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Haze Information

Hotspots and Smoke Haze
Air Quality Indicators
Dispersion Model Forecast


Haze ImageTransboundary smoke haze from land and forest fires during the traditional dry period between June and October has been a recurrent feature in the southern ASEAN region in the past few decades. These annual fires are caused mainly by land clearing and “slash and burn” agricultural practices in Indonesia, particularly Sumatra and Kalimantan. In the northern ASEAN region, agricultural burning activities are common during the traditional dry season between December and March can also cause large scale smoke haze at times. The smoke haze situation is usually exacerbated when it coincides with the El NiƱo, a climatic phenomenon that often leads to prolonged and drier weather conditions in the region. 
Apart from satellite imageries, various haze related information, air quality indicators and dispersion model forecasts are used as monitoring and assessment tools in regional fire and smoke haze surveillance


Hotspots and Smoke Haze

To facilitate the interpretation of satellite-derived haze information, schematic maps of haze information are generated operationally by the ASMC. The maps depict the location of the hotspots and coverage of smoke haze/plumes identified from processed satellite imageries. Charts of hotspot counts for the different ASEAN regions are also updated daily to provide a trend analysis of the hotspot activity across the region.

Air Quality Indicators

The prevalence of airborne smoke particles often leads to deterioration in ambient air quality. Various indices of air quality are adopted around the world. One of them is the Pollutant Standards Index (PSI) developed by the United States Environmental Protection Agency (USEPA) which provides an accurate, timely and easily understandable indicator of daily levels of air pollution.
The PSI values are reported as a numeric scale and enable the public to determine whether the air pollution levels in a particular location are good, unhealthy or hazardous. These values are derived from five major pollutants – particulate matter of 10 micrometres or less (PM10), sulphur dioxide, carbon monoxide, ozone and nitrogen dioxide. The pollutant with the highest index over a 24-hour period is used to describe the air quality for the particular day. In hazy conditions, the index is likely to report PM10.
The PSI value gives an indication of the air quality as shown:
 PSI Value
 PSI Descriptor
 0 to 50
 51 - 100
 101 - 200
 201 - 300
 Very unhealthy
 Above 300
Other air quality indices similar to the PSI such as Air Pollution Index (API) and Air Quality Index (AQI) are used in Malaysia and Thailand respectively.


Dispersion Model Forecast

Atmospheric dispersion models can be used as tools to forecast the transport and dispersion of smoke haze particles. These three-dimensional models employ mathematical algorithms to estimate or predict the downwind concentration of air pollutants (haze particles) emitted from sources (fires). They require input fields which include forecasts of meteorological conditions (e.g. wind speed and direction, air temperature, atmospheric stability, presence of inversion, etc) and emission parameters (e.g. source location and height, emission rate). The model products are concentration forecasts showing the spatial diffusion of the smoke particles.
To simulate the dispersion of smoke haze from land and forest fires, the definition of the fire sources presents some uncertainties. For instance, the emission rates of smoke particles from detected fires cannot be quantified accurately.  It is also not possible to determine the location of future fires, which are mostly induced by human activities. To overcome these uncertainties, a number of simplified approaches and assumptions must be incorporated into the model. Additionally, the other input fields of forecast meteorological conditions are subject to errors. In interpreting the model products, it is thus important to be aware of the model’s limitations and treat the forecasts as broad-scale guidance on the dispersion of smoke haze.
The dispersion model used by the ASMC is the HYSPLIT (HYbrid Single-Particle Lagrangian Integrated Trajectory) model developed by the Air Resource Laboratory of US NOAA. The model products are generated operationally during smoke haze episodes in the region.

©2007 National Environment Agency