Air pollution in the city, which is the country's tourism centre, has approached the top of the 151-200 level, which means unhealthy according to the Air Quality Index (AQI).
According to the current data of the AQI website, which measures air quality, Chiang Mai became the most polluted city in the world with 195.
Dhaka, the capital of Bangladesh, ranked second with 184, Beijing, the capital of China, ranked third with 166, Phnom Penh, the capital of Cambodia, ranked fourth with 163 and New Delhi, the capital of India, ranked fifth with 160.
The Thai Department of Environmental Pollution Control stated that air pollution in 8 regions, including Chiang Mai, has reached levels that will adversely affect human health.
A research team from NASA, in co-operation with the Geo-Informatics and Space Development Agency of the Thai Ministry of Higher Education, Science, Research and Development, will be in Thailand for 4 days to study air pollution.