Transport of ammonium nitrate and organic aerosol into the extratropical stratosphere associated with the Asian monsoon outflow

The Asian Monsoon Anticyclone (AMA) is of global importance because of its role in transporting pollutants over long distances through dynamic processes such as eddy shedding. Its impact extends beyond the Asian region to Europe and North America. To study the composition of the extratropical Upper Troposphere and Lower Stratosphere (UTLS) under the influence of the export of AMA air masses, airborne measurements were conducted on board the research aircraft HALO from Anchorage (Alaska) in August/September 2023.Our instrument ERICA (ERC Instrument for the Chemical composition of Aerosols) was a part of this mission, with the objective to analyze the chemical composition of particles in the outflow region of the AMA. ERICA combines the aerosol mass spectrometer ERICA-AMS, which is designed for bulk measurements of aerosol particles, and the single-particle mass spectrometer ERICA-LAMS.The objective of our study was to determine whether aerosol particles are transported from the AMA into the extratropical UTLS region. Measurements of methane and dichloromethane were employed to identify air masses originating from the AMA. To distinguish between the tropospheric and stratospheric air masses, ozone and nitrous oxide were utilized. Our results demonstrate that UTLS air masses exhibit elevated concentrations of ammonium, nitrate and organic matter based on ERICA-AMS data, along with enhanced methane and dichloromethane mixing ratios. These results are consistent with previous high-altitude measurements in the center of the AMA, showing the presence of enhanced ammonium nitrate and organic particle concentrations (Appel et al., 2022). These findings lead to the conclusion that particles from the AMA were transported from the center of the AMA into the extratropical UTLS region. Initial data analysis suggests a quasi-horizontal isentropic transport of these particles from subtropical to extratropical regions.