Non-neural BOLD variability in block and event-related paradigms

Block and event-related stimulus designs are typically used in fMRI studies depending on the importance of detection power or estimation efficiency. The extent of vascular contribution to variability in block and event-related fMRI-BOLD response is not known. With scaling, the extent of vascular variability in the fMRI-BOLD response during block and event-related design tasks was investigated. Blood oxygen level-dependent (BOLD) contrast data from healthy volunteers performing a block design motor task and an event-related memory task requiring performance of a motor response were analyzed from the regions of interest (ROIs) surrounding the primary and supplementary motor cortices. Average BOLD signal change was significantly larger during the block design compared to the event-related design. In each subject, BOLD signal change across voxels in the ROIs had higher variation during the block design task compared to the event-related design task. Scaling using the resting state fluctuation of amplitude (RSFA) and breath-hold (BH), which minimizes BOLD variation due to vascular origins, reduced the within-subject BOLD variability in every subject during both tasks but significantly reduced BOLD variability across subjects only during the block design task. The strong non-neural source of intra- and intersubject variability of BOLD response during the block design compared to event-related task indicates that study designs optimizing for statistical power through enhancement of the BOLD contrast (for, e.g., block design) can be affected by enhancement of non-neural sources of BOLD variability.     

Direct measurement of oxygen extraction with fMRI using 6% CO2 inhalation

The blood-oxygenation-level-dependent (BOLD) signal is an indirect hemodynamic signal that is sensitive to cerebral blood flow (CBF), cerebral blood volume (CBV) and cerebral metabolic rate of oxygen. Therefore, the BOLD signal amplitude and dynamics cannot be interpreted unambiguously without additional physiological measurements, and thus, there remains a need for a functional magnetic resonance imaging (fMRI) signal, which is more closely related to the underlying neuronal activity. In this study, we measured CBF with continuous arterial spin labeling, CBV with an exogenous contrast agent and BOLD combined with intracortical electrophysiological recording in the primary visual cortex of the anesthetized monkey. During inhalation of 6% CO2, it was observed that CBF and CBV are not further increased by a visual stimulus, although baseline CBF for 6% CO2 is below the maximal value of CBF. In contrast, the electrophysiological response to the stimulation was found to be preserved during hypercapnia. As a consequence, the simultaneously measured BOLD signal responds negatively to a visual stimulation for 6% CO2 inhalation in the same voxels responding positively during normocapnia. These observations suggest that the fMRI response to a sensory stimulus for 6% CO2 inhalation occurs in the absence of a hemodynamic response, and it therefore directly reflects oxygen extraction into the tissue.     

Coupling of neural activity and fMRI-BOLD in the motion area MT

The fMRI-BOLD contrast is widely used to study the neural basis of sensory perception and cognition. This signal, however, reflects neural activity only indirectly, and the detailed mechanisms of neurovascular coupling and the neurophysiological correlates of the BOLD signal remain debated. Here we investigate the coupling of BOLD and electrophysiological signals in the motion area MT of the macaque monkey by simultaneously recording both signals. Our results demonstrate that a prominent neuronal response property of area MT, so-called motion opponency, can be used to induce dissociations of BOLD and neuronal firing. During the presentation of a stimulus optimally driving the local neurons, both field potentials [local field potentials (LFPs)] and spiking activity [multi-unit activity (MUA)] correlated with the BOLD signal. When introducing the motion opponency stimulus, however, correlations of MUA with BOLD were much reduced, and LFPs were a much better predictor of the BOLD signal than MUA. In addition, for a subset of recording sites we found positive BOLD and LFP responses in the presence of decreases in MUA, regardless of the stimulus used. Together, these results demonstrate that correlations between BOLD and MUA are dependent on the particular site and stimulus paradigm, and foster the notion that the fMRI-BOLD signal reflects local dendrosomatic processing and synaptic activity rather than principal neuron spiking responses.     

