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H
ealth
droughts and floods in Asian countries,
3
others have
suggested that BC leads to the advancement and inten-
sification of monsoons.
4
There have been reports that BC
blocks sunlight from reaching the Earth’s surface and leads
to reduced crop yields.
5
As most of these are based on
model outputs, which use transport model simulations as
input for the global/regional distribution of BC, they are
not adequately validated. Limited validation exercises have
shown that the transport models underperform, at least
in simulating BC, over India.
6
All these point to the need
for and importance of accurate measurements of BC from
ground and airborne platforms.
Evolution of BC studies
Systematic and long-term measurements of BC over the
Indian region was initiated in 2000, under the ISRO-GBP
Aerosol Climatology and Effects project, in response
to recommendations made in an interim assessment
of the aerosol characteristics over the region in 1998.
The first long-term measurement was initiated in 2000
Atmospheric aerosols, particulate suspension in the atmosphere,
affects radiation balance by scattering and absorbing the radiation
(direct effects), modifying the microphysical and radiative properties of
clouds (indirect effects), and degrading air quality with adverse effects
on health. Among the various aerosol types, there has been increased
interest in BC aerosols due to their high absorption characteristics over
a wide wavelength range from ultraviolet to infrared. In addition to
exerting its own radiative impacts, BC can substantially alter the radia-
tive properties of the entire aerosol system and their ability to act as
cloud condensation nuclei. The overall effect of aerosols when viewed
from space is a brightening of the planet and net climatic cooling at the
surface. However, BC contributes significantly to dimming as well as to
the warming of the lower atmosphere, producing an effect analogous to
greenhouse warming, which is amplified if the BC aerosol layer occurs
over highly reflective landmass (snow/ice /glaciers) or highly scattered
clouds.
1
On the other hand, BC within the cloud can lead to ‘cloud
burn-off’ and a reduction of cloud cover.
2
In addition to these climate
implications, BC is a health hazard and is believed to be carcinogenic.
In recent years there have been several studies of the climate impact
of BC aerosols. While some of these have argued that BC intensifies
Source: ARFI
Top panels: The instrumented aircraft used to measure BC profiles (left) and the inside view of the aircraft with instruments. Bottom
Panels: Locations of aircraft measurements of BC with aircraft symbol (left). The altitude distribution of BC over Indian region during
winter and pre-monsoon seasons (right panels).