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Title: Effects of mass air flow rate through an open-circuit gas quantification system when measuring carbon emissions

Author
item Gunter, Stacey
item Bradford, James
item Moffet, Corey

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/18/2016
Publication Date: 2/2/2017
Publication URL: https://handle.nal.usda.gov/10113/5642518
Citation: Gunter, S.A., Bradford, J.A., Moffet, C. 2017. Effects of mass air flow rate through an open-circuit gas quantification system when measuring carbon emissions. Journal of Animal Science. 95:475-484. doi:10.2527/jas2016.0933.

Interpretive Summary: Methane and carbon dioxide represent 11 and 81%, respectively, of all man-made greenhouse gas emissions. Agricultural methane emissions account for approximately 43% of all man-made methane emissions. Most agricultural methane emissions are attributed to ruminal fermentation within ruminant livestock, so there is significant interest in quantifying and mitigating this source. The automated, open-circuit gas quantification system (GQS; GreenFeed, C-Lock, Inc., Rapid City, SD) evaluated here can be placed in a pasture with grazing cattle and can measure their methane and carbon dioxide emissions. However, improper management of the GQS can have a significant effect on emission estimates. One factor affecting the quality of emission estimates is the air-flow rates through the GQS to ensure a complete capture of the breath cloud emitted by the animal before gas analysis. It is hypothesized that at lower air-flow rates, this cloud will be incompletely captured and underestimate the animal’s emissions. This research showed slower air-flow rates resulted in incomplete capture of the breath cloud and underestimates of methane and carbon dioxide emissions. Further, this research also showed that data with slow air-flow rates can be corrected by adjusting the emission estimates relative to air-flow rate. However, maintaining mass air flow through a GQS at rates greater than the recommended rate is the best method for producing high quality carbon dioxide and methane emission estimates.

Technical Abstract: Methane (CH4) and carbon dioxide (CO2) represent 11 and 81%, respectively, of all anthropogenic greenhouse gas emissions. Agricultural CH4 emissions account for approximately 43% of all anthropogenic CH4 emissions. Most agricultural CH4 emissions are attributed to enteric fermentation within ruminant livestock; hence, the heightened interest in quantifying and mitigating this source. The automated, open-circuit gas quantification system (GQS; GreenFeed, C-Lock, Inc., Rapid City, SD) evaluated here can be placed in a pasture with grazing cattle and can measure their CH4 and CO2 emissions with spot sampling. However, improper management of the GQS can have a significant effect on emission estimates. One factor affecting the quality of emission estimates is the air-flow rates through the GQS to ensure a complete capture of the breath cloud emitted by the animal. It is hypothesized that at lower air-flow rates this cloud will be incompletely captured. To evaluate the effect of air-flow rate through the GQS on emission estimates, a data set was evaluated with 758 CO2 and CH4 emission estimates with a range in air flows of 10.7 to 36.6 L/s. When air flow through the GQS was between 26.0 and 36.6 L/s, CO2 and CH4 emission estimates were not affected (P equal to 0.14 and 0.05, respectively). When air-flow rates were less than 26.0 L/s, CO2 and CH4 emission estimates were lower and decreased as air-flow rate decreased (P less than 0.0001). We hypothesize that when air flow through the GQS decreases below 26 L/s, breath capture was incomplete and CO2 and CH4 emissions are underestimated. Maintaining mass air flow through a GQS at rates greater than 26 L/s is important for producing high quality CO2 and CH4 emission estimates.