On the Presence of Ammonium Nitrate and Organic Aerosol in the Extratropical Lower Stratosphere Linked to the Asian Summer Monsoon (Invited Presentation)

Motivated by the limited knowledge of the extratropical UTLS region influenced by the Asian summer monsoon outflow, we performed the aircraft-based mission PHILEAS (Probing High Latitude Export of air from the Asian Summer Monsoon). The mission took place in August/September 2023 out of Oberpfaffenhofen (Germany) and Anchorage (Alaska). The research aircraft HALO was equipped with a comprehensive suite of in-situ and remote-sensing aerosol and gas instruments. We obtained vertically-resolved submicron aerosol composition measurements up to 400 K potential temperature (~14.5 km altitude) by using the ERICA aerosol mass spectrometer. Several trace gas measurements (CH­₂Cl₂, CH₄, CO etc.) were used to differentiate air masses associated with the Asian monsoon region and/or with biomass burning [1,2].

This study investigates the influence of the Asian monsoon outflow on the abundance of ammonium nitrate and organic matter [3] into the extratropical lower stratosphere (ExLS) in boreal summer and autumn. We observed increasing concentrations of nitrate, ammonium, and organic matter with increasing potential temperature above 370 K potential temperature. We have indications that these air masses originate in the Asian monsoon region. By comparing with our previous measurements during StratoClim and ACCLIP, we have evidence that the transport pathway of these particles is mainly given by the slow diabatic uplift within the anticyclonic motion over Asia and subsequent quasi-horizontal isentropic mixing into the extratropics [4]. Global simulations with the ECHAM/MESSy Atmospheric Chemistry model (EMAC) can demonstrate that this export of ammonium nitrate from the Asian monsoon region into the ExLS is persistent from July to September and recurring each year. It is as such essential to better understand the processes that control the physicochemical aerosol properties in the ExLS.

[1] Lauther, V., Vogel, B., Wintel, J., Rau, A., Hoor, P., Bense, V., Müller, R., and Volk, C. M.: In situ observations of CH₂Cl₂ and CHCl₃ show efficient transport pathways for very short-lived species into the lower stratosphere via the Asian and the North American summer monsoon, Atmos. Chem. Phys., 22, 2049–2077, https://doi.org/10.5194/acp-22-2049-2022, 2022.

[2] Tomsche, L., Pozzer, A., Ojha, N., Parchatka, U., Lelieveld, J., and Fischer, H.: Upper tropospheric CH₄ and CO affected by the South Asian summer monsoon during the Oxidation Mechanism Observations mission, Atmos. Chem. Phys., 19, 1915–1939, https://doi.org/10.5194/acp-19-1915-2019, 2019.

[3] Appel, O., Köllner, F., Dragoneas, A., Hünig, A., Molleker, S., Schlager, H., Mahnke, C., Weigel, R., Port, M., Schulz, C., Drewnick, F., Vogel, B., Stroh, F., and Borrmann, S.: Chemical analysis of the Asian tropopause aerosol layer (ATAL) with emphasis on secondary aerosol particles using aircraft-based in situ aerosol mass spectrometry, Atmos. Chem. Phys., 22, 13607–13630, https://doi.org/10.5194/acp-22-13607-2022, 2022.

[4] Ploeger, F., Konopka, P., Walker, K., and Riese, M.: Quantifying pollution transport from the Asian monsoon anticyclone into the lower stratosphere, Atmos. Chem. Phys., 17, 7055–7066, https://doi.org/10.5194/acp-17-7055-2017, 2017.