Detectability of blood oxygenation level-dependent signal changes during short breath hold duration

Blood oxygenation level-dependent (BOLD) signal increases induced by hypercapnia stress has been recently investigated in human brains, which may be clinically relevant because it reflects cerebral hemodynamic response to vasodilatation. The aims of this study were to investigate the detectability of BOLD signal changes due to short breath holding and the feasibility of this technique in routine clinical practice. The results showed that significant BOLD responses could be detected in the gray matter for a breath hold duration as short as 10 s. Breath hold duration correlated strongly with the full width at half maximum of the hemodynamic response (r(2) = 0.975, p < 0.02), but not with the maximum signal change or the onset time. The fraction activation volume increased as the breath hold duration lengthened, reaching a plateau approximately at 20 s. Considering breath-holding capability of patients and detectability of BOLD signal changes, breath holding with a 20-s duration is suggested to be applied for clinical applications.     

Deconvolution filtering: Temporal smoothing revisited

Inferences made from analysis of BOLD data regarding neural processes are potentially confounded by multiple competing sources: cardiac and respiratory signals, thermal effects, scanner drift, and motion-induced signal intensity changes. To address this problem, we propose deconvolution filtering, a process of systematically deconvolving and reconvolving the BOLD signal via the hemodynamic response function such that the resultant signal is composed of maximally likely neural and neurovascular signals. To test the validity of this approach, we compared the accuracy of BOLD signal variants (i.e., unfiltered, deconvolution filtered, band-pass filtered, and optimized band-pass filtered BOLD signals) in identifying useful properties of highly confounded, simulated BOLD data: (1) reconstructing the true, unconfounded BOLD signal, (2) correlation with the true, unconfounded BOLD signal, and (3) reconstructing the true functional connectivity of a three-node neural system. We also tested this approach by detecting task activation in BOLD data recorded from healthy adolescent girls (control) during an emotion processing task.     

Neural and vascular variability and the fMRI-BOLD response in normal aging

Neural, vascular and structural variables contributing to the blood oxygen level-dependent (BOLD) signal response variability were investigated in younger and older humans. Twelve younger healthy human subjects (six male and six female; mean age: 24 years; range: 19–27 years) and 12 older healthy subjects (five male and seven female; mean age: 58 years; range: 55–71 years) with no history of head trauma and neurological disease were scanned. Functional magnetic resonance imaging measurements using the BOLD contrast were made when participants performed a motor, cognitive or a breath hold (BH) task. Activation volume and the BOLD response amplitude were estimated for the younger and older at both group and subject levels. Mean activation volume was reduced by 45%, 40% and 38% in the elderly group during the motor, cognitive and BH tasks, respectively, compared to the younger. Reduction in activation volume was substantially higher compared to the reduction in the gray matter volume of 14% in the older compared to the younger. A significantly larger variability in the intersubject BOLD signal change occurred during the motor task, compared to the cognitive task. BH-induced BOLD signal change between subjects was significantly less-variable in the motor task-activated areas in the younger compared to older whereas such a difference between age groups was not observed during the cognitive task. Hemodynamic scaling using the BH signal substantially reduced the BOLD signal variability during the motor task compared to the cognitive task. The results indicate that the origin of the BOLD signal variability between subjects was predominantly vascular during the motor task while being principally a consequence of neural variability during the cognitive task. Thus, in addition to gray matter differences, the type of task performed can have different vascular variability weighting that can influence age-related differences in brain functional response.     

