Authorities have launched cloud seeding missions to try and alleviate toxic air pollution in northern Thailand.

The Department of Royal Rainmaking and Agricultural Aviation dispatched two aircraft to sow rain-triggering chemicals across Chiang Mai province and the country's northern region on February 3.

Six areas, including forests and mountainous regions believed to be at risk of wildfires, were targeted to mitigate the haze situation.

The operations were commenced after fine particulate matter in the air crossed the 'safe' threshold of 50 micrograms per cubic metre of air, with Chiang Mai districts reaching values between 56 to 96 instead.

The Department of Royal Rainmaking and Agricultural Aviation is urging the public to refrain from all types of burning to avoid adding the air pollution.

However, farmers prefer to use the cheaper and easier method of clearing harvested sugar cane husks by setting the fields alight in a process known as 'slash and burn'.

Scientists found that smog is at its worst in the country when farmers burn waste crops to cheaply clear their land between late October and April. This is combined with high numbers of polluting cars on the road and large construction projects across the capital.

The seasonal lack of wind and rain, combined with a winter low-pressure system in which cold air is trapped closer to the ground by warm air above – prevent the pollution from being dispersed naturally.

The Thai government has been criticised for failing to tackle the country's air pollution crisis, with bizarre measures such as spraying water into the air and giant purifiers having no impact.

Data scientist engineer Worasom Kundhikanjana said: 'PM 2.5 pollution has a seasonal trend in Bangkok and the northern provinces, but has only recently received public attention. During this winter haze, the harmful particle pollution level is high throughout the day, including on weekends.

'Unfortunately, spraying water into the air does not appear to be effective, since the volume of water is minuscule compared to actual rain.

'With the start of the monsoon season, the weather in Bangkok will get better, and public attention on this issue will likely fade. However, without immediate policy measures, the problem will come back again next winter.'