Predicting aviation non-volatile particulate matter emissions at cruise via convolutional neural network.

Aviation emissions are the only direct source of anthropogenic particulate pollution at high altitudes, which can form contrails and contrail-induced clouds, with consequent effects upon global radiative forcing. In this study, we develop a predictive model, called APMEP-CNN, for aviation non-volatile particulate matter (nvPM) emissions using a convolutional neural network (CNN) technique. The model is established with data sets from the newly published aviation emission databank and measurement results from several field studies on the ground and during cruise operation. The model also takes the influence of sustainable aviation fuels (SAFs) on nvPM emissions into account by considering fuel properties. This study demonstrates that the APMEP-CNN can predict nvPM emission index in mass (EIm) and number (EIn) for a number of high-bypass turbofan engines. The accuracy of predicting EIm and EIn at ground level is significantly improved (R2 = 0.96 and 0.96) compared to the published models. We verify the suitability and the applicability of the APMEP-CNN model for estimating nvPM emissions at cruise and burning SAFs and blend fuels, and find that our predictions for EIm are within ±36.4 % of the measurements at cruise and within ±33.0 % of the measurements burning SAFs in average. In the worst case, the APMEP-CNN prediction is different by -69.2 % from the measurements at cruise for the JT3D-3B engine. Thus, the APMEP-CNN model can provide new data for establishing accurate emission inventories of global aviation and help assess the impact of aviation emissions on human health, environment and climate. SYNOPSIS: The results of this paper provide accurate predictions of nvPM emissions from in-use aircraft engines, which impact airport local air quality and global radiative forcing.

Mitigation effects of alternative aviation fuels on non-volatile particulate matter emissions from aircraft gas turbine engines: A review.

Global air transportation has grown rapidly in the past decade until the recent coronavirus pandemic. Previous research has demonstrated that particulate matter (PM) emissions from aircraft gas turbine engines can impair human health and environment, and may play a significant role in global climate change via direct absorption of solar radiation and indirect effect by their interaction with clouds. Using alternative aviation fuels (AAFs) from different sources have become a promising means to reduce aviation PM emissions and ensure energy sustainability. This work presents a review of non-volatile PM (nvPM) emission characteristics of aircraft gas turbine engines burning conventional aviation fuel (CAF) and CAF/AAF blends from recent ground and cruise tests. Current engine emission regulations, as well as available aviation PM emission prediction models and inventories are also discussed. Available nvPM emission characteristics, including particle number, particle mass, and particle size distribution (PSD), are analyzed and compared among different studies. The synthesized results indicate that burning AAFs tends to generate smaller size nvPM and reduce up to 90% nvPM number as well as 60-85% nvPM mass. The reduction is the most significant at low engine power settings, but becomes marginal at high engine power settings. The utilization of AAF blends reduces nvPM emission yet increases water vapor emission, which may promote contrail and even widespread cirrus cloud formation. Therefore, more investigation is required to quantify the potential impact of burning AAF at cruise altitudes on cloud formation and climate change. An appropriate estimation method for the particle number emissions from aircraft gas turbine engines fueled by both CAF and CAF/AAF blends is also in need aiming to establish a global aviation nvPM emission inventory and improve relevant global climate models.

PM2.5 composition and sources in the San Joaquin Valley of California: A long-term study using ToF-ACSM with the capture vaporizer.

The San Joaquin Valley (SJV) of California has suffered persistent particulate matter (PM) pollution despite many years of control efforts. To further understand the chemical drivers of this problem and to support the development of State Implementation Plan for PM, a time-of-flight aerosol chemical speciation monitor (ToF-ACSM) outfitted with a PM2.5 lens and a capture vaporizer has been deployed at the Fresno-Garland air monitoring site of the California Air Resource Board (CARB) since Oct. 2018. The instrument measured non-refractory species in PM2.5 continuously at 10-min resolution. In this study, the data acquired from Oct. 2018 to May 2019 were analyzed to investigate the chemical characteristics, sources and atmospheric processes of PM2.5 in the SJV. Comparisons of the ToF-ACSM measurement with various co-located aerosol instruments show good agreements. The inter-comparisons indicated that PM2.5 in Fresno was dominated by submicron particles during the winter whereas refractory species accounted for a major fraction of PM2.5 mass during the autumn associated with elevated PM10 loadings. A rolling window positive matrix factorization analysis was applied to the organic aerosol (OA) mass spectra using the Multilinear Engine (ME-2) algorithm. Three distinct OA sources were identified, including vehicle emissions, local and regional biomass burning, and formation of oxygenated species. There were significant seasonal variations in PM2.5 composition and sources. During the winter, residential wood burning and oxidation of nitrogen oxides were major contributors to the occurrence of haze episodes with PM2.5 dominated by biomass burning OA and nitrate. In autumn, agricultural activities and wildfires were found to be the main cause of PM pollution. PM2.5 concentrations decreased significantly after spring and were dominated by oxygenated OA during March to May. Our results highlight the importance of using seasonally dependent control strategies to mitigate PM pollution in the SJV.

