Mapping Human Impact on Air Quality

PARIS, France, October 12, 2004 (ENS) - Scientists working with data from the European Space Agency's Envisat, the world's largest satellite for environmental monitoring, have produced a map that shows the human causes of air pollution in colorful clarity.

Envisat, launched in February 2002, has 10 instruments aboard including one called the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY), which records the spectrum of sunlight shining through the atmosphere.

These results are then analyzed to find what scientists call "spectral absorption fingerprints" of trace gases in the air.

Teams from the Universities of Bremen and Heidelberg in Germany, the Belgian Institute for Space Aeronomy and the Royal Netherlands Meteorological Institute have successfully processed SCIAMACHY data to generate the sharpest maps yet made of the vertical columns of nitrogen dioxide in the troposphere.

Based on 18 months of Envisat observations, this high-resolution global atmospheric map of nitrogen dioxide pollution shows how human activities affect air quality. (Map courtesy European Space Agency)

Nitrogen dioxide (NO2) is a gas generated by human activities and lightning. Excess exposure causes lung damage and respiratory problems.

NO2 plays an important role in atmospheric chemistry, because it leads to the production of ozone in the troposphere, which cooks in the presence of sunlight to produce smog.

The Earth's protective ozone layer is higher up in the stratosphere, which extends 50 kilometers (31 miles) above the Earth.

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.

"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, who is responsible for the map.

"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," Beirle said.

"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."

"Results from this and other similar sensors could be used for chemical weather and air quality prediction in future," Beirle said.

"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."