The prediction of the local meteorology in the tropical region has always been a challenge, more so for the fragmented land areas in equatorial Southeast Asia, often termed as the maritime continent. Within the past decade, one of the environmental problems that has affected the region was related to the rapid land use changes, where biomass burned from the large-scale conversion from forests to oil palm plantations have released much smoke/aerosols to the atmosphere. The transboundary haze events during the burning season have reduced the air quality and visibility of the region.

A major air pollution episode that occurred in August 2005 was declared a haze emergency state in two districts of Peninsular Malaysia due to the burning activities from neighboring Sumatera, as shown by the scattered active fire counts from the MODIS satellite. The weak low level equatorial wind conditions impeded efficient transportation of the smoke, and thus affected the areas near the sources of pollution. The mesoscale features of the daily sea and land breeze conditions near the eastern coast of Sumatera and the western coast of the Peninsular Malaysia was simulated within the planetary boundary layer for a duration of seven days in August 2005 by the limited area three dimensional meteorological and dispersion model, The Air Pollution Model (TAPM). Offshore conditions were reproduced over the land areas in Sumatera and Peninsular Malaysia during nighttime, while over the Straits of Malacca, strong southwest monsoon associated with the sea breeze circulations were replicated during daytime. A tracer analysis of air particles from Sumatera revealed that the aged air particles were recirculated landwards and seawards over the Straits of Malacca throughout the simulation. The land and sea breeze conditions in addition to the presence of a wind divergence highlighted the poor capability of the low level winds over the Straits of Malacca in dispersing and transporting the excessive amount of aerosols from the biomass burned in Sumatera.

Model prediction of the smoke through dispersion analysis showed the slow advection of the smoke plume in a northeastward direction from Sumatera towards Peninsular Malaysia. The time taken for the plume to reach the western coast of Peninsular Malaysia from Riau, Sumatera was approximately 17 hours after the start of simulation. The smoke pollutants were confined near the sources with high concentrations in the weak wind regime. Patterns of the maximum daily concentration of particulates displayed a northeastward propagation, which showed the influence of the prevailing southwest monsoon.

Hourly sequence of the dispersion analysis of the PM10 pollutant from the active fire counts revealed the evolution of plumes from the individual fire sources. The amalgamation of smoke plumes occurred approximately four hours from the start of simulation. The plumes at the height of 10 m were mainly confined within Sumatera due to the constraints of the prevailing onshore winds of the sea breeze. Only twelve hours later did the plumes arrive on the western coast of Peninsular Malaysia.