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.

据报告，反刍动物和粪便管理产生的CH ₄排放量在大气自上而下的计算中要比自下而上（BU）的清单高2倍。我们通过使用美国环境保护署（US EPA）的方法（用于BU清单）和3种独立的测量技术来估算加利福尼亚州2个乳品厂的CH ₄排放量，从而探索了这种差异：（1）使用反向色散建模的开放路径测量（此后称为开放路径），（2）使用示踪剂通量比方法进行车辆测量，以及（3）使用封闭路径方法进行飞机测量。所有这三种技术均用于估算整个设施的CH ₄2016年夏季，每个农场3至6 d的温室气体排放量。此外，使用开放路径估算了2017年冬季每个农场13至14 d的全设施CH ₄排放量。我们的目标是（1）使用不同的测量技术比较全设施CH _4的测量结果；（2）将全设施CH _4的测量结果与美国EPA清单方法学估计值进行比较；（3）比较两个奶场之间的CH ₄排放量。在测量技术中，整个设施的CH ₄估算值相似。未检测到动物住房产生的CH _4的季节性变化，但是CH ₄夏季，液态粪肥储存的排放量比冬季测量期间的排放量高3至6倍。这些发现证实了以前的研究，表明整个工厂需要全年测量CH ₄排放量，以估算和评估年度清单。液态粪便存储排放物的开路测量与夏季期间美国EPA的每月估算值相似，但与冬季测量期间不同。但是，考虑到年度排放估算，数值差异相对较小。粪便CH ₄排放占整个设施CH _4的69％至79％和26％至47％夏季和冬季测量期间的排放量。农场之间动物饲养场的甲烷产量相似（平均20.9 g CH ₄ / kg干物质摄入量），但通过液态粪便存储中的挥发性固体（VS）负荷将CH ₄排放归一化（g CH ₄每天/ kg在夏季（234 vs. 137 g CH ₄ / kg V​​S）和冬季测量期（78 vs. 22 g CH2），在1个奶牛场，所有牛每天产生的VS分别比其他牛分别多1.7和3.5倍。通道₄/ kg的VS）。我们将这种差异的大部分归因于以液态（厌氧）形式存储的粪肥的比例，并建议减少粪便以液态形式存储的粪便固体量的粪肥管理实践可以显着减少乳制品CH _4的排放。