Tracking nitrous oxide emission processes at a suburban site with semicontinuous, in situ measurements of isotopic composition
Tracking nitrous oxide emission processes at a suburban site with semicontinuous, in situ measurements of isotopic composition
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DOI：
10.1002/2016jd025906
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发表时间：
2017-02-16
影响因子：
4.4
通讯作者：
Mohn, Joachim
中科院分区：
文献类型：
--
作者：
Harris, Eliza;Henne, Stephan;Mohn, Joachim
在瑞士杜本多夫郊区，用预浓集耦合量子级联激光光谱仪，以近似35 min的频率，在1-6 d的间歇期内，连续测量了大气中一氧化二氮（N2O）的同位素组成。对于δ O-18、位点偏好和δ N-15（散装），所实现的测量重复性分别为0.08%、0.11%和0.10%，这优于或等于基于标准烧瓶采样的同位素比质谱性能。所观察到的平均昼夜周期反映了同位素重对流层背景上的同位素光源的N2O的积累。测量结果用于确定源同位素组成，与现场监测的化学和气象参数相比，源同位素组成变化很大。FLEXPART-COSMO运输模型结合修改后的排放数据库全球大气研究库存排放量被用来模拟N2O摩尔分数在网站上。此外，同位素签名估计不同的来源类别使用文献数据，并用于模拟N2O同位素组成的测量期间。该模型能够捕获的变化，以及N2O摩尔分数，但模拟的同位素组成与观测结果不一致。特别是，测得的源同位素组成表现出一个幅度较大的变化比模拟，清楚地表明，从文献中估计的同位素源签名的范围显着低估了源签名的真实变化。源三角洲O-18签名被认为是最敏感的示踪剂城市/工业与农业N2O。δ N-15（批量）和场地偏好可能比人为源类别的划分更能深入了解微生物和化学排放过程。
The isotopic composition of atmospheric nitrous oxide (N2O) was measured semicontinuously, at similar to 35 min frequency in intermittent periods of 1-6 days over one and a half years, using preconcentration coupled to a quantum cascade laser spectrometer at the suburban site of Dubendorf, Switzerland. The achieved measurement repeatability was 0.08%, 0.11%, and 0.10% for delta O-18, site preference, and delta N-15(bulk) respectively, which is better than or equal to standard flask sampling-based isotope ratio mass spectrometry performance. The observed mean diurnal cycle reflected the buildup of N2O from isotopically light sources on an isotopically heavy tropospheric background. The measurements were used to determine the source isotopic composition, which varied significantly compared to chemical and meteorological parameters monitored at the site. FLEXPART-COSMO transport modeling in combination with modified Emissions Database for Global Atmospheric Research inventory emissions was used to model N2O mole fractions at the site. Additionally, isotopic signatures were estimated for different source categories using literature data and used to simulate N2O isotopic composition over the measurement period. The model was able to capture variability in N2O mole fraction well, but simulations of isotopic composition showed little agreement with observations. In particular, measured source isotopic composition exhibited one magnitude larger variability than simulated, clearly indicating that the range of isotopic source signatures estimated from literature significantly underestimates true variability of source signatures. Source delta O-18 signature was found to be the most sensitive tracer for urban/ industry versus agricultural N2O. delta N-15(bulk) and site preference may provide more insight into microbial and chemical emission processes than partitioning of anthropogenic source categories.