CO2在气体水合物结构特性的固体核磁共振波谱与拉曼光谱实验研究

天然气水合物是蕴含着巨大能源潜力的非常规能源,2017年和2020年两次我国南海探索性试采的成功,加快了天然气水合物项目的进展。二氧化碳置换开采法,既能开发CH₄,又能封存CO₂。同时水合物法分离烟气中CO₂具有很好的应用前景,而CO₂在气体水合物的微观结构和特性尚不明确,实际应用存在一定的未知影响。为了考察其特性,利用13C固体核磁技术（NMR）和拉曼光谱（Raman）进行CO₂置换CH₄水合物、合成13CO₂-H₂-CP混合水合物实验表征,讨论CO₂在水合物中的定量问题,研究CO₂分子在笼型结构中的分布,探讨CO₂分子在气体水合物中的结构类型和特性。结果表明：（1）利用Raman费米低频共振1 277.5 cm-1峰积分得到CO₂在I型大笼（51262笼）的占有率为0.978 2,CH₄在Ⅰ型小笼（512笼）和大笼（51262笼）的占有率为0.059 3和0.009 5,水合数7.61,Raman费米高频共振1 381.3 m-1峰积分得到CO₂在51262笼的占有率为0.984 3,CH₄在512笼和51262笼的占有率为0.023 7和0.003 3,水合数7.70,CO₂几乎占满了大笼,CO₂气体的加入会导致水合物中,CH₄的大、小笼占有率均大幅度降低,置换后水合数略低于纯甲烷水合物,未标记的CO₂水合物在核磁中较难测出信号,CO₂气体置换后CH₄在小笼的占有率仅0.097 5,大笼占有率为0.317 2,两种方法差异主要原因为核磁的CO₂未出峰。（2）利用拉曼费米低频共振1 273.4 cm-1峰积分得到H₂、CO₂在512笼、CP在51262的占有率分别为0.124 8,0.304 2和0.997 8,水合数9.16;Raman费米高频共振1 380.6 cm-1峰积分得到H₂、CO₂在512笼、CP在51262的占有率分别为0.123 6,0.577 1和0.985 1,水合数7.12。13C标记CO₂分子在水合物中达到较好的固体核磁分辨率,首次确认CO₂在Ⅱ型小笼中的化学位移为124.8 ppm,计算得到CO₂的小笼占有率为0.783 1,CP的大笼占有率为0.971 8,水合数6.70,Raman高频频费米共振峰（1 380.6 cm-1）定量计算与13C NMR结果更接近。（3）对CO₂的13C NMR化学位移进行了归属,并结合Raman与13C NMR的对比分析,为CO₂水合物的13C NMR研究和拉曼定量提供参考。     

Decoding neural events from fMRI BOLD signal: A comparison of existing approaches and development of a new algorithm

Neuroimaging methodology predominantly relies on the blood oxygenation level dependent (BOLD) signal. While the BOLD signal is a valid measure of neuronal activity, variances in fluctuations of the BOLD signal are not only due to fluctuations in neural activity. Thus, a remaining problem in neuroimaging analyses is developing methods that ensure specific inferences about neural activity that are not confounded by unrelated sources of noise in the BOLD signal. Here, we develop and test a new algorithm for performing semiblind (i.e., no knowledge of stimulus timings) deconvolution of the BOLD signal that treats the neural event as an observable, but intermediate, probabilistic representation of the system's state. We test and compare this new algorithm against three other recent deconvolution algorithms under varied levels of autocorrelated and Gaussian noise, hemodynamic response function (HRF) misspecification and observation sampling rate. Further, we compare the algorithms' performance using two models to simulate BOLD data: a convolution of neural events with a known (or misspecified) HRF versus a biophysically accurate balloon model of hemodynamics. We also examine the algorithms' performance on real task data. The results demonstrated good performance of all algorithms, though the new algorithm generally outperformed the others (3.0% improvement) under simulated resting-state experimental conditions exhibiting multiple, realistic confounding factors (as well as 10.3% improvement on a real Stroop task). The simulations also demonstrate that the greatest negative influence on deconvolution accuracy is observation sampling rate. Practical and theoretical implications of these results for improving inferences about neural activity from fMRI BOLD signal are discussed.     

