Biosphere/Atmosphere Interactions: Shepson Atmospheric Chemistry Group: Purdue University

Biosphere/Atmosphere Interactions


  1. To understand the processes governing atmospheric oxidation of species emitted by the forest in the presence of nitrogen oxides.
  2. To understand the mechanism of isoprene, alpha pinine, and other biological volatile organic compounds oxidation and the behavior and identification of the secondary products, such as aldehydes, ketones, and organic nitrates.
  3. To quantify nitrogen deposition in a forest environment and understand how the deposited nitrogen affects photosynthetic rates and carbon sequestration.



Isoprene (C5H8) and monoterpenes (C10H16) comprise the most abundant non-methane biogenic volatile organic compounds (BVOCs) emitted from the forest to the atmosphere. These compounds degrade during daylight largely due to reactions with hydroxyl radicals and at night by nitrate radicals (NO3) to produce oxygenated VOCs (OVOCs). In the presence of nitrogen oxides (NOx), these compounds can generate lower volatility organic nitrates (ON), e.g., hydroxy nitrates (HORONO2), which can partition to aerosol particles, act as a sink for NOx, and thus influence ozone (O3) on a global scale. We conduct laboratory and field studies and use mass spectrometry to better understand the oxidation kinetics and formation of ON under different environmental conditions, and the role of ON in secondary organic aerosol formation.

Current Projects

Organic Nitrate Formation from Polyolefin Monoterpene Oxidation:

Polyolefinic monoterpenes are largely emitted in the northern continental U.S., but their impact on atmospheric composition and air quality are poorly understood. Here we are trying to better understand the influence of polyolefinic monoterpene oxidation on the yields of gas and particle ON. This work involves chamber studies where we can oxidize organic compounds under controlled conditions. Examples include OH radical oxidation of trans-ocimene, a light-dependent monoterpene common of the Midwest.


Uptake of Organic Nitrates by Aerosol Particles:


The semivolatile nature of ON means that they can partition to the aerosol phase. However, the efficiency at which ON are incorporated into the aerosol phase depends on their uptake kinetics, which can be influenced by particle liquid water, acidity, and phase state or viscosity. In this work, we will be coupling a custom-made aerosol flow tube to our chemical ionization mass spectrometer to study the uptake kinetics of synthetic ON by aerosol particles under different environmental conditions.


Learn more about related projects by clicking the links below:

Photochemical Reaction Experiments

Secondary Organic Aerosols

Atmospheric Nitrogen Chemistry

Cloudwater Collection