Biogenic volatile organic compounds (VOCs) participate in the formation of tropospheric ozone, influence the oxidative capacity of the atmosphere, and produce aerosols. Thus, it is important to quantify fluxes of biogenic VOCs to the atmosphere. Current global models that estimate emissions of biogenic VOCs focus on isoprene and monoterpenes, which are predicted to make up the largest fraction of biogenic VOCs globally. There is some evidence to suggest that there are large emissions of oxygenated VOCs that the models do not accurately characterize, due to a lack of emissions data. The lack of data is in part, due to the analytical difficulties of measuring oxygenated VOCs, which include oxygenated VOCs partitioning into sampled water. This thesis describes biogenic fluxes of some oxygenated VOCs from pine forests and the measurement techniques used to acquire them. Flux data and some leaf level experiments are presented for 2-methyl-3-buten-2-ol (MBO), acetone, and methanol.

Many pine trees of the western U.S. emit the oxygenated VOC MBO. Canopy level fluxes of MBO were measured from towers at two pine forest sites; one composed exclusively of the MBO emitter, ponderosa pine, and the other was a mixed coniferous forest which included the MBO emitter, lodgepole pine. Fluxes were estimated using relaxed eddy accumulation (REA) techniques. Flux data acquired in the field were then compared to modeled flux estimates, using a model originally developed for isoprene emissions.

Different REA techniques were developed for the measurements made at each of the sites. At the ponderosa pine site, a bag REA was used to collect samples, and the samples were analyzed on site by gas chromatography (GC). Measured MBO fluxes averaged 1.1 mg C m-2 h-1 at midday. For measurements at the mixed forest site, a cartridge REA instrument was developed. The sampled cartridges from this device were taken back to the laboratory for GC analysis. Here, measured fluxes of MBO averaged 1.0 mg C m-2 h-1 at midday. This REA technique and the subsequent GC analysis were specifically designed for the analysis of oxygenated VOCs. The GC used 2-dimensional chromatography to separate water from oxygenated VOCs.

At the mixed conifer forest site, fluxes of acetone and methanol were also measured using the cartridge REA. Fluxes of acetone were higher than those of any other VOC at that site with a midday average of 2.5 mg C m-2 h-1; methanol fluxes were in the range of 1.0 mg C m-2 h-1. High leaf level fluxes of acetone were also observed from MBO emitters in the laboratory. However, the leaf level measurements do not scale up to match the canopy level flux data. This could be due to sources of acetone at the coniferous forest other than the trees, or due to phenological and seasonal variations in emissions.

In addition, leaf and plant level flux measurements of MBO showed significant differences from isoprene emissions in their emission patterns. Treating a ponderosa pine tree with 13CO2 resulted in 13C labeling in MBO of about 50%. Other similar studies done with isoprene emitters have demonstrated almost complete 13C labeling of the emitted carbon. This suggests that unlike isoprene, MBO is derived from two different metabolic pools.

The presented data demonstrates the importance of MBO as a major flux of reactive VOC from many forests in the western U.S., and represents the first canopy level flux measurements of acetone and methanol reported from any forest site. These measurements also demonstrate the need for more attention to oxygenated VOCs in regional and global biogenic VOC inventories.

More information available at: http://www.ias.sdsmt.edu/staff/Baker/bradweb/temp/webp.htm