长光程共振式二氧化碳气体光声传感器研究

二氧化碳(CO₂)是植物光合作用的原材料,也是一种温室气体,其过量地排放会影响动植物的生态环境。在碳达峰、碳中和的背景下,研制高灵敏度的CO₂检测装置具有重要意义。为了监测大气环境中CO₂含量的变化,设计了一种长光程共振式CO₂气体光声传感器,并以此搭建了光声检测装置。以中心波长为2 004 nm的分布式反馈激光器(DFB)作为激发光源,激光射入由漫反射材料制成的球型吸收腔,在腔内多次反射以增加气体的吸收路径。吸收腔外部被两个高热传导率的铝制半球包裹,降低由池体吸收光能后产生的热噪声。吸收腔上耦合一根声学管,当其工作在一阶纵向共振模态时,光声信号被放大,在管子末端达到极大值。为了进一步增大光声信号,通过饱和加湿样品的方式来加快CO₂气体的弛豫速率,加湿后的样品产生的光声信号是干燥样品的2.1倍左右。使用一系列浓度的湿润CO₂样品标定光声检测装置,结果表明,光声信号与浓度之间呈现良好的线性关系。在此基础上,通过对标准气体的检测实验,验证了装置的准确性与稳定性...     

O2/CO2气氛下CO对煤焦异相还原NO影响的研究

为揭示O₂/CO₂燃烧过程中高浓度的CO对煤焦异相还原NO的影响,在1073 K温度下使用山西褐煤在卧式炉上进行了实验。分别对O₂/CO₂浓度比及CO浓度下NO的还原特性进行详细实验研究。研究结果表明:在O₂/CO₂气氛下,O₂浓度为30%时具有较高的还原率;相同O₂浓度下O₂/CO₂气氛较空气气氛NO还原率高,表明在CO存在的条件下,高浓度的CO₂会促进NO的还原;当CO浓度从1.5%逐渐升高时,NO的还原率逐渐降低,到CO浓度为5%时,NO还原率比没有加入CO时还要低,而在空气气氛下CO浓度的变化对NO的还原率影响较小。     

Effect of the thickness of the gas-sensitive layer on the response of solid state electrochemical CO2 sensors

This paper reports the effect of the sensitive layer thickness on the response of Nasicon based electrochemical CO₂ sensors. It was found that: (a) the cell voltage dependence on the thickness of the thin film Na₂CO₃ auxiliary electrode is well described within the theory of Schottky barriers formation in ionic crystals; and (b) sensors with relatively thick gas-sensitive layer are more reliable in dry CO₂ atmosphere.     

基于傅里叶变换红外光谱技术测量大气中CO_2的稳定同位素比值

长期监测大气中CO_2及其稳定同位素不仅可以获得CO_2源和汇信息,还可以确定不同排放源对大气中CO_2的贡献.傅里叶变换红外光谱技术是目前大气中痕量气体柱浓度高精度遥测的一种重要方法.本研究基于地基高分辨率傅里叶变换红外光谱仪采集的近红外太阳吸收光谱反演出大气中CO_2的稳定同位素~(13)CO_2和~(12)CO_2.在选择的~(13)CO_2的三个光谱窗口和~(12)CO_2的两个光谱窗口光谱拟合残差都很小,光谱拟合质量高.实验观测期间CO_2同位素~(13)CO_2和~(12)CO_2的反演误差平均值分别为(1.18±0.27)%和(0.89±0.25)%;利用Allan方差计算出观测系统的碳同位素比值δ~(13)C的测量精度为0.041‰.获得了2015年9月18日至2016年9月24日一年内大气中碳同位素比值δ~(13)C的长时间序列.结果表明,在整个测量期间δ~(13)C在-7.58‰--11.66‰范围内变化,平均值为(-9.5±0.57)‰;δ~(13)C有着明显的季节变化,冬季最小,夏季最大.分析了取暖导致的化石燃料燃烧排放增多是冬季大气中CO_2重同位素~(13)CO_2贫化的原因.观测结果显示了高分辨率傅里叶变换红外光谱仪具有准确和高精度观测大气中CO_2的稳定同位素和同位素比值δ~(13)C的能力.     

