Reactive uptake coefficients for multiphase reactions determined by a dynamic chamber system

Dynamic flow-through chambers are frequently used to measure gas exchange rates between the atmosphere and biosphere on the Earth's surface such as vegetation and soils. Here, we explore the performance of a dynamic chamber system in determining the uptake coefficient γ of exemplary gases (O3 and SO2) on bulk solid-phase samples. After characterization of the dynamic chamber system, the derived γ is compared with that determined from a coated-wall flow tube system. Our results show that the dynamic chamber system and the flow tube method show a good agreement for γin the range of 10−8 to 10−3. The dynamic chamber technique can be used for liquid samples and real atmospheric aerosol samples without complicated coating procedures, which complements the existing techniques in atmospheric kinetic studies.</p

Analysis of Oil-Air Two-Phase Flow Characteristics inside a Ball Bearing with Under-Race Lubrication

Under-race lubrication can increase the amount of lubricating oil entering a bearing and greatly improve lubrication and cooling effects. The oil-air two-phase flow characteristics inside a ball bearing with under-race lubrication play a key role in lubrication and cooling performance. The motions of ball bearing subassemblies are complicated. Ball spin affects the oil volume fraction. In this paper, the coupled level set volume of fluid (CLSVOF) method is used to track the oil-air two-phase flow inside the ball bearing with under-race lubrication. The influence of various factors on the oil volume fraction inside the ball bearing with under-race lubrication is investigated, particularly rotating speeds, inlet velocity and the size of oil supply apertures under the inner ring. The influence of the ball spinning is analyzed separately. The result demonstrates that, on account of the centrifugal force, lubricating oil is located more on the outer ring raceway at rotational speeds of 5000 r/min, 10,000 r/min, 15,000 r/min and 20,000 r/min. The oil volume fraction inside the bearing gradually increases at an oil inlet velocity of 5 m/s, 10 m/s and 15 m/s. The circumferential distribution of oil is also similar. As the diameter of the oil supply aperture increases from 1.5 mm to 2 mm, the oil volume fraction increases inside the ball bearing. However, the oil volume fraction slightly decreases from 2 mm to 2.5 mm of oil supply aperture diameter. Ball spin does not affect the circumferential distribution trend of the lubricating oil, but slightly reduces the oil volume fraction. Furthermore, ball spin causes the surface fluid to rotate around its rotation axis and increases the speed

Wear Characteristics of Different Groove-Shaped Friction Pairs of a Friction Clutch

To investigate the influence of the groove shape of friction disks on the wear of a friction clutch friction pair, a wear calculation model that considers the actual sliding distance between the friction clutch friction pair is presented based on the Archard adhesive wear model. The wear of three different groove-shaped friction pairs was calculated and analyzed. The wear test was carried out on the SAE#2 testing rig to obtain the actual wear amount and verify the accuracy and validity of the mathematical model. The results show that, among the three types of grooves, the friction disks with waffle grooves were the most prone to wear, followed by three-way parallel grooves. The wear performance of the two-way parallel grooves was the best, and the wear from one-time engagement can better reflect the change in the dynamic engagement of the friction pair. With the increase in the engagement time, the increase of the wear amount decreases

Dynamic analysis of planetary gear train system with double moduli and pressure angles

The planetary gear transmission with double moduli and pressure angles gearing is proposed for meeting the low weight high reliability requires. A dynamic differential equation of the NGW planetary gear train system with double and pressure angles is established. The 4-Order Runge-Kutta numerical integration method is used to solve the equations from which the result of the dynamic response is got. The dynamic load coefficients are formulated and are compared with those of the normal gear train．The double modulus planetary gear transmission is designed and manufactured. The experiment of operating and vibration are carried out and provides

Dynamic analysis of planetary gear train system with double moduli and pressure angles

The planetary gear transmission with double moduli and pressure angles gearing is proposed for meeting the low weight high reliability requires. A dynamic differential equation of the NGW planetary gear train system with double and pressure angles is established. The 4-Order Runge-Kutta numerical integration method is used to solve the equations from which the result of the dynamic response is got. The dynamic load coefficients are formulated and are compared with those of the normal gear train．The double modulus planetary gear transmission is designed and manufactured. The experiment of operating and vibration are carried out and provides

Photochemical Aging of Beijing Urban PM_2.5: HONO Production

Photochemical aging represents an important transformation process of aerosol particles in the atmosphere, which greatly influences the physicochemical properties and the environmental impact of aerosols. In this work, we find that Beijing urban PM_2.5 aerosol particles release substantial HONO, a significant precursor of •OH radicals, into the gas phase during the photochemical aging process. The generation of HONO exhibits a high correlation with the amount of nitrate in PM_2.5. The formation rate of HONO becomes gradually decreased with the irradiation time, but can be restored by introducing the acidic proton, indicative of the essential role of the acidic proton in the HONO production. Other environmental factors such as relative humidity, light intensity, and reaction temperature also possess important influences on HONO production. The normalized photolysis rate constant for HONO (<i>J</i>_HNO3→HONO) is in the range of 1.22 × 10^–5 s^–1 ∼ 4.84 × 10^–4 s^–1, which is 1–3 orders of magnitude higher than the reported photolysis rate constant of gaseous HNO₃. The present study implies that the photochemical aging of Beijing PM_2.5 is an important atmospheric HONO production source

Direct Formation of Electronic Excited NO₂ Contributes to the High Yield of HONO during Photosensitized Renoxification

