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BookmarkScienceDaily (Sep. 2, 2005) —
China's spectacular economic growth during the last decade
has brought many benefits – and some challenges. Global atmospheric
mapping of nitrogen dioxide pollution performed by ERS-2's GOME and
Envisat's SCIAMACHY reveals the world's largest amount of NO2 hanging
above Beijing and northeast China, as reported in Nature this week.
As
part of ESA's Dragon Programme, European and Chinese researchers are
using results returned from the Global Ozone Mapping Experiment (GOME)
on ERS-2 and the Scanning Imaging Absorption Spectrometer for
Atmospheric Chartography (SCIAMACHY) on Envisat to monitor and forecast
Chinese air quality.
See also:
In this context, researchers at the
University of Bremen, the Max-Planck Institute of Meteorology in
Hamburg and France's Centre National de la Recherche Scientifique
(CNRS) have been studying the retrieval of nitrogen dioxide variability
from space and modelling its global behaviour.
The team have
published an article in the 1 September 2005 edition of the science
journal Nature about the global changes in nitrogen dioxide observed in
the last decade from space and highlighted the dramatic changes over
China.
Nitrogen dioxide (NO2) is associated with nitrogen oxide
(NO) in the atmosphere and the sum of the two is called NOX. This is
released into the troposphere from power plants, heavy industry and
road transport, along with biomass burning, lightning in the atmosphere
and microbial activity in the soil. The emission of nitrogen oxides has
increased about six-fold since pre-industrial times and in cities above
a thousand times more NOX is present than in the pristine and remote
marine boundary layer.
Exposure to nitrogen dioxide in large
quantities is known to cause lung damage and respiratory problems,
although little is known about the consequences of long term exposure
to elevated atmospheric amounts. The presence of this gas is a
significant driver of the production of low-level ozone, which, within
the troposphere (the lowest part of the atmosphere, extending eight to
16 kilometres in height) is itself a harmful toxic pollutant, a major
ingredient of photochemical smog.
"While nitrogen dioxide
vertical column concentrations above central and eastern Europe and
parts of the East Coast of the United States have been either static or
exhibiting a small decrease, there is a clear and significant increase
over China," explains John Burrows of the University of Bremen's
Institute of Environmental Physics, SCIAMACHY's Principal Investigator.
"Before
SCIAMACHY was flying we previously retrieved NO2 data from its
precursor instrument, GOME on ESA's ERS-2 mission. Although GOME had
lower resolution, the article shows that China's nitrogen dioxide
retrievals from the two instruments overlap seamlessly.
"What the
combined data show are that nitrogen dioxide levels have risen by
around 50% since 1996, and this behaviour is continuing."
Space-based
sensors are the only way to carry out effective global and regional
monitoring of the atmosphere. While GOME demonstrated the first
satellite sensitivity to tropospheric nitrogen dioxide, SCIAMACHY
possesses superior performance, with a spatial resolution of 60 x 30
kilometres compared to 320 x 40 km for its predecessor.
SCIAMACHY
also observes the atmosphere in two different ways – downwards or
nadir-sounding' as well as 'limb-sounding' along the direction of
flight – and with a larger spectral range than its predecessor.
The
increase in nitrogen dioxide levels seen is an unfortunate side effect
of economic success. China's industrial boom has seen it become the
world's largest consumer of copper, aluminium and cement and the second
bigger importer of oil. Car ownership within the country has been
doubling every few years.
"China's nitrogen dioxide concentration
varies according to season," Burrows adds. "There is more in the winter
as a result of differing emission patterns and meteorology. For example
more fuel is burned for heating and nitrogen dioxide persists longer in
the atmosphere at that less sunny time of year – lasting around a day
rather than hours, as in the summer.
"Meteorology also plays a role. There is a peak before Christmas: this
is not because industrial activity, domestic heating or transportation
is suddenly reduced after the holiday season but because there is an
eastward outflow of air that was previously revolving around Asia. This
is the same type of phenomenon that carries dust from the Gobi Desert
across to the West Coast of the US."
China is reliant on coal to
meet 75% of its national energy needs, and that means high levels of
another atmospheric pollutant called sulphur dioxide (SO2) also
detectable by SCIAMACHY. Large SO2 sources over China that overlap with
nitrogen dioxide plumes are linked to power plants. Further to the west
there is also sulphur dioxide produced from smouldering underground
coal seam fires.
Burrows is the scientist who – supported by an
international team – proposed both GOME and SCIAMACHY to national space
agencies and ESA in the first place. He explained that the two
instruments were originally chosen to fly because of their ability to
measure stratospheric ozone, but were also selected in order to
investigate the amount of useful information that could be retrieved
from the troposphere.
"The instruments are now being used to monitor a significant number of key tropospheric trace gases including formaldehyde, methane, sulphur dioxide and carbon monoxide and dioxide," Burrows remembers. "Back when we were starting out, many people thought it would be impossible to get any useful results out of the troposphere. There are many important issues to deal with, such as cloud cover and the highly variable reflectivity of the surface, as well as having the absorption or emission of stratospheric and upper atmospheric species situated between the troposphere and the instrument.
"First with GOME and now much better with SCIAMACHY we are demonstrating it can be done. The success so far is an important step on the way to establishing an operational global observing system for the Earth's atmosphere. This is something we need as we enter the geological age of the Anthropocene, where the activities of mankind and its interactions with natural phenomena are the driving force in global climate change.
"Next
we are hoping for follow-up satellite missions, in particular from
geostationary orbit to monitor atmospheric pollution, which has a
strong diurnal variation and thereby determine objectively the changing
atmospheric composition."
SCIAMACHY: surveying the world in six days
SCIAMACHY is a
spectrometer, and it works by measuring sunlight – either transmitted,
reflected or scattered by the Earth's atmosphere or surface in the
ultraviolet, visible and near infrared regions. Mathematical inversion
of these data yields the amounts and distribution of trace gases, ozone
and related chemicals, clouds and dust particles throughout the
atmosphere. With a 960-km swath and alternate limb and nadir
observations, SCIAMACHY covers the entire world every six days at the
equator and more often at high latitudes.
This versatile instrument represents a national contribution to ESA's Envisat mission. It was funded by the German government through the German Aerospace Center (DLR), the Dutch government through the Netherlands Agency for Aerospace Programmes (NIVR) and also the Belgian government through the Belgian Institute for Space Aeronomy (BIRA-IASB).
SCIAMACHY is
part of a family of atmospheric sounders that also includes GOME on
ERS-2 and also the forthcoming GOME-2 instrument due to launch next
year aboard ESA's and EUMETSAT's first MetOp spacecraft.
About Dragon
The Dragon Programme is a joint undertaking
between ESA, the Ministry of Science and Technology (MOST) of China and
the National Remote Sensing Centre of China (NRSCC). Its purpose is to
encourage increased exploitation of ESA space resources within China as
well as stimulate increased scientific co-operation in the field of
Earth Observation science and applications between China and Europe.
