Ammonia detected in Earth's troposphere for first time

Berlin: For the first time, researchers have discovered ammonia in the Earth's lowest atmospheric layer with highest emissions of the gas encountered in North India and Southeast China.

Scientists of Karlsruhe Institute of Technology (KIT) in Germany together with researchers from US and Mexico analysed satellite measurements by the MIPAS infrared spectrometer and found increased amounts of ammonia (NH3) between 12 and 15 km height in the area of the Asian monsoon.

This suggests that the gas is responsible for the formation of aerosols, smallest particles that might contribute to cloud formation, researchers said.

Ammonia, a chemical compound of nitrogen and hydrogen, mainly originates from agricultural processes, in particular from life-stock farming and fertilisation.

Highest ammonia emissions are encountered in North India and Southeast China. Due to population growth and global warming, global ammonia emissions are expected to increase strongly in the future, researchers said.

Gaseous ammonia reacts with acids, such as sulfuric acid or nitric acid, to the corresponding ammonium salts. However, ammonia does not only pollute the ecosystems.

Particles of ammonium salts can attach to each other and form aerosol particles acting as condensation nuclei in cloud formation.

Such aerosols of anthropogenic origin have a cooling effect in the atmosphere and might compensate part of the anthropogenic greenhouse effect.

In this connection, it is important to determine vertical distribution of atmospheric ammonia. Concentrations of ammonia in the middle and upper troposphere, the bottom layer of the atmosphere, have hardly been studied so far.

Now, researchers of from KIT's Institute for Meteorology and Climate Research (IMK-ASF) and University of Colorado at Boulder and the Universidad Nacional Autonoma de Mexico for the first time detected ammonia in the upper troposphere.

They evaluated measurements made by the MIPAS infrared spectrometer on the European environmental satellite ENVISAT from 2002 to 2012.

MIPAS recorded highly resolved spectra in the middle infrared range, from which gases can be identified clearly. Every gas emits specific infrared radiation.

The scientists calculated the average of three-month measurements in areas of ten degrees longitude and ten degrees latitude each. At 12 to 15 km height, in the area of the Asian monsoon, they found an increased concentration of ammonia of up to 33 pptv (33 NH3 molecules per trillion air molecules).

Similarly high concentrations were measured in no other season and no other region.

"Observations show that ammonia is not washed out completely when air ascends in monsoon circulation. Hence, it enters the upper troposphere from the boundary layer close to the ground, where the gas occurs at relatively high concentrations," said Michael Hopfner, Head of the Remote Sensing Using Aircraft and Balloons Group of IMK-ASF.

The research was published in the journal Atmospheric Chemistry and Physics.