Photosensitized renoxification of HNO3 is found to produce HONO in an unexpectedly high yield, which has been considered an important source for atmospheric HONO. Conventionally, the production of HONO is ascribed to the secondary photolysis of the primarily formed NO2. In this study, by using humic acid (HA) as a model environmental photosensitizer, we provide evidence of the direct formation of NO2 in its electronic excited state (NO2*) as a key intermediate during the photosensitizing renoxification of HNO3. Moreover, the high HONO yield originates from the heterogeneous reaction of the primarily formed NO2* with the co-adsorbed water molecules on HA. Such a mechanism is supported by the increase of the product selectivity of HONO with relative humidity. Further luminescence measurements demonstrate clearly the occurrence of an electronic excited state (NO2*) from photolysis of adsorbed HNO3 on HA. This work deepens our understanding of the formation of atmospheric HONO and gives insight into the transformation of RNS

Self-Cleaning Organic Vapor Sensor Based on a Nanoporous TiO₂ Interferometer

Porous thin films of TiO₂ are prepared and their use as chemical sensors for organic vapor analytes is investigated. Thin-film optical interference (Fabry-Perot) fringes in the reflectance spectrum are monitored using Reflectometric Interference Fourier Transform Spectroscopy (RIFTS). Three analytes are employed to probe the sensitivity of the porous TiO₂–based sensors as a function of analyte vapor pressure: dodecane, isopropyl alcohol (IPA), and pentane. Measured lower limits of detection (3, 30, and 11 000 ppmv for dodecane, IPA, and pentane, respectively) track the saturation vapor pressures (<i>P</i>_sat) of the analytes (0.134, 45, and 513 Torr at 25°C for dodecane, IPA, and pentane, respectively); the analyte with the lowest value of <i>P</i>_sat shows the lowest LLOD. Recovery of the sensor after a saturation dose of analyte is also dependent on <i>P</i>_sat: the sensor displays good recovery from pentane and IPA, and sluggish and incomplete recovery from dodecane. However, irradiation of the porous TiO₂ sensor with UV light in the presence of air accelerates recovery, and this process is attributed to photo-catalyzed oxidation of the analyte at the TiO₂ surface

Atmospheric measurements at Mt. Tai – Part I: HONO formation and its role in the oxidizing capacity of the upper boundary layer

International audienceAbstract. A comprehensive field campaign, with measurements of HONO and related parameters, was conducted in summer 2018 at the foot (150 m a.s.l.) and the summit (1534 m a.s.l.) of Mt. Tai (Shandong province, China). At the summit station, high HONO mixing ratios were observed (mean ± 1σ: 133 ± 106 pptv, maximum: 880 pptv), with a diurnal noontime peak (mean ± 1σ: 133 ± 72 pptv at 12:30 local time). Constraints on the kinetics of aerosol-derived HONO sources (NO2 uptake on the aerosol surface and particulate nitrate photolysis) were performed and discussed, which enables a better understanding of the interaction of HONO and aerosols, especially in the polluted North China Plain. Various evidence of air mass transport from the ground to the summit level was provided. Furthermore, daytime HONO formation from different paths and its role in radical production were quantified and discussed. We found that the homogeneous reaction NO + OH could only explain 8.0 % of the daytime HONO formation, resulting in strong unknown sources (Pun). Campaigned-averaged Pun was about 290 ± 280 pptv h−1, with a maximum of about 1800 pptv h−1. Aerosol-derived HONO formation mechanisms were not the major sources of Pun at the summit station. Their contributions to daytime HONO formation varied from negligible to moderate (similar to NO + OH), depending on the chemical kinetic parameters used. Coupled with sensitivity tests on the kinetic parameters used, the NO2 uptake on the aerosol surface and particulate nitrate photolysis contributed 1.5 %–19 % and 0.6 %–9.6 % of the observed Pun, respectively. Based on synchronous measurements at the foot and the summit station, an amount of field evidence was proposed to support the finding that the remaining majority (70 %–98 %) of Pun was dominated by the rapid vertical transport from the ground to the summit level and heterogeneous formation on the mountain surfaces during transport. HONO photolysis at the summit level initialized daytime photochemistry and still represented an essential OH source in the daytime, with a contribution of about one-quarter of O3. We provided evidence that ground-derived HONO played a significant role in the oxidizing capacity of the upper boundary layer through the enhanced vertical air mass exchange driven by mountain winds. The follow-up impacts should be considered in regional chemistry transport models

A Novel Mechanism for NO₂‑to-HONO Conversion on Soot: Synergistic Effect of Elemental Carbon and Organic Carbon

Soot, mainly composed of elemental carbon (EC) and organic carbon (OC), plays an important role in the formation of atmospheric nitrous acid (HONO) through the heterogeneous reaction with nitrogen dioxide (NO2). In this study, we found that fresh soot exhibits a much higher HONO yield than its EC or OC components alone. This does not support the previously proposed hydrogen-abstraction mechanism for HONO formation at a single reductive site on the soot surface. Based on our observations of infrared (IR) spectroscopy and flow tube experiments, we propose a new mechanism that involves the synergistic participation of two sites: one located at OC and the other at EC. They provide a proton and an electron necessary for NO2 reduction to HONO, respectively, via a proton-coupled electron transfer pathway. This mechanism highlights the important roles of OC and EC in HONO release from soot and underscores the significant implications of soot compositions in atmospheric oxidative capacity