Industrial growth has created high levels of air pollution in Thailand. Vehicles and factories contribute to air pollution, particularly in Bangkok.[4]
The Bangkok metropolitan area, which consists of the Bangkok Metropolitan Administration (BMA) and the four surrounding provinces (Nonthaburi, Pathum Thani, Nakhon Pathom, and Samut Prakan), holds about 20% of the national population and over half of the country's factories. Due to a lack of treatment facilities, increasing volumes of hazardous substances generated by the thriving industrial activities have caused serious dumping issues. Unless treatment facilities are built and institutions starts to regulate strictly, environmental contamination caused by hazardous waste threatens to become Thailand's worst environmental problem in the future.[1]
The Pollution Control Department and other agencies have developed standards in order to reduce air pollution. The standards focus on shifting to lower-emissions vehicle engines and improving public transportation. Environmentally-unfriendly motorbikes represent around 75% of the vehicles on the road in Thailand.[citation needed] Diesel trucks and buses also contribute many pollutants. In most areas of the country, air pollutants for vehicles are now within acceptable levels according to national standards.
Factories and power plants have been required to reduce emissions. Bangkok and the rest of the Central Region contribute between 60–70% of the country’s industrial emissions. Most power plants rely on burning fossil fuels.[citation needed]
Other sources of air pollution include garbage burning, open cooking and agricultural burning practices, including deliberate forest fires.
Agricultural burning in Southeast Asia often creates a haze. In 2003 Thailand ratified the ASEAN Agreement on Transboundary Haze Pollution to reduce the haze from forest fires, but issues throughout the region are still common.[5] Wildfires are started by local farmers during the dry season in northern Thailand for a variety of purposes,[6][7] with February and March as the two months when conditions are at their worst.[8][9] In research conducted between 2005 and 2009 in Chiang Mai, average PM10 rates during these months were found to be well above the country's safety level of 120 μg/m3,[10] peaking at 383 μg/m3 on 14 March 2007.[11] They are the main cause of the intense air pollution in the Thai highlands[12] and contribute to the floods in the country by completely denuding the undergrowth of the woods.[13] The dry forest soil leads to lower water intake for the trees to extract when the rains arrive.[14]