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首页> 外文期刊>Atmospheric chemistry and physics >Source apportionment of methane and nitrous oxide in California's San Joaquin Valley at CalNex 2010 via positive matrix factorization
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Source apportionment of methane and nitrous oxide in California's San Joaquin Valley at CalNex 2010 via positive matrix factorization

机译：通过正矩阵分解，加利福尼亚州圣华金河谷在CalNex 2010上甲烷和一氧化二氮的源分配

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Sources of methane (CH4) and nitrous oxide (N2O) were investigatedusing measurements from a site in southeast Bakersfield as part of the CalNex(California at the Nexus of Air Quality and Climate Change) experiment frommid-May to the end of June 2010. Typical daily minimum mixing ratios of CH4and N2O were higher than daily minima that were simultaneously observedat a mid-oceanic background station (NOAA, Mauna Loa) by approximately70 ppb and 0.5 ppb, respectively. Substantial enhancements of CH4 andN2O (hourly averages > 500 and > 7 ppb,respectively) were routinely observed, suggesting the presence of largeregional sources. Collocated measurements of carbon monoxide (CO) and a rangeof volatile organic compounds (VOCs) (e.g., straight-chain and branchedalkanes, cycloalkanes, chlorinated alkanes, aromatics, alcohols, isoprene,terpenes and ketones) were used with a positive matrix factorization (PMF)source apportionment method to estimate the contribution of regional sourcesto observed enhancements of CH4 and N2O.The PMF technique provided a "top-down" deconstruction of ambientgas-phase observations into broad source categories, yielding a seven-factorsolution. We identified these emission source factors as follows: evaporativeand fugitive; motor vehicles; livestock and dairy; agricultural and soilmanagement; daytime light and temperature driven; non-vehicular urban; andnighttime terpene biogenics and anthropogenics. The dairy and livestockfactor accounted for the majority of the CH4 (70–90 %) enhancementsduring the duration of experiments. The dairy and livestock factor was alsoa principal contributor to the daily enhancements of N2O (60–70 %).Agriculture and soil management accounted for ~ 20–25 % ofN2O enhancements over a 24 h cycle, which is not surprising giventhat organic and synthetic fertilizers are known to be a major source ofN2O. The N2O attribution to the agriculture and soil managementfactor had a high uncertainty in the conducted bootstrapping analysis. Thisis most likely due to an asynchronous pattern of soil-mediated N2Oemissions from fertilizer usage and collocated biogenic emissions from cropsfrom the surrounding agricultural operations that is difficult to apportionstatistically when using PMF. The evaporative/fugitive source profile,which resembled a mix of petroleum operation and non-tailpipe evaporativegasoline sources, did not include a PMF resolved-CH4 contribution thatwas significant (< 2 %) compared to the uncertainty in thelivestock-associated CH4 emissions. The uncertainty of the CH4estimates in this source factor, derived from the bootstrapping analysis, isconsistent with the ~ 3 % contribution of fugitive oil andgas emissions to the statewide CH4 inventory. The vehicle emissionsource factor broadly matched VOC profiles of on-road exhaust sources. Thissource factor had no statistically significant detected contribution to theN2O signals (confidence interval of 3 % of livestock N2Oenhancements) and negligible CH4 (confidence interval of 4 % oflivestock CH4 enhancements) in the presence of a dominant dairy andlivestock factor. The CalNex PMF study provides a measurement-basedassessment of the state CH4 and N2O inventories for the southernSan Joaquin Valley (SJV). The state inventory attributes ~ 18 % oftotal N2O emissions to the transportation sector. Our PMF analysisdirectly contradicts the state inventory and demonstrates there were nodiscernible N2O emissions from the transportation sector in thesouthern SJV region.
机译：甲烷的来源（CH 4 ）和一氧化二氮（N 2 O）的调查使用了贝克斯菲尔德东南部作为CalNex（加利福尼亚空气连结点）一部分的测量值质量和气候变化）实验于2010年5月中旬至2010年6月底进行。CH 4 和N 2 O的典型每日最低混合比高于同时每日最低排放的在大洋中部本底站（NOAA，莫纳罗亚河）观测到的速度分别约为70 ppb和0.5 ppb。常规观察到CH 4 和N 2 O的显着增强（分别分别为每小时平均值> 500和> 7 ppb），这表明存在较大的区域源。一氧化碳（CO）和一系列挥发性有机化合物（VOC）（例如，直链和支链烷烃，环烷烃，氯代烷烃，芳烃，醇，异戊二烯，萜烯和酮）的并置测量与正矩阵分解（PMF）一起使用）的资源分配方法，以估算区域性资源对观测到的CH 4 和N 2 O增强作用的贡献。 PMF技术提供了一种“自上而下的将环境气相观测分解为广泛的来源类别，产生了七个要素的解决方案。我们确定了这些排放源因素如下：蒸发和逃逸;机动车;畜牧业和奶业;农业和土壤管理;白天光照和温度驱动;非车辆城市夜间萜类生物基因和人为基因。在实验过程中，奶牛和牲畜因子占了CH 4 增强的大部分（70-90％）。奶牛和牲畜因子也是N 2 O每日增加的主要贡献者（60–70％）。农业和土壤管理约占N 2 的20–25％在24小时周期内> O增强，这不足为奇，因为已知有机和合成肥料是N 2 O的主要来源。进行自举分析时，N 2 O归因于农业和土壤管理因素具有较高的不确定性。这很可能是由于肥料使用与土壤介导的N 2 排放的异步模式以及周围农业生产的作物生物源排放的并置模式所致，这在使用PMF时很难进行统计分配。类似于石油操作和非尾气蒸发汽油源混合的蒸发/逸散源分布图，不包括PMF分解的CH 4 贡献，与不确定性相比，显着（<2％）与牲畜相关的CH 4 排放。自举分析得出的CH 4 估计值在该源因子中的不确定性与全州CH 4 清单中约有3％的逃逸油气排放量一致。车辆排放源因子与道路排放源的VOC分布大致匹配。该来源因素对N 2 O信号（牲畜N 2 增强的3％的置信区间）的检测结果无统计学意义，而CH 4 的影响可忽略不计（占主导地位的牲畜CH 4 增强的4％的置信区间）存在显性的乳制品和牲畜因子。 CalNex PMF研究为南部圣华金河谷（SJV）的州CH 4 和N 2 O清单提供了基于测量的评估。州库存占交通部门N 2 O排放总量的18％。我们的PMF分析直接与国家清单相矛盾，并表明在SJV南部地区运输部门没有明显的N 2 O排放。

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