Molecular polymorphism: microwave spectra, equilibrium structures, and an astronomical investigation of the HNCS isomeric family.

The rotational spectra of thioisocyanic acid (HNCS), and its three energetic isomers (HSCN, HCNS, and HSNC) have been observed at high spectral resolution by a combination of chirped-pulse and Fabry-Pérot Fourier-transform microwave spectroscopy between 6 and 40 GHz in a pulsed-jet discharge expansion. Two isomers, thiofulminic acid (HCNS) and isothiofulminic acid (HSNC), calculated here to be 35-37 kcal mol(-1) less stable than the ground state isomer HNCS, have been detected for the first time. Precise rotational, centrifugal distortion, and nitrogen hyperfine coupling constants have been determined for the normal and rare isotopic species of both molecules; all are in good agreement with theoretical predictions obtained at the coupled cluster level of theory. On the basis of isotopic spectroscopy, precise molecular structures have been derived for all four isomers by correcting experimental rotational constants for the effects of rotation-vibration interaction calculated theoretically. Formation and isomerization pathways have also been investigated; the high abundance of HSCN relative to ground state HNCS, and the detection of strong lines of SH using CH3CN and H2S, suggest that HSCN is preferentially produced by the radical-radical reaction HS + CN. A radio astronomical search for HSCN and its isomers has been undertaken toward the high-mass star-forming region Sgr B2(N) in the Galactic Center with the 100 m Green Bank Telescope. While we find clear evidence for HSCN, only a tentative detection of HNCS is proposed, and there is no indication of HCNS or HSNC at the same rms noise level. HSCN, and tentatively HNCS, displays clear deviations from a single-excitation temperature model, suggesting weak masing may be occurring in some transitions in this source.

Measurement of naphthalene uptake by combustion soot particles.

In this study, we designed and constructed an experimental laboratory apparatus to measure the uptake of volatile organic compounds (VOCs) by soot particles. Results for the uptake of naphthalene (C10H8) by soot particles typical of those found in the exhaust of an aircraft engine are reported in this paper. The naphthalene concentration in the gas phase and naphthalene attached to the particles were measured simultaneously by a heated flame ionization detector (HFID) and a time-of-flight aerosol mass spectrometer (ToF AMS), respectively. The uptake coefficient for naphthalene on soot of (1.11 ± 0.06) × 10(-5) at 293 K was determined by fitting the HFID and AMS measurements of gaseous and particulate naphthalene to a kinetic model of uptake. When the gaseous concentration of naphthalene is kept below the saturation limit during these experiments, the uptake of naphthalene can be considered the dry mass accommodation coefficient.

Probing the chemical nature of dihydrogen complexation to transition metals, a gas phase case study: H2-CuF.

This work details a gas phase study of the bonding of hydrogen to the metal in a simple diatomic analogue of a metal organic framework (MOF), copper fluoride, via dihydrogen complexation. This is the first microwave study of these types of interactions. J = 1-0 transitions of para-H(2)-CuF, ortho-D(2)-CuF, and HD-CuF have been measured and analyzed. The complexes were prepared by laser ablating a metal copper rod in the presence of a gas mix of 0.6% SF(6) and 3% H(2) in Ar undergoing supersonic expansion. The binding energy of this complex is addressed through quantum chemical calculations and measured nuclear quadrupole coupling constants for copper and deuterium. The significant change in the calculated binding energy and nuclear quadrupole coupling constants in relation to similar molecules suggest bonding greater than that typical of van der Waals interactions.

Identification of lubrication oil in the particulate matter emissions from engine exhaust of in-service commercial aircraft.

