Abstract
Climate extremes are projected to cause unprecedented deviations in the emission and transformation of volatile organic compounds (VOCs), which trigger feedback mechanisms that will impact the atmospheric oxidation and formation of aerosols and clouds. However, the response of VOCs to future conditions such as extreme heat and wildfire events is still uncertain. This study explored the modification of the mixing ratio and distribution of several anthropogenic and biogenic VOCs in a temperate oak–hickory–juniper forest as a response to increased temperature and transported biomass burning plumes. A chemical ionization mass spectrometer was deployed on a tower at a height of 32 m in rural central Missouri, United States, for the continuous and in situ measurement of VOCs from June to August of 2023. The maximum observed temperature in the region was 38 °C, and during multiple episodes the temperature remained above 32 °C for several hours. Biogenic VOCs such as isoprene and monoterpene followed closely the temperature daily profile but at varying rates, whereas anthropogenic VOCs were insensitive to elevated temperature. During the measurement period, wildfire emissions were transported to the site and substantially increased the mixing ratios of acetonitrile and benzene, which are produced from burning of biomass. An in-depth analysis of the mass spectra revealed more than 250 minor compounds, such as formamide and methylglyoxal. Extreme heat and presence of wildfire plumes modified the overall volatility, reactivity, O: C, and H: C ratios of the extended list of VOCs. The calculated OH reactivities during extreme temperature condition and transport of biomass burning plumes were 106.37 ± 4.27 and 106.22±5.15 s−1, respectively, which are substantially higher than background level of 98.78±1.16 s−1. Multivariate analysis also clustered the compounds into five factors, which highlighted the sources of the unaccounted-for VOCs. Ultimately, results here underscore the effect of extreme heat and wildfire emissions on the overall chemical properties VOC in a temperate forest.
| Original language | English |
|---|---|
| Pages (from-to) | 16611-16629 |
| Number of pages | 19 |
| Journal | Atmospheric Chemistry and Physics |
| Volume | 25 |
| Issue number | 22 |
| DOIs | |
| State | Published - Nov 24 2025 |
Funding
This research has been supported by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory (ORNL) (Project ID: 11244). MOFLUX operations are supported by ORNL's Terrestrial Ecosystem Science Scientific Focus Area under the Office of Biological and Environmental Research within the U.S. Department of Energy's (U.S. DOE) Office of Science. This research is sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the US Department of Energy. The U.S. Drought Monitor, which provided the drought data of Boone County, MO, is jointly produced by the National Drought Mitigation Center at the University of Nebraska-Lincoln, the United States Department of Agriculture, and the National Oceanic and Atmospheric Administration. The authors gratefully acknowledge the NOAA Air Resources Laboratory (ARL) for the provision of the HYSPLIT transport and dispersion model (https://www.ready.noaa.gov, last access: 17 November 2025) used in this publication. This research has been supported by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory (ORNL) (Project ID: 11244). MOFLUX operations are supported by ORNL’s Terrestrial Ecosystem Science Scientific Focus Area under the Office of Biological and Environmental Research within the U.S. Department of Energy’s (U.S. DOE) Office of Science.