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Harvard Forest Symposium Abstract 2013

  • Title: Seasonal cycles of biogenic volatile organic compound (BVOC) mixing ratios and fluxes from PTR-TOF-MS measurements at Harvard Forest
  • Primary Author: Karena McKinney (Harvard School of Engineering and Applied Sciences)
  • Additional Authors: Ying Liu (Amherst College)
  • Abstract:

    Biogenic volatile organic compound (BVOC) emissions from vegetation contribute nearly 90% of global VOC emissions. To quantify both emission and deposition fluxes of typical BVOCs and their oxidation products is essential to further understanding their roles in tropospheric chemistry, especially their contributions to the formation of ozone and secondary organic aerosol. In this study, a newly acquired PTR-TOF-MS and a conventional PTR-MS were deployed synchronously to measure mixing ratios of BVOCs above the canopy at Harvard Forest from early June to early October 2012. The inter-comparison of the two PTR instruments showed no significant discrepancy in the mixing ratios of most BVOCs, and the average relative deviations for methanol, acetone and MVK+MACR were within the range of 4%.



    The emission rate of isoprene, the dominant BVOC at Harvard Forest, is dependent on both leaf temperature and light. The measured midday isoprene concentrations closely tracked the emission rates predicted using a standard emission algorithm constrained with the measured temperatures and radiation levels. The seasonal pattern in midday isoprene concentrations, obtained by normalizing the measurements for variations in temperature and radiation, demonstrated relatively high levels during late spring and summer, and then decreased starting from early September, in keeping with seasonal cycles observed in past years.



    The high time resolution (5Hz) and high mass resolving power (over 4000 m/∆m) of PTR-TOF-MS allow separation and simultaneous measurement of a full range of VOCs, including isobars, and meet the necessary prerequisites for direct eddy covariance flux determination. The BVOC fluxes obtained from the PTR-TOF-MS will be compared with disjunct eddy covariance fluxes measured with the conventional PTR-MS but will allow for flux determinations for a much wider range of compounds than is possible with conventional instrument. The results will also add to the multi-season record of BVOC flux data from the site.

  • Research Category: Forest-Atmosphere Exchange