Lubrication oil was identified in the organic particulate matter (PM) emissions of engine exhaust plumes from in-service commercial aircraft at Chicago Midway Airport (MDW) and O'Hare International Airport (ORD). This is the first field study focused on aircraft lubrication oil emissions, and all of the observed plumes described in this work were due to near-idle engine operations. The identification was carried out with an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF AMS) via a collaborative laboratory and field investigation. A characteristic mass marker of lubrication oil, I(85)/I(71), the ratio of ion fragment intensity between m/z = 85 and 71, was used to distinguish lubrication oil from jet engine combustion products. This AMS marker was based on ion fragmentation patterns measured using electron impact ionization for two brands of widely used lubrication oil in a laboratory study. The AMS measurements of exhaust plumes from commercial aircraft in this airport field study reveal that lubrication oil is commonly present in organic PM emissions that are associated with emitted soot particles, unlike the purely oil droplets observed at the lubrication system vent. The characteristic oil marker, I(85)/I(71), was applied to quantitatively determine the contribution from lubrication oil in measured aircraft plumes, which ranges from 5% to 100%.

Determination of the emissions from an aircraft auxiliary power unit (APU) during the Alternative Aviation Fuel Experiment (AAFEX).

The emissions from a Garrett-AiResearch (now Honeywell) Model GTCP85-98CK auxiliary power unit (APU) were determined as part of the National Aeronautics and Space Administration's (NASA's) Alternative Aviation Fuel Experiment (AAFEX) using both JP-8 and a coal-derived Fischer Tropsch fuel (FT-2). Measurements were conducted by multiple research organizations for sulfur dioxide (SO2, total hydrocarbons (THC), carbon monoxide (CO), carbon dioxide (CO2), nitrogen oxides (NOx), speciated gas-phase emissions, particulate matter (PM) mass and number, black carbon, and speciated PM. In addition, particle size distribution (PSD), number-based geometric mean particle diameter (GMD), and smoke number were also determined from the data collected. The results of the research showed PM mass emission indices (EIs) in the range of 20 to 700 mg/kg fuel and PM number EIs ranging from 0.5 x 10(15) to 5 x 10(15) particles/kg fuel depending on engine load and fuel type. In addition, significant reductions in both the SO2 and PM EIs were observed for the use of the FT fuel. These reductions were on the order of approximately 90% for SO2 and particle mass EIs and approximately 60% for the particle number EI, with similar decreases observed for black carbon. Also, the size of the particles generated by JP-8 combustion are noticeably larger than those emitted by the APU burning the FT fuel with the geometric mean diameters ranging from 20 to 50 nm depending on engine load and fuel type. Finally, both particle-bound sulfate and organics were reduced during FT-2 combustion. The PM sulfate was reduced by nearly 100% due to lack of sulfur in the fuel, with the PM organics reduced by a factor of approximately 5 as compared with JP-8.

Characterization of lubrication oil emissions from aircraft engines.

In this first ever study, particulate matter (PM) emitted from the lubrication system overboard breather vent for two different models of aircraft engines has been systematically characterized. Lubrication oil was confirmed as the predominant component of the emitted particulate matter based upon the characteristic mass spectrum of the pure oil. Total particulate mass and size distributions of the emitted oil are also investigated by several high-sensitivity aerosol characterization instruments. The emission index (EI) of lubrication oil at engine idle is in the range of 2-12 mg kg(-1) and increases with engine power. The chemical composition of the oil droplets is essentially independent of engine thrust, suggesting that engine oil does not undergo thermally driven chemical transformations during the ∼4 h test window. Volumetric mean diameter is around 250-350 nm for all engine power conditions with a slight power dependence.

Conformational stability from variable temperature FT-IR spectra of krypton solutions, r0 structural parameters, vibrational assignment, and ab initio calculations of 4-fluoro-1-butene.

Variable temperature (-115 to -155 degrees C) studies of the infrared spectra (3200-400 cm-1) of 4-fluoro-1-butene, CH2=CHCH2CH2F, dissolved in liquid krypton have been carried out. The infrared spectra of the gas and solid as well as the Raman spectra of the gas, liquid, and solid have also been recorded from 3200 to 100 cm-1. From these data, an enthalpy difference of 72 +/- 5 cm-1 (0.86 +/- 0.06 kJ x mol-1) has been determined between the most stable skew-gauche II conformer (the first designation refers to the position of the CH2F group relative to the double bond, and the second designation refers to the relative positions of the fluorine atom to the C-C(=C) bond) and the second most stable skew-trans form. The third most stable conformer is the skew-gauche I with an enthalpy difference of 100 +/- 7 cm-1 (1.20 +/- 0.08 kJ x mol-1) to the most stable form. Larger enthalpy values of 251 +/- 12 cm-1 (3.00 +/- 0.14 kJ x mol-1) and 268 +/- 17 cm-1 (3.21 +/- 0.20 kJ x mol-1) were obtained for the cis-trans and cis-gauche conformers, respectively. From these data and the relative statistical weights of one for the cis-trans conformer and two for all other forms, the following conformer percentages are calculated at 298 K: 36.4 +/- 0.9% skew-gauche II, 25.7 +/- 0.1% skew-trans, 22.5 +/- 0.2% skew-gauche I, 10.0 +/- 0.6% cis-gauche, and 5.4 +/- 0.2% cis-trans. The potential surface describing the conformational interchange has been analyzed and the corresponding two-dimensional Fourier coefficients were obtained. Nearly complete vibrational assignments for the three most stable conformers are proposed and some fundamentals for the cis-trans and the cis-gauche conformers have been identified. The structural parameters, dipole moments, conformational stability, vibrational frequencies, infrared, and Raman intensities have been predicted from ab initio calculations and compared to the experimental values when applicable. The adjusted r0 structural parameters have been determined by combining the ab initio predicted parameters with previously reported rotational constants from the microwave data. These experimental and theoretical results are compared to the corresponding quantities of some similar molecules.

