The CU mobile Solar Occultation Flux instrument: structure functions and emission rates of NH 3 , NO 2 and C 2 H 6
The CU mobile Solar Occultation Flux instrument: structure functions and emission rates of NH 3 , NO 2 and C 2 H 6
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DOI：
10.5194/amt-10-373-2017
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发表时间：
2016-08
影响因子：
3.8
通讯作者：
Natalie Kille;S. Baidar;P. Handley;I. Ortega;R. Sinreich;O. Cooper;F. Hase;J. Hannigan;G. Pfister;R. Volkamer
中科院分区：
文献类型：
--
作者：
Natalie Kille;S. Baidar;P. Handley;I. Ortega;R. Sinreich;O. Cooper;F. Hase;J. Hannigan;G. Pfister;R. Volkamer
抽象的。介绍了科罗拉多大学移动太阳掩星流量计(CU MOBILE SOF)。该仪器由一个数字移动太阳跟踪器和一个分辨率为0.5 cm−-1的傅里叶变换光谱仪和一个分辨率为0.55 nm的紫外可见光谱仪组成。该仪器用于同时测量氨(NH3)、乙烷(C2H6)和二氧化氮(NO2)在移动实验室的直射太阳光上的吸收。这些直射太阳观测提供了高的光子通量，使垂直柱状密度(VCD)的测量具有几何大气质量因子、2 S的高时间分辨率和5-19m的空间分辨率，表明FTS的仪器线形(ILS)与太阳跟踪器的方位和仰角指向无关。此外，在国家大气研究中心(HR-NCAR-FTS)高分辨率FTS旁的配置测量表明，CU移动的NH3和C2H6 SOF测量是精确和准确的，高信噪比下的VCD误差为2-7%。在2014年7月21日至9月3日在科罗拉多州进行的前沿空气污染和光化学实验(FRAPPE)期间，CU移动SOF仪器测量到的VCD中值(最小值和最大值)为4.3(0.5，45)×1016分子厘米−2NH3，0.3(0.06，2.23)×1016分子厘米−2NO2和3.5(1.5，7.7)×1016分子厘米−2 C2H6。在科罗拉多前锋山脉的城市、半污染农村和偏远农村地区记录的光谱中，95%的较大范围内检测到了所有气体。我们计算了基于VCDs的结构函数，VCDs描述了气柱随距离的变异性，并发现NH3的变异性最大。结构功能表明，目前可用的卫星可分辨研究区观测到的NH3和NO2 VCD变率的约10%。利用质量平衡法，即VCD与风速的闭环矢量积分，进一步量化了集中饲养动物作业(CAFO)中微量气体NH3和C2H6的排放通量和NO2的产生率。NH3通量的重现性很好，连续2天的NO2产生率也有较小程度的重复性；对于C2H6，通量受到不同上风条件的影响。平均排放因子为12.0和11.4gNH3 h−1 Head−1在30°C时，饲养场可容纳∼54 000头牛和∼7400头牛；汇集比率为11.8±2.0gNH3 h−1 Head−1与文献值上限一致。在这个排放速率下，CO的韦尔德县(766头牛)的NH3源可能被低估了2-10倍。CAFO土壤被发现是NOx的一个重要来源。氮氧化源占氨氮排放的∼1.2%，有可能使维尔德县的氮氧化物排放总量增加10%，使偏远地区的氮氧化源增加一倍。CAFO在区域尺度上影响环境NOx浓度的这种潜力是相关的，因为在科罗拉多锋面范围内，臭氧的形成对NOx是敏感的。NH3和NOx的排放与光化学臭氧和二次气溶胶的形成有关。
Abstract. We describe the University of Colorado mobile Solar Occultation Flux instrument (CU mobile SOF). The instrument consists of a digital mobile solar tracker that is coupled to a Fourier transform spectrometer (FTS) of 0.5 cm−1 resolution and a UV–visible spectrometer (UV–vis) of 0.55 nm resolution. The instrument is used to simultaneously measure the absorption of ammonia (NH3), ethane (C2H6) and nitrogen dioxide (NO2) along the direct solar beam from a moving laboratory. These direct-sun observations provide high photon flux and enable measurements of vertical column densities (VCDs) with geometric air mass factors, high temporal resolution of 2 s and spatial resolution of 5–19 m. It is shown that the instrument line shape (ILS) of the FTS is independent of the azimuth and elevation angle pointing of the solar tracker. Further, collocated measurements next to a high-resolution FTS at the National Center for Atmospheric Research (HR-NCAR-FTS) show that the CU mobile SOF measurements of NH3 and C2H6 are precise and accurate; the VCD error at high signal to noise ratio is 2–7 %. During the Front Range Air Pollution and Photochemistry Experiment (FRAPPE) from 21 July to 3 September 2014 in Colorado, the CU mobile SOF instrument measured median (minimum, maximum) VCDs of 4.3 (0.5, 45) × 1016 molecules cm−2 NH3, 0.30 (0.06, 2.23) × 1016 molecules cm−2 NO2 and 3.5 (1.5, 7.7) × 1016 molecules cm−2 C2H6. All gases were detected in larger 95 % of the spectra recorded in urban, semi-polluted rural and remote rural areas of the Colorado Front Range. We calculate structure functions based on VCDs, which describe the variability of a gas column over distance, and find the largest variability for NH3. The structure functions suggest that currently available satellites resolve about 10 % of the observed NH3 and NO2 VCD variability in the study area. We further quantify the trace gas emission fluxes of NH3 and C2H6 and production rates of NO2 from concentrated animal feeding operations (CAFO) using the mass balance method, i.e., the closed-loop vector integral of the VCD times wind speed along the drive track. Excellent reproducibility is found for NH3 fluxes and also, to a lesser extent, NO2 production rates on 2 consecutive days; for C2H6 the fluxes are affected by variable upwind conditions. Average emission factors were 12.0 and 11.4 gNH3 h−1 head−1 at 30 °C for feedlots with a combined capacity for ∼ 54 000 cattle and a dairy farm of ∼ 7400 cattle; the pooled rate of 11.8 ± 2.0 gNH3 h−1 head−1 is compatible with the upper range of literature values. At this emission rate the NH3 source from cattle in Weld County, CO (535 766 cattle), could be underestimated by a factor of 2–10. CAFO soils are found to be a significant source of NOx. The NOx source accounts for ∼ 1.2 % of the N flux in NH3 and has the potential to add ∼ 10 % to the overall NOx emissions in Weld County and double the NOx source in remote areas. This potential of CAFO to influence ambient NOx concentrations on the regional scale is relevant because O3 formation is NOx sensitive in the Colorado Front Range. Emissions of NH3 and NOx are relevant for the photochemical O3 and secondary aerosol formation.