Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Global air pollution map produced by Envisat’s SCIAMACHY

12.10.2004


Based on 18 months of Envisat observations, this high-resolution global atmospheric map of nitrogen dioxide pollution makes clear just how human activities impact air quality.



ESA’s ten-instrument Envisat, the world’s largest satellite for environmental monitoring, was launched in February 2002. Its onboard Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) instrument records the spectrum of sunlight shining through the atmosphere. These results are then finely sifted to find spectral absorption ’fingerprints’ of trace gases in the air. Nitrogen dioxide (NO2) is a mainly man-made gas, excess exposure to which causes lung damage and respiratory problems. It also plays an important role in atmospheric chemistry, because it leads to the production of ozone in the troposphere – which is the lowest part of the atmosphere, extending up to between eight and 16 kilometres high.

Nitrogen dioxide is produced by emissions from power plants, heavy industry and road transport, along with biomass burning. Lightning in the air also creates nitrogen oxides naturally, as does microbial activity in the soil.
Localised in-situ measurements of atmospheric nitrogen dioxide are carried out in many western industrial countries, but ground-based data sources are generally thin on the ground.



Space-based sensors are the only way to carry out effective global monitoring: the first satellite sensitivity to tropospheric nitrogen dioxide was demonstrated with the Global Ozone Monitoring Experiment (GOME) on ESA’s ERS-2. However GOME was only a sub-scale precursor of the German, Dutch and Belgian financed SCIAMACHY flying on Envisat.

While both instruments function in the same way, GOME has a limited spatial resolution of only 320 x 40 km, compared to a typical 60 x 30 km with SCIAMACHY, which also observes the atmosphere in two different views –downwards or ’nadir’ looking as well as making ’limb’ observations in the direction of flight – and has a significantly larger spectral range than its predecessor.

Teams from the Universities of Bremen and Heidelberg in Germany, the Belgian Institute for Space Aeronomy (BIRA-IASB) and the Royal Netherlands Meteorological Institute (KNMI) have successfully processed SCIAMACHY data to generate the sharpest maps yet made of the vertical columns of tropospheric nitrogen dioxide. "The higher spatial resolution delivered by SCIAMACHY means we see a lot of detail in these global images, even resolving individual city sources" said Steffen Beirle of the University of Heidelberg’s Institute for Environmental Physics, responsible for the map shown above.

"High vertical column distributions of nitrogen dioxide are associated with major cities across North America and Europe, along with other sites such as Mexico City in Central America and South African coal-fired power plants located close together in the eastern Highveld plateau of that country. "Then a very high concentration is found above north eastern China. Also across South East Asia and much of Africa can be seen nitrogen dioxide produced by biomass burning. Ship tracks are visible in some locations: look at the Red Sea and the Indian Ocean between the southern tip of India and Indonesia. The smoke stacks of ships crossing these routes send a large amount of NO2 into the troposphere.

This map is average out across all available data, spanning 18 months. This has the effects of reducing seasonal variations in biomass burning and also those due to human activity changes due to the time of year." Like GOME, SCIAMACHY works by observing atmosphere-scattered ultraviolet, visible and near-infrared radiation. The hard work comes on the ground, where researchers attempt to retrieve very weak trace gas absorption patterns within the overall spectrum of backscattered light, a feat comparable to finding a needle in a haystack.

The method they use is called Differential Optical Absorption Spectroscopy (DOAS), which is basically a complex filtering process also used with ground-based air-sampling instruments. DOAS removes the predominant spectral ’noise’ from air particles’ Rayleigh scattering of light (the same phenomenon that causes the sky appear blue) along with the absorption patterns from the oxygen, nitrogen and water molecules that make up most of the atmosphere.

Left behind after these subtractions is the desired ’signal’ of narrower trace gas spectral absorption patterns, to be identified against sample cross sections. Applied to SCIAMACHY results, this technique is sufficiently sensitive to retrieve columns lower than a few parts of nitrogen dioxide per billion parts of air. To give an idea of scale, above highly polluted conurbations such as London, NO2 mixing ratios can reach values as high as a hundred parts per billion.

Nitrogen dioxide maps like that shown here have been produced using nadir-sounding data: while NO2 vary widely across the troposphere they are evenly spread across the upper atmosphere, the stratosphere. So nitrogen dioxide levels measured above the remotest parts of the Pacific were used to determine a general column for stratospheric nitrogen dioxide, which could be subtracted from the global data to determine tropospheric vertical column values.

"Results from this and other similar sensors could be used for chemical weather and air quality prediction in future," Beirle added. "For now we are focused on using the SCIAMACHY results to quantify the contributions of the different sources of nitrogen oxides – such as fossil fuel combustion, biomass burning, lightning – especially as the value of the latter is still highly uncertain."

Mariangela D’Acunto | alfa
Further information:
http://www.esa.int

More articles from Ecology, The Environment and Conservation:

nachricht Preservation of floodplains is flood protection
27.09.2017 | Technische Universität München

nachricht Conservationists are sounding the alarm: parrots much more threatened than assumed
15.09.2017 | Justus-Liebig-Universität Gießen

All articles from Ecology, The Environment and Conservation >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

 
Latest News

Terahertz spectroscopy goes nano

20.10.2017 | Information Technology

Strange but true: Turning a material upside down can sometimes make it softer

20.10.2017 | Materials Sciences

NRL clarifies valley polarization for electronic and optoelectronic technologies

20.10.2017 | Interdisciplinary Research

VideoLinks
B2B-VideoLinks
More VideoLinks >>>