Journal of Quantitative Spectroscopy & Radiative Transfer最新文献

The largest share of greenhouse gas (GHG) emissions related to livestock originates from methane (CH₄) and nitrous oxide (N₂O) which have a far higher influence on global warming, it is therefore necessary to accurately monitor CH₄ and N₂O emissions to provide theoretical and practical basis for further estimating and regulating GHG emissions from livestock and improving livestock production performance. For the purpose of sensing CH₄ and N₂O emissions during livestock living process in real time, an optical sensor based on continuous-wave (CW) external cavity quantum cascade laser (EC-QCL) operating at room temperature was developed. CH₄ and N₂O absorption lines, located around 8 μm, of the ν₄ and ν₁ fundamental vibrational bands, respectively, were chosen for direct absorption spectroscopy, which allows for sensitive, selective and simultaneous measurement of CH₄ and N₂O concentrations. Use of a Herriot multi-pass cell with an effective path-length of 100 m, 1σ (SNR = 1) limits of detection of 26.8 ppbv, 20.3 ppbv and 0.01 % for CH₄, N₂O and H₂O vapor were achieved, respectively. Field measurement of CH₄ and N₂O emissions from horses has been carried out in a stable over two weeks at the Vernaelde farm in Couderkerque Branche city, France. Concentrations of CH₄ and N₂O up to 10 times and 1.5 times higher than their levels in the local ambient air (∼ 2.12 ppmv and ∼ 427 ppbv) were observed, respectively.

In this study the prediction accuracy of latest versions of FSK and SLW models (Rank correlated) and WSGG model is assessed at the limit of smallest computation cost. The results of these predictions are compared with the Line-by-Line benchmark calculations. One-dimensional decoupled radiation calculation is performed on a variety of case studies in order to investigate the limit of computational cost where the accuracy of FSK and SLW model are able to surpass WSGG. The subpar performance of RC-SLW at three quadrature points is addressed by optimizing model parameters. The possibility of using an approximated mixture database is also assessed where the RC-FSK model is able to yield satisfactory results with as low as four quadrature points. Regarding the utilization of approximated curves, again the method seems to be working slightly better with RC-FSK. The outcomes of this analysis may serve as guidance regarding the efficient implementation of FSK or SLW models in CFD codes.

Near-field radiative heat transfer (NFRHT) in point-dipole nanoparticle networks is complicated due to the multiple scattering of thermally excited electromagnetic wave (namely, many-body interaction, MBI). The MBI regime is analyzed using the many-body radiative heat transfer theory at the particle scale for networks of a few nanoparticles. Effect of MBI on radiative heat diffusion in networks of a large number of nanoparticles is analyzed using the normal-diffusion radiative heat transfer theory at the continuum scale. An influencing factor $\psi$ is defined to numerically figure out the border of the different many-body interaction regimes. The whole space near the two nanoparticles can be divided into four zones, non-MBI zone, enhancement zone, inhibition zone and forbidden zone, respectively. Enhancement zone is relatively smaller than the inhibition zone, so many particles can lie in the inhibiting zone that the inhibition effect of many-body interaction on NFRHT in nanoparticle networks is common in literature. Analysis on the radiative thermal energy confirms that multiple scattering caused by the inserted scatterer accounts for the enhancement and inhibition of NFRHT. By arranging the nanoparticle network in aspect of structures and optical properties, the MBI can be used to modulate radiative heat diffusion characterized by the radiative effective thermal conductivity ($k_{\mathrm{eff}}$) over a wide range, from inhibition (over 55% reduction) to amplification (30 times of magnitude). To achieve a notable MBI, it is necessary to introduce particles that have resonances well-matched with those of the particles of interest, irrespective of their match with the Planckian window. This work may help for the understanding of the thermal radiation in nanoparticle networks.

