WHAT IS HAZE?
Malaysian Meteorological Department
What is Haze?
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. Haze is not confined to urban environments; it may also be observed in rural areas.
Haze Particles - 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. |  Open burning |  Vehicle emissions |
Atmospheric Conditions That Favour Haze Formation
In the tropics, wind speeds are generally low. During certain periods of the year, particularly during the Southwest Monsoon season, the atmosphere is very stable and horizontal as well as vertical air movements are reduced. The subsiding air mass does not favour active cloud development, thus the weather is dry. Several factors such as prolonged dry weather, a stable atmosphere, and an abundant supply of pollutants from urban or rural sources are the ideal ingredients for the formation of haze. Particulates emitted into the atmosphere are trapped within the stagnant air mass causing the particulate concentration to increase thus producing a hazy condition. In Peninsular Malaysia, haze is most likely to occur during the months from January to February and June to August.
On the other hand, during the Northeast Monsoon season, the moisture-rich northeasterly winds blowing from the South China Sea are generally stronger and therefore more effective in dispersing haze pollutants. The Northeast Monsoon is often associated with more frequent widespread rain, thus haze is seldom observed.
What Causes The Haze To Clear?
In our changing atmosphere, just as there are hazy days, there are also days which are clear and clean. What can bring about this change? 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.
Haze, Mist or Fog?
Often, haze is confused with mist and fog. During the early morning or after rain showers when temperatures are low and humidity is high, mist and sometimes fog forms in valleys and lowlands, gradually clearing when the sun reappears. Mist and fog are formed as a result of the condensation of water vapour on particulates suspended in the atmosphere. Meteorologically, mist is defined as being present if diminished visibility occurs (with no other weather condition being present) and relative humidity of the atmosphere at the surface of the earth is above 95%. When the horizontal visibility falls below 1000 metres the phenomenon is classified as fog.
Is Haze Harmful?
Haze originating from natural sources such as sea salt and soil dust is generally harmless to humans. Slight, transient haze visible in most towns and cities has not been proven to cause any serious long-term health effects on the population. However, during a severe haze episode, prolonged exposure to high concentrations of particulates can be harmful to health. Associated with previous haze episodes, there have been reports of increases in incidences of eye and throat irritations and respiratory difficulties among sensitive groups. During a haze episode, the public are strongly urged to follow the advice issued by the local health authorities.
How Can We Reduce The Incidence Of Haze?
Firstly, we should refrain from open burning of waste. Most incidences of local haze can be traced to this activity. Motor vehicles, due to their increasing numbers, are also major sources of haze particulates in urban areas. To reduce haze, vehicles should be well maintained. Choose fuels which are the least polluting. Large scale land clearing which exposes large tracts of barren land, not only results in soil erosion and degradation, but also provides a source of particulates to the atmosphere. Promoting efforts such as rapid replanting and staggered land clearing can reduce haze. Remember that every individual has a role to play to preserve the quality of our environment as a legacy for our future generations.
What Is The Government's Role?
MMD monitors atmospheric conditions related to weather as well as some parameters relating to the ambient air quality. One of the parameters measured is total suspended particulate (TSP) concentration in air which is directly related to haze intensity. Other meteorological parameters such as horizontal visibility, relative humidity and wind velocity are useful indicators in understanding the haze phenomenon and forecasting its occurrence and dispersal. The monitoring and research activities conducted by MMD are part of the national effort to control and mitigate haze.
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Close cooperation among all related government agencies, local authorities and the mass media are essential during a haze episode to ensure all necessary data required for decision making is acquired, and any advice is rapidly disseminated to the public. At the regional level, ASEAN has initiated an ASEAN Cooperation Plan on the Management of Transboundary Pollution to address issues such as transboundary haze.
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