BVOC Emissions and Chemistry
Isoprene and monoterpenes are biogenic volatile organic compounds (BVOCs) and are major sources of carbon into the atmosphere, with the former alone accounting for 440-660 teragrams of carbon every year. Once in the atmosphere, they are oxidized by OH and form secondary organic aerosols (see Aerosol-cloud interactions or Aerosol particle sources and chemistry).
Isoprene is largely emitted from certain broadleaf deciduous trees (particularly oak trees). Biochemically, this isoprene originates from the methylerythritol 4-phosphate (MEP) pathway, which uses intermediates from the Calvin cycle to supply the carbons necessary to synthesize isoprene within the chloroplasts. Physiologically, isoprene may protect leaves from heat stress and reactive oxygen species, although the exact mechanism for this process is still unknown.
Notably, isoprene emissions tend to increase with increasing temperature and decrease with increasing carbon dioxide concentrations, indicating some uncertainty in how climate change, droughts, and wildfires will affect isoprene emissions. One recent project within the group aims to use vegetation indices to study how changes in plant physiology, meteorology, and atmospheric chemistry couple to alter remotely-sensed isoprene concentrations in regions like the Ozark Mountains and Northern California. By understanding how isoprene emissions change in response to plant physiology, we hope to better understand what role isoprene plays in heat and drought tolerance and whether we can predict changes in isoprene emissions by looking at the plants themselves.