Haze

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.

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.

 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.

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.