In order to study the transport characteristics of air pollution in Linfen City, based on the hourly air quality index (AQI) data in Linfen City from the Ministry of Ecology and Environment from 2016 to 2017, the six-hour reanalysis data and the global data assimilation system (GDAS) data with a horizontal resolution of 1°×1° from the National Centers for Environmental Prediction (NCEP), the influence of topography and weather situation on air pollution during the 24 pollution processes in Linfen City was analyzed by using backward trajectory clustering analysis of HYSPLIT4 (hybrid single-particle lagrangian integrated trajectory) model. The results are as follows: (1) The sea-level circulation situation during the 24 pollution processes mainly included the following six types: front of Mongolian high pressure bottom type, front of low pressure type, rear of North China high pressure type, front of invert trough near the Hetao area type, uniform pressure field and low pressure belt type. (2) The 24 h and 60 h backward trajectory can represent the impact of topography conditions and weather conditions on pollution in Linfen City, respectively. (3) The 24 h backward trajectories show that the air flow can sink and transport pollutants along the leeward slope of the Lüliang Mountain. The pollution in Linfen City was formed from inverted “concave” shape terrain opening to the south and the southwest wind near the ground. The air flow can also return to Linfen City after touching the surrounding mountains. Among them, the transportation along the subsidence of the Lüliang Mountain from the northwest direction was main. (4) The 60 hour backward trajectories show that the air flow transporting pollutants met with the easterly or southerly airflow under the influence of the weather situation, and then turned back to Linfen City. The pollutant particles hygroscopic grew with the increase of humidity caused by southwesterly or easterly wind. The topography and weather situation have an impact on the transport route of air pollution in Linfen City.

Based on observation data of CO₂, CH₄ mole fraction and temperature, relative humidity, wind speed and wind direction at Linfen station of Shanxi from 2013 to 2018, and ERA-5 PBL (planet boundary layer) reanalysis data from the European Center for Mediumrange Weather Forecasts (ECMWF) and GDAS (global data assimilation system) reanalysis data from the National Centers for Environmental Prediction (NCEP), the spatio-temperal distribution characteristics of two greenhouse gases concentration and their influence factors were analyzed in Linfen with high carbon emission. The results show that the annual average CO₂ and CH₄ mole fractions were 441.7×10^-6 and 2359.5×10^-9 at Linfen station, respectively, they were higher than that at background stations of globe and Waliguan of Qinghai Province and other city stations such as Pudong of Shanghai. There are very significantly positive correlations between CO₂ and CH₄ concentrations at Linfen in spring, autumn and winter, which indicates that the anthropogenic emissions dominate to carbon cycle of Linfen. The monthly change of CO₂ and CH₄ mole fraction with single peak and single valley pattern was obvious at Linfen, and the CO₂ mole fraction was the highest in winter and the lowest in summer, while the CH₄ mole fraction was the highest in winter and the lowest in spring. The CO₂ and CH₄ mole fraction were higher from 06:00 BST to 09:00 BST, while those were lower from 15:00 BST to 17:00 BST at Linfen, and their diurnal change ranges were the smallest in spring, while that of CO₂ and CH₄ mole fraction was the greatest in summer and winter, respectively. Apart from carbon emission source, the influence of meteorological conditions on CO₂ and CH₄ concentration is obvious in Linfen. The influence of temperature and humidity was more in summer, while that in other seasons was less. The photosynthesis and photochemical reactions enhance in summer, which lead to the decrease of CO₂ and CH₄ concentration, therefore the high temperature and low humidity are beneficial to the decrease of concentration. The average wind speed has significantly negative correlation with two greenhouse gases mole fraction, and the low wind speed is beneficial to the increase of concentration. In addition, the northeast and southeast winds are likely to transport industrial and other emission gases to the observation site and surrounding, which lead to the increase of two gases concentration at the site. Due to the influence of anthropogenic emission sources is most, the spatial distribution characteristic of CO₂ concentration is better similar to CH₄ concentration in Linfen in winter. In addition, the CH₄ concentration in eastern Linfen is higher in the whole year, which may be attributed to the Qinshui coal field with the most yields in China.