June 25, 2009

First global ammonia maps measured by the IASI French instrument

The first complete map of the ammonia sources on Earth was just built by a LATMOS-IPSL's team (CNRS/UPMC/UVSQ) in partnership with Belgium investigators of the Free University of Brussels.  

These works were performed thanks to the infrared measurements of the IASI (Infrared Atmospheric Sounding Interferometer) French instrument mounted on the CNES' MetOp meteorological satellite. In a publication released in the Nature Geoscience magazine issued on June 21st, the team described an unexpected result for the IASI mission and identified some thirty major sources of ammonia in 2008.

Ammonia distribution in 2008 measured by the IASI/MetOp sounding instrument above Europe, superimposed on an image obtained by the MODIS instrument [Image MODIS, L. Gonzalez and C. Deroo (LOA and University of Lille, France)]. From yellow to red, the colours indicate the increasingly higher concentrations of ammonia. The white structures are clouds. © ULB, CNES and INSU-CNRS

 

Volatile compound with lasting effects

Ammonia (NH3) significantly contributes to the particle formation involved in the pollution events. It principally comes from the fertilisers and the cattle intensification. The emission sources have increased fivefold since the industrial revolution.

Ammonia is the most poorly known pollutant regulated by the European directives on air quality. The emissions registers are quite imprecise and the global and systematic monitoring of this compound is difficult: Once emitted, ammonia only remains a short time in the atmosphere but triggers a series of environmental effects. High concentrations of ammonia affect wildlife, plants and local air quality.

An unexpected harvest

Iasi embarqué à bord de Metop-A (crédit ESA)
IASI on board Metop-A (credits ESA)
Even if the IASI instrument was not initially expected to detect ammonia in the Earth's atmosphere, the investigators designed a method to isolate this volatile compound's signature from the instrument's background noise.

Thanks to its spectrometer, several atmospheric components have been observed: ozone, carbon monoxide, methane, carbon dioxide.

By filtering the data on ammonia and accumulating them during a year of continuous observations (more than one million measurements per day flying by every point of the whole planet, twice), the investigators could obtain concentration maps and compare them to the recent atmospheric patterns.

Some thirty new sources identified

Distributions d'ammoniac en 2008 au dessus de la San Joachin valley (Californie).
Ammonia distributions in 2008 above the San Joachin valley (Californy)

These works put in evidence underestimates of the ammonia sources number provided by the current inventories:

  • in the agricultural valleys in the North Hemisphere, especially in America (regions of San Joaquin in California and Snake River Valley in Idaho);
  • in Europe (Ebro and Po valleys).

The biggest differences are localised in Central Asia with sources which did not exist in the previous inventories. In total, some thirty new major ammonia sources were identified in 2008.
 
Thanks to these works and more generally to the Metop programme, the day-to-day monitoring of the pollution peaks can be improved.

The METOP programme

Vue générale de METOP (crédit : EUMETSAT)
General view of METOP (credits: EUMETSAT)
The METOP programme is a partnership between CNES and Eumetsat (European Meteorological Satellites) which will spend 15 years continuously observing the atmospheric composition with three successive launches.

MetOp-A is the first of a series of European meteorological satellites. It was successfully launched on October 19th, 2006 by a Soyouz Rocket.

It features twelve instruments of meteorological measurements including the IASI sounding instrument developed by CNES. Placed into sun-synchronous polar orbit at an altitude of 800 km, it observes the whole atmosphere twice a day.

The Metop-A's payload

  • IASI (Infrared Atmospheric Sounding Interferometer): an interferometer which uses the infrared radiation emitted by the Earth to perform temperature sounding and water vapour monitoring for the needs of operational meteorology. It can also monitor the concentrations of the compounds directly involved in the global warming and air quality;
  • MHS (Microwave Humidity Sounder): a five-channel microwave sounder to pinpoint humidity. It is designed to collect information on liquid water in clouds and can also provide a qualitative assessment of precipitation rate;
  • GOME 2: a spectrometer for global monitoring of atmospheric ozone;
  • ASCAT: an advanced scatterometer;
  • GRAS (GNSS Receiver for Atmospheric Sounding);
  • AVHRR 3 (Advanced Very High Resolution Radiometer): a 6-channel multi spectral imaging instrument in the visible and infrared ranges. Its main goal is to characterize the clouds, sea temperatures and ice, snow and vegetation coverages.
  • AMSU/A (Advanced Microwave Sounding Unit): to sound temperatures above the cloud area and help the other infrared instruments to detect the cloud
  • HIRS (High Resolution Infrared Radiation Sounder): with its 19 channels in the infrared and 1 channel in the visible range, it provides temperature and humidity profiles.
  • SEM 2: a spectrometer used to measure the ionized particle flux into space.

Article references

Global ammonia distribution derived from infrared satellite observations Nature Geoscience Lieven Clarisse1, Cathy Clerbaux2, Frank Dentener3, Daniel Hurtmans1 & Pierre-François Coheur1 Nature Geosciences. Published online: 21 June 2009

1 Spectroscopie de l'Atmosphère, Service de Chimie Quantique et Photophysique, Université Libre de Bruxelles (ULB), 1050 Brussels, Belgium
2
UPMC Univ. Paris 06, LATMOS-IPSL; CNRS/INSU, LATMOS-IPSL, 75252 Paris Cedex 05, France
3 European Commission, Joint Research Centre (JRC), I-21027
Ispra, Italy.

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