Terrestrial-Atmospheric Processes

The terrestrial ecosystem is a major source of aerosols and chemical species to the atmosphere. These include biological aerosol particles such as pollen and soil microorganisms or cell fragments, soil minerals ejected during rainfall or entrained during wind erosion, and volatile organic compounds (VOCs) released by plants (which produce familiar aromas). These particles, ranging in size from nano- to micrometers, remain aloft and undergo extensive chemical transformations as they react with other atmospheric constituents. Notably, these processes include warm and cold cloud droplet formation. Aerosols thus play important roles in regulating Earth’s hydrological and biogeochemical cycles. 

The molecular processes by which aerosols transform and age strongly influence these behaviors. The Environmental Molecular Sciences Laboratory’s (EMSL’s) Terrestrial-Atmospheric Processes Integrated Research Platform (TAP IRP) is investigating these molecular transformations, the physical processes that control them, and the coupling of terrestrial and atmospheric processes. Knowledge from these studies allows us to understand the mechanisms regulating Earth’s hydrological and biogeochemical cycles. 

The science 

Research examining terrestrial and atmospheric processes advances fundamental scientific understanding by addressing the release mechanisms of aerosols and gases from plants and soil into the atmosphere and develops molecular-level understandings of the multiphase interfacial chemistry and aging processes occurring near Earth’s surface and extending up to the atmospheric boundary layer. We investigate how aerosols participate in warm and cold cloud formation by acting as cloud condensation nuclei or ice-nucleating particles and how these impact Earth’s hydrological cycles. We also study the deposition of aerosols on terrestrial ecosystems. These activities generate critical experimental and observational data to grow American scientific leadership in Earth system models and the understanding of impacts to American energy reliability. 

The key science topics covered by this IRP include 

• molecular compositions of biogenic and anthropogenic VOCs emitted from soil–plant–atmosphere systems 
• formation and evolution of secondary aerosols and their phase states and volatility distributions 
• emission processes of primary biological aerosol particles and their transport and fate in the atmosphere 
• aging processes and multiphase chemistry of biogenic, geogenic, and anthropogenic aerosols in the atmosphere 
• physical and chemical properties of long-range transported particles in the free troposphere 
• physical, chemical, and optical properties of atmospheric aerosols and their impact on Earth’s radiative budget 
• physical and chemical processes that influence warm and cold cloud formation by atmospheric aerosols 
• molecular mechanisms of atmospheric ice formation on aerosols 
• mechanisms of coupling between biogeochemical and atmospheric processes, such as the roles of aerosolized soil microbe cell fragments in atmospheric ice formation and nucleation mechanisms specific to these particles 
• compositions of aerosols deposited onto terrestrial ecosystems and the processes by which deposition occurs. 

Synergy and relationship with other Environmental Transformations and Interaction IRPs 

Aerosol release from plants and soils is highly complementary to the Rhizosphere Function Integrated Research Platform (RF IRP), which studies belowground root–soil interactions and the Biogeochemical Transformations Integrated Research Platform (BGT IRP) that investigates the relationships between soil organic matter, microbiomes, and minerals. The TAP IRP mechanistically connects the BGT and RF IRPs to atmospheric processes and illuminates how belowground, surficial, and atmospheric components interact as a complex system-of-systems. TAP research further advances fundamental science by supporting the Molecular Observation Network (MONet) strategic research areas, including field sensors, model–experiment (ModEx) integration and multiscale modeling, and MONet field sites. 

How we do the science 

EMSL uses a multimodal suite of capabilities to study complex atmospheric systems and provide data for Earth system models. Chief among these are microscopy imaging, spectroscopy, and multi-ionization high-resolution mass spectrometry approaches. EMSL capabilities and instruments that uniquely support this IRP science mission include 

• computer-controlled scanning electron microscopy (CCSEM) to study the size-resolved chemical composition of atmospheric aerosols 
• single-particle mass spectrometry (MiniSPLAT) to characterize the in situ and real-time physicochemical properties of individual particles 
• nanospray desorption electrospray ionization (nano-DESI) high-resolution mass spectrometry to investigate the molecular composition of aerosols 
• long high-resolution time-of-flight aerosol mass spectrometry (L-ToF AMS) to measure real-time, nonrefractory, size-resolved particulate chemical composition and mass 
• custom-built ice nucleation stage integrated into environmental scanning electron microscopy (IN-ESEM) to study atmospheric ice formation at the single-particle level and characterize ice-nucleating particles 
• ice nucleation chamber to study atmospheric ice formation 
• wideband integrated bioaerosol sensor (WIBS) to study in situ bioaerosol characterization 
• photoacoustic spectrometer to study the optical properties of aerosols 
• thermal desorption gas chromatography–quadrupole time-of-flight mass spectrometry (TD-GC-QTOF-MS) to measure VOCs emitted into the atmosphere 
• field-deployable size- and time-resolved aerosol collection (STAC) system integrated with environmental sensors to collect particles for offline analysis. 

Research in action

Ice-Nucleating Particle Characteristics Shown to Vary Seasonally and with Altitude 

Ice-nucleating particles are tiny atmospheric specks that trigger ice crystal formation in clouds, but they remain poorly understood, especially in remote marine regions. In a study conducted over Portugal’s Azores islands as part of the Aerosol and Cloud Experiments in the Eastern North Atlantic campaign, researchers collected and analyzed these particles at different altitudes and seasons. Their findings reveal that ice-nucleating particles vary with location and conditions, offering valuable insights for Earth system models and highlighting the need for continued research. 

Revealing How Tar Particles from Wildfire Smoke Absorb and Refract Solar Radiation, Light in Atmosphere 

Days after a wildfire, a type of smoke that contains tiny, brown, spherical, light-absorbing particles known as tar balls can linger in the atmosphere. These particles are believed to have a significant impact on Earth’s radiative balance. A multi-institutional team of researchers collected and analyzed tar balls from over a mountainous region in northern Italy to understand their impact on Earth’s radiative balance. Using advanced microscopy and spectroscopy tools, they determined the particles’ optical properties and refractive indices. The findings provide insights into how these particles influence Earth’s energy balance, emphasizing the need for further research on their environmental effects. 

Discovering How Transport and Source Affect Properties of Aerosol Particles 

Tiny aerosol particles can form cloud droplets or ice nuclei depending on their chemical makeup and physical state—solid, semisolid, or liquid. To understand how these phases shift during long-distance transport, scientists studied individual particles carried across the North Atlantic in the free troposphere. They found that particle phases varied more than expected and were strongly influenced by both their origin and journey through the atmosphere.