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Harvard Forest Data Archive

HF288

Fluxes of Molecular Hydrogen (H2) at Harvard Forest EMS Tower 2010-2012

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Data

Overview

  • Lead: Laura Meredith, Steven Wofsy, Ronald Prinn
  • Investigators: Roisin Commane, William Munger, Jim Tang
  • Contact: Laura Meredith
  • Start date: 2010
  • End date: 2012
  • Status: completed
  • Location: Prospect Hill Tract (Harvard Forest)
  • Latitude: +42.537755
  • Longitude: -72.171478
  • Elevation: 340 meter
  • Taxa:
  • Release date: 2016
  • Revisions:
  • EML file: knb-lter-hfr.288.2
  • DOI: digital object identifier
  • Related links:
  • Study type: short-term measurement
  • Research topic: forest-atmosphere exchange
  • LTER core area: inorganic nutrients
  • Keywords: atmospheric deposition, biogeochemistry, gas flux, hydrogen, snow, wind direction, wind speed
  • Abstract:

    Molecular hydrogen (H2) is an atmospheric trace gas with a large microbe-mediated soil sink, yet cycling of this compound throughout ecosystems is poorly understood. Measurements of the sources and sinks of H2 in various ecosystems are sparse, resulting in large uncertainties in the global H2 budget. Constraining the H2 cycle is critical to understanding its role in atmospheric chemistry and climate. We measured H2 fluxes at high frequency in a temperate mixed deciduous forest for 15 months using a tower-based flux-gradient approach to determine both the soil-atmosphere and the net ecosystem flux of H2. The data presented here along with other data available at Harvard Forest can be used for efforts to model the H2 soil sink.

  • Methods:

    H2, CO2, H2O mole fractions and gradients

    Between December 2010 and March 2012, mole fractions of H2, CO2, and H2O were measured year-round at high frequency from gas inlets installed at heights above the ground of 24 m and 28 m (EMS tower above the forest canopy) and 0.5 m and 3.5 m (small tower below the canopy and over undisturbed soil 14 m to the west). H2 was measured with a gas chromatograph (Agilent, 6890, Santa Clara, CA) equipped with a pulsed discharge helium ionization detector (Valco, D-3, Houston, TX) and CO2 and H2O with non-dispersive, infrared gas analyzers (LI-COR, 6262, Lincoln, NE). Mole fractions were measured to high precision (0.06-0.11% for H2, 0.025-0.043% for CO2, and 0.04-0.05% for H2O) and were calibrated against H2 and CO2 standards traceable to National Oceanic and Atmospheric Administration (NOAA) Earth System Research Laboratory Global Monitoring Division (ESRL/GMD) primary standard scales. We used well-mixed integrating volumes to smooth out temporal fluctuations in mole fractions occurring at a higher frequency than our ability to measure their vertical gradients. Routine null bias tests were used test that no bias existed (offsets in measured mole fractions) between gas inlets. Here, we report mole fractions measurements of H2, CO2, and H2O at the following tower inlet heights and the resulting vertical mole fraction gradients d[H2]/dz.

    Mole fractions: H2 (parts per billion; ppb; 1e-9; nmol mol-1). CO2 (parts per million; ppm; 1e-6; umol mol-1). H2O (parts per thousand; ppth; 1e-3; mmol mol-1).

    Inlet heights: 28 m (above forest canopy, EMS tower). 24 m (above forest canopy, EMS tower). 3.5 m (below forest canopy, small tower 14 m to west of EMS tower, undisturbed soil). 0.5 m (below forest canopy, small tower 14 m to west of EMS tower, undisturbed soil).

    Mole fraction gradients: dH2dz_26 m (H2_28m – H2_24 m)/(28 m – 24 m) [units: ppb m-1]. dH2dz_10 m (H2_24m – H2_3.5 m)/(24 m – 3.5 m) [units: ppb m-1]. dH2dz_2 m (H2_3.5m – H2_0.5 m)/(3.5 m – 0.5 m) [units: ppb m-1].