Effects of mild hypoxic hypoxia on poststimulus undershoot of blood-oxygenation-level-dependent fMRI signal in the human visual cortex

Characteristics of the blood-oxygenation-level-dependent (BOLD) functional magnetic resonance imaging (fMRI) signal poststimulus undershoot in the visual cortex were studied at varying levels of arterial blood oxygen saturation (Ysat). Undershoot with an amplitude of -0.6+/-0.2% appeared after positive BOLD response (+1.7+/-0.5%) under control conditions. Cerebral blood volume (CBV), as determined with vascular-space-occupancy-dependent fMRI, increased by 26-43% during the positive BOLD peak, but the CBV proceeded at baseline level during the BOLD poststimulus undershoot. Mild hypoxic hypoxia (Ysat ranging from 0.82 to 0.89) had no effect on the amplitude or duration of poststimulus undershoot in activated BOLD pixels. Hypoxia did not influence CBV during the BOLD poststimulus undershoot. In contrast, the positive BOLD signal at the level of all activated pixels was smaller in hypoxia than in normoxia. The present results show that the BOLD poststimulus undershoot is not influenced by curtailed oxygen availability and that, during the undershoot, CBV is not different from resting state.     

Visual cortex reactivity in sedated children examined with perfusion MRI (FAIR)

Sleeping and sedated children can respond to visual stimulation with a decrease in blood oxygenation level dependent (BOLD) functional MRI signal response. The contribution of metabolic and hemodynamic parameters to this inverse signal response is incompletely understood. It has been hypothesized that it is caused by a relatively greater increase of oxygen consumption compared to rCBF (regional cerebral blood flow) increase. We studied the rCBF changes during visual stimulation in four sedated children, aged 4-71 months, and four alert adults, with an arterial water spin labeling technique (FAIR) and BOLD fMRI in a 1.5T MR scanner. In the children, FAIR signal decreased by a mean of 0.96% (range 0.77-1.05) of the baseline periods of the non-selective images, while BOLD signal decreased by 2.03% (range 1.99-2.93). In the adults, FAIR and BOLD signal increased by 0.88% (range 0.8-0.99) and 2.63% (range 1.99-2.93), respectively. Thus, in the children, an rCBF increase could not be detected by perfusion MRI, but indications of a FAIR signal decrease were found. An rCBF decrease in the primary visual cortex during stimulation has not been reported previously, but it is a possible explanation for the negative BOLD response. Future studies will have to address if this response pattern is a consequence of age or sleep/sedation.     

Evidence for bicarbonate formation on vacuum annealed TiO2(110) resulting from a precursor-mediated interaction between CO2 and H2O

