Improving Regional Biogenic VOC Emission Estimates Using an Airborne PTRMS Eddy Flux Measurement System.

摘要

Vegetation in California comprises a large source of isoprene, terpenes, and other biogenic volatile organic compounds (BVOC). The emitted BVOC react in the presence of NOx and sunlight leading to production of ozone and particulate matter. Current models of BVOC emissions for California have major uncertainties, and there are very few emission measurements available to validate existing model inventories. In order to assess and improve the model inventories of BVOC emissions for use in air quality State Implementation Planning (SIP), spatially resolved data on BVOC emissions are required. We contracted to collect a data set using an airborne PTRMS Eddy Flux measurement system over regions of California expected to have substantial isoprene emissions and to use those data to test regional BVOC emission model estimates. In the first year of the project we conducted a field measurement planning exercise to optimize the amount of information that 14 could be gained from airborne flux observations. Oaks are the main source of isoprene in California and they grow dominantly in certain elevations (400-800 m) along the foothills encompassing the Central Valley and along the Coastal Range Mountains. These specific locations and relatively constant elevations make oaks an ideal subject for flux observations from aircraft. We examined oak distribution data used in the BEIGIS and the MEGAN BVOC emission models. We also reviewed recent advances in satellite derived landcover information, including the National Land Cover Dataset (NLCD), and plant species distribution data developed by UC-Berkeley, including oak tree distribution data, for potential use in BVOC emission modeling. Using mainly the USGS National Gap Analysis Program (GAP) landcover database, we planned our survey flights (to measure surface fluxes over long transects at constant altitude) and racetrack flights (vertical profiles to characterize flux divergence) over more or less homogeneous oak woodlands consisting of the Blue Oak Woodlands (BOW), Valley Oak Woodlands (VOW) and Coastal Oak Woodlands (COW).