Abstract
Abstract. Ammonia (NH3) has been detected in the upper troposphere by the analysis of averaged MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) infrared limb-emission spectra. We have found enhanced amounts of NH3 within the region of the Asian summer monsoon at 12–15 km altitude. Three-monthly, 10° longitude × 10° latitude average profiles reaching maximum mixing ratios of around 30 pptv in this altitude range have been retrieved, with a vertical resolution of 3–8 km and estimated errors of about 5 pptv. These observations show that loss processes during transport from the boundary layer to the upper troposphere within the Asian monsoon do not deplete the air entirely of NH3. Thus, ammonia might contribute to the so-called Asian tropopause aerosol layer by the formation of ammonium aerosol particles. 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.
Highlights
In the Earth’s atmosphere the trace gas ammonia (NH3) represents the major form of reduced nitrogen
The reaction of NH3 with sulfuric acid (H2SO4) or nitric acid (HNO3) forms aerosol particles composed of ammonium sulfate ((NH4)2SO4) or ammonium nitrate (NH4NO3) (e.g., Behera et al, 2013, and references therein)
We have presented the first evidence of ammonia being present in the Earth’s upper troposphere above 10 km by an analysis of Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) infrared limb-emission spectra
Summary
In the Earth’s atmosphere the trace gas ammonia (NH3) represents the major form of reduced nitrogen. Burgess et al (2006) report on first attempts to retrieve global distributions of ammonia using limb infrared emission spectra measured by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on Envisat They obtained one climatological vertical profile with NH3 volume mixing ratios below 5 pptv at altitudes above 9 km. The mean NH3 profiles of the western part show no clear enhancements during the years 2007, 2009, and 2011 These values are below our estimated detection limit (see below). Plausibility by comparing it with the few previous observations and atmospheric model results
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