Abstract: Based on the radiosonde observation data from 1975 to 2020 and the daily concentration data of PM_2.5 and PM₁₀ from 2001 to 2020, the characteristics of lower-to-middle tropospheric temperature inversions and their effects on air pollution in the the western Sichuan Basin over the past 45 years were analyzed. The results show that the two height ranges with the highest frequency of temperature inversions in the middle and lower troposphere are 0~600 m and 2000~3600 m, respectively. The temperature inversions are most frequent (except surface-based inversions, SIs), strongest and thickest in winter, while least frequent, thinnest and weakest in summer. The monthly variation of each characteristic value presents a U-shaped distribution. The temperature inversion frequency was stable in the late 20th century but increased in the 21st century. The inversion thickness decreased significantly after 2003, while the inversion intensity increased significantly after 2005. SIs are the thinnest and strongest, lower tropospheric inversions (LTIs) are the most frequent and thickest, and elevated inversions (EIs) are the least frequent and weakest. All kinds of temperature inversions turned into more frequent occurrences in 2013 and less frequent in 2004 (except EIs). The correlation between temperature inversion and pollution at 20:00 is generally stronger than that at 08:00 (except EIs), and the correlation between PM_2.5 concentration and temperature inversion is generally higher than that of PM₁₀. Inversion frequency shows the strongest and positive correlation with pollution (most pronounced for SIs), while intensity, temperature difference and thickness also have a positive correlation with pollution (strongest for boundary layer inversions, BLIs). In contrast, bottom height has a negative correlation with pollution (most pronounced for LTIs).