, putting those in the vicinity of blazes at risk for lung problems.

When wildfires erupt, health officials typically tell those not in the fire zone to stay indoors to reduce the amount of fine particulate matter they inhale. But doing so, it has been noted, has varying levels of benefit depending on building conditions.

In more developed countries, people often retreat into well-sealed homes with air conditioning and/or air filtration systems. In less developed countries, people may find little improvement if the buildings have no glass covering their windows, no AC and no filtration.

For this new study, the researchers in China sought to make estimates of the fine particulates people have breathed due to wildfires over the past two decades.

To make their estimates, the research team used a global database of information on wildfires based on satellite imagery for the years 2003 to 2022. Assuming that people spent most of their time indoors, they could then calculate how many people were indoors breathing air with fine particulates at least once per year.

The researchers then simulated three scenarios that involved air purifier deployment indoors. These scenarios were aligned with the World Health Organization's guideline and modeled indoor levels being reduced to 25, 15, and 5 μg/m³, respectively. For each scenario, they also applied a cost assessment model.

Overall, the results of the study suggest that more than 1 billion people experienced at least one day per year where they were exposed to high levels of wildfire-related indoor air pollution. The researchers also uncovered significant global disparities, demonstrating how people living in poorer parts of the world are facing far more health threats from wildfires than people living in richer areas.