Predicting gas–particle partitioning coefficients of atmospheric molecules with machine learning

The formation, properties, and lifetime of secondary organic aerosols in the atmosphere are largely determined by gas–particle partitioning coefficients of the participating organic vapours. Since these coefficients are often difficult to measure and to compute, we developed a machine learning model to predict them given molecular structure as input. Our data-driven approach is based on the dataset by Wang et al. (2017), who computed the partitioning coefficients and saturation vapour pressures of 3414 atmospheric oxidation products from the Master Chemical Mechanism using the COSMOtherm programme. We trained a kernel ridge regression (KRR) machine learning model on the saturation vapour pressure (Psat) and on two equilibrium partitioning coefficients: between a water-insoluble organic matter phase and the gas phase (KWIOM/G) and between an infinitely dilute solution with pure water and the gas phase (KW/G). For the input representation of the atomic structure of each organic molecule to the machine, we tested different descriptors. We find that the many-body tensor representation (MBTR) works best for our application, but the topological fingerprint (TopFP) approach is almost as good and computationally cheaper to evaluate. Our best machine learning model (KRR with a Gaussian kernel + MBTR) predicts Psat and KWIOM/G to within 0.3 logarithmic units and KW/G to within 0.4 logarithmic units of the original COSMOtherm calculations. This is equal to or better than the typical accuracy of COSMOtherm predictions compared to experimental data (where available). We then applied our machine learning model to a dataset of 35 383 molecules that we generated based on a carbon-10 backbone functionalized with zero to six carboxyl, carbonyl, or hydroxyl groups to evaluate its performance for polyfunctional compounds with potentially low Psat. The resulting saturation vapour pressure and partitioning coefficient distributions were physico-chemically reasonable, for example, in terms of the average effects of the addition of single functional groups. The volatility predictions for the most highly oxidized compounds were in qualitative agreement with experimentally inferred volatilities of, for example, α-pinene oxidation products with as yet unknown structures but similar elemental compositions.

Measured solid state and subcooled liquid vapour pressures of nitroaromatics using Knudsen effusion mass spectrometry

Knudsen effusion mass spectrometry (KEMS) was used to measure the solid state saturation vapour pressure (PSsat) of a range of atmospherically relevant nitroaromatic compounds over the temperature range from 298 to 328 K. The selection of species analysed contained a range of geometric isomers and differing functionalities, allowing for the impacts of these factors on saturation vapour pressure (Psat) to be probed. Three subsets of nitroaromatics were investigated: nitrophenols, nitrobenzaldehydes and nitrobenzoic acids. The PSsat values were converted to subcooled liquid saturation vapour pressure (PLsat) values using experimental enthalpy of fusion and melting point values measured using differential scanning calorimetry (DSC). The PLsat values were compared to those estimated by predictive techniques and, with a few exceptions, were found to be up to 7 orders of magnitude lower. The large differences between the estimated PLsat and the experimental values can be attributed to the predictive techniques not containing parameters to adequately account for functional group positioning around an aromatic ring, or the interactions between said groups. When comparing the experimental PSsat of the measured compounds, the ability to hydrogen bond (H bond) and the strength of the H bond formed appear to have the strongest influence on the magnitude of the Psat, with steric effects and molecular weight also being major factors. Comparisons were made between the KEMS system and data from diffusion-controlled evaporation rates of single particles in an electrodynamic balance (EDB). The KEMS and the EDB showed good agreement with each other for the compounds investigated.

Hydrometeorological Study of Saturated Vapour Pressure (SVP) of Warri, Nigeria

The amount of water vapour present in the air is indirectly expressed through vapour pressure and for any given temperature there is a limit for water vapour that can be held by air. If the air is holding water vapour which is equal to the maximum that it can hold at a given temperature, then the air is said to be saturated. Hydrometeorological study was carried out using vapour pressure (VP) and maximum temperature data for Warri through 2009 – 2018 (10 years) Saturation Vapour Pressure (SVP) were estimated. A graph is established showing the relationship between the Saturation Vapour Pressure (SVP) and the temperature also the graphical representation showing variational trend of SVP and VP were plotted. The study shows the dew point (Td) ranging from 29.9°C to 31.5°C which explained the likely rainfall at any temperature below Td. The study also confirmed increase in SVP bringing increase in Temperature and the variational trend shows the same pattern all through.

Experimental study of the POP technique: focus on the physical basis of the process

Introduction: Central or peripheral vascular access devices have been in use for many decades. However, despite adequate care and maintenance, complete occlusion may occur, and its impact cannot be overlooked. A new procedure using a percussion technique has been published and referred as ‘the POP technique’. Methods: A hydrodynamic bench was used permitting both the recording of the movement of the piston with a fast camera and the pressure variations in the polyurethane and silicone catheters while connected to 2- and 3-piece syringes. Results: The results are twofold. First the upward movement of the piston leads to the installation of a saturation vapour pressure in the body of the syringe. During this sequence, the clot is submitted to a force of aspiration. Then the release of the plunger leads to a pulse pressure whose dynamics and intensity are dependent of the types of syringes and catheters. Conclusions: The experiments bring to light the importance of practical features such as the orientation of the syringe and the nature of the polyurethane or silicone catheters. Then the analysis enables the definition of practical rules for safe practice of the POP technique. This study will impact clinicians as many may be tempted to use the technique in hope to resolve the occlusion safely, in a timely manner.