The reaction of CO₂ and H₂O to form bicarbonate (HCO⁻₃) was examined on the nearly perfect and vacuum annealed surfaces of TiO₂(110) with temperature programmed desorption (TPD), static secondary ion mass spectrometry (SSIMS) and high resolution electron energy loss spectrometry (HREELS). The vacuum annealed TiO₂(110) surface possesses oxygen vacancy sites that are manifested in electronic EELS by a loss feature at 0.75 V. These oxygen vacancy sites bind CO₂ only slightly more strongly (TPD peak at 166 K) than do the five-coordinated Ti⁴⁺ sites (TPD peak at 137 K) typical of the nearly perfect TiO₂(110) surface. Vibrational HREELS indicates that CO₂ is linearly bound at the latter sites with a ν_a(OCO) frequency similar to the gas phase value. In contrast, oxygen vacancies dissociate H₂O to bridging OH groups which recombine to liberate H₂O in TPD at 490 K. No evidence for a reaction between CO₂ and H₂O is detected on the nearly perfect surface. In sequentially dosed experiments on the vacuum annealed surface at 110 K, CO₂ adsorption is blocked by the presence of preadsorbed H₂O, adsorbed CO₂ is displaced by postdosed H₂O, and there is little or no evidence for bicarbonate formation in either case. However, when CO₂ and H₂O are simultaneously dosed, a new CO₂ TPD state is observed at 213 K, and the 166 K state associated with CO₂ at the vacancies is absent. SSIMS was used to tentatively assign the 213 K CO₂ TPD state to a bicarbonate species. The 213 K CO₂ TPD state is not formed if the vacancy sites are filled with OH groups prior to simultaneous CO₂+H₂O exposure. Sticking coefficient measurements suggest that CO₂ adsorption at 110 K is precursor-mediated, as is known to be the case for H₂O adsorption on TiO₂(110). A model explaining the circumstances under which the proposed bicarbonate species is formed involves the surface catalyzed conversion of a precursor-bound H₂O–CO₂ van der Waals complex to carbonic acid, which then reacts at unoccupied oxygen vacancies to generate bicarbonate, but falls apart to CO₂ and H₂O in the absence of these sites. This model is consistent with the conditions under which bicarbonate is formed on powdered TiO₂, and is similar to the mechanism by which water catalyzes carbonic acid formation in aqueous solution.     

利用便携式FTIR光谱仪研究环境大气中CO2浓度变化

高准确和高精度测量环境大气CO₂浓度,对于监测区域和城市温室气体的排放至关重要。基于傅里叶变换红外（FTIR）光谱技术,利用便携式FTIR光谱仪采集近红外太阳吸收光谱,基于非线性最小二乘算法,反演获得了2016年9月至2020年5月期间合肥地区环境大气的CO₂柱浓度。观测结果表明,CO₂气体的柱浓度有着明显的季节变化,在春季出现最大值,夏季下降速度快,秋季达到最小值。柱平均干空气混合比浓度XCO₂的日均值位于(401.23±0.60)和(418.41±0.31) ppm之间,而2017年观测的月均值有着6.96 ppm的季节幅值。并且,观测期间XCO₂呈现逐年增长的趋势,年平均增长率为(2.71±0.66) ppm·yr-1。为了验证便携式FTIR光谱仪观测的准确性和可靠性,我们将其观测结果与高分辨率FTIR仪器同步测量结果进行比较,发现观测的XCO₂的偏差均值为1.32 ppm,二者的相关系数r为0.97,两个数据显示高度一致性。同时将观测结果与GOSAT卫星数据作了横向比较,两个数据的平均偏差为(0.63±1.76) ppm,二者的相关系数r为0.86,显示出地基数据与卫星数据有高相关性。最后,将合肥站点2020年秋季观测数据与上海站点同期观测数据进行了比较,发现上海站点与合肥站点的CO₂柱浓度变化基本一致,合肥观测点的XCO₂日均值位于(415.09±0.84)和(417.80±0.67) ppm之间,上海观测点的XCO₂日均值位于(411.87±1.07)和(416.63±1.70) ppm之间,表明同步观测期间合肥的CO₂柱浓度略高于上海市。地基FTIR光谱仪的观测结果可为追踪合肥地区温室气体的碳源与碳汇提供基础数据。     

注气驱替煤层气数值模拟

建立一种注气驱替煤层气的双重介质数学模型,考虑注气驱替煤层气中多组分气体渗流、吸附/解吸、扩散及孔隙度和渗透率敏感性等多物理场的耦合,用有限差分方法对数学模型数值求解,并验证模型的有效性.通过实例模拟,对比分析注入CO₂、N₂和70%N₂+30%CO₂提高采收率、产出组分动态及储层物性.计算表明:注入CO₂、N₂及其混合气体均能显著提高煤层气藏采收率,提高程度可达28%以上;N₂在注入后迅速突破产出,而CO₂突破时间较晚;注气后基质的收缩/膨胀效应在孔隙度和渗透率敏感性中起主导作用,CO₂吸附造成孔隙度和渗透率减小,而N₂吸附将增大孔隙度和渗透率.     

