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Harvard Forest Symposium Abstract 2019

  • Title: Solar absorption measurements of CO2, CH4, and CO at Harvard Forest
  • Primary Author: Jonathan Franklin (Harvard University)
  • Additional Authors: John Budney (Harvard University); Taylor Jones (Not specified); J. William Munger (Harvard University); Steven Wofsy (Harvard University)
  • Abstract:

    Complete author list (all Harvard University):

    Jonathan E. Franklin
    Elaine Gottlieb
    Taylor Jones
    John Budney
    Bruce Daube
    J. William Munger
    Steven Wofsy

    In early May 2018 a ground-based solar-viewing spectrometer was installed next to the Fisher Meteorological Station at Harvard Forest to support regional studies of greenhouse gas emissions. The Bruker EM27/SUN is a small Fourier transform spectrometer that records the near-infrared solar spectrum from 0.85 - 2.5 microns every 6 seconds. A remotely operated enclosure protects the unit from adverse weather and enables regular cloud-free daytime measurements. Column-averaged dry-air mole fractions of CO2, CH4, and CO are retrieved from the solar spectra using the GGG software suite used by the global Total Carbon Column Observing Network. Since installation we have ~100 days of solar measurements from Harvard Forest.

    The sensor was originally designed to serve as a "clean-air" background site in support of a second EM27/SUN regularly operating in Cambridge, MA. Observing days with westerly winds enable us to quantify the urban enhancement of methane concentrations associated with the distribution and usage of natural gas in the greater Boston area. However, even alone the Harvard Forest column measurements contain insights into both long-range transport events and regional carbon fluxes. Multiple biomass burning plumes originating from fires in western USA, Canada, and even eastern Russia were observed during summer 2018. During these events strong enhancements in CO correlate with high fine-mode aerosol optical depths as recorded by the nearby AERONET station (Figure 1.)

    Observations during the 2018 summer also show a clear signal of daily CO2 photosynthetic uptake (Figure 2.) The amplitude of this drawdown is less than observed at the EMS flux tower which reflects the greater diversity of surface types within the larger footprints of the column observations. The regional uptake produces a diel cycle in the urban-rural gradient of CO2, measurements of which provide critical context to observations from sun-synchronous satellites (e.g., GOSAT, OCO-2, TROPOMI) that always measure locally at the same time of day.

    Column measurements will continue during 2019 at Harvard Forest, and future work will include a detailed comparison of the regional CO2 uptake from the EMS flux tower and the EM27/SUN observations. Harvard Forest will also be targeted by OCO-3 once it has been deployed on the International Space Station in spring 2019, and our column measurements will be used in validation of the OCO-3 mission.

  • Research Category: Regional Studies; Forest-Atmosphere Exchange

  • Figures:
  • Figure1.pdf