Research Projects

Project at a Glance

Title: Whole ecosystem measurements of biogenic hydrocarbon emissions.

Principal Investigator / Author(s): Goldstein, Allen H.

Contractor: UC Berkeley

Contract Number: 98-328


Research Program Area: Emissions Monitoring & Control, Atmospheric Processes

Topic Areas: Modeling, Natural (Biogenic) Sources


Abstract:

We intended to determine rates of biogenic VOC and OVOC emissions from one of the dominant conifer ecosystems of California. Specifically, we needed to develop and deploy a new measurement system for ecosystem scale biogenic emissions of 2-methyl-3-buten-2-ol (MBO), acetone, monoterpenes, and other oxygenated hydrocarbons, and supporting the California Air Resources Board use of this data to validate their biogenic emissions inventory system (BEIGIS). OVOCs were predominantly of natural origin. However, the relative impact of biogenic and anthropogenic emissions was different for each individual OVOC. MBO emissions were completely of biogenic origin, whereas methanol, ethanol, acetone, and acetaldehyde all had a combination of anthropogenic and biogenic sources. We found that biogenically emitted compounds included MBO, methanol, ethanol, acetaldehyde, acetone, and several monoterpenes. These were the most abundant VOCs at this site, excluding methane, and biogenic compounds dominated the total VOC reactivity in the region. The OVOCs were highly correlated with each other, especially during daytime. Fluxes were dominated by MBO and methanol with daytime average emissions of ~1.3 mg C m -2 h -1 . Ethanol, acetaldehyde, monoterpene, and acetone fluxes were approximately a factor of 5 lower. All fluxes showed diurnal cycles with maxima around noon and minima at night. Temperature and light were the main drivers for the MBO emissions, and the canopy level flux responses were virtually identical with previously measured leaf level fluxes from ponderosa pine trees at the same site. Ambient temperature appeared to be the most important driver of the other VOC fluxes, but moisture also played a role, particularly for monoterpenes, ethanol and acetone. Humidity impacts monoterpene fluxes particularly during extreme events, such as summer rain storms or prolonged summer droughts, both relatively common in the Mediterranean climate of the Sierra Nevada mountains. Soil and litter emissions, measured using a Pyrex glass chamber, contributed significantly to the canopy level fluxes of methanol, acetaldehyde, monoterpenes and acetone, and had a much smaller contribution to the canopy fluxes of ethanol. Analyses of concentration of ozone, isoprene and isopreneís oxidation products showed that a substantial amount of the ozone observed at the mid elevations of the Sierra Nevada Mountains was formed through oxidation of biogenically emitted isoprene. On hot days when isoprene emissions were highest, ozone production in this region was dominated (more than 50%) by isoprene oxidation.


 

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