Haze is traditionally an atmospheric phenomenon where dust,
smoke and other dry particles obscure the clarity of the sky. The haze we see
in our city skyline is caused by tiny particulates suspended in the atmosphere.
At high concentrations, these particulates scatter and absorb sunlight
resulting in diminished horizontal visibility thereby giving the atmosphere a
characteristic opalescent appearance.
Seen from afar and depending upon the direction of view with
respect to the sun, haze may appear brownish or bluish, while mist tends to be
bluish-grey.
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| Haze over North China Plain |
HAZE PARTICLE-THEIR ORIGIN
The particles that cause the haze phenomenon can originate
from many sources, some of which are natural and some anthropogenic. Natural
sources include the oceans, forests and ground surface. However the majority of
the particulates are from human activities which include open burning, land clearing,
vehicular use and combustion of fossil fuels in industrial boilers.
TRANSBOUNDARY HAZE
Haze has become one of the causes of international disputes
among neighboring countries. Haze migrates to adjacent countries and thereby polluting
other countries as well. In 2013, due to forest fire in Indonesia the capital
city of Malaysia Kuala Lumpur and surrounding areas became shrouded in a pall
of noxious fumes, smelling of ash and coal for more than a week, in the
country’s worst environmental crisis since 1997.
The source of the haze is
Indonesia’s Sumatra Island, where farmers, plantation owners and miners have
set hundreds of fires in the forests to clear land during dry weather. Winds
blow most of the fumes across the narrow Strait of Malacca to Malaysia,
although parts of Indonesia are also affected. The 2015 Southeast Asian haze is
an air pollution crisis affecting several countries in Southeast Asia,
including Brunei, Indonesia, Malaysia, Singapore, Southern Thailand, and
Vietnam, Cambodia and the Philippines.
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| collage showing various landmarks in the haze. Top: An-Nur Great Mosque, Pekanbaru, Indonesia Bottom-left: The Grand Mosque of Palangkaraya,Indonesia Bottom-right: Swissôtel The Stamford, Singapore |
The haze has affected Indonesia from at least late June, eventually
turning into an international problem for other countries from September. It is
the latest occurrence of the Southeast Asian haze, a long-term issue that
occurs in varying intensity during every dry season in the region. It is caused
by forest fires resulting from illegal slash-and-burn practices, principally on
the Indonesian islands of Sumatra and Kalimantan, which can then spread quickly
in the dry season.
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| A NASA satellite image showing the extent of the haze on 24 September 2015. |
WHAT CAUSES HAZE TO CLEAR?
Particulates in the atmosphere are removed through several
processes. A proportion, particularly the heavier particles, settles to the
ground or onto surfaces by gravitational sedimentation.
The finer particles are removed by a process called "rainout"
involving condensation of water vapour onto minute particles to form water
droplets eventually producing clouds. Particles are also removed below cloud by
collision and adhesion with falling raindrops through another process called
"washout".
Yet another removal mechanism involves the role of turbulence
in transporting the haze particulates up to the higher levels of the atmosphere
for more effective dispersion. In this case, widespread heavy
rain/thunderstorms with strong updrafts and downdrafts are more effective,
whereas light rain showers of short duration are usually quite inefficient in
cleansing the atmosphere in a severe haze situation.