Rotational spectra of the van der Waals complexes of molecular hydrogen and OCS.

The a- and b-type rotational transitions of the weakly bound complexes formed by molecular hydrogen and OCS, para-H2-OCS, ortho-H2-OCS, HD-OCS, para-D2-OCS, and ortho-D2-OCS, have been measured by Fourier transform microwave spectroscopy. All five species have ground rotational states with total rotational angular momentum J=0, regardless of whether the hydrogen rotational angular momentum is j=0 as in para-H2, ortho-D2, and HD or j=1 as in ortho-H2 and para-D2. This indicates quenching of the hydrogen angular momentum for the ortho-H2 and para-D2 species by the anisotropy of the intermolecular potential. The ground states of these complexes are slightly asymmetric prolate tops, with the hydrogen center of mass located on the side of the OCS, giving a planar T-shaped molecular geometry. The hydrogen spatial distribution is spherical in the three j=0 species, while it is bilobal and oriented nearly parallel to the OCS in the ground state of the two j=1 species. The j=1 species show strong Coriolis coupling with unobserved low-lying excited states. The abundance of para-H2-OCS relative to ortho-H2-OCS increases exponentially with decreasing normal H2 component in H2He gas mixtures, making the observation of para-H2-OCS in the presence of the more strongly bound ortho-H2-OCS dependent on using lower concentrations of H2. The determined rotational constants are A=22 401.889(4) MHz, B=5993.774(2) MHz, and C=4602.038(2) MHz for para-H2-OCS; A=22 942.218(6) MHz, B=5675.156(7) MHz, and C=4542.960(7) MHz for ortho-H2-OCS; A=15 970.010(3) MHz, B=5847.595(1) MHz, and C=4177.699(1) MHz for HD-OCS; A=12 829.2875(9) MHz, B=5671.3573(7) MHz, and C=3846.7041(6) MHz for ortho-D2-OCS; and A=13 046.800(3) MHz, B=5454.612(2) MHz, and C=3834.590(2) MHz for para-D2-OCS.

Rovibrational spectra of the N2-HF complex at the vHF=3 level.

We report the analyses of the three intermolecular combination bands of the hydrogen-bonded N2-HF complex at vHF=3, observed by molecular beam intracavity laser induced fluorescence. The origin of the HF intermolecular bending combination band, (3001(1)0)<--(00000), is 11 548.45(3) cm(-1), 328.2 cm(-1) higher than that of the (30000)<--(00000) transition with an origin at 11 220.250(1) cm(-1). The average rotational constant of the (3001(1)0) level is 0.103 63(1) cm(-1), a 4.8% reduction from B(30000)=0.109 21(1) cm(-1). Perturbations are observed as line splittings, increased line widths, and reduced peak intensities of a number of lines of the e and f components of (3001(1)0). In addition, the centrifugal distortion coefficients of both components are large, negative, and different. The N2 intermolecular bend transition (30001(1))<--(00000) has an origin at 11 288.706(1) cm(-1), 68.456(2) cm(-1) above that of the (30000)<--(00000) transition. This is the lowest combination state at v(HF)=3 level. It is unperturbed, yielding B(30001(1))=0.110.10(1) cm(-1). The transition to the intermolecular stretching state, (30100)<--(00000), has an origin at 11 318.858(1) cm(-1) with B(30100)=0.105 84(1) cm(-1). Both the (30100) and (30000) levels show an isolated perturbation at J=4. The Lorentzian component of the line widths, which show considerable variation with soft mode, are GammaL(30000)=490(30) MHz, GammaL(30100)=630(30) MHz, GammaL(3001(1)0)=250(30) MHz, and GammaL(30001(1))=500(50) MHz.