High adsorption and separation performance ofCO2 over N2 in azo-based (N=N) pillar[6]arene supramolecular organic frameworks

Azo-based pillar[6]arene supramolecular organic frameworks are reported for CO₂ and N₂ adsorption and separation by density functional theory and grand canonical Monte-Carlo simulation. Azo-based pillar[6]arene provides suitable environment for CO₂ adsorption and selectivity. The adsorption and selectivity results show that introducing azo groups can effectively improve CO₂ adsorption and selectivity over N₂, and both CO₂ adsorption and CO₂ selectivity over N₂ follow the sequence pillar[6]arene_N4 > pillar[6]arene_N2 > pillar[6]arene. Pillar[6]arene_N4 exhibits CO₂ adsorption capacity of ～ 1.36 mmol/g, and superior selectivity of CO₂ over N₂ of ～ 116.75 with equal molar fraction at 1 bar (1 bar=10⁵ Pa) and 298 K. Interaction analysis confirms that both the Coulomb and van der Waals interactions between CO₂ with pillar[6]arene frameworks are greater than that of N₂. The stronger affinity of CO₂ with pillar[6]arene_N4 than other structures and the larger isosteric heat differences between CO₂ and N₂ rendered pillar[6]arene_N4 to present the high CO₂ adsorption capacity and high CO₂ selectivity over N₂. Our results highlight the potential of azo-functionalization as an excellent means to improve pillar[6]arene for CO₂ capture and separation.     

基于微型多次反射腔的TDLAS二氧化碳测量系统

海气界面CO₂测量对于海洋科学研究具有重要意义,在目前的海洋CO₂测量仪器中,基于可调谐二极管激光吸收光谱技术(TDLAS)的设备因灵敏度高、环境适应性强等特点受到关注。TDLAS系统的体积和灵敏度通常受限于多次反射腔的大小和光程。针对海洋CO₂脱气量小且灵敏度高的测量需求,自主设计了一套微型多次反射腔,用于TDLAS系统的CO₂测量。该微型多次反射腔采用两片口径为25.4 mm、焦距为50 mm的球面反射镜,以38 mm的腔长实现了253次反射,获得了约10 m的光程,封装后的样品池体积仅有90 mL。基于该微型多次反射腔搭建了一套直接吸收TDLAS的CO₂气体浓度测量系统,通过标准气体对该系统进行了测试,检测限约为26×10-6,不同浓度气体线性相关度R2为99.986%。同时还将该系统与LGR公司生产的便携式温室气体分析仪(UGGA)进行了对比测量,结果表明二者在白天CO₂浓度波动较大和夜晚CO₂浓度变化较平稳两种情况下均表现出较好的一致性,R2大于97%。实验结果证明了系统性能,下一步将优化试验装置并进行现场应用。     

气溶胶对大气CO_2短波红外遥感探测影响的模拟分析

气溶胶引起的光学路径长度改变是影响高分辨率近红外光谱反演大气CO_2浓度的重要误差源.本文利用高精度大气辐射传输模式模拟中国碳卫星观测,结合CALIPSO(Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations)卫星的气溶胶廓线产品研究了不同特性的气溶胶对卫星观测光谱的影响.模拟结果显示:气溶胶散射引起的光学路径长度改变与气溶胶类型、模态以及垂直分布密切相关;城市型和海洋型气溶胶对观测光谱影响很大;多层分布的积聚模态大陆型和海洋型气溶胶在光学厚度小于0.3时,会引起5%以内的负辐射变化,随光学厚度不断增加会引起正的辐射变化;主要以粗粒子模态存在的气溶胶在不同的垂直分布情况下均会引起辐射的负变化,从而造成CO_2浓度的高估;另外,随气溶胶分布高度变高,负的辐射变化程度会逐渐减小.