Abstract
Abstract. Tracer flux ratio methodology was applied to airborne measurements to quantify methane (CH4) emissions from two dairy farms in central California during the summer. An aircraft flew around the perimeter of each farm measuring downwind enhancements of CH4 and a tracer species released from the ground at a known rate. Estimates of CH4 emission rates from this analysis were determined for whole sites and major sources within a site (animal housing and liquid manure lagoons). Whole-site CH4 flux rates for each farm, Dairy 1 (6108±821 kg CH4 d−1, 95 % confidence interval) and Dairy 2 (4018±456 kg CH4 d−1, 95 % confidence interval), closely resembled findings by established methods: ground-based tracer flux ratio and mass balance. Individual source emission rates indicate a greater fraction of the whole-site emissions come from liquid manure management than animal housing activity, similar to bottom-up estimates. Despite differences in altitude, we observed that the tracer release method gave consistent results when using ground or air platforms.
Highlights
Methane (CH4) released into the atmosphere as a result of agricultural activity, such as enteric fermentation and anaerobic digestion, significantly contributes to overall greenhouse gas emissions in the United States (USEPA, 2017)
Since Scientific Aviation (SA) had a tunable infrared laser direct absorption spectrometers (TILDAS) on board measuring C2H6 during these times, it was possible to treat these flights as a tracer release experiment similar to that performed with the ground-based equipment
The plane gradually flew a sequence of stacked circles around the facility with an average radius of ∼ 900 m depending on the ratio of the strength of the horizontal wind to the surface heating (Conley et al, 2017.) At Dairy 1, flights went as low as 79 m above ground level (a.g.l.), while achieving a maximum altitude of 1244 m a.g.l
Summary
Methane (CH4) released into the atmosphere as a result of agricultural activity, such as enteric fermentation and anaerobic digestion, significantly contributes to overall greenhouse gas emissions in the United States (USEPA, 2017). The. California Air Resources Board (CARB) attributes approximately 60 % of recent anthropogenic CH4 emissions in California to agriculture, with 45 % of CH4 emissions directly related to dairy farm activity for 2013 (CARB, 2017). Reduction strategies proposed by CARB seek to lower California’s CH4 emissions to 40 % below 2013 rates by 2030 (CARB, 2017), thereby emphasizing the need for accurate methods to directly quantify the contribution of different CH4 sources within agricultural operations. Other methods to estimate CH4 emissions from ruminants involve direct atmospheric measurements. Several studies of various CH4 sources (e.g., natural gas pipelines, landfills, dairy farms) assert that inventory-based calculations tend to underestimate emissions compared to atmospheric observations and modeling
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