Two-dimensional observations of dichloromethane-rich air masses transported from the Asian summer monsoon region across the North Pacific

Dichloromethane (CH₂Cl₂) is known to be emitted by industrial processes and suspected to be capable of delaying the recovery of the stratospheric ozone layer significantly. A rapid rise of its global emissions over the last decades, with the majority being located in East and South East Asia, is documented in the literature. We present unique observations of CH₂Cl₂-rich air masses over the North Pacific, Canada and Alaska by the infrared limb imager GLORIA (Gimballed Limb Observer for Radiance Imaging of the Atmosphere). During the boreal summer of 2023, GLORIA was deployed aboard the German research aircraft HALO (High Altitude and LOng Range Research Aircraft) in the framework of the PHILEAS campaign (Probing High Latitude Export of Air from the Asian Summer Monsoon). Two-dimensional vertical cross-sections of CH₂Cl₂ derived from GLORIA observations in August and September 2023 show large plumes with high mixing ratios of typically up to ~300 pptv far away from their anticipated source regions. Up to 450 pptv are observed locally, which corresponds to ~700% of the northern hemispheric background in that season. Air masses with high CH₂Cl₂ mixing ratios are detected in the free troposphere and moderately enhanced mixing ratios are observed partly also in the tropopause region. Using backward trajectories and simulations by the Chemical Lagrangian Model of the Stratosphere (CLaMS), the transport pathways and timescales of the observed air masses are analysed. Our analysis suggests that East Asia is a major source region of the observed air masses. Together with the model data and in situ observations by HAGAR-V (High Altitude Gas AnalyzeR-V) and GhOST (Gas chromatograph for Observational Studies using Tracers), the GLORIA observations provide new insights into the long-range transport of CH₂Cl₂-rich airmasses from the Asian Summer Monsoon region. GLORIA is an airborne demonstrator for the ESA Earth Explorer 11 candidate CAIRT (Changing-Atmosphere Infra-Red Tomography explorer), which is currently in the final selection round and would provide new opportunities to study a multitude of ozone- and climate-relevant trace species continuously.