Clouding the issue

Clouding the issue - Cybermed Berita MMA

Clouding the issue

There had been recent calls from different quarters asking for the air-pollution index or API for short in Malaysia to be made available. In a recent article in BBC "Row over Malaysian haze" (6/08/99) and Malaysian government under fire over haze (6/08/99) the Malaysian environment minister, Law Hieng Ding, has accused foreign news organisations of using the data to scare away tourists. More recently, the Visibility data site which was the "pseudo-index" for air pollution has a "under construction" sign. (9 August 1999)

Is the API a good index to scare tourist? Lets have an objective look at this issue.

What is regional haze?

Haze consists of sufficient smoke, dust, moisture, and vapor suspended in air to impair visibility. The term regional haze means haze that impairs visibility in all directions over a large area.

Haze is caused by particulate matter from many sources including smoke, road dust, and other particles emitted directly into the atmosphere, as well as particulate matter formed when gaseous pollutants react in the atmosphere. These particles often grow in size as humidity increases, further impairing visibility. Sources hundreds or even thousands of miles away can contribute to visibility problems at remote locations, such as national parks.

What is Visibility

Visibility impairment occurs as a result of the scattering and absorption of light by particles and gases in the atmosphere. It is most simply described as the haze which obscures the clarity, color, texture, and form of what we see. The same particles which are linked to serious health effects [sulfates, nitrates, organic carbon, soot (elemental carbon), and soil dust] can significantly affect our ability to see.

High relative humidity can significantly increase the effect of pollution on visibility. Some particles, such as sulfates, accumulate water and grow to sizes at which they are more efficient at scattering light and creating haze.

What is API?

The Air Pollutant Index and Malaysian Air Quality Index (MAQI) was developed based on the Pollutant Standards Index (PSI) developed by the United States Environmental Protection Agency (USEPA). They have been modified to suit Malaysian Guidelines developed by the Department of Environment (DOE). The Air Pollutants Index (API) provides a uniform system of measuring air pollution levels. The measured level of each of the 5 pollutants (PM10, carbon monoxide, sulphur dioxide, nitrogen dioxide and ozone) is converted to a scale (index) from 0 to 500. The most important number on this index is 100, since this level corresponds to that level at which health effects can occur. The Department of Environment has developed guidelines for each of the air pollutants measured. The recommended level corresponds to an index of 100 for each pollutant. An API level of 100 and above means that a pollutant is in the unhealthy range on a given day. The API is determined for each of the five pollutants, and the highest of the five indices is then reported. More recently the DOE has also begun to report the pollutant with the highest index. From the API is derived an index of air quality, the MAQI, which is characterized as good, moderate, unhealthy, very unhealthy and hazardous. The API and MAQI are used as triggers for action to be taken. While the manner in which the API is calculated is similar to that used in calculating the Pollutant Substances Index (PSI) of the USEPA, the standards set by the USEPA and levels recommended by the Department of Environment in Malaysia differ and the actions recommended at the different levels of the PSI and the API also differ.

Air Pollutant Index (API)

Malaysian Air Quality Index (MAQI)

0 - 50


51 - 100


101 - 200


201 - 300

Very Unhealthy

301 - 500


Visibility or API?

The haze can be characterized using two measures : the Air Pollutants Index and the Visibility Index.Some use visibility as a basic indicator of air pollution. While these two measures are interrelated the relationship may not be a simple direct one. The haze phenomenon is due to impairment of visibility as a result of the scattering and absorption of light by particles and gases in the atmosphere. It is called the haze because it obscures the clarity, color, texture and form of what we see. Visibility is usually measured as the furthest distance from which a person can see a landscape. However the same amount of pollution is known to have different effects on visibility and it is useful to know that changes in visual range (a measure of visibility) are not proportional to our perception. A five kilometer change in visual range can either be very apparent or imperceptible depending on the amount of pollution before the change. This means small amounts of air pollution in cleaner areas can have a marked effect on visibility and a much greater reduction in pollution will be needed in heavily polluted areas to make a noticeable difference. Hence visual range may not be the best indicator of visibility. A deciview scale (analogous to the decibel scale for sound) has been developed to address this problem. A change of one deciview is considered perceptible by the average person and a deciview of zero represents pristine conditions. In Malaysia the reports we receive are on visual ranges from the Meteorological Services Department. This in some cases causes confusion among the public who more familiar with the Air Pollutants Index use it alone for assessing the haze (in their minds "polluted air") as opposed to also looking at the visibility index.

PSI why is it important (EPA)

The Pollutant Standards Index (PSI) has been developed by the Environmental Protection Agency (EPA) to provide accurate, timely, and easily understandable information about daily levels of air pollution. Index figures enable the public to determine whether air pollution levels in a particular location are good, moderate, unhealthful, or worse. In addition, EPA and local officials use the PSI as a public information tool to advise the public about the general health effects associated with different pollution levels, and to describe whatever precautionary steps may need to be taken if air pollution levels rise into the unhealthful range. (See PSI vs MAPI )






Up to 50 Good  None for the general population  None required 
51 to 100 Moderate  Few or non for the general population  None required 
101 to 200 Unhealthy  Mild aggravation of symptoms among susceptible persons ie. those  with underlying conditions such as chronic heart or lung ailments ; transient symptoms of irritation eg. eye irritation, sneezing or coughing in some of  the healthy population.  Persons with existing heart or respiratory ailments should reduce physical exertion and outdoor activity. 

The general population should reduce vigorous outdoor activity. 

Appropriate public advisories regarding the use of respiratory masks and other health matters will be given. 

201 to 300 Very Unhealthy  Moderate  aggravation of symptoms and decreased tolerance in persons with heart or lung disease ; more widespread symptoms of transient irritation in the healthy population.  Elderly and persons with existing heart or lung disease should stay indoors and reduce physical exertion and outdoor activity. 

The general population should avoid vigorous outdoor activity. 

Appropriate public advisories on air cleaning devices for homes and offices will be given.

301 to 


Hazardous Early onset of certain diseases in addition to significant aggravation of symptoms in susceptible persons; and decreased exercise tolerance in healthy persons.  Children, elderly  and persons with existing diseases should stay indoors and avoid outdoor activity.   

The general population should avoid all unnecessary outdoor activity. 

Over 400  Hazardous  PSI levels above 400 may be life-threatening to ill and elderly persons. Healthy people may experience adverse symptoms that affect normal activity.  Children, elderly  and persons with existing diseases should stay indoors, keeping the windows and doors closed  and avoiding physical exertion as far as possible.

Outdoor activity should be avoided. 

The general population should keep physical exertion and outdoor activity to as low a level as possible. 



With that I let your "mouse" or your "keyboard" do the "talking".

Till next month, "Happy Surfing".

Cyberdoc (

The links to URL mentioned above are valid at the time of writing (10 August 1999).

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Last Updated 11 May 2005.