    H2 gradient fluxes

    H2 fluxes were determined by the flux-gradient method, which assumes a proportional relationship between trace gas fluxes, F, and their vertical (z) concentration gradients (d[H2]/dz) scaled by the rate of turbulent exchange or eddy diffusivity, k: F = -kd[H2]/dz. Briefly, we used two flux-gradient approaches to infer k by 1) similarity to the flux and gradient of other trace gases (Modified Bowen Ratio) or 2) parameterization of the eddy diffusivity (k parameterization). For the Modified Bowen Ratio (1) we used mole fraction gradients of CO2 or H2O and the following independent flux measurements: eddy covariance CO2 and H2O flux measurements made above the forest canopy at a height of 29 m (HF001) or automated soil chamber CO2 respiration rates from a site approximately 0.6 km south of the EMS tower with similar soils and vegetation (HF284). We parameterized K (2) from the friction velocity and and heat flux from the sonic anemometer. Here, we present H2 fluxes calculated by the following methods and filtered as described below:

    H2 fluxes: FH2_26 m [units: nmol m-2 s-1] -- Method 1: Modified Bowen Ratio using eddy covariance CO2 flux and CO2 gradient, gap-filled with Modified Bowen Ratio using eddy covariance H2O flux and H2O gradient. Above canopy 26 m gradients used from June-November; whole canopy 10 m gradients used in other months when above canopy H2 gradient was exceedingly small.

    FH2_2 m [units: nmol m-2 s-1] -- Method 1: Modified Bowen Ratio using CO2 soil respiration flux and 2 m CO2 gradient, gap-filled Method 2: K parameterization using sonic anemometer at 2 m.

    FH2_2 m represents soil-atmosphere fluxes; little to no sub-canopy vegetation was present in the footprint of below-canopy measurements. FH2_26m represents net ecosystem Negative values of the H2 flux indicates trace gas uptake by the soil, ecosystem, or aboveground components from the atmosphere, while positive fluxes indicate emissions to the atmosphere. In addition to the flux, we also calculate the concentration-independent uptake rate of H2 to account for differences in ambient H2 that can influence first-order uptake rates:

    H2 deposition velocity, vd = -Fs⁄[H2]; cm s-1

    Data were filtered to eliminate the following from calculated fluxes: small gradients in the denominator (less than 0.1 times the standard deviation of the gradient measurement), periods with more than 0.3 mm of rain per 30 min, poorly developed turbulence (friction velocity, u* less than 0.07 m s-1 and u* less than 0.17 m s-1, below and above canopy, respectively), and unrealistic large values of the implied turbulent transfer coefficients, k (|k |≤0.1 m2 s-1 and |k|≤30 m2 s-1, below and above canopy, respectively). We did not filter based on the wind sector because we found no interference from the tower and instrument shed to the east (45 to 180 degrees).

    Snow depth and porosity

    Snow depth (SD) was determined from the number of stripes visible on five painted graduated snow stakes (PVC with alternating vertical red and white stripes of 5 cm height) distributed within the field of vision of the subcanopy webcam mounted on the EMS tower that takes images every 30 minutes during daylight hours (HF158). The snowpack water content (snow water equivalent, SWE) was continuously measured in a nearby forest stand (HF155). Snow porosity (percent air-filled space) was determined from SWE and SD as (1- SD/SWE)x100% and represents an average bulk porosity of the snow profile.

    Below canopy sonic anemometer

    A sonic anemometer was installed on a small tower at a height of 2 m above the ground over undisturbed soil 14 m to the west of the main EMS tower (3D sonic anemometer (CSAT3, Campbell Scientific Inc. (CSI), Logan, Utah). Small tower was in the field of view of the EMS subcanopy PhenoCam (HF158-02). Data were collected from the sonic at less than 1Hz frequency and are averaged into 30-min intervals here.

  • Use:

    This dataset is released to the public under Creative Commons license CC BY (Attribution). Please keep the designated contact person informed of any plans to use the dataset. Consultation or collaboration with the original investigators is strongly encouraged. Publications and data products that make use of the dataset must include proper acknowledgement.

  • Citation:

    Meredith L, Wofsy S, Prinn R. 2016. Fluxes of Molecular Hydrogen (H2) at Harvard Forest EMS Tower 2010-2012. Harvard Forest Data Archive: HF288.

