Ammonia, a compound of nitrogen and hydrogen with the formula NH3, has been found for the first time in the upper troposphere of our planet.
Distribution of the atmospheric ammonia concentration in June, July, and August 2008 at 9.3 mile (15 km) height as observed by MIPAS. Bright areas are measurement gaps due to high cloud cover. Image credit: Michael Höpfner / Karlsruhe Institute of Technology.
An international research team led by Karlsruhe Institute of Technology scientist Dr. Michael Höpfner analyzed data collected from June 2002 to April 2012 by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) instrument, an infrared spectrometer on the European environmental satellite ENVISAT.
MIPAS recorded highly resolved spectra in the middle infrared range, from which gases can be identified clearly. Every gas emits specific infrared radiation.
The researchers found enhanced amounts of ammonia (up to 33 pptv, or 33 ammonia molecules per trillion air molecules) within the region of the Asian summer monsoon at 7.5-9.3 mile (12-15 km) altitude.
This suggests that the gas is responsible for the formation of aerosols, smallest particles that might contribute to cloud formation.
“We have presented the first evidence of ammonia being present in the Earth’s upper troposphere above 6.2 miles (10 km) by an analysis of MIPAS infrared limb-emission spectra,” the authors said.
“The region and period of detection is confined to the Asian summer monsoon system.”
“Maximum average values of around 30 pptv over a 3-month period have been retrieved, thus demonstrating that part of ammonia released at the ground survives the loss processes on its way to the upper troposphere.”
“Observations show that ammonia is not washed out completely when air ascends in monsoon circulation,” Dr. Höpfner added.
“Hence, it enters the upper troposphere from the boundary layer close to the ground, where the gas occurs at relatively high concentrations.”
“It is therefore assumed that part of the Asian tropopause aerosol layer consists of ammonium salts.”
Outside of the area of the Asian monsoon, concentrations of ammonia in the upper troposphere were found to be below the detection limit of a few pptv.
“On a global scale, outside the monsoon area and during different seasons, we could not detect enhanced values of NH3 above the actual detection limit of about 3–5 pptv. This upper bound helps to constrain global model simulations,” the scientists said.
Details of the research were recently published in the journal Atmospheric Chemistry and Physics.
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Michael Höpfner et al. 2016. First detection of ammonia (NH3) in the Asian summer monsoon upper troposphere. Atmos. Chem. Phys 16 (22): 14357-14369; doi: 10.5194/acp-16-14357-2016
