Yuanming Jia

In this study, the PM_2.5 pollution transport budget in the atmospheric boundary layer (ABL) of Beijing–Tianjin–Hebei (BTH) and Chengdu–Chongqing (CY) was quantitatively evaluated from the perspective of horizontal and vertical exchange. Based on the aircraft meteorological data relay (AMDAR) observation data, the study found that the vertical exchange process of pollutants is mainly influenced by the combined effects of meteorological conditions and topographical factors. Meteorological factors determine the direction and intensity of the vertical exchange, while the complexity of the terrain affects the exchange pattern through local circulation and air flow convergence. The characteristics of the pollution transport budget between the BTH and CY regions show that the BTH region has a net output of pollutants throughout the year, while the CY region has a net input of pollutants. The total transport budget of the four typical representative seasons in BTH is negative. It indicated that BTH, as the region with the highest intensity of air pollution emission in China, is dominated by outward transport of air pollutants to surrounding regions. Due to the influence of topographic and meteorological conditions in the CY region, the air pollutants tend to accumulate in the basin rather than diffuse. The transport budget relationship of the four seasons is positive and the input of air pollutants can be obviously simulated. Combined with the results of the vertical wind profile, Beijing is more vulnerable to the prevailing cold air sinking in the northwest in winter, which is characterized by the inflow of the free troposphere (FT) into the ABL. As for Chongqing, it is blocked by mountains so that the gas convection at the top of the ABL is obvious. This horizontal convergence phenomenon induces upward vertical movement, which makes Chongqing show a strong characteristic of the ABL transport to the FT.

Nanoparticles can reduce the friction coefficient and present a self-restorative effect and MoDTC is important as a friction-reducing additive. Both are important for improving lubricating performance. In this study, the tribological performances of nanoparticles in the presence of MoDTC were studied. The chemical synthetic and ball-milled nanoparticles were selected as test samples, and tribological performances were evaluated by a block-ring friction test rig. Experimental results show that the synthetic serpentine particle with a 200–800 nm diameter exhibits the lowest friction coefficient and wear, while the ball-milled kaolin particle shows the highest friction and wear. A synergistic lubricating effect has been shown when mixing the synthetic nano serpentine particle and MoDTC. The friction coefficient of “BD + synthetic serpentine” reduced from 0.011 to 0.055 after the compound with MoDTC. At 150 °C, the “BD + synthetic serpentine + MoDTC” improves the production of MoS₂ on the friction surface, which further reduced the friction coefficient and wear, while the ball-milled kaolin reduced the production of MoS₂, which leads to a high friction coefficient. The synthetic serpentine shows a round surface without any sharp edge, which shows the minimal ploughing effect on the friction surface. Based on the experimental results, the synthetic nanoparticles have the best antiwear and friction reduction performance when compounded with MoDTC.