Detailed Metadata

hf288-01: H2, CO2, H2O mole fractions and gradients; H2 fluxes

  1. gmt: matlab serial datenum; days since January 0, 0000; greenwich mean time (unit: number / missing value: NA)
  2. est: matlab serial datenum; days since January 0, 0000; eastern standard time (unit: number / missing value: NA)
  3. year: year
  4. doy: day of year (unit: nominalDay / missing value: NA)
  5. datetime: date and time
  6. h2.28m: H2 mole fraction at 28 m (ppb) (unit: dimensionless / missing value: NA)
  7. h2.24m: H2 mole fraction at 24 m (ppb) (unit: dimensionless / missing value: NA)
  8. h2.3.5m: H2 mole fraction at 3.5 m (ppb) (unit: dimensionless / missing value: NA)
  9. h2.0.5m: H2 mole fraction at 0.5 m (ppb) (unit: dimensionless / missing value: NA)
  10. d.h2dz.26m: H2 gradient between 28 and 24 m (ppb m-1) (unit: dimensionless / missing value: NA)
  11. d.h2dz.10m: H2 gradient between 24 and 3.5 m (ppb m-1) (unit: dimensionless / missing value: NA)
  12. d.h2dz.2m: H2 gradient between 3.5 and 0.5 m (ppb m-1) (unit: dimensionless / missing value: NA)
  13. co2.28m: CO2 mole fraction at 28 m (ppm) (unit: dimensionless / missing value: NA)
  14. co2.24m: CO2 mole fraction at 24 m (ppm) (unit: dimensionless / missing value: NA)
  15. co2.3.5m: CO2 mole fraction at 3.5 m (ppm) (unit: dimensionless / missing value: NA)
  16. co2.0.5m: CO2 mole fraction at 0.5 m (ppm) (unit: dimensionless / missing value: NA)
  17. dco2dz.26m: CO2 gradient between 28 and 24 m (ppm m-1) (unit: dimensionless / missing value: NA)
  18. d.co2dz.10m: CO2 gradient between 24 and 3.5 m (ppm m-1) (unit: dimensionless / missing value: NA)
  19. d.co2dz.2m: CO2 gradient between 3.5 and 0.5 m (ppm m-1) (unit: dimensionless / missing value: NA)
  20. h2o.28m: H2O mole fraction at 28 m (ppth) (unit: dimensionless / missing value: NA)
  21. h2o.24m: H2O mole fraction at 24 m (ppth) (unit: dimensionless / missing value: NA)
  22. h2o.3.5m: H2O mole fraction at 3.5 m (ppth) (unit: dimensionless / missing value: NA)
  23. h2o.0.5m: H2O mole fraction at 0.5 m (ppth) (unit: dimensionless / missing value: NA)
  24. d.h2odz.26m: H2O gradient between 28 and 24 m (ppth m-1) (unit: dimensionless / missing value: NA)
  25. d.h2odz.10m: H2O gradient between 24 and 3.5 m (ppth m-1) (unit: dimensionless / missing value: NA)
  26. d.h2odz.2m: H2O gradient between 3.5 and 0.5 m (ppth m-1) (unit: dimensionless / missing value: NA)
  27. f.h2.26m: H2 flux at 26 m; H2 net ecosystem flux (unit: nanomolePerMeterSquaredPerSecond / missing value: NA)
  28. f.h2.2m: H2 flux at 2 m; H2 soil-atmosphere flux (unit: nanomolePerMeterSquaredPerSecond / missing value: NA)
  29. vd.h2.2m: H2 deposition velocity; concentration-independent soil-atmosphere flux (unit: centimeterPerSecond / missing value: NA)

hf288-02: snow depth and bulk porosity

  1. gmt: matlab serial datenum; days since January 0, 0000; greenwich mean time (unit: number / missing value: NA)
  2. est: matlab serial datenum; days since January 0, 0000; eastern standard time (unit: number / missing value: NA)
  3. year: year
  4. doy: day of year (unit: nominalDay / missing value: NA)
  5. datetime: date and time
  6. snow.depth: snow depth (unit: centimeter / missing value: NA)
  7. snow.porosity: snow porosity (1-bulk density) (unit: dimensionless / missing value: NA)

hf288-03: below canopy sonic anemometer

  1. gmt: matlab serial datenum; days since January 0, 0000; greenwich mean time (unit: number / missing value: NA)
  2. est: matlab serial datenum; days since January 0, 0000; eastern standard time (unit: number / missing value: NA)
  3. year: year
  4. doy: day of year (unit: nominalDay / missing value: NA)
  5. datetime: date and time
  6. ustar.2m: friction velocity at 2 m height (unit: metersPerSecond / missing value: NA)
  7. wspd.2m: wind speed at 2 m height (unit: metersPerSecond / missing value: NA)
  8. wdir.2m: wind direction at 2m height (unit: degree / missing value: NA)
  9. t.2m: sonic temperature at 2m height (unit: celsius / missing value: NA)