We first present quantitative, broadband absorbance cross sections of the C=O stretch fundamental rovibrational band of methyl formate in the 1670–1850 cm⁻¹ range at temperatures of 300, 600, 800, and 1000 K and pressures of 1–2 atm. The title molecular spectra were additionally studied across the pressure range of 1 to 35 atm at room temperature. Elevated temperature measurements were taken in argon bath gas behind the reflected shock wave of a shock tube by a rapid-tuning, broad-scan external cavity quantum cascade laser. The room temperature cross section of methyl formate was collected to validate our method and agreed well with previous room-temperature measurements by Sharpe et al. Then, to extend the utility of the collected data across intermediate temperatures, a pseudo-line-list (PLL) absorbance model was generated through a simultaneous fit of line-by-line intensities and lower-state energies to the measured cross sections. This PLL model was able to replicate the measurements within 3% across most of the spectral range and within 8% around the extremely sharp Q-branch feature present at room temperature. Cross-validation was then performed by re-fitting the PLL excluding the 800 K data set and demonstrated that the PLL approach is effective in interpolating between measured absorption cross sections at discrete temperatures. Finally, the additional room-temperature measurements from 1 to 35 atm were collected in a high-pressure static cell in nitrogen bath gas. These measurements revealed a notable Q-branch cross section pressure dependence while the P- and R-branch wings remained largely pressure independent across this wide pressure range. The collected methyl formate cross sections comprise the latest addition to the Stanford ShockGas-IR database for mid-infrared polyatomic absorption cross sections at elevated temperatures.

We present recent advances in path-integral formulations designed for unbiased Monte Carlo sensitivity estimation (in the form of partial derivatives) within a coupled physics model. We establish the theoretical foundation and illustrate the approach by estimating instantaneous atmospheric radiative forcings. In climate studies, these quantities amount for the change in top-of-atmosphere (TOA) net radiative flux induced by an isolated change in surface or atmospheric constitution. Based on a path-integral framework, our approach results in estimations consistent with well-established radiative forcings in the climate community. We highlight how physics coupling through path-integral formulations yields unbiased sensitivity estimation of a radiative quantity (integrated TOA flux) to a spectroscopic parameter (fraction change in gas concentration). Furthermore, we emphasize the method’s scalability, demonstrating its compatibility with computer science acceleration techniques. These latter play a key role in rendering the computational time weakly sensitive to the system’s multidimensional and multiphysics complexity.

We solve the radiative transfer equation (RTE) in anisotropically scattering media as an infinite series. Each series term represents a distinct number of scattering events, with analytical solutions derived for zero and single scattering. Higher-order corrections are addressed through numerical calculations or approximations.

The RTE solution corresponds to Monte Carlo sampling of photon trajectories with fixed start and end points. Validated against traditional Monte Carlo simulations, featuring random end points, our solution demonstrates enhanced efficiency for both anisotropic and isotropic scattering functions, significantly reducing computational time and resources. The advantage of our method over Monte Carlo simulations varies with the position of interest and the asymmetry of light scattering, but it is typically orders of magnitude faster while achieving the same level of accuracy. The exploitation of hidden symmetries further accelerates our numerical calculations, enhancing the method’s overall efficiency.

In addition, we extend our analysis to the first and second moments of the photon’s flux, elucidating the transition between transport and diffusive regimes.

Methane (CH₄) is the second-largest greenhouse gas contributing to global warming, surpassed only by CO₂, has a large difference in its vertical concentration distribution, and closely affects the global environment and climate change. The variations in the vertical concentrations of CH₄ need to be monitored. Ground-based infrared hyperspectrometers can measure the fine variations of the CH₄ concentrations in the vertical distribution within the planetary boundary layer (PBL). However, different detection channels are easily affected by instrumental noise and other environmental factors, leading to differences in the channel spectral characteristics and thereby affecting the accuracy of the CH₄ profile retrieval. In this study, an information-weighted channel selection method is proposed for the CH₄ profile retrieval using the Atmospheric Sounder Spectrometer by Infrared Spectral Technology (ASSIST) to address the differences in the channel characteristics from the different interference factors. This method leverages the information content of CH₄ and its environmental interference factors in each channel to derive the weighting factors, and a comprehensive weighting approach is subsequently applied to ascertain the effective information content of CH₄. The method then establishes the threshold for the effective CH₄ information content, considering the influence of noise, to select the optimal channels. We employ this method in our study, and 22 channels are selected as the optimal channels for the CH₄ profile retrieval. We also evaluate the retrieval capability of the CH₄ profile and the anti-interference ability of the selected channels using simulated spectra under clear-sky conditions. When retrieving the CH₄ profile using the 1200–1390 cm⁻¹ band (394 channels in total), the CH₄ profile is mainly affected by temperature, water vapor, aerosol optical depth (AOD) and N₂O. In addition, the mean absolute error (MAE) and the root mean square error (RMSE) for the CH₄ profile retrieval using the selected channels are substantially reduced.

