Research

[POSTECH analyzed the contribution of wildfires to changes in fine particulate matter PM_2.5 concentrations during drought periods.]

POSTECH Professor Hyung Joo Lee’s research team, including integrated program students Min Young Shin and Na Rae Kim, has published the results of a study analyzing how the combined effects of droughts and wildfires influence fine particulate matter (PM_2.5) in California, U.S., using 15 years of data. The study was published in the international environmental science journal Environment International.

PM_2.5 refers to fine particles with an aerodynamic diameter of 2.5 micrometers (µm) or less. Because these particles can penetrate deep into the lungs when inhaled, causing respiratory and cardiovascular diseases and even premature death, they are strictly regulated worldwide.

The research team focused on California because of its unique climate, characterized by frequent droughts and large-scale wildfires. Until now, however, few long-term, large-scale studies had investigated the combined effects of droughts and wildfires on air quality in this region.

Using air monitoring data and computer modeling from 2006 to 2020, the researchers showed that as drought severity increased (for each one-unit decrease in the Standardized Precipitation Evapotranspiration Index, SPEI), average PM_2.5 concentrations rose by 1.5 µg/m³. More severe droughts also substantially raised wildfire risk, with each one-unit decrease in SPEI leading to approximately a 90% higher probability of wildfire occurrence. Under extreme drought conditions combined with wildfires, PM_2.5 concentrations increased to an average of 9.5 µg/m³ compared to normal conditions.

The separate analysis of wildfire impacts was particularly striking: most of the PM_2.5 increase associated with drought was actually due to wildfires. In cases where no wildfire occurred, even severe drought did not lead to notable changes in PM_2.5 levels.

This study serves as a critical warning in the era of climate change. As climate change is expected to intensify the frequency and severity of droughts and wildfires worldwide—including in South Korea—protecting clean air will require not only the control of anthropogenic emissions but also comprehensive strategies that include wildfire prevention and management.

Professor Hyung Joo Lee of POSTECH stated, “This study quantitatively demonstrated the complex relationship between droughts, wildfires, and PM_2.5 air pollution using long-term data. Since South Korea also experiences periodic droughts and has seen an increase in large-scale wildfires, the implications are highly significant.” He added, “Going forward, wildfire prevention and management will play a crucial role in improving air quality and protecting public health.”

DOI: https://doi.org/10.1016/j.envint.2025.109678