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Dark Skies
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Approximately
20-30% of all respiratory diseases appear to be caused by air
pollution. In addition, urban air pollutants contribute to atmospheric
problems such as acidification and global climate change, which have
impacts on crop productivity, forest growth, biodiversity, buildings
and cultural monuments. Urban Air Pollution Management and Practice in
Major and Megacities of Asia, UNEP/WHO.
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What is air pollution?
The World Health Organization (WHO) lists six 'classic' air pollutants:
carbon monoxide (CO), lead
(Pb), nitrogen dioxide (NO2),
sulphur dioxide (SO2),
tropospheric ozone (O3)
and suspended particulate matter
(SPM) - including dust, fumes, mists and smoke -). PM is
distinguished as different inhalable fractions that are classified as
coarse and fine particulates with aerodynamic
diameters below 10 µm (PM10) and 2.5 µm (PM2.5) respectively.
The burning
of fossil fuels and biomass is the most significant
source of air pollutants such as SO2, CO,
certain nitrous oxides such as NO and NO2 (known
collectively as NOx), SPM, volatile organic
compounds (VOCs) and some heavy metals. It is also the major anthropogenic
source of carbon dioxide (CO2), one of the
important greenhouse gases.
Beside effects on
human health, air pollution has adverse impacts on crop yields, forest
growth, ecosystem structure and function, materials and visibility.
Air pollution has
decreased in some cities in different parts of the world through a
combination of technology improvement and policy measures (Polluter Pays Principle). However,
increasing human activity is offsetting some of the gains.
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Air pollution in Asia
The most polluted cities are now found in Asia. This is a consequence
of the massive industrial expansion. In most of Asian cities, both SO2,
NO2 and PM10 levels are above the WHO
guidelines. Throughout Asia, lead emissions from vehicles are also well
above safe levels.
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Of the 15 cities
in the world with the highest levels of PM, 12 are located in Asia.
Of these cities, 6 also have the highest levels of atmospheric SO2.
Beijing (photo), Calcutta, Jakarta, New Delhi, Shanghai and Tehran are
notorious for high levels of suspended particulates and SO2
levels. Source |
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Young Vietnamese lady wearing mask to keep out pollution in Hanoi,
Vietnam.
Source
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Which pollutants?
Particulate
matter
The most important air pollutant from a disease perspective is fine
particulate matter. WHO estimated that particulates in urban areas
worldwide cause about 2% of mortality from cardiopulmonary disease in
adults, 5% of mortality from cancers of the trachea, bronchus and lung,
and about 1% of mortality from acute respiratory infections in
children, amounting to about 1% of premature deaths in the world each
year.
About
2.4 million people die prematurely every year due to fine particles:
one third due to outdoor urban PM10 and two-thirds due to indoor PM10.
The highest number of estimated annual premature deaths occurs in
developing countries of Asia and the Pacific.
Premature deaths
(in thousands) due to outdoor urban PM10 exposure by region in 2000
Source: Cohen and others 2004
NOx and
SO2
Over the last two decades, emissions of S02 and NOx
have increased, sometimes dramatically, in the industrializing nations
of Asia. For instance, from 2000 to 2005 the Chinese SO2
emissions increased by approximately 28%, and satellite data suggest
that NOx emissions in China have grown by 50%
between 1996 and 2003.
Sulfur dioxide emissions, which lead to acid
precipitation which in turn damages crops, forests and
eats away at synthetic structures and other materials, are increasing
in respond to the growing use of coal and other high sulphur fuels in
Asia. At least two-thirds of acid depositions in the region are caused
by coal-fired power plants with outdated pollution control equipment.
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Estimated annual
average concentrations of PM10 in cities with populations greater than
100 000, and in national capitals, for 1999. The current WHO annual
mean guideline for PM10 is 20 µg/m3.
Source: Cohen and others 2004
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Global estimates
of disease attributed to urban PM10 pollution, measured in proportion
of DALYs |
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What are the
causes?
Outdoor
pollution
Transport
has become a major source of urban air pollution. The motorized fleet
has been growing rapidly; for example, the number of cars in Delhi and
Manila has been doubling every seven years for the past 30 years. This
fact, combined with poor roads, fuel quality and vehicle maintenance,
makes vehicular air pollution an alarming issue.
The other sources
include industrial emissions, burning of solid and
liquid fuels for power generation,
and burning of biomass and other fuels such as charcoal for household
use.
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Traffic. Amount
of space required to transport the same number of passengers by car,
bus or bicycle.
(Poster in city of Muenster Planning Office,
August 2001 Credit: Press-Office City of Münster, Germany) |
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Haze
are clouds - known as Atmospheric Brown Clouds - of tiny aerosol
particles from emissions hang over a number of Asian regions. These
seasonal layers of haze reduce the amount of sunlight that can reach
the Earth’s surface, which has potential direct and indirect impacts on
the water cycle, agriculture and human health. Simulations with global
climate models indicate that the haze could have major impacts on the
monsoon circulation, regional rainfall patterns and vertical
temperature profile of the atmosphere.
Haze problems are also prevalent in the region due to forest fires in
Southeast Asia. The most serious episode occurred in 1997, when the
effects of forest fires in Indonesia extended to neighbouring countries.
Smoke and smog over Indonesia, TOMS
Earth-probe (22/10/97).
This image shows a huge smoke plume (in white) mixed with smog hanging
over Indonesia. Colours represent variations in ozone amounts. Smog is
composed of low-level tropospheric ozone and fine particles usually
produced by industries and transports. This blanket of pollution was
caused by the many forest fires that spread over Indonesian islands in
the second half of 1997. Source: NASA/GSFC
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Indoor
pollution
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Indoor air pollution is often a more severe
health hazard than outdoor air pollution. Most rural inhabitants in the
region use twigs, grass, dried animal dung, crop residues, wood,
charcoal and kerosene as household fuels. Coupled with inadequate
ventilation, this results in highly contaminated indoor air. Given the
high levels of harmful emissions and the number of people using
traditional cooking fuels - Asia produces nearly half of the world's
woodfuel - the scale of exposure is large.
A total of 1.6 million people
(mainly women and children) are estimated to die
prematurely each year due to indoor air pollution
exposure. Health effects include acute respiratory infection in
children, chronic obstructive lung disease, adverse pregnancy outcomes
and lung cancer.
The key areas for intervention are: use of
cleaner fuels such as low-propane gas and kerosene; development of
high-grade biomass fuels; improvements in stove design and better
dissemination of stoves; improvements in housing; and improvements in
environmental awareness and education.
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Global estimates of disease attributed to indoor air pollution,
measured in proportion of DALYs.
One DALY (Disability Adjusted Life Year) is equivalent to the loss of
one year of healthy life. Source: WHO 2002 |
Sources
GEO-3 GLOBAL ENVIRONMENT OUTLOOK (UNEP)
Chapter 2/Atmosphere/Asia and the Pacific
GEO-4:
GLOBAL ENVIRONMENT OUTLOOK (UNEP) / Atmosphere
Urban Air Pollution in Asian Megacities
NASA SATELLITE TRACKS HAZARDOUS SMOKE
Links
Aerosols over
Beijing
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