Nasa officials have arrived to work with the Higher Education Science Research and Innovation Ministry to study air pollution in Thailand as part of the US agency’s project to survey Asia’s air quality.

The “Love Airplanes” Facebook page yesterday posted pictures of two aeroplanes belonging to the US National Aeronautics and Space Administration (Nasa) as they were landing in Thailand this week.

It said that a Douglas DC-8-72 with licence number NB17NA arrived at U-Tapao airport from Seoul, South Korea, on Wednesday, while a Gulfstream C-20A with licence number N520NA arrived from Angeles City, the Philippines, yesterday.

Both aeroplanes will be used to observe the air quality throughout Thailand from today until March 25 before leaving the country on March 27, according to Thailand’s Geo-Informatics and Space Technology Development Agency (Gistda).

Gistda confirmed the two aircraft belonged to Nasa.

Supamas Isarabhakdi, Higher Education Science Research and Innovation Minister, said yesterday that the ministry would sign a partnership agreement with Nasa to survey Thailand’s air quality under Nasa’s Airborne and Satellite Investigation of Asian Air Quality project.

Under the project, Nasa is partnering with South Korea, Taiwan, the Philippines, Malaysia and Thailand to survey the quality of air in the region, she said.

“It took us about three years to reach the agreement today,” Ms Supamas said before the signing. “Security is strict because the officials who came with the aircraft are high-ranking officials.”

Meanwhile, Chiang Mai had the highest level of fine particulate matter smaller than 2.5 microns in the world yesterday, online data showed.

According to IQ Air, a popular tracking website, at about 5pm yesterday, Chiang Mai ranked No.1 for being the most polluted city in the world, with its air quality index measuring 173.