Canopy level emissions of 2-methyl-3-buten-2-ol, monoterpenes, and sesquiterpenes from an experimental Pinus taeda plantation.

ABSTRACT

Emissions of Biogenic Volatile Organic Compounds (BVOCs) observed during 2007 from an experimental Pinus taeda plantation in Central North Carolina are compared with model estimates from the Model of Emissions of Gases and Aerosols from Nature (MEGAN) version 2.1. Relaxed eddy accumulation (REA) estimates of 2-methyl-3-buten-2-ol (MBO) fluxes are a factor of 3-4 higher than MEGAN estimates. MEGAN monoterpene emission estimates were a factor of approximately two higher than REA flux measurements. MEGAN ß-caryophyllene emission estimates were within 60% of growing season REA flux estimates but were several times higher than REA fluxes during cooler, dormant season periods. The sum of other sesquiterpene emissions estimated by MEGAN was several times higher than REA estimates throughout the year. Model components are examined to understand these discrepancies. Measured summertime leaf area index (LAI) (and therefore foliar biomass) is a factor of two higher than assumed in MEGAN for the P. taeda default. Increasing the canopy mean MBO emission factor from 0.35 to 1.0mgm(-2)h(-1) also reduces MEGAN vs. REA flux differences. This increase is within current MBO emission factor uncertainties. The algorithm within MEGAN which adjusts isoprene emission estimates as a function of the temperature and light of the previous 24h seems also to improve the seasonal MEGAN MBO correlation with REA fluxes. Including the effects of the previous 240h, however, seems to degrade temporal model correlation with fluxes. Monoterpene and sesquiterpene composition data from the REA are compared with MEGAN2.1 estimates and also branch enclosure and needle extract data collected at this site. To our knowledge, the flux data presented here are the first reported for MBO and sesquiterpenes from a P. taeda ecosystem.