This work reports on the first measurements of the lowest-lying singlet states as studied by photon spectroscopy for para-fluorotoluene, 4-C₇H₇F. Here we present the high-resolution vacuum ultraviolet photoabsorption spectrum in the 4.3–10.8 eV energy-range, with assignments supported by ab initio calculations (vertical excitation energies and oscillator strengths) at two different levels of theory, equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) and time-dependent density functional theory (TD-DFT). The electronic state spectroscopy of 4-C₇H₇F reveals the main character of the transitions to be valence, mixed valence-Rydberg and Rydberg, with the associated vibronic series. The absolute cross-section measurements were obtained and used to estimate the photolysis lifetime of 4-fluorotoluene from the sea level up to limit of the stratopause (50 km) in the Earth's atmosphere.

Spectrophotometers or optical benches using integrating spheres to measure normal-hemispherical transmittance $T_{NH}$ are widespread laboratory equipments. Although it is known that they cannot be used for ”highly turbid” samples, because multiple scattering may lead transmitted radiation to miss the entrance of the integrating sphere, very little is generally known about their exact validity range. Here we present a method to characterize the validity range of any such spectrophotometer and observe that most of them fail to measure $T_{NH}$ for scattering optical thickness above 0.25 (i.e. for $T_{NH}<0.9$ in the case of non absorbing media with $g=0$). We also show how it is possible to continue using spectrophotometers even outside their $T_{NH}$ measurement validity range, without any calibration, thanks to a proper simulation of radiative transfer and geometrical optics. We make available the corresponding radiative transfer simulation tools as open access codes, that have been developed for a straightforward implementation on a wide range of experimental setups. The method is validated on three different spectrophotometers or optical benches using standardized latex microspheres, then its practical implementation is illustrated in the case of semi-conductor particles and photosynthetic microalgae. Errors in analysis arising from the misuse of such optical devices are discussed throughout the article.

We present broadband dual frequency comb laser absorption measurements of 2 % H₂O (natural isotopic abundance of 99.7 % H₂¹⁶O) in air from 6600 to 7650 cm⁻¹ (1307–1515 nm) with a spectral point spacing of 0.0068 cm⁻¹. Twenty-nine datasets were collected at temperatures between 300 and 1300 K (±0.82 % average uncertainty) and pressures ranging from 20 to 600 Torr (±0.25 %) with an average residual absorbance noise of 8.0E-4 across the spectrum for all measurements. We fit measurements using a quadratic speed-dependent Voigt profile to determine 7088 absorption parameters for 3366 individual transitions found in HITRAN2020. These measurements build on the line strength, line center, self-broadening, and self-shift parameters determined in the Part I companion of this work. Here we measure air-broadened width (with temperature- and speed-dependence) and air pressure shift (with temperature-dependence) parameters. Various trends are explored for extrapolation to weak transitions that were not covered in this work. Improvements made in this work are predominantly due to the inclusion of air pressure shift temperature dependence values. In aggregate, these updates improved RMS absorbance error by a factor of 4.2 on average, and the remaining residual is predominantly spectral noise. This updated database improves high-temperature spectroscopic knowledge across the 6600-7650 cm⁻¹ region of H₂O absorption.