The diurnal variation and distribution of lunar surficial hydration (OH/H2O) is of great significance for understanding the solar wind implantation and water cycle on the Moon. Lunar south pole is an ideal place to study the diurnal variation of surficial hydration due to the large number of repeat observations of the same region, which is very limited in mid- or low-latitudes. Here we showed clear 0.5-hr interval diurnal variation of surficial hydration at lunar south pole. The variation of hydration band depth with local time is exactly the opposite to the variation of temperature, indicating that lunar surficial hydration changes sufficiently with temperature. This relationship indicates that both the diurnal variation and hydration content are latitude dependent. Our observations support the hypothesis that the diurnal variation of hydration on the Moon is due to the formation of metastable hydroxyl. Hydration (OH/H2O) has been found on the surface of the Moon due to the implantation of solar wind. Hydration contents in the morning and evening were observed to be higher than that at local noon. Lunar south pole is a very good place to study the diurnal variation of surficial hydration compared with other places of the Moon as there are a lot of repeat observations of the same area at different local times. We conducted a detailed investigation of surficial hydration at the lunar south pole based on repeat Moon Mineralogy Mapper near-infrared data. We found surficial hydration at lunar south pole gradually decreases toward local noon, and then recovers to the morning level at evening. The variation trend is exactly the opposite to the temperature, indicating lunar surficial hydration changes sufficiently with instantaneous temperature. These observations provide clues for studies on the formation and evolution of volatiles on the Moon and other airless bodies. 0.5-hr interval diurnal variation of lunar surficial hydration was revealed at lunar south pole for the first time Lunar surficial hydration changes sufficiently with instantaneous temperature Lunar surficial hydration did not change when the Moon enters the Earth's magnetotail

Black carbon (BC) is one important component contributing to global warming and its climate-related impacts strongly depend on mixing state. Previous observations at ground level indicated BC aging was at a fast rate in daytime with efficient photochemical reactions, while BC aging significantly weakened at night. Here we present evidences that BC aging still occurs efficiently at night in the residual layer (RL). The ratio of thickly coated refractory BC (rBC) in total rBC (f(BC)) increased from 51.3% at 00:00 LST to 61.5% at 07:00 LST at the CITIC station, which located in the RL at night, with an increasing rate of 1.4% per hour. Such an increasing rate was even higher than that during noontime (11:00 to 15:00 LST, 0.7% per hour). Similar trend also reflected in the coating thickness (Dp/Dc) of rBC particles, which increased from 1.52 at 00:00 LST to 1.63 at 07:00 LST. The aging of rBC in the RL at night enhances light absorption of rBC particles correspondingly; calculated absorption enhancement (E-abs) increased from 1.64 at 00:00 LST to 1.79 in at 07:00 LST. Further analysis indicated that the Eabs depends not only on the D-p/D-c of rBC particles, but also on its size. An increase in the size of rBC particles in polluted episode can also enhance the Eabs. Combined observations of development of boundary layer and pollutants at the CITIC station suggested that rBC particles were upwards transported in daytime and trapped in the RL at night, where they were aged efficiently. These results will improve our understanding on rBC aging in the atmosphere, and hence help to evaluate its radiative forcing.