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Abstract：
Reported estimates of CH4 emissions from ruminants and manure management are up to 2 times higher in atmospheric top-down calculations than in bottom-up (BU) inventories. We explored this discrepancy by estimating CH4 emissions of 2 dairy facilities in California with US Environmental Protection Agency (US EPA) methodology, which is used for BU inventories, and 3 independent measurement techniques: (1) open-path measurements with inverse dispersion modeling (hereafter open-path), (2) vehicle measurements with tracer flux ratio method, and (3) aircraft measurements with the closed-path method. All 3 techniques were used to estimate whole-facility CH4 emissions during 3 to 6 d per farm in the summer of 2016. In addition, open-path was used to estimate whole-facility CH4 emissions over 13 to 14 d per farm in the winter of 2017. Our objectives were to (1) compare whole-facility CH4 measurements utilizing the different measurement techniques, (2) compare whole-facility CH4 measurements to US EPA inventory methodology estimates, and (3) compare CH4 emissions between 2 dairies. Whole-facility CH4 estimates were similar among measurement techniques. No seasonality was detected for CH4 emissions from animal housing, but CH4 emissions from liquid manure storage were 3 to 6 times greater during the summer than during the winter measurement periods. The findings confirm previous studies showing that whole-facility CH4 emissions need to be measured throughout the year to estimate and evaluate annual inventories. Open-path measurements for liquid manure storage emissions were similar to monthly US EPA estimates during the summer, but not during the winter measurement periods. However, the numerical difference was relatively small considering yearly emission estimates. Manure CH4 emissions contributed 69 to 79% and 26 to 47% of whole-facility CH4 emissions during the summer and winter measurement periods, respectively. Methane yields from animal housing were similar between farms (on average 20.9 g of CH4/kg of dry matter intake), but CH4 emissions normalized by volatile solids (VS) loading from liquid manure storage (g of CH4 per day/kg of VS produced by all cattle per day) at 1 dairy were 1.7 and 3.5 times greater than at the other during the summer (234 vs. 137 g of CH4/kg of VS) and winter measurement periods (78 vs. 22 g of CH4/kg of VS), respectively. We attributed much of this difference to the proportion of manure stored in liquid (anaerobic) form, and suggest that manure management practices that reduce the amount of manure solids stored in liquid form could significantly reduce dairy CH4 emissions.
摘要：
报告的反刍动物和粪肥管理的CH4排放量估计在大气自上而下的计算中是自下而上（BU）清单的2倍。我们通过使用美国环境保护署（USEPA）方法估算加利福尼亚州2家乳品工厂的CH4排放量来探索这种差异，用于BU库存，和3种独立的测量技术：（1）具有逆色散模型的开放路径测量（以下简称开放路径），(2)车辆测量用示踪通量比法,(3)用闭合路径法测量飞机。所有3种技术均用于估算2016年夏季每个农场3至6天的整个设施CH4排放量。此外,开放路径用于估算2017年冬季每个农场13至14天的整个设施CH4排放量。我们的目标是(1)使用不同的测量技术比较整个设施的CH4测量值，(2)将整个设施CH4测量值与美国EPA清单方法估计值进行比较，和(3)比较2个奶牛场之间的CH4排放量。整个设施CH4的估计值在测量技术中相似。没有检测到来自动物舍的CH4排放的季节性，但是夏季液态粪肥储存产生的CH4排放量比冬季测量期间高3至6倍。研究结果证实了以前的研究，表明需要全年测量整个设施的CH4排放量，以估计和评估年度清单。液态粪肥储存排放的开放路径测量与夏季美国EPA每月的估计相似，但不是在冬季测量期间。然而,考虑到年排放量估计，数值差异相对较小。在夏季和冬季测量期间，肥料CH4排放量占整个设施CH4排放量的69％至79％和26％至47％，分别。来自动物饲养的甲烷产量在农场之间相似（平均20.9gCH4/kg干物质摄入量），但是，通过液体粪便储存产生的挥发性固体（VS）负荷（每天gCH4/每天所有牛产生的kgVS）标准化的CH4排放量在夏季比另一个奶制品高1.7倍和3.5倍（234vs.137gCH4/kgVS）和冬季测量期（78vs.22克CH4/千克VS)，分别。我们将这种差异的大部分归因于以液体（厌氧）形式储存的粪便比例，并建议减少以液体形式存储的粪便固体量的粪便管理实践可以显着减少乳制品CH4的排放。
