Swedish
and Indian researchers constrain the sources
of climate and health-afflicting soot pollution
over South Asia - Stockholm, 23 January
2009 - A gigantic brownish haze from various
burning and combustion processes is blanketing
India and surrounding land and oceans during
the winter season. This soot-laden Brown
Cloud is affecting South Asian climate as
much or more than carbon dioxide and cause
premature deaths of 100 000s annually, yet
its sources have been poorly understood.
In this week's issue of Science Örjan
Gustafsson and colleagues at Stockholm University
and in India use a novel carbon-14 method
to constrain that two-thirds of the soot
particles are from biomass combustion such
as in household cooking and in slash-and-burn
agriculture.
Brown Clouds, covering
large parts of South and East Asia, originate
from burning of wood, dung and crop residue
as well as from industrial processes and
traffic. Previous studies had left it unclear
as to the relative source contributions
of biomass versus fossil fuel combustion.
Combustion-derived soot
particles are key components of the Brown
Cloud in Asia. The soot absorbs sunlight
and thereby heats the atmosphere while cooling
Earth's surface by shading.
The net effect of soot
on climate warming in South Asia is rivaling
that of carbon dioxide.
The Swedish-Indian team
managed to address the uncertainty of the
soot sources by the first-ever microscale
measurements of natural C-14 (half-life
of 5700 years) of atmospheric soot particles
intercepted on a mountain top in western
India and outside SW India on the Hanimaadhoo
island of the Maldives. Their results, presented
in the Science article, demonstrated that
the brown cloud soot was persistently about
two-thirds from burning of contemporary
biomass (C-14 "alive") and one-third
from fossil fuel combustion (C-14 "dead").
These findings provide
a direction for actions to curb emissions
of Brown Clouds. Örjan
Gustafsson, a professor
of biogeochemistry at Stockholm University
and leader of the study, says that the clear
message is that efforts should not be limited
to car traffic and coal-fired power plants
but calls on fighting poverty and spreading
India-appropriate green technology to limit
emissions from small-scale biomass burning.
"More households in South Asia need
to be given the possibility to cook food
and get heating without using open fires
of wood and dung" says Gustafsson.
The rewards of decreasing
soot emissions from biomass combustion may
be rapid and sizeable. Globally, soot accounts
for roughly half the warming potential of
carbon dioxide. While carbon dioxide levels
in the atmosphere respond on a sluggish
100 yr timescale to reductions in emissions,
Brown Cloud soot particles only reside in
the atmosphere for days-weeks raising the
hope for a rapid response of the climate
system.
Several additional positive
effects would result from a reduction on
Brown Cloud soot particle emissions. A recent
report by the United Nations Environment
Program, Atmospheric Brown Clouds: Regional
Assessment Report with Focus on Asia (http://www.rrcap.unep.org/abc/impact/)
outlines severe effects including melting
of the Himalayan glaciers and weather systems
becoming more extreme. The Brown Cloud is
also having impact on agriculture and air
quality in Asia. Henning Rodhe, a professor
of chemical meteorology at Stockholm University,
vice-chair of the UNEP Atmospheric Brown
Cloud
Program and also co-author
of the Science article, states that the
report finds that 340 000 people in China
and India die each year from cardiovascular
and respiratory diseases that can be traced
to human-induced emissions of combustion
particles. "The impact on health alone
is a strong reason to reduce these Brown
Clouds" says Rodhe.
Professor Örjan Gustafsson, Department
of Applied Environmental Science and the
Bert Bolin
Climate Research Centre, Stockholm University
Professor Henning Rodhe, Department of Meteorology
and the Bert Bolin Climate Research
Centre, Stockholm University
Reporters may contact the AAAS-Science SciPak
