Ammonium nitrate particles formed in upper troposphere from ground ammonia sources during Asian monsoons


The rise of ammonia emissions in Asia is predicted to increase radiative cooling and air pollution by forming ammonium nitrate particles in the lower troposphere. There is, however, a severe lack of knowledge about ammonia and ammoniated aerosol particles in the upper troposphere and their possible effects on the formation of clouds. Here we employ satellite observations and high-altitude aircraft measurements, combined with atmospheric trajectory simulations and cloud-chamber experiments, to demonstrate the presence of ammonium nitrate particles and also track the source of the ammonia that forms into the particles. We found that during the Asian monsoon period, solid ammonium nitrate particles are surprisingly ubiquitous in the upper troposphere from the Eastern Mediterranean to the Western Pacific—even as early as in 1997. We show that this ammonium nitrate aerosol layer is fed by convection that transports large amounts of ammonia from surface sources into the upper troposphere. Impurities of ammonium sulfate allow the crystallization of ammonium nitrate even in the conditions, such as a high relative humidity, that prevail in the upper troposphere. Solid ammonium nitrate particles in the upper troposphere play a hitherto neglected role in ice cloud formation and aerosol indirect radiative forcing.

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Fig. 1: AN observed by CRISTA in the UT in 1997.
Fig. 2: Time series of AN and NH3 in the AMA.
Fig. 3: Airborne limb-imaging observations of AN and NH3 in the UT above India during the 2017 Asian monsoon season.
Fig. 4: Airborne in situ aerosol observations in the Asian monsoon UT on 31 July 2017.

Data availability

The data sets generated and analysed during the current study are available from the corresponding author upon request. Additionally, the CRISTA data set of AN is publicly available at MIPAS and GLORIA data for NH3 and AN as well as trajectory information and AIDA spectra can be downloaded from the KITopen archive at IASI data on NH3 are available at


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We acknowledge the Geophysica pilots and crew as well as the local support in Kathmandu. We are grateful to the instrument development and operation teams of GLORIA at KIT and Jülich, and of ERICA at MPI-C and IPA-JGU and to the technical team of AIDA at KIT. The work at KIT and Jülich was supported by the Helmholtz ATMO program. We thank the teams at ULB/LATMOS (Université Libre de Bruxelles/Laboratoire Atmosphères, Milieux, Observations Spatiales) for provision of the IASI NH3 data. The European Space Agency is acknowledged for MIPAS data provision. Meteorological analysis data were provided by the European Centre for Medium-Range Weather Forecasts. ERA5 trajectory computations were generated using Copernicus Climate Change Service Information. D. Offermann and his team are acknowledged for conducting the CRISTA observations in the AMA region. We thank M. L. Santee for helpful discussions on satellite data sets. Funding for the ERICA instrument development was provided by the European Research Council Advanced Grant to S. Borrmann (EXCATRO project, grant no. 321040). Part of this work was supported by the European Community’s Seventh Framework Programme (FP7/2007–2013) under grant agreement no. 603557, CEFIPRA5607-1, ANR-17-CE01-0015 and by the German “Bundesministerium für Bildung und Forschung” (BMBF) under the joint ROMIC-project SPITFIRE (01LG1205A). We also thank the Aeris data infrastructure for providing access to the MSG1 and Himawari data.

Author information

M.H. conducted the analysis of MIPAS and GLORIA data, produced Figs. 24 and wrote the paper with all the authors contributing. J.U. conducted the analysis of the CRISTA data, helped with analysis of the GLORIA data and produced Fig. 1. A.D., S.M., A.M.B., O.A., A.H. and S. Borrmann performed and analysed the aircraft in situ measurements of ERICA. C.M. and R. Weigel prepared the analyses for Fig. 4a and O.A. for Fig. 4b. C.M. and R. Weigel conducted the measurements and data analyses for UHSAS and COPAS, respectively. R. Wagner, H.S., O.M. and T.L. conceived and performed the AIDA experiments and contributed to their interpretation. R.S. discovered the AN emission feature in the CRISTA data. M. Riese conceived the reanalysis of the CRISTA data with respect to signals of the ATAL. G.S. contributed to the analysis of the MIPAS data. B.L. and S. Bucci conducted the TRACZILLA trajectory calculations. F.C. performed the MAS aircraft observations and conducted their analysis. F.F.-V. conducted the GLORIA aircraft observations. S.J. analysed the trajectory data sets in combination with the IASI measurements. S.J. and L.K. helped with the analysis of the GLORIA data. P.P. contributed to the CRISTA and GLORIA data analysis. T.N. helped to perform the GLORIA observations. R.M. contributed to the interpretation of the observations. J.O. contributed to the interpretation of spectroscopic issues with AN and NH3. F.S. and M. Rex. defined the flight region, the general approach, general flight patterns and instrumentation of the aircraft campaign and organized it. I.W. developed the ATLAS model and provided the trajectory calculations from it, with contributions from M. Rex.

Correspondence to Michael Höpfner.

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