Observation of CH ₄ , CO and N ₂ O in the upper troposphere and lower stratosphere over the Qinghai–Tibet Plateau

Abstract The Asian summer monsoon (ASM) anticyclone provides an efficient pathway for the upward transport of anthropogenic pollutants into the upper troposphere and lower stratosphere (UTLS). However, in-situ measurements of key trace gases in the UTLS remain scarce over the Qinghai–Tibet Plateau (TP), a core region of the ASM anticyclone. In August 2019, the first AirCore observations over the northern TP were conducted, providing high-resolution vertical profiles of CH 4 , CO and N 2 O from the surface up to 22 km. Instrument and campaign details are described. Notably, enhanced concentrations of CH 4 and CO were observed at 13–14 km when the observation site was located within the ASM anticyclone, indicating that the primary influence of deep convection occurs at this altitude. Back-trajectory analyses indicate that these enhanced layers originated from northern India, the Bay of Bengal, and southern China. On average, CH 4 and CO concentrations inside the anticyclone were 30.2 ppb and 52.5 ppb higher, respectively, than those outside. N 2 O concentrations remain relatively constant throughout the troposphere but show a sharp decline approximately 2 km above the tropopause, indicating the onset of significant stratospheric influence and a weakening of ASM anticyclone confinement at this altitude. These results demonstrate the capability of the AirCore system to resolve the fine-scale vertical structure of trace gases, offering critical insights into the upward transport of surface pollutants to the UTLS via the TP during the ASM.