How Ecosystems and Atmosphere Exchange Volatile Organic Compounds
Did you know that every time you walk through a forest, you're surrounded by an invisible chemical conversation?
Trees, soil, and even microbes are constantly releasing and absorbing thousands of volatile organic compounds (VOCs) in a complex dialogue with the atmosphere. While we often associate these compounds with the familiar scent of pine forests or the fragrance of flowers, scientists are discovering that this exchange is far more extensive and consequential than previously imagined.
Recent research reveals that ecosystems don't just emit these compounds—they also actively consume them in a bidirectional flow that influences everything from air quality to climate regulation 6 . This dynamic two-way street of chemical exchange represents a critical frontier in our understanding of Earth's atmospheric systems, with implications for predicting climate change and managing air quality in an increasingly human-dominated world.
Detected Ions
Measured by advanced instrumentation
Active Compounds
With detectable gross fluxes
Model Underprediction
Of total VOC carbon and reactivity fluxes
Terrestrial ecosystems play a dual role in the global atmospheric cycle—they are simultaneously the largest source and a major sink for volatile organic compounds 6 . This two-way exchange, known as bidirectional flux, means that the same forest that emits VOCs into the atmosphere also draws other VOCs back down, creating a complex chemical dance that we're only beginning to understand.
Naturally produced by plants, trees, and soil microbes. These include compounds like isoprene and monoterpenes that give forests their characteristic scents.
Human-made compounds from industrial processes, fuels, and consumer products. These contribute to urban air pollution and health concerns 5 .
VOCs interact with nitrogen oxides to form ground-level ozone, a key component of smog that poses health risks and damages crops 5 .
They serve as precursors for secondary organic aerosols, tiny particles that influence cloud formation and climate patterns 9 .
Some VOCs, like benzene, are toxic air pollutants that pose direct health risks, particularly in urban and industrial areas 5 .
In 2018, a team of researchers led by Dylan Millet set out to answer a fundamental question: "How many VOCs matter in ecosystem-atmosphere exchanges?" Their pioneering study, published in ACS Earth and Space Chemistry, represented a quantum leap in our ability to detect and quantify these mysterious chemical flows 6 .
Previous research had focused on measuring a relatively small number of known, abundant VOCs. This approach was like trying to understand a conversation by listening to only every tenth word. The Millet team employed a state-of-the-art proton transfer reaction-quadrupole interface time-of-flight mass spectrometer (PTRQiTOF) that could detect VOCs across an unprecedented mass range (m/z 0-335) 6 . This instrument offered the sensitivity and resolution to identify hundreds of previously overlooked compounds participating in the atmospheric exchange.
The research was conducted over a mixed temperate forest—an ideal natural laboratory that included various tree species, soil types, and microbial communities. The team positioned their instrument to continuously measure VOC concentrations above the forest canopy, employing advanced eddy covariance techniques to calculate upward and downward fluxes simultaneously.
The methodology behind this research represents a remarkable feat of analytical chemistry. The centerpiece of the investigation—the PTRQiTOF mass spectrometer—works by using proton transfer reactions to ionize volatile organic compounds without fragmenting them, then precisely separates these ions by their mass-to-charge ratio using time-of-flight detection 6 .
Extended measurement campaigns collecting data throughout multiple days and nights across different weather conditions.
Using eddy covariance techniques to correlate VOC concentrations with wind velocity and direction.
Novel humidity correction method to distinguish real VOC fluxes from measurement artifacts.
Comparing empirical findings with predictions from the GEOS-Chem chemical transport model 6 .
The results of the study revealed an astonishing complexity in the volatile exchange between forests and the atmosphere. Of the 636 detected ions measured by the sophisticated instrument, 377 exhibited detectable gross fluxes during the study period 6 . This discovery meant that nearly 60% of the detected compounds were actively participating in two-way exchange between the ecosystem and atmosphere—far more than previously recognized.
VOCs emitted by the ecosystem, dominated by a relatively small number of compounds in terms of both carbon mass and atmospheric reactivity.
VOCs being absorbed by the ecosystem, spread across a much wider array of compounds 6 . This pattern suggests that ecosystems are more selective in what they emit than in what they consume.
| Performance Metric | Short-chain Oxygenated VOCs | Terpenoids | Sesquiterpenes | Overall VOC Flux |
|---|---|---|---|---|
| Carbon flux prediction | Severe underprediction | Moderate underprediction | Variable | 40-60% underprediction |
| Reactivity flux prediction | Severe underprediction | Moderate underprediction | Significant underprediction | 40-60% underprediction |
| Gross flux representation | Poor | Moderate | Poor to moderate | Poor for oxygenated VOCs |
"For oxygenated VOCs, the model performed particularly poorly, severely underpredicting both gross fluxes and net exchange. For this class of compounds, unrepresented VOCs played a larger role, accounting for approximately 30% of the carbon flux and 50% of the reactivity flux 6 ."
The discovery that ecosystems exchange hundreds of VOCs with the atmosphere, rather than just a few dozen, has profound implications for atmospheric science and environmental policy. Perhaps the most significant revelation is that current atmospheric models likely underestimate the full impact of vegetation on air quality and climate 6 . This modeling gap means we may be overlooking important feedback loops in climate change projections.
As global temperatures rise, emissions of highly reactive compounds like sesquiterpenes are increasing disproportionately because of their heightened temperature sensitivity .
Research at Biosphere 2 revealed that when soils experience drought stress, microbial VOC emissions increase while carbon dioxide production decreases 7 .
"There are efforts to reduce industrial sources of VOCs, but personal products remain unlegislated, and are becoming the more dominant VOC source within cities" 2 .
Warming Temperatures
Increased SQT Emissions
More Aerosol Formation
Potential Cooling Effects
The invisible conversation between ecosystems and the atmosphere is far more complex and chemically diverse than scientists previously imagined.
What we once viewed as a relatively simple one-way emission of a few prominent compounds has revealed itself as a sophisticated bidirectional exchange involving hundreds of volatile organic compounds. This revised understanding forces us to reconsider how terrestrial ecosystems influence atmospheric chemistry, air quality, and climate feedback loops.
Understanding how drought and warming reshape VOC emissions 7 .
Deciphering the specific roles of individual VOCs in plant and microbial communication.
Enhancing atmospheric models to better represent the full spectrum of volatile exchange.
The next time you walk through a forest, remember that you're witnessing only the visible part of a much richer ecological drama. Beneath your feet and in the air around you, microbes, plants, and the atmosphere are engaged in a continuous chemical dialogue—one that we are only beginning to understand, but one that ultimately shapes the health of our planet and the air we all share.