Nuclear hyperfine interaction of rotating hydrogen: a spectroscopic investigation of hydrogen-OCS van der Waals complexes.

The rotational spectra of five weakly bonded hydrogen-OCS complexes (paraH(2), orthoH(2), HD, orthoD(2), and paraD(2)) are measured. Hyperfine structure is resolved and analyzed in all except the complex with paraH(2), where I=0. For the two j=1 species, orthoH(2)-OCS and paraD(2)-OCS, nuclear hyperfine coupling constants are found to be d(a)=21.2(2) and 8.4(2) kHz, respectively, indicative of nearly free uniaxial rotation of the hydrogen around the b-inertial axis. Similar analyses for HD-OCS and orthoD(2)-OCS yield the quadrupole coupling constants eqQ(a)=16(2) and 30(2) kHz, respectively, showing that the internal rotational motions of HD and orthoD(2) in the complex are slightly hindered producing a small nonspherical distribution. For orthoD(2)-OCS, the observed hyperfine structure indicates that the nuclear spin states I=0 and 2 are strongly coupled in the rotation of the complex.

The (4,0) mode of HF dimer at 14,700 cm(-l).

The deltaK = 0 and 1 subbands of the (4,0) <-- (0,0) transition of (HF)2, near 14,700 cm(-1), have been measured by molecular-beam intracavity laser-induced fluorescence. The hydrogen interchange tunneling is basically quenched in (4, 0) for both K = 0 and 1 levels, consistent with the early suggestion from a phenomenological model [H.-C. Chang and W. Klemperer, J. Chem. Phys. 104, 7830 (1996)]. The band origin upsilon0 = 14,700.458(7) cm(-1) and rotational constant (B + C)/2 = 0.22278(31) cm(-1) are determined for K = 0 of the (4, 0) mode. From the observed deltaK = 1 <-- 0 spectrum, we determined that A = 24.3 cm(-1), (B + C)/2 = 0.22296(20) cm(-1), and (B-C) = 4.5(2) x 10(-3) cm(-1). The predissociation linewidths of both K = 0 and 1 levels are 470(30) MHz with no apparent rotational dependence.

Asymmetry in angular rigidity of hydrogen-bonded complexes.

The asymmetry in angular rigidity of the proton donor and proton acceptor of hydrogen-bonded hydrogen fluoride binary complexes is investigated. The intermolecular bending frequency of HF, as the proton donor, is linearly proportional to the square root of the dissociation energy, whereas that of the proton acceptor is always much lower. The asymmetry, measured by the ratio of bending elastic constants of HF to that of the proton acceptor, is generally >2, and varies pronouncedly with the acceptors reaching values >20. Molecules with nitrogen as the bridged acceptor atom show an angular rigidity nearly one order of magnitude greater than the group with oxygen as the proton acceptor.

Spectroscopy of the OC-HF hydrogen-bonded complex at vHF=3.

The v(HF)=3 levels of the linear OC-HF complex are observed in the range of 10,800-11,500 cm(-1) using intracavity Ti-sapphire laser-induced fluorescence. The vibrational predissociation linewidths of both (30000) and (3001(1)0) states exceed 5 GHz; thus, the measured spectra are not rotationally resolvable. Under the assumption that these levels are not strongly perturbed, the rotational constants of the two levels are determined to be 0.1100(1) cm(-1) for (30000), 0.1081(1), and 0.1065(1) cm(-1) for f and e sublevels of (3001(1)0), respectively, through band contour fitting. The (30000)<--(00000) band origin is at 10,894.46(1) cm(-1), showing a HF wave number redshift of 478.3 cm(-1). The 4.07 redshift ratio of v(HF)=3 to that of v(HF)=1 indicates a significantly nonlinear increase of the intermolecular interaction energy through HF valence excitation. An ab initio interaction potential surface for HF valence coordinates varying from 0.8 to 1.25 A is used to examine vibrational dynamics. The HF valence vibration v(1) is treated perturbatively, showing that the vibrational redshifts are determined essentially in first order with only a very small second-order contribution. The (3001(1)0)<--(00000) combination transition is observed with the band origin at 11,432.66(1) cm(-1), giving the HF intermolecular bending mode to be 538.2 cm(-1). The high frequency of this vibration, compared to that in similar HF complexes, shows the strong angular anisotropy of the intermolecular interaction potential of OC-HF with respect to the HF subunit. The lifetime of the (3001(1)0) level increases to 28 ps from 14 ps for (30000).