Measured solid state and sub-cooled liquid vapour pressures of nitroaromatics using Knudsen effusion mass spectrometry

Knudsen Effusion Mass Spectrometry (KEMS) was used to measure the solid state saturation vapour pressure (PSsat) of a range of atmospherically relevant nitroaromatic compounds over the temperature range from 298 to 328 K. The selection of species analysed contained a range of geometric isomers and differing functionalities, allowing for the impacts of these factors on saturation vapour pressure (Psat) to be probed. Three subsets of nitroaromatics were investigated, nitrophenols, nitrobenzaldehydes and nitrobenzoic acids. The PSsat were converted to sub-cooled liquid saturation vapour pressures (PLsat) using experimental enthalpy of fusion and melting point values measured using differential scanning calorimetry (DSC). The PLsat were compared to those estimated by predictive techniques and, with a few exceptions, were found to be up to 7 orders of magnitude lower. The large differences between the estimated PLsat and the experimental can be attributed to the predictive techniques not containing parameters to adequately account for functional group positioning around an aromatic ring, or the interactions between said groups. When comparing the experimental PSsat of the measured compounds the ability to hydrogen bond (H-Bond), and the strength of a H-bond formed appear to have the strongest influence on the magnitude of the Psat with steric effects and molecular weight also being major factors. Comparisons were made between the KEMS system and data from diffusion-controlled evaporation rates of single particles in an electrodynamic balance (EDB). The KEMS and the EDB showed good agreement with each other for the compounds investigated.

Performance of the Castor Oil in Methanol-Gasoline as a Bi-Functional Additive

In this paper, the castor oil, as additives, has been investigated on the phase separation temperature of M15, M30, M50 and M65 methanol gasoline at-25.0°C to 40.0°C, respectively. The effect of the additives on the phase stability and saturation vapour pressure was discussed. It was found that castor oil derivatives have good phase stability to various ratio methanol gasoline blends. Introducing water in the methanol gasoline blends need much amount of methyl castor oil to realize phase mixable. Besides, the castor oil can depress the saturation vapour pressure of methanol gasoline effective as well. With these data, it can be concluded that the castor oil have the great potential to be used gasoline-methanol additives.

Numerical Modelling and Sensitivity Analysis of Natural Draft Cooling Towers

Cooling towers are a relatively inexpensive and consistent method of ejecting heat from several industries such as thermal power plants, refineries, and food processing. In this research, an earlier model from literature was to be validated across three different case studies. Unlike previous models, this model considers the height of the fill as the discretised domain, which produces results that give it in a distribution form along the height of the tower. As there are limitations with the software used (gPROMS) where differential equations with respect to independent variables in the numerator and denominator cannot be solved, a derivative of the saturation vapour pressure with respect to the temperature of the air was presented. Results shown were in agreement with the literature and a parametric sensitivity analysis of the cooling tower design and operating parameters were undertaken. In this work the height of fill, mass flowrates of water and air were studied with respect to sensitivity analysis. Results had shown large variations in the outlet temperatures of the water and air if the mass flows of water and air were significantly reduced. However, upon high values of either variable had shown only small gains in the rejection of heat from the water stream. With respect to the height of the fill, at larger heights of the fill, the outlet water temperature had reduced significantly. From a cost perspective, it was found that a change in the water flowrate had incurred the largest cost penalty with a 1 % increase in flowrate had increased the average operating cost by 1.2 %. In comparison, a change in air flowrate where a 1 % increase in flowrate had yielded an average of 0.4 % increase in operating cost.

The effects of snow and salt on ice table stability in University Valley, Antarctica

The Antarctic Dry Valleys represent a unique environment where it is possible to study dry permafrost overlaying an ice-rich permafrost. In this paper, two opposing mechanisms for ice table stability in University Valley are addressed: i) diffusive recharge via thin seasonal snow deposits and ii) desiccation via salt deposits in the upper soil column. A high-resolution time-marching soil and snow model was constructed and applied to University Valley, driven by meteorological station atmospheric measurements. It was found that periodic thin surficial snow deposits (observed in University Valley) are capable of drastically slowing (if not completely eliminating) the underlying ice table ablation. The effects of NaCl, CaCl2 and perchlorate deposits were then modelled. Unlike the snow cover, however, the presence of salt in the soil surface (but no periodic snow) results in a slight increase in the ice table recession rate, due to the hygroscopic effects of salt sequestering vapour from the ice table below. Near-surface pore ice frequently forms when large amounts of salt are present in the soil due to the suppression of the saturation vapour pressure. Implications for Mars high latitudes are discussed.

Spectroscopic measurement of the vapour pressure of ice

We present a laser absorption technique to measure the saturation vapour pressure of hexagonal ice. This method is referenced to the triple-point state of water and uses frequency-stabilized cavity ring-down spectroscopy to probe four rotation–vibration transitions of at wavenumbers near 7180 cm −1 . Laser measurements are made at the output of a temperature-regulated standard humidity generator, which contains ice. The dynamic range of the technique is extended by measuring the relative intensities of three weak/strong transition pairs at fixed ice temperature and humidity concentration. Our results agree with a widely used thermodynamically derived ice vapour pressure correlation over the temperature range 0 ° C to −70 ° C to within 0.35 per cent.