Air pollution has become a serious environmental and health issue in Thailand. The pollution levels in the country follow predictable patterns, which highlight the presence of a peak pollution season.

For Bangkok, the highest levels of pollution are seen between November and February each year. The first step in any effort to mitigate air pollution is to understand the magnitude of the problem and the sources of pollution.

The most common measure of air quality is the Air Quality Index (AQI). The AQI is based on measurement of particulate matter (PM2.5 and PM10), Ozone (O3), Nitrogen Dioxide (NO2), Sulfur Dioxide (SO2) and Carbon Monoxide (CO) emissions. Using a composite index of air quality as the AQI is extremely important in understanding the magnitude of the problem.

To go a step further and design mitigation actions someone has to perform more detailed analysis and “decipher” the meaning of a single numerical measure in order to identify the sources of pollution.

A hazy Bangkok skyline – or an invisible city skyline – is the most evident indication of air pollution, as small particles, generally referred to as particulate matter of 10 or 2.5 microns in width, are suspended in the air.

Of these two sets of particles the PM2.5 draw big attention because of their high contribution to air pollution and the detrimental health effects they can cause in our respiratory systems. Although these small particles are measured by size, there are significant differences in their chemical composition depending on their origin.

By analyzing this chemical fingerprint, we can determine the cause of pollution as well as different toxicity factors and health impacts of the PM2.5 particles. ESCAP has initiated a large study in Thailand that is looking at several aspects of air pollution in Bangkok, Chiang Mai and Nakhon Si Thammarat.

The results of this study will be published soon, and this article provides some main finding of this work. When analyzing the data we look at two levels: the source and the contributing factors.

The source indicates the generation of the problem and the different pollutants and is related to different economic activities (from power generation to industrial production, agriculture and transport).

The contributing factors refer to local weather conditions (temperature, wind, humidity) that are responsible for the temporal and spatial distribution of the pollutants and therefore for the specific AQI in a location. All these data, generated from ground-based measurement stations, are combined with observations from satellites and are fed into machine learning models to identify the most significant factors and the most effective tools for reducing air pollution levels.

The preliminary analysis of data and our study show the following: while internal combustion vehicles are an important source of air pollutants, they are not the primary sources of air pollution in most cities in Thailand.

Agricultural fires and forest fires are the main source of pollution

While vehicles do play a larger role in cities such as Bangkok or Nakhon Si Thammarat their overall contribution to the AQI in these cities is much smaller than other factors. In this context, smoke released by agricultural fires and forest fires are the main source of pollution and are related to unsustainable practices of natural resources management.

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