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Primary work on the planetary boundary layer (PBL) climatic features and associated air pollution in Beijing was carried out based on a 40-year dataset. The main results are identified as follows. The annual mean PBL height was 906 m (1455 m in daytime and 357 m in nighttime). Within the PBL, the average potential temperature, specific humidity, and wind speed were 287.3 K, 5.1 g kg−1, and 6.5 m s−1. Significant seasonal variations were observed in the PBL variables, leading to distinct pollutant diffusion conditions. The PM2.5 concentrations varied seasonally, with a high value in winter (97 µg m−3) and a low value in summer (74 µg m−3). The summertime PM2.5 was closely related to the local emission intensity (R = 0.79) and declined with a reduction in the emission intensity, while the winter PM2.5 showed large interannual variabilities and trends, relying more on the PBL conditions. A comparison of polluted and clean winters was performed, revealing that polluted winters were associated with a warmer layer above the PBL that inhibited the development of the PBL (933 m vs. 1283 m, daily maximum height for polluted vs. clean winters) and led to a humid (1.4 g kg−1 vs. 0.8 g kg−1) and weak wind (5.8 m s−1 vs. 8.2 m s−1) layer within the PBL. In terms of synoptic impacts, the warm advection above the PBL (0.07 K h−1) and subsidence heating (0.21 K h−1) near the top of the PBL contributed to the occurrence of a stable and polluted PBL. [ABSTRACT FROM AUTHOR]

Based on bias-corrected future projections from the Providing REgional Climates for Impacts Studies (PRECIS) regional climate model under both RCP4.5 and 8.5 scenarios over China, extreme climatic events at the middle and end of the twenty-first century are investigated in this paper. The model performance of PRECIS is validated using comparisons with observations and HadGEM2-ES projections, and the bias correction adds fidelity to the projections of basic climate variables and extreme climate events. In the future, our single-realisation estimates show that the number of frost days is projected to decrease and days with tropical nights are projected to increase. Including northeast China, Sichuan Basin, middle and lower reaches of Yangtze River and south China, the number of consecutive dry days will increase from our single-realisation estimates, which will exhibit a spatial distribution almost similar to that of consecutive wet days in the coming decades. Although precipitation indices associated with duration will increase, a simple precipitation index depicting the intensity of extreme events will decrease over east and south China in the future from our single-realisation projections. Daily rainfall above 50 mm, which is usually regarded as a rainstorm event, is predicted to increase under the RCP4.5 scenario over most of China from our single-realisation estimates; while the same change pattern will occur in southernmost China, similarly spatially distributed for the RCP8.5 scenario, the number of rainstorm will first increase in the middle of the twenty-first century and then slow at the end of the twenty-first century in the Yangtze River region. In conclusion, our single-realisation estimates indicate that the persistence of extreme precipitation will increase with time, but the change of extreme precipitation intensity is not significant in the future. The comparison of climatic extreme events under the RCP4.5 scenario with those under the RCP8.5 scenario shows that extreme climate events will be enhanced under the higher emissions scenario; hence, reductions in greenhouse gas emissions will help alleviate climate change effects in the future. [ABSTRACT FROM AUTHOR]

Low-level temperature inversions play crucial roles in inhibiting vertical exchange of energy and mass, and may lead to air pollutants accumulation. The climatological study of them provides a fundamental overview of the static stability of atmosphere and is indispensable for air pollution controls. Based on high-vertical-resolution radiosondes at 00 and 12 UTC during 2011–2018, this work comprehensively examined the spatial and temporal variability of three characteristics (occurrences, strengths, and depths) of low-level inversions in China. Results revealed that inversions are prevalent (more than 80% of the observation records) over Eastern China. The northern part of Eastern China is dominated by the thick strong surface-based inversions with median thickness and strength of 200 m and 3 K, while the southern part by thin weak elevated ones of 80 m and 0.8 K. Tibetan Plateau experiences rare inversions (less than 50% of the time) which tend to be strong thick surface-based inversions with median depth and intensity of 170 m and 4 K. Inversion depths and strengths are positively correlated. The three properties of inversions present remarkable seasonal variations. Generally, inversions are strongest, thickest, and most frequent in winter and least so in summer, with median intensity and depth ranging from 0.3 K and 80 m to 5 K and 220 m. This paper also analyzed the monthly variations of inversions of four representative stations (Harbin, Urumqi, Beijing, and Chongqing) in details. These four cities are known for frequent severe air pollution events. The quantitative investigations of inversions may play a significant role in atmospheric environmental management. [ABSTRACT FROM AUTHOR]